NASA CR-1785, Radiation Effects Design Hdbk

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RADIATION EFFECTS DESIGN HANDBOOK
Section 1. Semiconductor Diodes
Prepared by
RADIATION EFFECTS INFORMATION CENTER
. .
BATTELLE MEMORIAL INSTITUTE
Columbus, Ohio 43201
f or
NA TI ONA L A ERONA UTI CS A ND SPA CE A DMI NI STRA TI ON WA SHI NGTON, D. C. J UL Y 1971
I
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TECH LIBRARY KAFB, NM
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1. Rep at No.
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2. Government Accession No. 3. Rscipient'r Catalog No.
NASA CR-1785
4. Title and Subtitle
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5. Report Date
RADIATION EFFECTS DESIGN HANDBOOK
Secti on 1. Semiconductor Diodes
J ul y 1971
6. Performing Orgnizatim Code
L" ~~~ . ~... .
7. Author(s) 8. Performing Organization Report No.
C. L. Hanks and D. .I. Hamman
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10. Work Unit No.
Q. Morming Organization Name and Addrm
I
RADIATION EFFECTS INFORMATION CENTER
Battel l e Memorial I nsti tute
11. Contract or Grant No.
Columbus L aboratori es
13. Type of Report and Period Covered
Columbus, Ohio 43201
NASW-1568
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12. Sponsoring Agency Name and Address
Contractor Rsport
Nati onal Aeronauti cs and Space Administration
Washington, D.C. 20546
14. Sponsoring Agency Code
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15. Supplementary Notes
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16. Abmact
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Thi s document contai ns summarized i nf ormati on rel ati ng to steady-state
radi ati on ef f ects on semi conductor di odes pl us an i ntroductory secti on on
terminology. The radi ati on consi dered i ncl udes neutrons, gamma rays, el ectrons,
and protons. The i nformati on is usef ul to the desi gn engi neer f or making esti mates
of radi ati on ef f ects on di odes.
I
17. Key' Words (Suggested by Author(s) ) 18. Distribution Statement
Radi ati on Effects, Di odes, Semi conductors
Si l i con eontrol l ed Recti f i ers, Radi ati on
Uncl assi fi ed - Unlimited
Damage
L- ." . ~ ~~ ~ ~
19. Security Classif. (of this report) 22. Rice* 21. NO. of' pager 20. Security Classif. (of this pge)
Uncl assi fi ed
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For sale by the National Technical Information Service, Springfield, Virginia 22151
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PREFACE
. . .
. ,
. .
This document i s the first section of a Radiation Effects
Design Handbook designed to aid engineers in the design of equipment
'for operation. in the radiation environments to be found in space, be
they natural or. artificial.. ' Thi s Handbook will provide the general '
background and informatioh necessary to enable the designers"t0 ' ' '
.. choose suitable types'of materials 0.r classes'of 'devices. I t also will
include, 'where possible, predictive. techniques for forecasting
behavior of materials, devices or equipment, and correlation factors
for comparing different radiation environments.
Future secti ons of the Handbook are expected to discuss such
subj ects as transi stors, el ectri cal i nsul ators, capaci tors, sol ar cel l s,
pol ymeri c materi al s, thermal -control coati ngs, structural metal s,
and interactions of radiation.
ACKNOWLEDGMENTS
The Radiation Effects I nformation Center owes thanks to several
individuals for their comments and suggestions during the preparation
of this document. The effort was monitored and funded by the Space
Vehicles Division and the Power and Electric Propulsion Division of the
Office of Advanced Research and Technology, NASA Headquarters,
Washington, D. C., and the AEC-NASA Space Nuclear Propulsion
Office, Germantown, Maryland. Also, we are indebted to the follow-
ing for their technical review and valuable comments on this section:
Dr. R. R. Brown, Boeing
Mr. F. Gordon, J r. , NASA-Goddard Space Flight Center
Dr. A. G. Holmes-Siedle, RCA
Mr. S. Manson, NASA
Mr. D. Miller, SNPO-W
Mr. A. Reetz, NASA
Dr. A. G. Stanley, MIT
Mr. Wm. White, NASA-Marshall Space Flight Center.
fABLE OF CONTENTS
Page
vii
GLOSSARY . . . . . . . . . . . . . . . . . . . .
SECTION 1 . SEMICONDUCTORS
INTRODUCTION
1
General Background . . . . . . . . . . . . . .
1
DIODES . . . . . . . . . . . . . . . . . . . .
5
Switching Diodes . . . . . . . . . . . . . . .
Rectifier s . . . . . . . . . . . . . . . . .
General-Purpose . . . . . . . . . . . . . . .
Voltage-Reference Diodes . . . . . . . . . . . .
Special-Purpose Diodes . . . . . . . . . . . . .
Tunnel Diodes . . . . . . . . . . . . . .
Varactor Diodes . . . . . . . . . . . . .
Microwave Mixer Diodes . . . . . . . . . .
Silicon-Controlled Devices . . . . . . . . . .
Schottky Barri er Di odes . . . . . . . . . .
7
11
14
15
16
19
20
20
20
22
REFERENCES . .
25
BIBLIOGRAPHY .
26
INDEX . . . . . . . . . . . . . . . . . . . . 29
V
GLOSSARY
. . "-
Absorbed Dose. The radiation energy absorbed per unit mass of a
material at the place or point of i nterest, or the time-integrated
absorbed-dose rate [Unit: rad (material)], one rad being equivalent
to 100 ergs/gram or 0.01 joule/kilogram. Dose is preferred. ,
Absorbed-Dose Rate. The energy absorbed per unit time and mass by
a given material from the radiation field to which it is exposed
[Unit: rad (materi al )/s] . Dose rate is preferred.
Breakdown Voltage.
age) at which the
through Zener or
The value of reverse voltage (negative anode volt-
current i ncreases by many orders of magnitude
avalanche breakdown.
Breakover Voltage. The value of positive anode voltage at which a
silicon-controlled rectifier or switch changes to the conductive state
with the gate circuit open.
Bremsstrahlung. German for "radiation resulting from a stopping
process" or, literally, "from braking". Designates electromag-
netic radiation generated when high-energy charged particles are
accel erated (or decel erated) by electric and/or magnetic fields.
Bremsstrahlung sources in the laboratory are typically generated
by the interaction of electron beams with the nuclear Coulomb field
of the atoms in target materials. The cross section for this inter-
action inc'reases strongly for electron energies above 1 MeV. The
bremsstrahlung energy spectrum is continuous and ranges from zero
up to the maximum energy of the incident particles. Bremsstrahlung
and high-energy X-radiation are of the same nature, with brems-
strahlung being the continuous portion of the X-ray spectrum.
Bulk Damage. Radiation-induced defects in the crystal lattice of a ma-
terial which, in a semiconductor, act as additional recombination
centers for mi nori ty carri ers and thus decrease the lifetime of the
mi nori ty carri ers.
Conduction Current (radiation controlled). An abnormally high leakage
current-flowing in insulators or semiconductors because of a
radiation-induced increase in their conductivity.
Diode Switching Time. .The time required for a diode to switch between
the conductive and nonconductive states.
vii
Displacement Effects. The effects of displacements in the lattice
structure of a materi al that resul ts from parti cul ate i rradi ati on.
See bulk damage.
Dose. Equivalent, but preferable, to absorbed dose.
Dose Rate. Equivalent, but preferable, to absorbed-dose rate.
Dynamic Resistance. Slope of the forward voltage and current
characteri sti cs in the "linear" operating region.
( r d
A V DI ODE
A i 'IoDE
AT SEL ECTED OP E R A T I N G P OI N T
Electromagnetic Radiation. Radiation associated with a periodically
varying electric and magnetic field that is traveling at the speed of
light, including radio waves, light waves, X-rays, and gamma
radiation.
El ectron. A small charged particle having charge equal to 4. 803 x
10-10 esu and a mass of 9. 109 x 10-28 gram. In general use, it
most often refers to a negative charged particle, which is more
correctl y termed negatron; posi tron refers to a particle having a
positive charge.
Energy Spectrum. The distribution of radi ati on, such as y-rays,
X-rays, neutrons, electrons, and protons, as a function of energy
Exposure. ' I . . . the quotient of A Q by A m, where A Q is the sum of
the electrical charges on all the ions of one sign produced in air
when all the electrons (negatrons and positrons) liberated by photons
in a volume element of ai r, whose mass i s A m, are compl etel y
stopped in air . . . Here A refers to an increment small enough
so that ' I . . . a further reduction in its size would not appreciably
change the measured value . . . and, on the other hand, is sti l l
large enough to contain many interactions and be traversed by many
parti cl es. Unit: roentgen(r) =2. 58 x 10-4 coulomb/kilogram. In
certain contexts the dictionary definition of exposure is implied.
Fission. The splitting of a heavy nucleus into two (or, very rarel y,
more than two) fragments - the fission products. Fission is ac-
companied by the emission of energy; kinetic energy of neutrons and
fission products and the associated gamma rays. It can be spon-
taneous or it can be caused by the impact of a neutron, a fast
charged parti cl e, or a photon.
viii
I -
Fluence. The number of particles or photons or the amount of energy
that enters an i magi nary sphere of unit cross-sectional area. The
time-integrated f l ux.
Flux. At a given point, the number of photons or parti cl es or energy
incident per unit time on a small sphere centered at that point,
divided by the cross-secti onal area of that sphere.
Forward Characteristic. The current-voltage characteristic of a diode
when biased in the forward direction or direction of l east resi stance
to current flow through the device. The anode is biased positive in
relation to the cathode.
Forward Current. The current that flows in a diode when biased in the
forward direction.
Forward Voltage. The voltage applied between the anode and cathode
of a diode whereby the diode operates in the conductive state.
Forward Voltage Drop, VF. The value of voltage between the anode
and cathode of a diode when biased in the forward direction. Gen-
eral l y measured at a specific current.
Gamma Rays. Highly penetrating, high-frequency electromagnetic
radiation from the nuclei of radioactive substances. They are of the
same nature as X-rays, but of nuclear rather than atomic origin.
(In many references, a distinction between gamma rays and X-rays
is not made. )
Gate Current. The current flowing between the gate and cathode of a
silicon-controlled rectifier or switch.
Gate Voltage. The voltage applied between the gate and cathode of a
silicon-controlled rectifier or switch.
Holding Current. The forward current below which a silicon-controlled
rectifier or switch returns to the forward blocking state after having
been in forward conduction, gate open.
I onization. The separation of a normal l y el ectri cal l y neutral atom or
molecule into electrically charged components.
I onizing Radiation. Electromagnetic radiation (gamma rays or X-rays)
or particle radiation (neutrons, electrons, etc. ) capable of producing
ions, i. e., el ectri cal l y charged atoms or mol ecul es, in its passage
through matter.
ix
-
IR. See reverse l eakage current.
IRo. The reverse l eakage current measured i ni ti al l y or at the begin-
-
ning of a test.
J unction Leakage Current. See reverse leakage current.
Leakage Currents. See reverse l eakage current.
Maj ori ty Carri er. I n semiconductors, the type of carri er that consti -
tutes more than half the total number of carri ers. The maj ori ty
carri ers are el ectrons in an n-type semiconductor and holes in a
p-type semiconductor.
Minority Carrier, The type of carri er that constitutes less than half
the total number of carri ers in a semiconductor. The minority
carri ers are hol es in an n-type semiconductor and electrons in a
p-type semiconductor.
Neutron. A particle with no el ectri c charge, but with a mass approxi -
mately the same as that of the proton. In nature, neutrons are
bound in the nucleus of an atom, but they can be emitted or knocked
out in various nuclear interactions.
Neutron Fluence. Time -integrated neutron flux (Unit: n/cm2)
Neutron Flux. The product of the neutron density (number per cubic
centi meter) and the neutron velocity; the flux is expressed as neu-
trons per square centimeter per second. It is numerically equal to
the total number of neutrons passing, in all directions, through a
sphere of 1 cm2 cross-secti onal area per second.
Neutrons, Fast. Neutrons with energies exceeding 10 keV, although
someti mes di fferent energy l i mi ts are gi ven.
Neutrons, Thermal. Neutrons in thermal equilibrium with their sur-
roundings. At room temperature thei r mean energy i s about
0.025 eV.
Nuclear Radiation. Particulate and electromagnetic radiation emitted
from atomic nuclei in various nuclear processes.
Permanent Effects. Changes i n materi al properti es that persi st for a
time long compared with the normal response time of the system of
which the material is a part.
X
Proton. An elementary particle having a positive charge equivalent to
the negative charge of an el ectron (4.803 x 10-10 esu) but possessing
a mass approximately 1845 times as great.
Rad. A unit of dose equal to 100 ergs per gram. In defining a dose,
-
the materi al must be defi ned, e. g., €320, C, Si.
Radioactivity. Spontaneous nuclear disintegration occurring in ele-
ments such as radium, uranium, and thorium and in some isotopes
of other el ements (e. g., Cob0) . The process is usually accom-
panied by the emission of alpha and beta particles and/or gamma
rays.
Reference Voltage. The value of voltage maintained by a reference or
Zener diode when operated at a specified current.
Replacement Current. A current tending to reestablish charge equi-
librium after perturbation of the normal charge distribution by
radiation.
Reverse Characteristic. The current-voltage characteristic of a diode
when biased in the reverse direction or direction of greatest resi st-
ance to current flow through the device. The anode is biased nega-
tive in relation to the cathode.
Reverse Current. See reverse l eakage current.
Reverse Leakage Current, I R. The current that flows when the diode
is biased in the direction of greatest resi stance. The reverse cur-
rent as normally measured is a combination of reverse saturati on
current, carri er generati on current, and surface leakage current.
Reverse Recovery Time. The time required for the reverse current
or voltage to reach a specified value after instantaneous switching
from a steady forward current to a reverse bias in a given circuit.
Temporary Effects. Changes i n materi al properti es that persi st for a
ti me, but which are followed by complete or nearl y compl ete re-
covery to the preirradiation condition.
Valley Current. The current flowing when a tunnel diode is so biased
in the forward direction that it is operating in the valley portion of
its current-voltage characteristic. The current at the second lower
positive voltage at which dI/dV =0.
-
VF. See forward voltage drop.
xi
VFo. The. forward voltage drop measured initially or at the beginning
of a test
Vz. See reference voltage
-
Vzo. The reference or Zener voltage measured initially or at the be-
ginning of a test.
Zener Voltage. See reference voltage.
xi i
I
SECTION 1. SEMICONDUCTOR DEVICES
INTRODUCTION
Semiconductor devices are the most sensitive of all electronic
components to radiation. Thus, for most applications, semiconductor-
device performance probably will determine the maximum radiation
f l ux and/or fluence that an electronic circuit will tolerate. Therefore,
radiation should be listed along with temperature and electrical bias
as one of the more important factors in the total environment that
determines semiconductor-device performance in an application.
Radiation affects semiconductor-device performance both perma-
nently and temporarily. Permanent effects are attributed to changes
in the physical properties of the irradiated semiconductor materials
(bulk damage) caused primarily by energetic particles (including
secondary electrons). The kind and magnitude of the effects observed
will depend upon the radiation type, flux, fluence, and energy.
Temporary effects are caused by the generation of excess free
carri ers i n the junction regions and result from exposure to ionizing
particulate radiation (electrons and protons), electromagnetic
radiation (X-rays or gamma-ray photons), or high-energy neutrons.
Semipermanent ionization effects include charge buildup on or in the
oxide layer and the creation of increased interface state density at the
interface between the oxide and the semiconductor material. This
type of damage is semipermanent in that at least partial recovery of
degradation in operating parameters is often observed when electrical
biasing is removed, and slow recovery generally is observed with
continuous electrical operation after exposure. This recovery can be
rapidly accelerated when devices are thermally annealed or operated
at elevated temperatures of electrical stressing.
General Background
Semiconductor devices generally may be separated into the two
categori es: maj ori ty-carri er devi ces and mi nori ty-carri er devi ces.
Fi el d-effect transi stors (FET's) and Schottky barri er di odes are the
pri mary representati ves of the majority-carrier device category.
Most other semiconductor devices including bipolar transistors, solar
cells, diodes, rectifiers, and silicon-controlled devices are minority-
carri er devi ces. A generalized pictorial representation of these
devices i s presented in the appropriate subsections.
The radiation effect of greatest i nterest i n mi nori ty-carri er
devices, such as bipolar transistors, is the decrease in the lifetime,
7, of the minority carriers. This decrease results from the
1
radiation-induced defects in the semiconductor crystal lattice which,
in turn, can act as additional recombination centers for the minority
carri ers. Thi s decrease i n 7 is reflected most prominently in a
decrease in transistor gain and the short-circuit current (and for
practical purposes the maximum available power) of solar cells.
These effects are normally referred to as bulk or permanent damage.
The expression usually used to relate lifetime decrease to
radiation fluence is
where
To i s the initial minority-carrier lifetime
TQ i s the lifetime after the radiation exposure
Q is the radiation fluence (particles/cm 2 )
KTi S the lifetime damage constant [ cm2/(parti cl e. s ) ] .
This expression will be developed further in the section on
transi stors to show i ts rel ati onshi p to the transi stor current-
amplification factor, hfe or p . The resulting expression will be
useful in predicting p degradation as a resul t of exposure to radiation.
Also to be presented later will be values of the constant, KT,
for use in prediction of device behavior.
In addition to bulk damage, radiation affects the semiconductor
surface properties. I onizing radiation can interact with atmospheric
gas at the semiconductor surfaces, with surface contaminants and
with passivation layers producing electric fields at the junction
surfaces, resulting in changes in the surface recombination behavior
of the current carri ers. These are the most apparent effects at l ow
fluences. As one would expect, the magnitudes of these effects vary
widely, even among units of the same type made by the same manu-
facturer. Larger differences can be expected between device types
and from manufacturer to manufacturer. Although some planar-
oxide passivated devices often show little vulnerability to ionizing
radiation, more recent data show that some of the devices most
sensitive to gain changes are indeed planar oxide-passivated devices.
This appears to be due, at least in part, to the creation of new i nter-
face states.
For radiation levels at which transistor-current gain, hfe, and
diode forward voltage drop, VF, are significantly altered, a
permanent increase in junction-leakage current can also be expected.
This effect may become very significant at higher fluences.
2
I oni zi ng radi ati on can create free-charge carri ers whi ch wi l l
participate in the conduction process. This has the effect of generat-
ing photocurrents, that is, currents that are generated i n the reverse
direc'tion across any p-n junction. .The photocurrents at the base-
emitter junction of transi stors may be ampl i fi ed by the current gain.
The magnitude of this effect will depend upon the radiation f l ux and,
although the magnitude of the photocurrents are general l y small when
compared with normal operating currents, they may be significant in
certain applications.
The preceding paragraphs have emphasized radiation effects on
mi nori ty-carri er devi ces because experi ence shows these to be
critical components in many current applications. However, majority-
carri er devi ces al so are cri ti cal i n many appl i cati ons. Experi mental
ily
work has shown that radiation can produce surface effects in field-
effect transistors (FET's) that will adversely affect the performance
of these devi ces. I t has been found, particularly in metal-oxide-
semiconductor field-effect transistors (MOS-FET's), that disruptive
radiation-induced changes in gate threshold voltage and channel con-
ductivity can in some instances occur at exposure levels comparable
to those at whi ch bi pol ar transi stors are sti l l useful . However, for
many radiation environments both junction FET's and the MOS-FET's
have proven as satisfactory as bipolar transistors used to accomplish
the same function. The expected significant superiority of FET tran-
sistors over bipolar transistors, because of their independence from
the mi nori ty-carri er l i feti me, has not been realized. This is primar
a surface passivation problem which is slowly being improved.
I t should be noted that some of the radiation-induced changes in
semiconductor-device parameters may be of some benefit for some
applications. For example, in switching applications, increased
switching speed and less chance of breakdown failure would resul t
from the radiation-induced decrease in diode switching time and
increase in breakdown voltage. The effects of radiation on semi -
conductor devices must be evaluated in terms of the tolerance of a
circuit application to radiation-induced changes in the critical device
parameters.
Neutron fluence values for radiation experiments normally are
reported in units of neutrons per unit area with energies above Some
threshold value, n/cm2 (E >?-). This E val ue vari es from one experi -
ment to another. Therefore, in order that data could be compared
on a common basis, the fluence values reported by the various experi-
menters were converted to n/cm2 (E >O. 01 MeV) using appropriate
dosimetry multiplication factors. The neutron-energy spectrum was
assumed, for convenience, to be of the form
-
n(E) = 0,453 e -E'o* 965 sinh (2.29E)
1/2*
,
where E is the neutron energy i n MeV. The multiplication factors
used from this expressi on were
For Fl uenc e Multiply
with E > by
0.1 MeV
0.3 MeV
1.0 MeV
2.9 MeV
1.01
1. 07
1.44
4. 34
to obtain fluence with E >0. 01 MeV. Thi s procedure may resul t i n
errors as great as 50 percent i f the actual energy spectrum is at
wide variance with the spectrum assumed.
Another useful method of discussing neutron displacement
effects in semiconductors is the use of "1 MeV equivalence". This
term i s more ful l y descri bed i n the section of this Handbook entitled
"The Radiations in Space and Their I nteractions with Matter".
For the purposes of this and future sections, the following radi-
ation environmental descriptions are used unless specifically noted
otherwise in the text.
Neutron radiation - that radiation environment re-
sulting from the operation of a steady-state nuclear
reactor. The spectrum is assumed to be of the
form given above, and the environment includes the
associated gamma radiation.
Gamma rays - highly penetrating, high-frequency
electromagnetic radiation from the nuclei of radio-
active substances. They are of the same nature as
X-rays, but of nuclear rather than atomic origin.
(I n many references, a distinction between gamma
rays and X-rays is not made. )
El ectron and proton radiation - particulate radiation,
produced by machine sources, that is used to simu-
late the environment in the Van Allen belts.
Subsequent portions of this Handbook will describe the typical
radiation-induced changes in important semiconductor device para-
meters to provi de a basis for helping to select candidate device types
for the user's application and for establishing the general sensitivity
to radiation of the application circuitry.
4
DIODES
This portion of the Handbook is concerned with the effects of
radiation on serniconductor diodes and includes information on single-
junction p-n devices and three multiple-junction special-purpose
devices. The single-junction devices, in their order of presentation
are switching diodes, rectifiers, general-purpose diodes, voltage-
reference diodes, tunnel diodes, varactor diodes, microwave mixer
diodes, and Schottky barrier diodes. Due to a lack of information on
the effects of radiation on thei r characteri sti cs and their limited
application tunnel, varactor, microwave mixer, and Schottky barrier
diodes are discussed in the final section of thi s part of the Handbook,
which is entitled "Special-Purpose Diodes". In addition to containing
information on these four devices, the effects of radiation on the
multiple-junction devices (silicon-controlled rectifier, silicon-
controlled switch, and Schockley diode) are also included in this
special-purpose diode section.
Semiconductor diodes, due to their sensitivity to radiation and
the quantities required in today's circuitry, have received considerable
attention to determine the effects of radiation on their electrical
properties. This attention has included exposure to various radiation
environments, with measurements of el ectri cal characteri sti cs before,
after, ,and/or during the irradiation. Results of these investigations
have shown permanent changes in diode characteristics including
increases in forward-voltage drop and reverse current and decreases
in reverse-recovery time. These permanent changes are the subject
of this section of the Handbook.
The major amount of the radiation testing has been concerned
with those devices classified as switching and voltage-reference
diodes and rectifiers. These are single-junction devices, whose
structural diagram shown in Figure 1 is basic to all single-junction
semiconductor devices. These devices differ only in junction width
and area, which contributes to the current and frequency capabilities
of the device. The doping of the basic material may also differ,
depending upon the ultimate purpose of the device. The information
available from various investigators on these units has been combined,
with the neutron radiation environments converted to show fluences
with E > 10 keV, assuming a fi ssi on spectrum of the form n(E) = Ae-E/B
s i n h a where E i s the neutron energy in MeV. This i s one of the
standard spectra used in describing the fast-neutron energy distribution
of the neutron leakage at a nuclear reactor coreface. (See I ntroduction
for correlation. ) Similarly, this same notation has been used where
information is limited but available from more than one investigator or
test program on lower-use devices such as varactor, tunnel, microwave,
and Schottky barrier diodes. However, if the information available was
limited to one investigator or test program, the radiation environment
has not been changed from that which was originally reported.
5
Forward Current (Conventional)
-
Anode 0 - w l - o Cathode
FIGURE 1. STRUCTURE DIAGRAM OF SINGLE-J UNCTION DEVICE
Parameters that are common to most of the single-junction
devices and indicative of thei r sati sfactory operati on are forward
voltage drop, reverse current, and breakdown voltage. These are
the parameters general l y measured i n determi ni ng the effects of
radiation on semiconductor diodes, with forward voltage drop being
the most sensitixre to radiation and the most often measured parameter.
The one exception to this i s the breakdown or reference-voltage of
zener or voltage-reference diodes which i s of greatest i mportance i n
the application of these devices and, therefore, receives the greatest
attention when determining the effects of radiation on these devices.
The order of data presentation in the following sections, when the
information i s available, is as follows: forward voltage drop,
reverse current, and breakdown voltage. The one exception i s the
section discussing the effects of radiation on voltage-reference diodes,
where reference voltage or breakdown voltage i s the predominant
parameter and the fi rst di scussed. Data presentati on is graphic
wherever possible and consists of shaded envelopes that enclose the
data points plotted for a parti cul ar parameter. A data set, as
referred to on the graphs, i s the information reported on a device or
group of devices having the same type number and which have been
exposed to the same radiation environment, under the same electrical
bias conditions, in a parti cul ar test.
In using the information given in the following paragraphs, the
reader should remember that the intent is to provide preliminary or
early design data. However, if the circuit is designed to tolerate a
specific fluence, it should be expected to function in a fluence slightly
below this value. This permits a smal l margi n of safety to exist.
6
I -
Switching Diodes
The failure mechanism or degradation process of greatest
significance which semiconductor diodes experience from radiation
exposure (nuclear or space) is the creation of defects in the semi-
conductor's lattice structure. These lattice defects act as additional
trapping centers and, therefore, increase the resistivity of the
material. Since diode current varies inversely with the resistivity
and exponentially with voltage", the forward-voltage drop at a specific
current increases with radiation fluence. Through this mechanism
the degradation of the forward characteristic is the dominant effect
of radiation on switching diodes or other diodes and rectifiers where
this characteristic is important in the application of the device.
The fluence at which a switching-diode experiences an increase
in forward-voltage drop sufficient for the diode to be unsatisfactory
for an application is, among other things, dependent upon junction and
cross-sectional area. The greater these areas (which have a direct
relationship to the diode's current or power rating) for similarly
manufactured devices, the lower the radiation fluence required to
cause substantial degradation of the diode's forward characteristic.
This i s i l l ustrated by a comparison of Fi gures 2, 3 , and 4, which
are composites from the available data and show changes observed
in forward-voltage drop (V,) as a function of neutron fluence. Silicon
switching diodes having current ratings equal to or less tnan
0.5 ampere, greater than 0.5 ampere and less than or equal to
1 ampere, and those rated above 1 ampere, respecti vel y, are repre-
sented by the curves in Figures 2, 3 , and 4. Data points shown on
these and other graphs in this diode section are representative and
are not meant to be comprehensive. A seri es of the same data-point
characters (0, A , +) on a graph is indicative of observed changes
with fluence in a set of data. Based upon an increase to twice the
initial value of VF as a fai l ure cri teri on, the diodes of lower current
ratings are satisfactory to minimum neutron fluences of 5. o x 1014
and 2 x 1014 n/cm2 (E >10 keV), while those of the higher current
ratings may exceed this criterion at 1 x 1014 n/cm2 (E > 10 keV).
This failure criterion has been chosen arbitrarily and may or may
not be suitable for a particular application. I t is, therefore, left
to the designer to establish his circuit's failure criteria and deter-
mine its limitations for radiation exposure.
Although the degradation of the forward characteristic of a
switching diode is normally the limiting factor in the useful life of
the diode in a radiation environment, permanent changes also are
experienced in the reverse characteristic, The creation of lattice
defects and the subsequent decrease in minority-carrier lifetime
*Beam, W. R , Electronics of Solids, McGraw-Hill (1965).
7
Neutron Fluence , n/crn' (E >IO keV 1 flsslon
FIGURE 2. COMPOSITE OF CHANGES IN FORWARD-VOLTAGE DROP VERSUS NEUTRON FLUENCE
FOR SWITCHING DIODES HAVING A CURRENT RATING OF 0.5 AMPERE OR LESS
15 Sets of Data
1
i
1
I
i
I o1
6
Neutron Fluence, n/cm2 (E >10heV 1 flsslon
FIGURE 3. COMPOSITE OF CHANGES IN FORWARD-VOLTAGE DROP VERSUS NEUTRON FLUENCE
FOR SWITCHING DIODES HAVING A CURRENT RATING GREATER THAN 0.5 AMPERE
BUT LESS THAN OR EQUAL TO 1 AMPERE
2 Sets of Data
Neutron Fluence , n/cm2 (E >IO heV 1 flsslon
FIGURE 4. COMPOSITE OF CHANGES IN FORWARD-VOLTAGE DROP VERSUS NEUTRON FLUENCE
FOR SWITCHING DIODES HAVING A CURRENT RATING GREATER THAN 1 AMPERE
7 Sets of Data
8
descri bed earl i er are responsi bl e for some of the change observed
i n the reverse characteri sti c. The reverse-saturati on current
i ncreases as the i nverse of the square root of the minority-carrier
lifetime, while the carrier -generation current is inversely propor-
tional to the minority-carrier lifetime. A third component of the
reverse-l eakage current is surface leakage which is generally not
calculable and is dependent upon surface condition, surface recom-
bination, and the presence of surface charge. These three components
of reverse current are not sati sfactory for categori zi ng the effects
of radiation on this parameter, however, because of an inability to
know in advance which component may be dominant. The information
regarding the effects of radiation on the reverse current of switching
diodes or similar types of devices is best separated by current or
power rating as was done above for forward-voltage drop. Composites
of the available information from various reports and technical
arti cl es on the effect of radiation on the reverse current of silicon
switching diodes are separated in this manner in Figures 5 and 6.
Changes in reverse-leakage current for the switching diodes having
current ratings of 1 ampere or l ess are pl otted as a function of
neutron fluence in Figure 5, while those for diodes rated in excess of
1 ampere are represented by Fi gure 6. Comparison of the composite
resul ts of the various investigators as presented in these two figures
shows little difference in the degradation of the reverse characteri sti cs
of the two groupings of diodes.
Comparison of Fi gures 5 and 6 with Figures 2, 3, and 4 show
a strong increase in reverse current at fluences as much as an order
of magnitude lower than those at which the forward-voltage drop shows
a similar increase. The degradation of the forward-voltage drop will
normally govern the useful limits of the diodes; however, since an
i ncrease i n l eakage currents from nanoamperes or even a few mi cro-
amperes to values 25 or 50 times greater than initial value usually
will not seriously impair the diodes' performance. An i ncrease of
several orders of magnitude in many instances would not be serious.
The decrease in minority-carrier lifetime that occurs with
increasing radiation fluence is also responsible for an improvement
i n two of the parameters important to the performance of a switching
diode. The switching time and storage time are directly dependent
upon minority-carrier lifetime, and decrease with radiation. Thus,
the speed of operation of the diode improves. Information available
on measurements of reverse-recovery ti me, whi ch i s a measure of
switching capability, is insufficient for providing graphic illustration
of the effect of radiation on this parameter. However, the informa-
tion which is available shows a variation of from l i ttl e or no change
to a decrease of 75 percent with exposure to a neutron fluence of
2 x 1014 n/cm2 (E > 10 keV) for silicon-switching diodes.
Breakdown voltage usually shows an increase with increasing
fluence. Insufficient data prevent the plotting of thi s parameter as a
9
Neutron Fluence, n/cm2 (E >10keV) fission
FIGURE 5. COMPOSITE OF CHANGES IN REVERSE CURRENT VERSUS NEUTRON FLUENCE FOR
SWITCHING DIODES HAVING A CURRENT RATING OF 1 AMPERE OR LESS
6 Sets of Data
Neutron Fluence, n/cm2 (E >IO keV) fission
FIGURE 6. COMPOSITE OF CHANGES IN REVERSE CURRENT VERSUS NEUTRON FLUENCE FOR
SWITCHING DIODES HAVING A CURRENT RATING GREATER THAN 1 AMPERE
4 Sets of Data
10
function of fluence and what data are available show little or no change
of consequence in the application of the diodes.
I nformation concerning permanent-degradation effects of electron
radiation on the characteristics of switching diodes is limited to one
report on silicon devices, and shows a maxi mum i ncrease i n forward
voltage drop of 26.1 percent after exposure to an electron fluence of
5 x 1015 e/cmZ (E = 1.5 MeV). (l ) Reverse currents i ncreased several
orders of magnitude with this fluence but remained within satisfactory
l i mi ts. One exception was a diode that had an initial reverse current
of 49 nanoamperes but increased to 1.85 milliamperes with exposure
to a fluence of 5 x 1015 e/cm2 (E = 1.5 MeV). It is believed that this
i ncrease is due to the destruction of the lattice near the junction by
rapid absorption at very high dose rates, i.e. , 1.77 x 10l 2 e/(cm2- s).
The reverse-recovery time decreased the same as with neutron
irradiation, the decrease varying from 10 percent to as much as
73 percent with this electron fluence.
Limited information on the effects of gamma radiation from a
cobalt-60 source indicates there is little or no change in diode charac-
teri sti cs with exposures to 8. 8 x 105 rads (C).
Rectifiers
Rectifiers experience the same degradation mechanisms
described above for switching diodes. These mechanisms cause the
forward-voltage drop-and reverse current of the rectifiers to increase
with increasing radiation fluence. The effect of neutron fluence cn the
forward-voltage drop of silicon rectifiers is presented graphically in
Fi gures 7, 8, and 9. The graphs are composites,of the available infor-
mation concerning the permanent degradation of this parameter and
show the amount of increase that may be expected with exposure to a
neutron environment. Figure 7 is representative of the change that
may occur with rectifiers having current ratings of 1 ampere or l ess,
and Figure 8 similarly represents rectifiers rated above 1 ampere but
l ess than or equal to 10 amperes. Fi gure 9 i s a composite of resul ts
on those rectifiers rated above 10 amperes. These fi gures show
little difference in the minimum fluence at which the rectifiers experi-
ence a strong increase in forward-voltage drop. The graphs indicate
that the higher current devices (above 1 ampere) may double their
forward-voltage drop at a minimum fluence of 1 x 1013 n/cm2
(E >10 keV) while those of the lower current rating increase similarly
at minimum fluence of 1.3 x 1013 n/cm2 (E > 10 keV).
Permanent effects of neutron irradiation on the reverse character-
i sti cs of si l i con recti fi ers are i l l ustrated i n Fi gures 10, 11, and 12,
These figures present composite graphs of information from various
investigators according to the current ratings of the rectifiers, with
11
Neutron Fluence , n/cm* (E >10keV ) flsslon
FIGURE 7. COMPOSITE OF CHANGES IN FORWARD-VOLTAGE DROP VERSUS NEUTRON FLUENCE
FOR RECTIFIERS HAVING A CURRENT RATING OF 1 AMPERE OR LESS
4 Sets of Data
Neutron Fluence, n/cmz (E> lOkeV ) flsson
FIGURE 8. COMPOSITE OF CHANGES IN FORWARD -VOLTAGE DROP VERSUS NEUTRON FLUENCE
FOR RECTIFIERS HAVING A CURRENT RATING GREATER THAN 1 AMPERE BUT LESS
OR EQUAL TO 10 AMPERES
13 Sets of Data
IO" lo'L
Neutron Fluence
I 0'' 1014
' , n /cm2 (E >10keV ) flsslon
FIGURE 9. COMPOSITE OF CHANGES IN FORWARD-VOLTAGE DROP VERSUS NEUTRON FLUENCE
FOR RECTIFIERS HAVING A CURRENT RATING GREATER THAN 10 AMPERES
5 Sets of Data
12
I -
Neut r on Fl uence, n/cr n2(E >10k eV) fi ssl on
FIGURE 10. COMPOSITE OF CHANGES IN REVERSE CURRENT VERSUS NEUTRON FLUENCE FOR
RECTIFIERS HAVING A CURRENT RATING OF 1 AMPERE OR LESS
4 Sets of Data
"
IO" 10'2 1013 1014
Neut r on Fl uence, n/cmZ (E >IO k eV) fi ssi on
FIGURE 11. COMPOSITE OF CHANGES I N REVERSE CURRENT VERSUS NEUTRON FLUENCE FOR
RECTIFIERS HAVING A CURRENT RATING GREATER THAN 1 AMPERE BUT LESS
OR EQUAL TO 10 AMPERES
6 Sets of Data
Neut r on Fl uence, n/crn2 ( E >10k eV) fl ssi on
FIGURE 12. COMPOSITE OF CHANGES IN REVERSE CURRENT VERSUS NEUTRON FLUENCE FOR
RECTIFIERS HAVING A CURRENT RATING GREATER THAN 10 AMPERES
4 Sets of Data
13
each group covering a specific range of current rati ng. The data
summari zed i n Fi gure 10 are from results o f radiation tests on
recti fi ers rated at 1 ampere or l ess. Fi gure 11 i s a similar summary
of data for recti fi ers rated above. 1 ampere and equal to or less than
10 amperes; data for those units having current ratings in excess of
10 amperes are summari zed i n Fi gure 12. These fi gures i l l ustrate
the i ncrease in sensitivity to radiation that occurs with increasing
current or power rati ng that i s characteri sti c of many semiconductor
devices. Based upon the information presented in these graphs,
recti fi ers rated above 10 amperes may experi ence a strong i ncrease
in reverse current at approxi matel y 1011 n/cm2 (E > 10 keV), while
those rated at 10 amperes or l ess do not experience a si mi l ar i ncrease
unti l at l east 10l 2 n/cm2 (E > 10 keV), an order of magnitude greater
neutron fluence. A si mi l ar di fference i n sensi ti vi ty may al so be noted
between the rectifiers having current ratings of 1 ampere or less and
those rated above 1 ampere.
Limited information on the effects of el ectron i rradi ati on on the
el ectri cal characteri sti cs of si l i con recti fi ers i ndi cate the forward-
voltage drop did not increase more than 20 percent and the dynamic
resistance doubled with an electron fluence of 5 x 1015 e/cm2
(E = 1.5 MeV). ( l ) The reverse current i ncreased by approxi matel y
one order of magni tude, from a few nanoamperes to a maximum of
2 mi croamperes.
General-Purpose Diodes
General-purpose diodes have received only a limited amount of
attention in the study of radiation effects on semiconductor diodes.
Therefore, information on the effects of radiation on diodes of this
type i s not sufficient for a graphic presentation of the effects observed.
The effects that have been observed are, as expected, the same as those
discussed above for switching diodes and rectifiers. Limited neutron
i rradi ati on resul ts show a fluence of approximately 1015 n/cm2
(E > 10 keV) as the exposure at which the forward-voltage drop of 250-
and 500-milliwatt silicon units may double in value. An i ncrease of
as much as a factor of four has been observed with a fluence of
2.5 x 1015 n/cm2 (E > 10 keV). I t is suggested that the graphs and
information on switching diodes be used as a guide in the application
of general-purpose diodes in a radiation environment.
Data on the effect of el ectron i rradi ati on on the characteri sti cs of
si l i con general -purpose di odes are al so very l i mi ted but do show an
i ncrease of 200 to 375 percent in forward-voltage drop following
exposure to an electron fluence of 8 x 1015 e/cm2 (E = 1.5 MeV). (l )
The reverse current remained below 10 nanoamperes.
14
Voltage-Reference Diodes
'Exposure to a radiation environment produces lattice defects in
voltage-reference or zener diodes as it does in rectifiers and switching
diodes. The degradation of a diode's electrical characteristics through
the production of these defects and the subsequent decrease in minority-
carri er l i feti me is as discussed previously in the section on switching
diodes .
Degradation that occurs from the irradiation of voltage-reference
diodes includes changes in breakdown voltage and increases in forward-
voltage drop and reverse current. The diodes' maintenance of a
constant breakdown voltage, or for some low voltage-reference units a
constant forward-voltage drop which determines the reference voltage,
i s important in the application of these devices. Therefore, any
changes i n these parameters from exposure to a radiation environment
must be considered by the circuit designer: allowances must be made
in his design or adequate shielding must be provided to limit the
radiation fluence. The composite graph of the changes in reference
voltage observed by various investigators as a function of neutron
fluence presented in Figure 13 presents the maxi mum change i n refer-
ence voltages that has been observed at the indicated fluence. Many
times the reference voltage remains within 1 or 2 percent out to
fluences of n/cm2 (E > 10 keV).
Neutron Fluence, n/cm2 (E >IO keV) fission
FIGURE 13. COMPOSITE OF CHANGES I N REFERENCE VOLTAGE
VERSUS NEUTRON FLUENCE FOR REFERENCE
DIODES
34 Sets of Data
15
Another factor that must be considered but that has had l i mi ted
investigation i s the combined effect of radiation and temperature on
reference voltage. Graphs of how temperature affects the amount of
change observed in reference voltage when 1N745A, 1N968B, 1N829,
and 1N939 di odes are i rradi ated are shown i n Fi gures 14 through 17. (2)
These graphs demonstrate that the amount of change in reference
vol tage from i rradi ati on may di verge, converge, or cross wi th
i ncreasi ng temperatures (Fi gures 14, 15, and 16) or remai n essen-
tially constant (Figure 17). The degradation of the reference voltage
from exposure to a radiation environment may also be sensitive to
the current at which the diode i s operating. Therefore, depending
upon the application, the amount of degradation of the reference voltage
from i rradi ati on must be determi ned at the current and temperature
at which the diode is expected to operate.
The forward-voltage drop of reference diodes remains
within f 25 percent of the initial value to neutron fluences of
approximately 2 x 1014 n/cm2 (E > 10 keV) but may increase by a
factor of three at 3 x 1015 n/cm2 (E > 10 keV), as shown i n Fi gure 18.
A change in forward-voltage drop may or may not be significant,
depending upon the application, and it i s left to the designer to deter-
mine whether such a change would be detrimental to the performance
of hi s ci rcui t.
Because most investigators do not include the measurement of
reverse current in testing the effects of radiation on reference diodes,
data are somewhat l i mi ted. The data that are avai l abl e i ndi cate
degradation similar to that experienced by switching diodes. That is,
the minimum fluence at whi ch the reverse current i ncreases by a
factor of 10 or more i s approximately 2 x 1014 n/cm2 (E > 10 keV).
I t i s recommended that the graph in Figure 3 be used as an indication
of rever se-current behavior with radiation fluence.
Gamma irradiation of reference diodes using cobalt-60 as a radi-
ation source has caused essentially no change in reference voltage with
total exposures of 8.8 x 105 rads (C).
Information on the effects of electron irradiation on voltage-
reference on zener diodes is too limited for a graphic presentation, but
do indicate that the reference voltage will change less than 1 percent at
fluences of 5 x 1015 or 1 x 1016 e/cm2 (E = 1.5 MeV). Reverse cur-
current also remains stable with little or no increase at this fluence.
Special-Purpose Diodes
The data available on the effects of radiation on special-purpose
or limited-use diodes and silicon-controlled devices are too limited
for graphical presentation, and the devices themselves are not com-
parable to other devices for which data are available.
16
7.0
6.9
6.8
6.7
6.6
6.5
6.4
6.3
-40 - 20 0 20 40 60
Temper at ur e, C
80 100 I20
FIGURE 14. VOLTAGE-TEMPERATURE CHARACTERISTICS FOR 1N745A(2)
21
20
19
18
- 40 - 20 0 20 40 60 80 I20
Temper at ur e, C
FIGURE 15. VOLTAGE-TEMPERATURE CHARACTERISTICS FOR IN968B(2)
17
6.2
6.175
2 6.15
-
0
>
6 6.125
(r
0
c
-
3 6.1
& 6.075
V
a,
L
v-
a,
a,
6.05
6.025
- 20
10
9.5
9.0
8.5
0 20 40 60 80
Temperature, C
FIGURE 16. VOLTAGE-TEMPERATURE CHARACTERISTICS FOR INS29(2)
100 I20
I
I
4 x toi4 n/cm2
-40 -20 0 20 40 60 80 100 I20
Temperature, C
FIGURE 17. VOLTAGE-TEMPERATURE CHARACTERISTICS FOR IN939(2)
18
I -
Neutron Fluence, n/ cd (E >IO keV) fission
FIGURE 18. COMPOSITE OF CHANGES IN FORWARD-VOLTAGE
DROP VERSUS NEUTRON FLUENCE FOR
REFERENCE DIODES
12 Sets of Data
Tunnel Diodes
Tunnel diodes are majority-carrier devices which exhibit a
negative resistance in their forward characteristic and may be used
in various circuits including amplifier, oscillator, logic, and switch-
ing. They are l ess sensi ti ve to a radiation environment than most
other semiconductor devices. Gallium arsenide units have operated
satisfactorily to fluences of 1017 n/cm2 (E > 10 keV), while germanium
units are expected to perform satisfactorily to 1016 n/cm2 and silicon
to 1015 n/cm2. ( 3 ) Silicon units have shown a 100 percent i ncrease i n
valley current at 1 to 3 x 1015 n/cm2, with the increased current
approaching the peak current value at 10l6 n/cm2 (E > 10 keV).
Study of N on P germanium tunnel diodes has shown them to be
more radiation resistant by a factor of two than similar P on N
devices. (4) Results of this study indicated that both types of devices
would perform sati sfactori l y i n a properly designed circuit to a
fluence of 1.5 x 1016 n/cm2 (E >0. 3 MeV) and 2.2 x 108 rads (C).
Early studies of the effect of electron radiation on tunnel diodes
showed sharp increases in valley current until the negative resistance
region was entirely destroyed at a fluence of 1017 e/cm2
(E = 800 keV). (5) Other studies indicated similar effects from electron
i rradi ati on as a 1-MeV fluence approaches 1017 e/cm2. (6)
19
Varactor Diodes
Varactor diodes are single-junction semiconductor devices
that are used in variable-capacitance applications, their capacitance
varying with applied voltage. I nformation available on the effects of
radiation on these devices is inadequate for reaching general conclu-
sions as to thei r resi stance to a radiation environment. A radiation
study in which this type of device was exposed to an electron fluence
of 8 x 1015 e/cm2 (E = 1.5 MeV) shows an increase in the reverse
current but not of a serious degree since the greatest permanent
i ncrease i n current observed was 245 nanoamperes. (1) The forward-
voltage drop was essentially unchanged.
Microwave Mixer Diodes
I nformation on the effects of neutron and electron radiation on
microwave mixer diodes indicates only minor variations in the d-c
characteristics to fluences of 2.6 x 1016 nlcrn2 (E >10 keV) and
8 x 1015 e/cm2 (E = 1.5 MeV). (l , 7 , The neutron fluence was from a
reactor environment, which also included a gamma dose of 2.9 x
108 rads (C).
Silicon-Controlled Devices
Silicon-controlled devices are among the most sensitive of al l
el ectroni c parts to a radiation environment. These include three
basic units: the silicon-controlled rectifier (SCR), the silicon-
controlled switch (SCS), and the Schockley diode. These units are
al l four-l ayer, pnpn semiconductor devices analogous to overlapping
pnp and npn transistors, and they differ only in the external accessi-
bility of the four layers through the attaching of el ectri cal l ead wi res.
The silicon-controlled switch has leads to all four l ayers of the pnpn
semiconductor structure, while the silicon-controlled rectifier
excludes the lead to the central n-region. The Schockley diode has
leads only to the outer p- and n-layers. The structures of these
devi ces are i l l ustrated pi ctori al l y i n Fi gure 19.
Exposure to radiation induces defects or bulk damage in silicon-
controlled devices which reduces the current-transfer ratios of the
two overlapping transistors. The reduction in transfer ratios increases
the gate current, holding current, and breakover voltage required to
switch these devices on or make them conduct. If the radiation fluence
is great enough that the product of the transfer ratios of the two
sections becomes less than one, no amount of gate current applied to
a silicon-controlled switch or rectifier or increase in the voltage
applied to a Schockley diode will cause them to conduct.
20
1 - -
Anode
gat e -l
Anode Cat hode
Cat hode
Si l i con-Cont r ol l ed Switch
+
Anodeo 0 Cat hode N P N P
-
Gat e
Si l i con-Cont rol l ed Rect i f i er
Anodeo P 0 Cathode N P N
+
-
Schockl ey Di ode
FIGURE 19. STRUCTURE DIAGRAMS OF SILICON-CONTROLLED DEVICES
21
Gate current requirements to fire a silicon-controlled rectifier
increase rapidly at fluences above 2 x 1011 n/cm2 (E > 10 keV). This
is not necessarily the minimum fluence at which problems may occur
with these units, since radiation-induced discontinuities have occurred
at fluences as low as 1. 09 x 108 n/cm2 (E >10 keV). (8) Complete
failure where the unit fails to fire occurs at fluences as low as 1013
n/cm2 (E > 10 keV). These problems indicate that the application of
these devices in a radiation environment generally should be avoided
if possible; if they must be used, the total fluence should not exceed
1011 n/cm2 (E >10 keV).
The application of silicon-controlled switches and Schockley
diodes, being similar devices, should be approached with the same
caution as that pointed out above, although data are unavailable for
verification.
Schottky Barri er Diodes
The Schottky barrier diode, being a maj ori ty-carri er devi ce,
should have a relatively low sensitivity to a radiation environment.
However, exposure to either ionizing or neutron radiation has resulted
in the degradation of this type of device. I onizing radiation, such as
low-energy electrons, gamma rays, and X-rays, produce surface
effects with a buildup of a positive space charge in the oxide and an
increase in the surface velocity of planar devices. These surface
effects are responsible for the degradation of the reverse current
and excess forward current when the Schottky barrier diode is
exposed to this ,environment. ( 9 ) The primary effect of neutron radia-
tion i s bulk damage, which includes carrier removal and decrease
in bulk lifetime. The series resistance of the diode i ncreases because
of the carrier removal, while the decrease in bulk lifetime results in
an increase in forward and reverse current.
The exposure of two different Schottky barrier diode-type
devices (gold-silicon and chromium-protactinium-platinum-silicon)
to a total gamma dose of 108 rads resulted in increases in the reverse
current that vari ed from a nominal change to almost four orders of
magnitude. (10) This total gamma dose also resulted in large variable
responses in the forward characteristic at currents below 100 mi cro-
amperes, with relatively small changes being experienced at higher
current levels. Reactor irradiation to a neutron fluence of 1014
n/cm2 resulted in negligible changes in the characteristics of these
same devices.
Annealing experiments following the irradiation of the above
devices resulted in significant annealing at 150 C for units experienc-
ing large changes in reverse current, while those having small
i ncreases requi red a temperature of 300 C.
22
Various physical configurations of aluminum-silicon Schottky
barrier diodes were irradiated with low-energy electrons (15 to 20 keV)
to a dose of 109 rads (SO2) at room temperature with their leads
shorted. (9) These configurations, which are illustrated in Figure 20,
include a p-n guard-ring diode, an overlap diode, and a non-overlap
diode. The p-n guard-ring diode experienced no degradation in reverse
current below a dose of 108 rad (SiOz) and an increase of approximately
one order of magnitude to 1.0 nanoampere at 109 rad (SiOz). The
overlap diode was more sensitive: the reverse current increased an
order of magnitude at l o8 rad (Si02) and approached another order of
magnitude increase at -5 x 108 rads (Si 02) for a reverse current of
100 nanoamperes. The non-overlap diode was even more sensitive to
the radiation environment.
The gate-controlled diode configuration, which is also illustrated
i n Fi gure 20, was constructed as platinum-silicon devices and
aluminum-silicon devices. The electron dose to which these units
were subjected was l o8 rad (SiOz), and resulted in a large increase
in reverse current. The platinum-silicon devices were considerably
more sensitive to the radiation than the aluminum-silicon devices in
this respect and also in the degradation of their forward characteristic,
in which they experienced increases in forward current at low voltages.
The forward characteristic of the aluminum-silicon units was insensi-
tive to the low-energy electron dose of 108 rad (SiOz), with any excess
current .from the irradiation being masked by the normal thermionic
emission current of these devices. The effect of the gate voltage
upon the forward and reverse currents of the gate-controlled diodes
was shifted by exposure to the low-energy electron environment in
such a manner as to require a more negative gate voltage to obtain a
change in current similar to that prior to irradiation.
Neutron irradiation to fluences of 1015 n/cm2 (E >0. 1 MeV)
also resulted in large amounts of excess current at low forward
voltages in the platinum-silicon devices because of recombination in
the space-charge region. (9) The normal thermionic emission current
of the aluminum-silicon devices again completely masked any increase
that might occur in these units. An increase in the diode series
resi stance from carri er removal was evi dent i n both the pl ati num-
silicon and aluminum-silicon devices.
23
Anode Gate
9 9
Met al
Gat e-cont rol led diode
Overlap diode
Vapor-deposited
SiOe
-Thermal ly grown
Si 02
Anode
Anode
P
Non-overlap diode
-
-
Anode
p-n guard ri ng diode
k+
FIGURE 20. STRUCTURE OF SCHOTTKY DIODES(9)
24
REFERENCES
(1) Stanley, A. G., "The Effect of El ectron I rradi ati on on Electronic
Devices", Massachusetts I nstitute of Technology, Lincoln Labora-
tory, Lexington, Massachusetts, ESD-TR-65-487 (November 3,
1965), Technical Report, AF 19 (628)-5167, 128 pp.
( 2) Ruwe, Victor W. , "The Effect of Neutron and Temperature
Environment on Sensistors, Stabistors, and Zener Diodes",
U. S. Army Missile Command, Redstone Arsenal, Alabama,
RG-TR-67-20 (August 15, 1967), 18 pp.
(4) Dowdey, J . E., Arlington State College, Arlington, Texas, and
Travi s, C. M., Ling-Temco-Vought, I nc., Dallas, Texas, "An
Analysis of Steady-State Radiation Damage of Tunnel Diodestt,
Paper presented at the Conference on Nxl ear Radi ati on Effects,
jointly sponsored by the I nstitute of Electrical and Electronics
Engineers, the Professional and Technical Group on Nuclear
Science, and the University of Washington, Seattle, Washington,
J uly 20-23, 1964, 12 pp.
(5) "How Radiation Effects Tunnel Diodes", Electronics, 33 (l 9),
32-33 (May 6, 1960).
-
(6) Maguire, Thomas, "Production-Line Diodes Being I rradiated",
El ectroni cs, 34 (4), p 28 (February 17, 1961).
-
(7) "Engineering I nvestigation and Tests Which Further Substantiate
System Feasibility and Provide Data Relative to the Development
of a Nuclear Low Altitude Supersonic Vehicle Part I1 - Technical
Information Volume 9 - Nuclear Radiation Effects Test No. 10 -
Flyaway", Ling-Temco-Vought, Inc. , Vought Aeronautics
Division, Dallas, Texas, ASD-TR-64-91, Part 11, Vol. 9,
NS-S-415 (December, 1964), Technical Report (October 1, 1963-
December 31, 1964), A F 33(657)-12517, 251 pp.
(8) ttComponents I rradiation Test No. 1 Transistors and SCR's",
Lockheed Aircraft Corporation, Lockheed-Georgia Company,
Georgia Nuclear Labs., Dawsonville, Georgia, ER-7685
(February 21, 1964), -NAS8-5332, 100 pp. Available: NASA,
X64- 14774.
25
(9) Yu, A. Y . C. , and Snow, E. H., "Radiation Effects on Silicon
Schottky Barriers", IEEE Transacti ons on Nuclear Science,
NS-16 (6), 220-226 (December, 1969.).
(10) Wilson, D. K ., Mitchell, J . P., Cuthbert, J . D., and
Bl ai r, R.. R., !'Effects of Radiation on Semiconductor Materials
and Devices", Western Electric Company, Bell Telephone
Laboratori es, I nc., New York, New York, AFCRL-67-0068
(December 31, 1966), Final Scientific Report (October 1, 1964 -
November 30, 1966), A F 19(628)-4157, 256 pp, Available: DDC,
AD 650195.
BIBLIOGRAPHY
1. Kaufman, A. B., and Eckerman, R. C., Litton Systems, I nc.,
Woodland Hills, Calif., "Diode Resistance to Nuclear Radiation",
Electronic I ndustries, 22 (8) (August, 1963), pp 134-136, 138.
-
2, Armstrong, E. L., "Results of I rradi ati on of Program 660A Pi ece
Parts at G. E. Vallecitos Laboratory", Lockheed Aircraft Corp.,
Missiles and Space Co., Sunnyvale, Calif. (J une 26, 1962), Prog.
Rpt. No. 15, 15 pp, Available: DDC, AD 298473.
3. Anthony, R. L., Honnold, V. R., and Schoch, C. B., "Analysis
of Failure Mechanisms with High-Energy Radiation", Hughes
Aircraft Co., Ground Systems Group, Fullerton, Calif., RADC-
TDR-63-226, FR-63-10-178 (May 1, 1963), Final Rpt. (J anuary 1,
1962 - March 31, 1963), AF 30(602)-2596, 95 pp, Available:
DDC, AD 412647.
4. "Components I rradiation Test No. 2 Transistors, Diodes, Quartz
Crystal s, and 2500 Volt Power Supply", Lockheed Aircraft Corp.,
Lockheed-Georgia Co., Marietta, Ga., ER-7346 (ND-4005)
(April 3, 1964), NAS8-5332, 71 pp.
5. I 1Components I rradiation Test No. 5 HPA-1002 and 1N1616 Diodes
S2N1724 and 2N2222 Transi stors 2N5 11 Flip Flop Bistable Network
SN522 Operational Amplifier", Lockheed Aircraft Corp. , Lockheed-
Georgia Co., Georgia Nuclear Labs., Marietta, Ga., ER-7510
(J uly 24, 1964), NAS8-5332, 56 pp.
6. "Components I rradiation Test No. 7 2N834 Transi stors 1N540 and
1N649 Diodes SlN752A Zener Diodes", Lockheed Aircraft Corp.,
Lockheed-Georgia Co., Georgia Nuclear Labs. , Marietta, Ga.,
ER-7620 (September 28, 1964), NAS8-5332, 52 pp.
26
7. "Components I rradiation Test No. 8 2N918 Transi stors, 1N250
Diodes, Tantalum Capacitors", Lockheed Aircraft Gorp.,
Lockheed-Georgia Co. , Georgia Nuclear Labs. , Marietta, Ga.,
ER-7686 (October 30, 1964), NAS8-5332, 62 pp.
8. Cocca, U., and Koepp-Baker, N. B., General Electric Co.,
Schenectady, N. Y ., "Radiation Induced on Surface Effects on
Selected Semiconductor Devices", Paper presented at the ANS-
ASTM J oint Conference on Radiation Effects in Electronics,
Syracuse, N. Y ., October, 1964, 35 pp.
9. "Engineering I nvestigation and Tests Which Further Substantiate
System Feasibility and Provide Data Relative to the Development
of a Nuclear Low Altitude Supersonic Vehicle Part I1 - Technical
I nformation Volume 10 - Nuclear Radiation Effects Test No. 18 -
Flyaway", Ling-Temco-Vought, Inc., Vought Aeronautics Div.,
Dallas, Tex., ASD-TR-64-91, Part 11, Vol. 10, NS-S-415
(December, 1964), Tech. Rpt. (October 1, 1963 - December 31,
1964), AF 33(657)-12517, 211 pp, Available: DDC, AD 459663.
10. Robinson, M. N., Kimble, S. G., Davies, N. F., and Walker,
D. M., "Low Flux Nuclear Radiation Effects on Electronic
Components", North American Aviation, I nc., Canoga Park,
Calif., NAA-SR-10284 (April 20, 1965), AT( 11-1)-Gen-8, 146 pp,
Available: NASA, N65-22999 and CFSTI.
11. "Components and Sub-Assemblies SNAP 8 Radiation Effects Test
Program - Volume I I I ", Lockheed Aircraft Corp., Lockheed
Georgia Co., Georgia Nuclear Labs., Marietta, Ga., ER-7644
(J anuary, 1965), 294 pp, Available: NASA, N65-23009.
12. IITOS Radiation Test. Series No. 2 (February 1965)", Radio
Corporation of America, Astro-Electronics Div. , Princeton,
N. J . (September, 1965), Engineering Rpt., 150 pp.
13. "SABRE Radiation Effects Data Book", Boeing Co., Seattle,
Washington, D2-90607, Vol. 1 (November 25, 1964) (Apri l 1 -
September 15, 1964), A F 04(694)-446, 432 pp.
14. "Components I rradiation Test No, 16 LDR-25 Photodiodes,
4H-504 Thermistors 1N3881 Diodes, Relaxation Oscillators,
Power Supplies, MSFC Seri es 300 Welded Modules", Lockheed
Aircraft Corp., Lockheed-Georgia Co., Georgia Nuclear Labs.,
Marietta, Ga., ER-8175 (August, 1965), NAS8-5332, 142 pp.
15. Knutson,. C. D., Hooper, H. O., and Bray, P. J ., Brown
University, Dept. of Physics, Providence, R. I ., "A Nuclear
Magnetic Resonance Study of Decomposition in Neutron-I rradiated
LiF", J ournal of Physics and Chemistry of Solids, 27 (l ),
147- 16 1 (J anuary, 1966).
-
27
16. Hendershott, D., "Nuclear Radiation Test Results on Electronic
Parts, Report 2", General El ectri c Co., Re-Entry Systems
Dept., Philadelphia, Pa., GE-65SD2022 (August, 1965), 59 pp.
17. Hanks, C. L., and Hamman, D. J ., "A Study of the Reliability
of Electronic Components in a Nuclear-Radiation Environment,
Vol. I - Results Obtained on J PL Test No. 6 17, Phase I1 to J et
Propulsion Laboratory", Battelle Memorial I nstitute, Columbus
Laboratories, Columbus, Ohio (J une 1, 1966), NASA-CR-81652,
Final Rpt., 800 pp, Available: NASA, N67-17969.
18. Smith, G. D., Fairchild Hiller Corporation, Bladensburg, Md.,
"Performance of Silicon Controlled Rectifiers in Radiation
Environment", I EEE Transactions on Nuclear Science, NS- 13
(6), 341-349 (December, 1966).
19. Smith, E. A., "Results of Semiconductor I rradiation Test at
Western New Y ork Nuclear Research Center, J anuary 19 and 20,
1965", Lockheed Aircraft Corp., Sunnyvale, Calif. (February 25,
1965), I nterdepartmental Communication, 29 pp.
20. "Prel i mi nary Resul ts of Experiments 11 through 17 Conducted
at the Western New Y ork Nuclear Research Center Reactor
During the Time Period December 17 through December 21,
1962", Westinghouse Electric Corp., Astronuclear Lab.,
Pittsburgh, Pa., WANL-TME-250 (J anuary 16, 1963), 15 pp.
21. Been, J . F., "Effects of Nuclear Radiation on a High-Reliability
Silicon Power Diode I -Change in I -V Design Characteristics",
NASA, Lewis Research Center, Cleveland, Ohio, NASA-TN-D-
4620 (J une, 1968), 36 pp, Available: NASA, N68-26662.
22, Weinstein, S. T., "The Effects of Reactor Radiation on 22-Volt
Silicon Voltage-Regulator Diodes", NASA, Lewis Research Center,
Cleveland, Ohio, NASA-TN-D-4923 (November, 1968), 21 pp,
Available: NASA, N69-10250 and CFSTI.
28
INDEX
1 MeV equivalence 4
Aluminum-silicon gate-controlled diode 23
Aluminum-silicon Schottky barrier diode 23
Annealing 22
Applied voltage 20
Associated gamma radiation 4
Atmospheric gas 2
Base-emitter junction 3
Beta 2
Bipolar transistor 1, 3
Breakdown failure 3
Breakdown voltage 3, 6, 9, 15
Breakover voltage 20
Bulk damage 1, 2, 20, 22
Bulk lifetime 22
Capacitance 20
Carrier-generation current 9
Carrier removal 22, 23
Channel conductivity 3
Charge buildup 1
Chromium-protactinium -platinum-silicon
Circuit application 3
Cobalt-60 4, 11, 16
Cross-sectional area 7
Crystal lattice 2
Current capabilities 5
Current gain 2
Current ratings 11, 14
Current -transfer ratio 20
D-C characteristics 20
Defects 2, 7, 15, 20
Degradation 7, 9, 22
Diode series resistance 23
Diode switching time 3
Displacement effects 4
Doping 5
Dynamic resistance 14
Electric fields 2
Electrical bias conditions 6
Electromagnetic radiation 1, 4
Electron fluence 11, 20, 23
Electron irradiation 14, 16, 19
Electron radiation 4, 11, 16, 19, 20
Electrons 1
Energetic particles 1
Energy spectrum 4
Excess forward current 22
Failure criterion 7
Fast -neutron energy distribution 5
Field -effect transistor (FET) 1, 3
Schottky barrier diode 22
Fission spectrum 5
Forward characteristic 7, 22
Forward current 22, 23
Forward voltage 23
Forward voltage drop 2, 5, 6, 7, 8, 9. 11,
Four-layer pnpn semiconductor device 20
Free-charge carriers 3
Frequency capabilities 5
Gain 2
Gallium arsenide diode 19
Gamma dose 20
Gamma irradiation 16, 19
Gamma radiation 11, 19
Gamma-ray photons 1
Gamma rays 22
Gate-controlled diode 23, 24
Gate current 20
Gate threshold voltage 3
Gate voltage 23
General-purpose diode 5, 14
Germanium tunnel diode 19
Gold -silicon Schottky barrier diode 22
We 2
Holding current 20
I onizing particulate radiation 1
I onizing radiation 2, 3, 22
Isotopic sources 4
J unction 11
J unction area 7
J unction-leakage current 2
J unction surfaces 2
Lattice 11
Lattice defects 7, 15
Lattice structure 7
Leakage currents 9
Low -energy electrons 22, 23
Machine sources 4
Microwave diode 5
Microwave mixer diode 5, 20
Minority-carrier lifetime 3, 7, 9, 15
Minority carriers 1
Multiple-junction devices 5
Neutron energy 4
Neutron environment 11
Neutron fluence 3, 7, 8, 10. 12. 13, 14,
Neutron irradiation 11, 14, 17, 18, 23
Neutron radiation 4, 19, 22
Neutrons 1
12, 13, 14, 15, 16, 20
MOS -FET's 3
15, 16, 19
29
INDEX
(Continued)
Non-overlap diode 23, 24
Operating current 16
Overlap diode 23, 24
Passivation layers 2
Permanent changes 5, 7
Permanent damage 2
Permanent degradation 11
Permanent effects 1, 11
Photocurrents 3
Planar -oxide passivated devices 2
Platinum -silicon gate -controlled diode 23
P-N guard-ring diode 23, 24
Positive space charge 22
Power rating 14
Proton radiation 4
Protons 1
Radiation fluence 7
Reactor irradiation 22
Recombination 23
Recombination centers 2
Recovery 1
Rectifier 1, 5, 7, 11, 12, 13, 14
Reference diode 15, 16, 19
Reference voltage 6, 15, 16
Resistivity 7
Reverse characteristic 7, 9, 11
Reverse current 5, 6, 9, 10, 11, 13, 14, 15,
Reverse -leakage current 9
Reverse-recovery time 5, 9, 11
Reverse-saturation current 9
Schockley diode 5, 20, 21, 22
Schottky barrier diode 1, 5, 22, 24
Semipermanent damage 1
Semipermanent ionization effects 1
Sensitivity 14
Series resistance 22
Shielding 15
Short -circuit current 2
Silicon-controlled devices 1, 19
Silicon-controlled rectifiers 5, 20, 21
16, 20, 22, 23
30
Silicon-controlled switch 5, 20, 21, 22
Silicon diode 19
Silicon general-purpose diode 14
Silicon rectifier 11
Silicon-switching diode 7, 9
Silicon-junction device 6, 20
Single-junction p -n device 5
Solar cells 1
Space -charge region 23
Special-purpose diode 5, 19
Storage time 9
Structural diagram 5, 6, 21, 24
Surface charge 9
Surface contaminants 2
Surface effects 3, 22
Surface leakage 9
Surface properties 2
Surface recombination 9
Surface velocity 22
Switching applications 3
Switching diode 5, 7, 8, 9, 10, 11, 14
Switching speed 3
Switching ti me 9
Temperature 16
Temporary effects 1
Thermally annealed 1
Thermionic emission current 23
Total gamma dose 22
Trapped belts 4
Trapping centers 7
Tunnel diode 5, 19
Valley current 19
Van Allen belts 4
Varactor diode 5, 20
Voltage-reference diode 5, 6, 15, 16
Voltage -temperature characteristics 17, 18
Vulnerability 2
X-ray environment 4
X-rays 1, 22
Zener diode 6, 15, 16
NASA-Langley, 1971 - 9 CR- 1785
I -
N A S A C O N T R A C T O R
R E P O R T
KIRTLAND AFB, N. M.
RADIATION EFFECTS DESIGN HANDBOOK
Section 2. Thermal-Control Coatings
by N. J. Broadway
Prepczred by
RADIATION EFFECTS INFORMATION CENTER
BATTELLE MEMORIAL INSTITUTE
1. Repon No. 3. Recipient's Catalog No. 2. Government Accaion No.
NASA CR-1786
4. Title 8nd Subtitle ' 6. Report Dot8
RADIATION EFFECTS DESIGN HANDBOOK
June 1971
SECTION 2. THERMAL-CONTROL COATINGS 6. Performing Orgrnization Coda
7. Author(s) 8. Parforming Orpnization Report No.
N. J. Broadway
%. Mwmi ng Organization Name and Addrar
10. Work Unit No.
RADIATION EFFECTS INFORMATION CENTER
Battel l e Memorial I nsti tute
Columbus L aboratori es
Columbus, Ohio . 43201
NASW-1568
12. Sponsoring Agency Name end Address
11. COntrrct or Grant No.
13. Type of Report and Period Cover d
Contractor Report
Nati onal Aeronauti cs and Space Admi ni strati on
Washington, D.C. 20546
14. Sponsoring Agency Code
I
15. Supplementary Notes
16. Abstract
Thi s document contai ns summari zed i nformati on rel ati ng to steady-state
radi ati on ef f ects on thermal -control coati ngs. The radi ati on i ncl udes nucl ear,
charged parti cl es and ul travi ol et. The data w i l l provi de useful i nformati on to,
the desi gn engi neer responsi bl e for choosi ng thermal -control coati ngs i n space
appl i cati ons.
17. Key' Words (Suggested by Author(r) ) 18. Distribution Statement
Radi ati on Effects, Thermal -Control Coati ngs,
Ul travi ol et Ef f ects, Temperature Control i n
Space Radi sti on Damage
Uncl assi fi ed - Unl i mi ted
19. huri ty Qrri f. (of this reportt
$3 201
Uncl assi fi ed Uncl assi fi ed
22. Price' 21. No. of' Pagas 20. Security Clroif. (of this pago)
For sale by the National Technical Information Service, Springfidd, Virginia 22151
I -
Q
PREFACE
This document is the second section of a Radiation Effects Design
Handbook designed to aid engineers in the design of equipment f or operation
in the radiation environments to be found in space, be they natural or artifi-
ci al . Thi s Handbook provides the general background and information neces-
sary to enabl e the desi gners to choose sui tabl e types of materi al s or cl asses
of devices.
Other sections of the Handbook will discuss such subjects as tran-is
si stors, el ectri cal i nsul ators and capaci tors, sol ar cel l s, structural
metals, and interactions of radiation.
iii
ACKNOWLEDGMENTS
The Radiation Effects I nformation Center owes thanks to several
individuals for their comments and suggestions during the preparation of
this document. The effort was monitored and funded by the Space Vehicles
Division and the Power and Electric Propulsion Division of the Office of
Advanced Research and Technology, NASA Headquarters, Washington,
D. C. , and the AEC-NASA Space Nuclear Propulsion Office, Germantown,
Maryland. Also, we are indebted to the following for their technical review
and valuable comments on this section:
Mr. A. Reetz, NASA, Hq
Dr. J . B. Schutt, NASA, Goddard SFC
Mr. E. R. Streed, Martin-Marietta, Denver
Our additional thanks are due to Academic Press, I ncorporated for
permission to use the copyrighted material from References 13 and 19.
V
TABLEOFCONTENTS
SECTION 2 . THERMAL-CONTROL COATINGS
-
Page
SUMMARY AND CONCLUSIONS . . . . . . . . ' . . . ' . . 1
INTRODUCTION . . . . . . . . . . . . . . . . . . . .
17
. 1 .
Radiation Environments to Whi* Thermal Control
Coatings May be Subjected . . . . . . . . . . . . . 19
Solar Electromagnetic Radiation . . . . . . . . . 19
Penetrating Radiation . . . . . . . . . . . . . 20
Pri mary Cosmi c Radi ati on . . . . . . . . . 20
Trapped Protons . . . . . . . . . . 21
Trapped El ectrons . . . . . . . . . . 21
Trapped Al pha Parti cl es . . . . . . . . 22
Calculation of Accumulated Fluxes . . . ' . 22
Sol ar Particles . . . . . . . . . . . . . 22
Sol ar Wind . . . . . . . . . . . . 23
Auroral Radi ati on . . . . . . . . . . . . 24
Man- Made Radiation . . . . . . . . . . . 24
Mi scel l aneous Natural Sources . . . . . . . . 25
Thermal -Energy Atoms i n Space . . . . . 25
Sol ar X.Rays . . . . . . . . . . . . 25
Neutrons . . . . . . . . . . . . . 25
Albedo Protons . . . . . . . . . . . 25
Al pha Parti cl es . . . . . . . . . . . 25
Geomagnetically Trapped Radiation . . . . ' . . 20
Sol ar-Fl are Radi ati on . . . . . . . . . . 23
ORGANIC COATINGS . . . . . . . . . . . . . . . . . 28
Zinc Oxide/RTV-602 Dimethyl Silicone Binder (S- 13) . . .
Effect of UV and Proton Exposure . . . . . . . .
Effect of UV and El ectron Exposure . . . . . . . .
Zinc Oxide [SP-500] Coated With Potassium Silicate/
RTV-602 Silicone (S- 13G) . . . . . . . . . . . . . . .
Effect of El ectron Bombardment . . . . . . . .
Proton Damage . . . . . . . . . . . . . .
B.1060 . . . . . . . . . . . ' . . . . . .
Titanium Dioxide-Silicone Coatings (Thermatrol White Paint)
Hughes Organic White Paint (H-10) . . . . . . . . .
Leafing Aluminum/Phenylated Silicone . . . . . . . .
. 28
. 30
. 30
. 31
. 34
. 35
. 35
. 37
. 39
. 40
TABLEOFCONTENTS
(Continued)
Page
.
Silicone Over Aluminum . . . . . . . . . . . . . . 40
Silicone-Alkyd- Modified Paints . . . . . . . . . . . . 41
Fuller Gloss White . . . . . . . . . . . . . . 41
PV- 100 (Ti02 in a Silicone Alkyd Vehicle) . . . . . . 42
Acryl i c Paints . . . . . . . . . . . . . . . . . 42
Polyvinyl Butyral . . . . . . . . . . . . . . . . 43
Epoxy Coatings . . . . . . . . . . . . . . . . . 43
White Skyspar . . . . . . . . . . . . . . . 43
Epoxy Flat Black ("Cat.a.1ac") . . . . . . . . . . 45
Polyurethane Coatings . . . . . . . . . . . . . . . 45
INORGANIC AND COMPOSITE COATINGS . . . . . . . . . . 46
Si l i cates . . . . . . . . . . . . . . . . . . . 46
Synthetic Li/A1/Si04 Coating . . . . . . . . 47
Lithium Aluminum Silicate Paint (Lithafrax) . . . . . 46
Hughes Inorganic White Coating (A1-Si04/K2Si03) . . . 48
Aluminum Oxide-Potassium Silicate . . . . . . . . 48
Zi rconi um Si l i cate Pai nts . . . . . . . . . . . . 49
Zi nc Oxi de i n Potassi um Si l i cate (2.93) . . . . . . . 50
Stability to Proton Bombardment . . . . . . . 51
Douglas White I norganic Paint (Z- 93 Type) . . . . 53
Titanium Dioxide in Potassium Silicate . . . . . . . 53
Lanthanum Oxide in Potassium Silicate . . . . . . . 53
Oxide Coatings . . . . . . . . . . . . . 54
Rokide c . . . . . . . . . . . . . . . . . . . . 54
Bright Anodized Coatings . . . . . . . . . . . . 54
Chromate Coatings (Alodine) . . . . . . . . . . . . 58
Composite Coatings . . . . . . . . . . . . . . . 58
Second-Surface Mirrors . . . . . . . . . . . . 58
Series-Emittance Thermal-Control Coatings . . . 58
Silver- and Aluminum-Coated Teflon . . . . 60
Coated, Vapor-Deposited Aluminum . . . . . . 63
Polyimide /Aluminum . . . . . . . . . 61
Silicon Oxide (SiO, ) . . . . . . . . . 63
Silicon Dioxide (Si02) . . . . . . . . . 64
Aluminum Oxide (AlZO3) . . . . . . . . 65
Magnesium Fluoride Over Evaporated Silver . 66
viii
TABLEOFCONTENTS
(Continued)
Page
Uncoated Aluminum . . . . . . . . . 66
Sol ar-Thermoel ectri c Systems . . . . . . . . . . 68
Optical Solar Reflector . . . . . . . . . . 67
Miscellaneous Coatings . . . . . . . . . . . . . . 69
3M 202-A- 10 . . . . . . . . . . . . . . . . 69
Aluminized Mylar . . . . . . . . . . . . . . 69
Aluminum [ 1100(2-S)Al] . . . . . . . . . . . . 70
Aluminum [ 1100(2-S)Al] . . . . . . . . . . . 70
Aluminum [ 1100(2-S)Al] . . . . . . . . . . . 70
Cameo Aluminum 2082 Porcel ai n Enamel . . . . . . 70
Bismuth Sulfide (Bi2Sg)-Dyed Anodized
Cobalt Sulfide (COS)-Dyed Anodized
Nickel Sulfide (NiS)-Dyed Anodized
Lead Sulfide (PbS)-Dyed Anodized Aluminum.
Sandoz Black BK-Dyed Anodized Aluminum.
and Sandoz Black OA-Dyed Anodized Aluminum . . . . 70
Du-Lite-3-D on Type 304 SS (Gri t Bl asted) . . . . . . 71
Black Nickel Plate on Aluminum [ 1100(2-S)Al] . . . . 71
Westinghouse Black on I nconel. Sodium Dichromate-
Blackened SS (Type 347). Sodium Dichromate-
Blackened I nconel. and Sodium Dichromate-
Blackened I nconel X . . . . . . . . . . . . . 71
Aluminum 1100(2-S)Al] and Pyromark
Pyromark Bl ack Refractory Paint on
Bl ack Refractory Paint on I nconel . . . . . . . . 72
PIGMENTS . . . . . . . . . . . . . . . . . . . . 73
Zinc Oxide . . . . . . . . . . . . . . . . . . . 73
Titanium Dioxide . . . . . . . . . . . . . . . . 76
Titanate s . . . . . . . . . . . . . . . . . . . 78
Zi rconi um Silicate . . . . . . . . . . . . . . . . 78
BINDERS . . . . . . . . . . . . . . . . . . . . . 79
Si l i cone Bi nders . . . . . . . . . . . . . . . . . 79
REFERENCES . . . . . . . . . . . . . . . . . . . 80
INDEX . . . . . . . . . . . . . . . . . . . . . 90
ix
TABLE OF CONTENTS
(Continued)
Page
APPENDI X A
THERMAL CONTROL MATERIALS FOR SOLAR AND FLAT
ABSORBERS AND REFLECTORS . . . . . . . . . . . A- 1
CONTOURS OF CONSTANT FLUX ELECTRONS AND PROTONS. . A - 1
APPENDI X B
TABLES AND FIGURES FOR ORGANIC THERMAL-CONTROL
COATINGS . . . . . . . . . . . . . . . . . . . B- 1
APPENDI X C
TABLES AND FIGURES FOR INORGANIC THERMAL-CONTROL
COATINGS . . . . . . . . . . . . . . . . . . . C- 1
X
SECTI ON 2. THERMAL-CONTROL COATINGS
SUMMARY AND CONCLUSIONS
Maintenance of a rather narrow range of temperatures wi thi n satel l i tes
is essential in both manned and unmanned vehicles. For electronic appa-
ratus, the most sui tabl e temperature range presentl y is 20 to 40 C. Manned
spacecraft must not exceed 11 0 F ( 43 C) f or periods longer than a few
minutes. (1)
Control of temperatures on an operati onal spacecraft i s based on the
exchange of radiant energy with the vehicle's environment, and therefore
upon the thermal-radiation properties of the exteri or surfaces. Thermal -
control coatings with the desired radiative properties have been used in the
aerospace i ndustry to mai ntai n a predetermined heat balance on space
vehicles. Solar absorptance, as , and hemispherical emittance, ch, of the
coating have been the prime characteristics with respect to controlling the
heat balance of a vehicle.
Design requirements often dictate the use of a surface with low ratios
of sol ar absorptance to emi ttance, a s / &. These surfaces are general l y
susceptible to damage by sol ar radi ati on, resul ti ng i n an i ncrease i n as .
Considerable effort has been spent in developing coatings which would be
stable in a space environment, relatively easy to apply and maintain, and
which would have the desired radiative properties.
I deally, thermal-control surfaces can be divided into four basic
cl asses, sol ar absorbers, sol ar refl ectors, fl at absorbers, and fl at refl ec-
tors. The sol ar absorbers are pri nci pal l y metal s and are rel ati vel y i mmune
to space radi ati on damage. The fl at absorbers [ absorbing incident energy
from ul travi ol et (UV) to the far i nfrared (IR)] are most easi l y obtai ned i n
general practice, and their stability to space environments presents few
problems unique to these coatings. Flat reflectors (reflecting energy inci-
dent upon it throughout the spectral range from UV to far IR) have been
prepared as paints pigmented with metal flakes or as silver or aluminum
vacuum-deposited coatings overlaid with a transparent coating.
1
The greatest research effort has been expended toward the devel opment of
sol ar refl ectors. Some of these have been adapted by suitable pigmentation
to provi de sol ar absorber systems.
”-
The pri nci pal probl em i n temperature control is presented by change
of the as/€ rati o of a coating due to degradation by space environments such
as UV radiation; proton, alpha particle, and electron bombardment; neutron
and gamma radiation; and micrometeoroid impact. These space environ-
mental factors are shown in Table 1. Those environments of importance to
coati ng damage are marked wi th an asteri sk.
TABLE 1. MAJ OR PORTIONS OF THE SPACE ENVIRONMENT(^)
Natural
Particle Radiation
Protons
El ectrons
Galactic
Van Allen*
Sol ar Fl are
Solar Wind*
Auroral
Van Allen96
Auroral*
Alpha Parti cl es Sol ar Wind
Sol ar Fl are
Electromagnetic
Sol ar Emi ssi ons*
Physi cal I mpact Atmospheri c Parti cl es
Micrometeoroid
Artificial
Persi stent
Electrons High-Altitude Nuclear Detonations*
Neutron/ Gamma Spacecraft-Borne Nuclear Reactors9;
Electron/Gamma
Spacecraft-Borne I sotope Power .Supplies
Transi ent
Burst Products Nuclear Weapons
Plume Contaminants Rocket Firing in Space
Tonsidered important with respect to thermal-control coatings.
2
The following generalizations concerning the effect of space environ-
mental factors on coatings may be made on the basis of a review of presently
available
(1 1
data:
The most damaging factor is UV radiation. Of the four basi c
types of thermal-control surfaces, only the sol ar refl ectors
(the, white paints primarily) are seriously damaged by space UV.
Specular surfaces and leafing aluminum are resistant to re-
flectance change in the I R wavelength region, but undergo sub-
stantial permanent reflectance losses in the visible and UV
wavelength regions. Diffuse coatings are subj ect to refl ec-
tance degradation over much or all of the measured 0.24 to
2. 5-micron wavelength region. ( 3 )
Nuclear radiation (gamma and neutron) is also damaging.
However, most of the present organic coatings will with-
stand doses of approximately l o8 rads (C) without appreciable
damage. I norganic coatings will probably withstand some-
what higher exposures.
Electron bombardment will adversely affect coatings. The
damage of particle radiation to organic coatings. i s si mi l ar
to that caused by UV. The damage mechanism i s, in effect,
the same. The better coatings will withstand 1 015 to 101 6
e/cm2 (E 145 keV). Higher doses may cause severe
damage.
Specular surfaces and leafing aluminum-silicone coatings
are, i n general , rel ati vel y resi stant to refl ectance degrada-
tion due to electron exposure (E <50 keV). Excepting leaf-
ing aluminum, the diffuse coatings or paints are, in general,
subject to severe, in-air recoverable degradation in the I R
wavelength region, and to substantial visible-region reflec-
tance l osses whi ch are less recoverable or "bleachable"
upon re-exposure to air. Coatings employing methyl sili-
cone binders sustain the greatest degree of reflectance deg-
radation in the IR wavelength region. Coatings using
potassium silicate binders suffer the largest electron-
induced reflectance losses in the visible region. ( 3)
3
I '
It has been found, in a seri es of tests on various coatings,
that over a wide range of fluxes and fluences (4 x l o8 to
1.7 x 10l 2 e/(cm2.s), and 1013 to 8 x 1015 e/cm2, no i r-
radiation rate effects from 50-keV electrons are evident.
El ectron damage at 77 K (-196 C) is general l y l ess severe
than at 298 K (25 C). The combination of UV and electron
damage is general l y more severe than the sum of the dam-
age caused by the individual factors. However, changes in
reflectance of anodi zed al umi num (both barri er- and sul -
furic acid-) and aluminum oxide-potassium silicate coating
produced by simultaneous electron-UV irradiations were
approximately equal to the sum of the changes produced by
separate irradiations to equivalent doses when irradiated
in vacuo at 77 K. (4)
(4) Gal acti c protons are rel ati vel y uni mportant because of the
relatively low f l ux, but Van Allen and solar-wind protons
are damagi ng to coati ngs. The l i mi ted data avai l abl e
suggest that auroral protons and l ow-energy sol ar-fl are
protons are uni mportant wi th respect to coati ng damage.
Coatings are available which will withstand about
3 x 1015 p/cm2 (E =3 - 468 keV). Above this exposure,
damage may be severe. Proton damage has been found to
be greater at 77 K (- 196 C) i n many cases than at 298 K
(25 C). Many times, the combination of proton and UV
radiation is only slightly more damaging than UV alone.
The UV tends to bleach the damage due to proton
i rradi ati on.
(5) Sol ar al pha parti cl es are consi dered of secondary i mpor-
tance to coating damage when compared to the effects of
solar-wind protons and solar UV i rradi ati ons. Thei r
numbers are l ess than those of solar protons. However,
their effectiveness on a arti cl e basi s is comparabl e to
proton-induced damage. pz)
(6) Resi dual hi gh-al ti tude earth-atmospheri c parti cl es are con-
sidered unimportant in their effects to satellite surfaces.
The micrometeoroid environment of space is not important
for optical damage, where damage is defined as ei ther a
change in as or E, or a change in the reflected angular
4
I -
distribution of sol ar energy. The l atter effect, however, i s
i mportant for sol ar concentrator and mi rror appl i cati ons. ( 2 )
Arti fi ci al envi ronments such as that caused by the Starfi sh
detonation and spacecraft-borne nuclear sources are
damaging. ( 2 ) However, the data on electron and nuclear
damage are applicable in considering these environments.
Rocket-plume contamination, the products of exhausts from
both solid- and liquid-fueled rockets, is a problem with
thermal control coati ngs. (2) More data are needed before
conclusions can be reached on this problem.
As was stated in (1) above, the most damaging of the environmental
factors i s UV radiation. Due to (a) the spectra from available UV sources
not matching the solar spectrum, (b) UV damage in vacuum being more
severe than UV damage i n ai r, and (c) recovery of damage often being
rapid when air is supplied to the coating, it is difficult to forecast UV dam-
age to coatings in space on the basis of l aboratory data. As a result, even
with "in situ" measurements, i . e. , reflectance values of coatings obtained
before being removed from the vacuum in which they were irradiated, labor-
atory data and those obtained from space satellites have not always been in
agreement.
Coatings that appear to be most stable to space environment include:
(1) A zinc oxide/potassium silicate coating ( 2 - 9 3 type) which has
shown no measurable damage in over 3000 hours of sol ar
exposure i n OSO-I1 and Pegasus I1 experiments. This coating
suffered somewhat greater damage on the interplanetary flights
such as Mari ner I V and Lunar Orbiter V. This damage
(nu, =0.05 after 1000 sun hours in flight on Lunar Orbiter V)
was believed due to the solar wind. The coating suffered less
damage than the others tested on this flight. The major
problems with this coating are the difficulty of application
and ease of soiling during preflight operations.
(2) Second surface mi rrors whi ch have shown excellent stability
to both UV and particle radiation. Silvered Teflon showed no
change on the OGO-VI after 4600 ESH. Aluminized 1-mil
Teflon showed a Aa, of 0. 043 after 5000 hours' exposure on
the Mari ner V. An SiOJ Aluminum reflector showed no
5
TABLE 2, EFFECT OF RADIATION ON
Effect of Ultraviolet
Coating Binder as E +Vacuum Effect of Nuclear Radiation
S-13
(B1056)
Si l i cone 0.21 0.88 800 ESH. AcLs=0.08
1500 ESH, A g=O. 18
(Pegasus I)
S-13 G
(B-1060)
Thermatrol
2A-100
Hughes Organic
White (H-10)
Silicone 0.19 0.88 1000 ESH, A%=0.04
(OSO-111)
0.19 0.88
Silicone 0.17 0.86 500 ESH, AacO. 06- No change at l o8 rads(C)
0.16
Silicone 0.15 0.86
Silicone (RTV 602)
Over Aluminum
(1199)
Leafing Aluminum Phenylated
Silicone
0.20 0.80 1141ESH, Aas=O.O1
1130 ESH, decrease
in refl ectance at
250 mp =24%
6
ORGANIC THERMAL CONTROL COATINGS
Effect of Proton Effect of Electron Effect of Effect of Combined Refer-
Bombardment Bombardment . Temperature Environment Satellite ences
Threshold damage
1014p/cm2 (E=
20 keV), severe
damage at
1016p/cm2
3~1015p/cm2,
Aas=O.O1
5x1016p/cm2,
(E=10 keV) ,
AaS=O. 42
3x1015p/cm2
(E=466 keV),
AaS=O. 01
No evidence of
cracking or spall-
ing when cycled
4 times from
260 to -190 C
1014 e/cm2 (E=50 keV)
Aas=O.Ol
lOI5 e/cm2, no effect No serious degrada-
1016 e/cm2, A%= tion at ascent
0.05, bond failure temperature, in-
1016 e/cm2 (E= crease in temp
80 keV), severe increases Aa
degradation
Moderate losses i n Extremely resistant
reflectance after to reflectance
1017p/cm2 (E =
change at 1016e/cm2
20 keV) (E=20 and 80 keV)
1000 hr AaS=O. 14 Lunar 16, 17.
(Lunar Orbiter I)
Orbiter 18, 20,
2000 hr Aa s=O. 20 I 49
(Mariner V)
Pegasus I
4600 hr Aa/,= 0.40 Mariner V
ATS -I ATS -I
6000 hr A CC/ ~I =O. 30
(ATS-I)
1300 hr A%=O. 16 Lunar 3. 14,
(Lunar Orbiter I V) Orbiters 17,
11, IV. 26
V
1300 ESHAa s=O. 12
(Lunar Orbiter
IV)
Nuclear +UV, Aas =
Proton causes an-
nealing effect with
UV. Combined
damage greater
than sum of sepa-
rate effects.
0.08
1500 sun hr. Aas=
0.18
(Lunar Orbiter V)
Lunar 14.
Orbiter 26
IV
21.
27 9
38 I
51
Lunar 14,
Orbiter 26
V
1500 sun hr bas= Lunar 14,
0.13 Orbiter 26
(Lunar Orbiter V)
V
3. 27
7
I I,. .
TABLE 2.
Effect of Ultraviolet
Coating Binder C C S E +Vacuum Effect of Nuclear Radiation
Fuller Gloss White Silicone- 0.25 0. 90 485 ESH, Aas=0.06 Excellent stability at l o8
alkyd 0.29 850 ESH, Aas=0.07 rads(C)
4. 5x107 rads(C), 4 . 5 ~1 0 ~
1. 8x108 rads(C), 1. 8x1Ol4
n/cm2, Aa,=O. 06
n/cm 2 , Aas=0.09
PV-100 Silicone-
alkyd
162 ESH, Aa=O. 17
S
White Skyspar EPOXY 0.22 0.91 485 ESH, Aas=0.24 2.2 x l o6 rads(C), no change
0.25 850 ESH, Aa,=O. 39 5x107 rads(C), Aas=0. 07;
2x108 rads(C), Aas=O. 12
Tinted White Acrylic 0.24 0.86 485 ESH, Aas=O. 11 5x107 rads(C), bs=0. 05
Kemacryl 0.28 1000 ESH, A a~0. 12 2x108 rads(C), Aas=0.06,
0.09
failure
1-3x108 rads(C), mechanical
Nonleafing Acrylic 0. 44 0.48 Ac~,=0.07
degrades
Aluminum/Acrylic Binder
- - -. ..
IIc~-__-_".--" -l_-
8
(Continued)
-~ ~ ..
Effect of Proton Effect of Electron Effect of Effect of Combined Refer -
Bombardment Bombardment Temperature Bombardment Satellite ences
10 16e/cm2, no change UV+Nuclear, 920 ESH, 3, 27,
in AQS lo8 rads(C), surface 33,
yellowed, paint 38
flaked off
_ _ _ _ _ _ ~ "" - . ~
3x1015p/crn2 (E=
4 ~1 0 ~~e/ c r n ~, damage
466 keV), Aas= approaches saturation
0.03 l evel
1016p/crn2, degraded
coating
6.4~10 p/crn2, 1015e/cm2, Aas=.03
6 . 4 ~1 0 ~~ p/crn2
2.1x1018 p/crn2
Aa,=O. 02 1016e/cm2, AaS=O. 07
A%=O. 04
AaS=O. 12
1015e/crn2;. ACX =
0.02
S
1016,/Crn2, Ass=
0.06
UV+Nuclear, 920 ESH,
l o8 rads(C), 180 F.
paint turned brown
and bubbled
35
oso-I 33, 3 4 ,
OSO-I1 38, 49
33,
38
I
9
. ..,
TABLE 3. EFFECT OF RADIATION ON INORGANIC
Effect of Ultraviolet
Coating Type as E +Vacuum Effect of Nuclear Radiation
Lithafrax/Na2Si03 0.15 0.86 485 ESH, A ac0. 06 5x1o7 rads(C), AagO.06
(Li/A1/Si04) 600 ESH, h S = O . 06 2x108 rads(C), Aas=O. 14
Degrades severely
1. 3x108 rads(C), Aas=O. 10
Synthetic 0.16 0.87 485 ESH, Aas=0.O9 1. 3~10 rads(C), Aas=O. 09
8
Li/A1/Si0i/Na2Si03 162 ESH, Aq=0.12
2- 93
(Zinc oxide/K2Si03)
Hughes Inorganic
White (H-2)
(Ti02/K2Si03)
Douglas White
Inorganic
Zirconium
silicate/K2Si03
2- 93
0.18 0.88 3000 sun hr, Aas=O. 00
0.20 0.93 (OSO-11, oso-111,
Pegasus 11)
0.14 0.89 1300 sun hr, Ass=
0.18 0.88 0.14
200 ESH, Aasin-
creased 10 percent
0.24 0.87 485 ESH, Aas=0.04
0.14 0.89
0.11 0.82 162 ESH, Aas=O. 13
AND COMPOSITE THERMAL CONTROL COATINGS
-~~~ ~~ "
_ _ ~ " - ""
Effect of Proton Effect of Electron Effect of Effect of Combined Refer -
Bombardment Bombardment Temperature Environment Satellite ences
1015e/cm2, Aa,=O. 05
10 16 e/cm', A ~HO. 10
Concurrent UV and
nucl ear more dam-
aging than UV fol -
lowed by nuclear
36 I
38
Low energy protons 10l5e/cm2, Aa,?O1.06
cause measurable 1016e/cm2, AcCsi?O, 09
damage.
466 keV), Aas=0.06
1015p/cm2 (E=
1. 6~10~~p/ c m~, Electrons tend to
1. 9x1018p/cm2,
Aa=O. 11
S
bleach
Aa,=O. 67
1016e/cm2, ~a, =
0.02
3x1015p/cm 2 (E=
466 keV), Ass=
0.02
34,
38
1500 sun hrs, A$= Mariner 13,
0.07 (Lunar
IV 14,
Orbiter V) Lunar 21,
73 hrs, Aa~0 . 0 7 Orbiter 26,
V 32.
OS0 11, 41,
111 49
Pegasus
I1
Thermal cycl i ng 1000 sun hrs, A%= Lunar 14,
4 ti mes from 0.09 (Lunar Or- Orbiter 16,
533 K to 83 K , biter IV) IV 26,
Aas=O. 03 Surveyor 28,
I 30
10 16e/cm2 and
485 sun hr.
Aa s=o. 06
41
30 1
38
Proton+UV only ATS-I 4,
slightly more 19,
damaging than
UV alone.
Electrons+UV en-
hanced stability
of refl ectance
4300 ESH,
A(as/c)=o.45
350 ESH and 5 . 8 ~
1015e/cm2 at
77 K , A%=O. 13
(ATS-I )
1 1
TABLE 3.
Effect of Ultraviolet
Coating Type E +Vacuum Effect of Nuclear Radiation
3M202-A-10
Anodized Aluminum
Si 0 on Aluminum
Rokide C
Alod ine
Optical Solar
Reflector
Magnesium fluoride/
Magnesium fluoride
Vinyl Silicone
Molybdenum/
on Aluminum
0.18 0.73 162 ESH. Aas=0.04 3x10 8 rads(C), Aa,=O.Ol
0.23 576 ESH, Aa s=O. 18
1152 ESH. Aa ~0 . 1 9
1580 ESH, AUs=O.OO
(OS0 -111)
Variable Severe degradation
depending
on thickness
of Si 0
0.90 0.85 No degradation
Chromate
finish on
al umi num
No. 1, Ag 0.05 0.81 485 ESH, no change i n
mirror Aac
No. 2, A1
mirror
0.10 0.81
0.85 0.53 Good UV stability
0.91 0.85
0.16 0.15 3800 ESH, no change
0.21 0. %(a)
Butvar on
Aluminum
0.18 0.45
(0.75 mils)
0.22 0.85
(3.2 mils)
0.22 0.88
(6.5 mils)
(a) Emittance dependent on coating thickness.
12
(Continued)
Effect of Proton Effect of Electron Effect of Effect of Combined Refer -
Bombardment Bombardment Temperature Environment Satellite ences
1016p/cm2 (E=3 keV), 4x1016e/cm2 (E;
degraded in visible 145 keV) damage
and IR approached a satura-
ti on l evel
1 0 1 5 ~/ ~~~ (E= 4x1016e/cm2 (E=
466 keV) Aa,=O.Ol 145 keV)
1016p/crn' (E=3 kev), No change
Ao! =no change
S
Emittance changed
0.07
3~10~~p/ c r n~, no 10 16e/cm2, no
change
change in Aa
35
2000 ESH, Aa=o.ll ATS-I11 4, 5.
(ATS-III) os0 -111 35,
48
Stable up to
2 years in all
charge and
particle environ-
ments and com-
bined environ-
ments of space
170 ESH, l o7 rads(C).
X-ray, Ao! s=O. 01
1720 ESH, l o8 rads
(C) X-ray, Ass=
0.02
Vanguard 2, 8
I1
9
49
55
37
37 100 ESH, l o7 rads
(C) X-ray, Ass=
0.01
1000 ESH, lo8 rads
(C), X-ray, Ao!= S
0.02
13
TABLE 3.
~ ~~ ~
Effect of Ultraviolet
Coating Type QS E +Vacuum Effect of Nuclear Radiation
Aluminized FEP 0.16 0.26-
Teflon 0.13- 0. 8da)
0.16 --
Silvered FEP
Teflon
Aluminized
Polyimide
SiO,/Al
SiO-Al-Kaptan
0.07- -- 5-mil silvered Teflon
0.09 4600 ESH, no change
incl (OW-VI)
0.44 0.78 20,000 ESH
(3 mi l Acl =O. 10
Kap -
ton)
0.146 0.30
0.111 1488 ESH Acl s=
0.01 to 0.03
0.136 0.25
Badly degraded by
uv
(a) Emittance dependent on coating thickness.
14
(Continued)
Effect of Proton Effect of Electron Effect of Effect of Combined Refer-
Bombardment Bombardment Temperature Environment Satellite ences
No change in absorptance
1015e/~m2 (E=
to 3x1015p/cm2 (E=
80 keV) (2, 5,
40 keV) 10 -mil Teflon) only
AahO.06 degradation
1. 4- 1. 8~10~~p/ cm~ minor reflectance
1016e/cm2, si gni fi -
cantly altered
No change i n absorptance
to 3 ~1 0 ~~p / c r n ~ (E=
40 keV)
1.2-1. 7x1016p/cm2,
AuS=O. 04
5x1014p/cm2 Ass=
0.03
1 ~1 0 ~~e / c m~ (E=l MeV)
no change
1017e/cm2 (E=
20 keV) only
small changes
1016p/cm2 (E=
I. 3x1016e/cm2
63 keV), little
( e145 keV),
change
slight reduction
in spectral re-
fl ectance
750 F, 30 sec in
Vac - no change
7900 F, film visi-
bly darkens
1150 ESH, 1 . 2 ~ Mariner 18,27
l o8 rads(C) X-ray, V 37,50
Aas =no change
1-mil aluminized
teflon 5000 ESH,
Aas=O. 04 (Mari -
ner V)
OGO-VI 50
4800 ESHA ( a/ €) =
3-1/2 yrs, no sig-
nificant degrada-
tion (Explorer
XXIII)
0.26 (ATS-I )
4400 ESH A ( c ~ / E ) =
0.16 ( ATS -I)
51
ATS-I 20,
Explorer 54
XXIII
53
ATS-I 20
Apollo 35,
52
15
degradati on after 3-1/2 years on Expl orer XXIII. An RTV/
silicone coated aluminum showed a Aas =0. 08 after
1100 hours on Lunar Orbiter V.
Optical solar reflectors (OSR), mi rrors consi sti ng of
vapor-deposited silver or aluminum on fused silica have
shown no change in as or E for extended missions up to
2 years. These refl ectors are cerami c mi rrors and
therefore are di ffi cul t to appl y, parti cul arl y on i rregul ar
surfaces. The mi rrors have to be mounted by means of
an adhesive or tape and the size of the mi rrors is approxi-
mately 1 x 1 x 0. 008 in.
(3) Coatings that are more easily applied generally have not
shown good stability. S-13G (ZnO/silicone) and Therma-
trol 2A-100 or Hughes Organic White (both Ti02/ silicone)
are representati ve of the most stabl e of these coatings.
Change in absorptance, Aa,, for S-13G was 0. 14 in
1200 hours on Mari ner V. Absorptance of a Ti O~/si l i cone
apparently increased from 0.24 to between 0.34 and 0.40
on the Apollo 9. The advantages of these coati ngs are that
they are easi er to appl y and requi re l ess prel aunch pro-
tecti on than the above thermal -control materi al s.
Unfortunately, the more, stable coatings are more difficult to apply
and to maintain during prelaunch activities. The coatings that do not re-
qui re el evated-temperature cures and can be repai red easi l y l ack envi ron-
mental stability. However, some of these l atter may be servi ceabl e de-
pending on flight requirements. Continued efforts are needed to develop a
stable coating that can be applied easily, cured at room temperature, and
is easily repaired or cleaned. The chief difficulty is that easily applied
coati ngs general l y requi re organi c bi nders and these are suscepti bl e to
radiation damage.
A summary of the effects of radiation on organic and inorganic coat-
ings is given in Tables 2 and 3.
INTRODUCTION
I n a hostile environment such as is encountered in space where vacuum,
cryogenic temperatures, solar radiation, and particulate radiation are pre-
sent, maintaining an operable temperature within a space vehicle is of the
utmost importance. The internal temperature of the vehicle must be con-
trolled within rather narrow limits in which its contents wi l l operate effi-
ciently. Many electronic components become inoperative at temperatures
above 140 F. Excess heat must be radi ated to space or the vehi cl e wi l l over-
heat. Conversely, i f the vehi cl e radi ates heat faster than it i s absorbed,
enough heat must be generated internally to maintain the necessary balance. (5)
The temperature of an object in space depends upon several factors.
The most important of these are (1) the absorption of radiation by the surface,
(2) the radiation or reradi ati on of energy from the surface, and ( 3 ) the genera-
tion of heat within the object. Other factors that affect the temperature are
the thermal conductivity and specific heat of the spacecraft components, and
the absorptance of earth-emi tted IR energy and earth-reflected solar radia-
tion. ( 6 ) The maintenance of the proper range of temperatures i n a space
vehicle is one of the more important and complex design problems.
Two techni ques are used to regulate the temperature of satel l i tes:
active temperature control and passive temperature control. Active control
consists of a feedback technique that usually employs electrical power and
moving parts. For example, bimetallic strips or thermostats control shut-
ters or vanes to vary the surface i n terms of effective optical properties.
Passi ve control rel i es on the use of surface materi al s with appropriate ther-
mophysi cal characteri sti cs. Frequentl y a combination of both methods is
used.
Much research has gone into the study and development of surface ma-
teri al s and coatings which have absorptive and radiative properties useful for
controlling temperature. It can be shown that the important parameter in de-
termining the surface equilibrium is the ratio of the solar absorptance (as) to
the hemi spheri cal emi ttance (6h) of the external surface where as i s the frac-
tion of incident solar energy absorbed and ch is the fraction of energy radi-
ated as compared to that from a black body at that temperature. (7) Four types
of thermal control surfaces are used to maintain a desi red temperature range
within a space vehi cl e. These are termed sol ar refl ector, sol ar absorber,
flat refl ector, and fl at absorber.
17
A sol ar refl ector i s a surface which reflects the incident solar energy
while emitting IR energy. (8) I t i s characteri zed by a very low a s / € rati o
rangi ng from 0.065 to 0.34. I t has a low as and high E;. White organic paints
with metallic- oxide pigments are representative of thi s cl ass.
A sol ar absorber i s a surface which absorbs energy while emitting a
small percentage of the IR energy. I t is characterized by a relatively high
a s / € ratio (greater than 1) and is approximated by polished metal surfaces.
I t has a high as and low E. Such surfaces reflect a relatively large amount
of incident solar energy (approximately 70 percent); however, they are much
more effi ci ent as sol ar absorbers than as emi tters of IR energy (typical
values, a, 0.25 and 6 0.05) and consequently, when exposed to solar
radiation in a vacuum, such surfaces will become hot. (9) The most success-
ful and widely used of the present sol ar absorbers are al umi num and gold
surfaces. Sol ar absorbers are extremel y sensi ti ve to contamination and
require careful prelaunch handling.
A flat reflector is a surface which reflects the energy incident upon it
throughout the spectral range from UV to far I R. ( 8 ) I t has a low as and low E .
Thi s cl ass of surfaces has been the most difficult to develop. The most prom-
ising class of materi al s for thi s use consi sts of paints pigmented with metal
flakes and very highly polished metal surfaces. These surfaces are gener-
ally characterized by a relatively low IR emittance with an a s / € = 1. 0. The
most favored flat reflector is nonleafing aluminum silicone paint, as = 0. 22,
E = 0 . 24. (9)
A flat absorber is a surface which absorbs the energy incident upon i t
throughout the spectral range from UV to far I R. ( 8 ) I t has a high as and
high E . Of the four basic surfaces, the flat absorber is the most easily ob-
tained in general practice. Generally, any rough black matte surface will be
a good approximation of a fl at absorber. Of the available finishes, Black
Kemacryl Lacquer and dull-black Micobond paint ( as z 0.93, E = 0.88) are
most widely used. (9) As a consequence of the relative ease with which a flat
absorber can be obtained, the considerations which dictate its choice are
those other than the thermal radi ati on characteri sti cs of the material, such
as temperature resi stance, mechani cal strength, abrasi on resi stance, adhe-
sive strength, flexibility, cost, and ease of application.
Figure A- 1 in Appendix A shows the ideal spectral absorptance of these
four types of surfaces and of production materials approximating them.
Tables A- 1 through A- 5 l i st by types the various materials for which a, / €
have been determined.
18
Radiation Environments to Which
Thermal Coatings May Be Subjected
Thermal coatings in a space environment are subjected to several types
of radiation and must be stable to these, or the changes which occur due to
radiation must be known SO that engineers can consider them in designing
space vehicles. The environment which probably affects coatings most seri-
ously is solar radiation, particularly UV. Much information is available on
the effects of UV and vacuum, both f rom laboratory tests and from space
flights. However, other electromagnetic and particle radiations wi l l cause
changes in thermal- control coatings, and information concerning these effects
is comparatively recent. Additional information is being obtained at the pre-
sent time, and results are not yet available. However, published studies
give an indication of what can be expected.
Solar Electromagnetic Radiation
The bulk of the energy in the solar spectrum lies between 0.3 and 4. 0 p
with approximately 1 percent of the energy lying beyond each of these l i mi ts. @)
IR and visible radiation do not possess sufficient energy per quantum to break
chemical bonds in ordinary reactions. The principal effect of IR radiation is
to increase thermal agitation. However, many reactions initiated by the
higher energy UV photons proceed at a higher rate because of the temperature
i ncrease caused by the IR. Due to differences in absorption coefficients, the
effects of radiation in the visible range should be somewhat less than those for
the thermal range and are negligible with respect to the possible effects in
the UV range.
Both the UV and the soft X-ray components of the solar spectrum pos-
sess sufficient energy per quantum to induce rupture of many chemical bonds
and thus initiate chemical reactions with organic coatings. The effect of UV
radiation on structural metals is negligible except for a static charge that is
produced by the removal of electrons by the photoelectric effect. (8)
A great deal of work has been done to determine the effect of UV radia-
tion and the combination of UV radiation and vacuum on thermal-control coat-
ings. However, the first space trips showed much of this information to be
unreliable, and the work had to be repeated "in situ". That is, optical mea-
surements had to be made while irradiated samples were still in vacuum. I n
earl i er tests, these measurements were made i n ai r after i rradi ati on i n vac-
uum, and it was found that damage had "healed" when the samples were
returned to an air environment.
19
UV damage to the individual coatings is di scussed i n other secti ons of
this report. However, it has been shown that of the four basic types of
thermal-control surfaces, only the solar reflectors (the white paints pri-
mari l y) are seri ousl y damaged by space UV radiation. ( 9 )
Penetrating Radiation
The penetrating-radiation environment of space may be due to a
variety of sources, of which the most important are cosmic radiation, trap-
ped radiation, auroral radiation, and solar-flare radiation. ( 8 ) Those portions
of the total space environment which are considered of importance in causing
opti cal damage to spacecraft surface materi al s are:(9, l o)
Van Allen electrons and protons
Solar-wind and solar-flare protons
Auroral el ectrons and protons
Artificial electron belt.
Following are discussions of the various types of penetrating radiation
and the particle fluxes which may be anticipated. Also, some generalities on
the stability of coatings are given.
Pri mary Cosmi c Radi ati on. Cosmi c pri mari es consi st pri nci pal l y of
protons (hydrogen nuclei) moving with relativistic or near-relativistic veloc-
i ti es (from 80-90 percent of the velocity of light). ( 8 ) Except for magnetic dis
turbances and variations on the order of f 2 percent with the solar cycle, the
cosmi c pri mary radi ati on fi el d i s essenti al l y constant wi th ti me.
The effecti ve i oni zati on dose rate due to cosmi c pri mari es is about 10-
rad/hr, and the approximate effective dose rate due to secondaries produced
in a space vehi cl e or i n the atmosphere i s about rad/hr. Hence, the
cosmic-ray-induced damage is regarded as being a very mi nor hazard.
Geomagnetically Trapped Radiation. For orbits near the earth [up to
approximately 20, 000 nautical miles (nm) or 23, 000 statute mi l es (sm) in alti-
tude], the Van Allen radiation is of great importance because of the high fluxes
The Van Allen radiation belts are usually discussed in terms of an inner and
an outer bel t. The more stabl e i nner bel t is normally considered to consist
of those magnetic shells for which L <2 (L = the radial distance of the shell
from the center of the earth at the geomagnetic equator), i. e., at altitudes
20
<3500 nm, and is populated with penetrating protons (E <500 MeV) and
low-energy electrons (mostly E <1 MeV). The outer belt includes shells
L .>3500 nm and consists almost entirely of sl i ghtl y more energeti c el ec-
trons than those i n the i nner bel t. (8)
Trapped Protons. The inner zone proton flux is relatively stable in
time although some changes at low altitudes occur over the solar cycle be-
cause of atmospheric changes. Farther out in the magnetosphere, the proton
di stri buti ons are more easi l y affected by magnetic disturbances, but in gen-
eral they are more stabl e than the el ectron fl uxes. (I 1)
The Van Allen proton environment has beembroken up into four energy
bands: 4 to 15, 15 to 30, 30 to 50, and >50 MeV. The contours of the flux
l evel s are shown in Fi gures A- 2 to A-5. (l o, ''1 I ntegral flux distributions
above 0. 4 MeV are shown in Figure A- 6. (l o) I t is evident from the difference
in spatial extent between the 0.4- MeV map and the four higher energy maps
that it is convenient to think of zones in the proton belt, one with virtually no
protons with energies greater than 4 MeV. This is called the "outer radiation"
zone and extends between an L value of about 4 (in units of earth radi i ) to the
outer boundary of particle trapping. (l o) This zone is characterized by time
variations in flux intensities and corresponding changes in energy spectra.
The intensities indicated in Figure A-6 probabl y are not upper limits for this
zone, but are more conservati ve for maki ng predi cti ons of damage to space-
craft. Energy spectra at the magneti c equator for vari ous L values in the
inner and outer proton zones are presented in Figures A-7 and A-8. Fluxes
of protons at energies lower than the limits shown in Fi gures A-7 and A-8
exist and may be of importance in producing surface damage in materials.
However, data describing these portions of the spectra are l i mi ted.
Trapped Electrons. The trapped-electron belt coincides spatially with
the proton belt, but has different configurations in its intensity and energy
spectrum distributions. The integral flux distribution above 0. 5-MeV electron
energy as of August, 1964, is given in Figure A-9. (l o, 12) This model was
derived from data accumulated between late 1962 and 1964. The measurements
were made after the creati on of the artificial electron belt by beta-decay
electrons from the Starfish high-altitude nuclear explosion on J uly 9, 1962.
Since trapped electrons of natural origin were not well measured before 1962,
present knowledge does not permit a clean separation in the inner radiation
belt between naturally occurring electrons and those of artificial origin.
21
As with trapped protons, the trapped-electron belt is divided into an
inner and outer zone, with the zone boundary being taken at a minimum in the
distribution of high-energy electrons at L -2. 5 to 3 earth radii. According
to Gaines and Imhof, (l o) the i nner zone i n l ate 1964 was characteri zed by
energy spectra general l y si mi l ar to a fission beta spectrum and by mono-
tonic losses in intensity, the loss rate being highest at very low L values
and fairly uniform at about a factor of 3 decrease i n i ntensi ti es each year
for L 5 1.3. Thus for the main portion of the inner zone, the fluxes of
artifically injected electrons should have been about two orders of magnitude
lower in late 1968 than those shown in Figure A-9. (l o, 12)
The electron flux in the outer zone (L 2 2.5) shown in Figure A-9 are
approxi mate mean val ues from data taken from 1962 to 1964, near a period
of minimum solar activity. I ntensities throughout this zone show fluctuations
of as much as two orders of magnitude over time periods of weeks or a few
months. (l o) Since changes in spectral shape might be expected to accompany
the intensity fluctuations, the spectra shown for L = 3.4 and 5 in Figure A- 10
are typi cal orlly. (10)
Trapped Alpha Particles. Alpha particles trapped in the geomagnetic
field have been observed. However, their integral intensities are low as
compared with protons and electrons and they are considered unimportant
with respect to radiation effects.
Calculation of Accumulated Fluxes. I t can be seen that the calculation
of particle fluxes accumulated by a parti cul ar spacecraft at a given time in-
volves many variables and is not simple to perform. The Government main-
tains an "Environmental Science Services Administration" at Goddard Space
Flight Center, Greenbelt, Maryland, 20771, where J ames I. Vette and staff
maintain an up- to- date computerized facility for determining the fluxes for
a spacecraft orbit for any required period of time. Lockheed Palo Alto
Research Laboratory has a similar facility. Figures A- 11 and A- 12 can be
used to determine upper limits for low-altitude circular orbits.
Solar Particles. The geomagnetic field deflects charged particles inci-
,dent on it from interplanetary space and thus provides very effective shielding
to the region of space between about 60 degree north and south magnetic lati-
tudes within the magnetosphere. Near the magnetic poles, and in interplane-
tary space outside the boundary of the magnetosphere, the direct charged-
particle radiation from the sun can be observed. This radiation consists of
22
two components: high-energy particles that occur sporadically, usually in
correlation with visible disturbances on the surface of the sun or sol ar fl ares;
and low-energy protons and electrons, which are present more continuously.
Sol ar-Fl are Radi ati on. Protons from sol ar fl ares present perhaps the
most i mportant source of damaging particles for many orbital configurations.
Since solar-proton events occur sporadically and vary widely in peak proton
flux and duration, the total flux of protons expected within a parti cul ar ti me
peri od i s treated stati sti cal l y. (l o) Fl uxes may be as hi gh as lo4 p/(crn2. s);
average dose rates may range from 1 to 100 rads/hr; and the total dose per
fl are would range from 10 to lo3 rads. (8)
Electrons in the energy range 40 to 150 keV have been measured when
accompanying a number of smal l sol ar fl ares duri ng sol ar mi ni mum. The
fluxes of electrons observed in all cases were small from a damage standpoint.
Alpha particles and charged nuclei of higher atomic number accompany
the fluxes of protons from sol ar fl ares. I n several cases where both al phas
and heavier nuclei have been observed, the ratio between their numbers has
been constant at about 60. The ratio of protons to alphas within the same
energy range appears to vary considerably, the number ranging from about
10 to several hundred. (l o)
Solar Wind. The solar wind i s a plasma consisting of protons, elec-
trons, and alpha particles which continuously streams radially outward from
the sun. The particle velocity in the vicinity of the earth was found to vary
with solar modulation between about 350 and 700 km/sec, which corresponds
to energies of approximately 0. 6 to 2. 6 keV for protons. The particle flux
intensity varied between about 3 x l o7 and 1 x l o9 parti cl es/(cm2- s). (l o)
Breuch states that the sol ar wind i s sel dom l ess than 500 eV or greater than
3000 eV and that an average of 1250 eV for the solar wind over the past
30 years i s suggested. ( 2 ) The surface dose rate will be approximately
10 rads/hr. (8) Fl uxes are l arge, but si nce the energy per parti cl e i s smal l ,
the damage to materials from solar-wind particles will be confined to
surfaces. (10)
6
I t has been demonstrated that solar-wind energies must be used in the
laboratory when studying solar-wind effects on thermal- control surfaces.
Major recovery effects exist in coatings exposed to simulated. solar-wind
protons and to combined simulated solar-wind protons plus solar-UV radia-
tion. Combined irradiation produces major synergistic effects and bleaching
effects which are coating dependent. (2)
23
Laboratory data including UV, 2 and 10-keV proton, and UV +proton
exposures were used to predict the changes in as of three coatings which
might have been expected on the OSO-111 had the satel l i te's orbi t been i n the
sol ar wind. ( 13) The values were then compared with data from i nterpl anetary
experiments (Lunar Orbiters I V, V, and Mariner V). The degradation in
space was greater than that predicted from the laboratory data. (13) Differ-
ences between the degradation of these coatings in near-earth orbits and those
i n i nterpl anetary orbi ts are attri buted pri mari l y to di fferences i n envi ron-
mental parameters between the two types of orbi ts. ( I 4) I t i s bel i eved that the
electrons, protons, and solar UV in the lunar or interplanetary environment
have a synergistic effect which results in a degradation rate higher than that
from sol ar uv exposure alone. (14)
Auroral Radiation. I ntense fluxes of protons and electrons have been
observed in the auroral regions from about 60 to 70 geomagnetic latitude
with somewhat lower fluxes at higher latitudes up to the magnetic poles. The
parti cl e i ntensi ti es fl uctuate over several orders of magnitude but may always
be present in these regions at altitudes to at least 500 nm. The exact origin
of these fluxes and the mechanisms of their trapping or storage and precipita-
tion into the atmosphere are not well understood. They seem to be correlated
with solar activity, however; and the most reasonable source with sufficient
total energy to produce the observed fluxes is the solar wind. (l o)
The average energies of el ectrons observed i n the auroral regi ons i s
of the order of a few kilovolts to tens of kilovolts. A rough estimate based
on the highest activity data and assuming an average energy of 10 keV gives
approximately 1012 electrons/ (cm2. day) for a low- altitude polar- orbiting
satellite. (10)
Observations of preci pi tati ng protons i n the auroral regi ons i n 1965
showed average particle energies of 10 to 20 keV and peak fluxes greater than
106 protons/(cm2. sa steradi an) for energi es greater than 20 keV. A rough
estimate for protons would be approximately 101o protons/(cm day), wi th
an average energy of 15 keV.
2
Man-Made Radiation. The most intense man-made radiations in space
have originated from high- altitude nuclear- device detonations. The intensities
of electron fluxes and the length of time they remain trapped after injection
depend on the yield of the device and the altitude and geomagnetic location of
the detonation. As a resul t of a nuclear detonation, high fluxes of el ectrons
24
can be injected into low-altitude regions of space where the fluxes of naturally
trapped electrons and protons are rather low.
Miscellaneous Natural Sources. These include thermal-energy atoms,
solar X-rays, neutrons, and albedo protons. Of these, the solar X-rays
are probably 'the most impoerant with respect to therm'al coatings. (8)
Thermal-Energy Atoms in Space. I n intergalactic space there exists
a density of about 1 atom/cm3 of thermal energi es (-125 K). These atoms
are predominantly protons. For a space vehicle traveling at l o8 cm/ sec
( 0 . 003 x velocity of light), the effective flux would be l o8 p/(cm2. s) in in-
tergal acti c space. At this velocity, the apparent proton energ is about
0.5 keV, and the surface dose rate would be approximately loy rads/hr.
The internal dose rate would be negligible. The population of thermal-energy
atoms in the solar system is estimated to be about 10 2 protons/cm3. ( 8 )
Solar X-Rays. Although the major portion of the electromagnetic radi-
ation from the sun which makes up the solar constant [ 2 cal /(cm2. mi n)] i s not
ionizing in nature, a very smal l porti on (-0. 1 percent) lies in the solar X-ray
region of a few kilovolts. On this basis, the surface dose rate is estimated
to be about 106 rads/hr. Si nce thi s X-ray energy i s absorbed strongl y by
materi al s, the i nteri or dose rate i s not important. (8)
Neutrons. Except for cosmic-ray interaction with matter such as the
earth's atmosphere, there appears to be no maj or natural source of neutrons.
The flux of neutrons from the cosmi c-ray effects on the earth's atmosphere
is about 1 n/(cm2. s) and poses no problem. ( 8 )
Albedo Protons. I mpingement of cosmi c parti cl es on the earth's atmo-
sphere al so produces a scattered flux of protons which has an intensity of
about 1 p/(cm2. s). The energy range i s 1 to 10 MeV, and the dose per year
i s probabl y l ess than 100 rads. (8)
Al pha Parti cl es. Sol ar al pha parti cl es are consi dered of secondary im-
portance in coating damage when compared to the effects of solar-wind protons
and solar UV i rradi ati ons. Thei r numbers are l ess than those of sol ar
25
protons; their effectiveness on a particle-to-particle basis in producing
optical damage is comparable to proton-induced damage. ( 2 )
I t should be noted that the charged-particle space environment has in-
creased importance for coatings over that normally associated with the degra-
dation of other satellite components and systems. The charged-particle envi-
ronment of space has been found to increase in intensity at the lower energies
and, at these lower energies, the particles are almost entirely stopped in the
satellite surface. This results in significant energy deposition in the external
thermal -control surfaces. The i mportant radi ati ons are the Van Allen and
solar-wind particles. ( 2 ) A summary of the various radiation sources is given
in Table 4. (l 5)
26
TABLE 4. EXTERNAL RADIATION SOURCES(15)
-
Radiation Type of Flux, Peculiar
Source Radiation Energy. E
particles/(cm2- s)
Characteristics
Gal acti c Protons 10 MeV - MeV 2
Least significant
cosmic rays (-9Wo)
Alpha
(-1 @l o 1
Solar wind
Solar cosmic Protons
ray events (95%)
(solar flares)
-1keV
Spectrum is very steep
above 30 MeV (-E-5);
below 10 MeV,
spectrum "~-1.2
Solar electro- I nfrared, 6000 K black body
ma gnet ic visible, radiator, erratic
ultraviolet,
below 1200 A(a)
soft X -rays
Trapped
radiations
Inner belt
(1.2 to 3.2
earth radi i )
Outer belt
(3 to 7 earth
radii)
Aurora
Protons and
electrons
Protons and
electrons
Electrons and
protons
Energy of protons
Energy of electrons
(Ep) <30 MeV (go"/)
(E,) <5 MeV (9w0)
Virtually all protons
less than 1 MeV
E, between 2 and
20 keV; E between
80 and 808 keV
2 x 108 at 1 A U ( ~) LOW energy restricts
hazard to surface
effects
Protons: 5 x 105
(E >1 MeV);
Electrons: 2 x l o7
(E >0.5 MeV)
Protons:
Electrons:
(E >10 keV): lo9
5.2 x 107 e-5E
(E in MeV)
1010 (electrons)
during auroral
storms;
<107 protons
Energy and number
of particles released
per event varies;
108 particles/cm2
for medium flare
Spectrum below
1200 Aca) depends
strongly on solar
cycl e
Flux varies with
magnetic latitude;
el ectron ppul a -
tions of both belts
subject to perturba-
tions due to high-
altitude nuclear
bursts; outer -belt
protons are non-
penetrating
Observed between
65" and 70" north
and south magnetic
latitudes at altitudes
between 100 and
1000 km
27
ORGANIC COATINGS
This section describes the principal coatings that have been studied for
use as thermal -control surfaces. A summary of available data on the effects
of space environment on these coatings is presented.
Zinc Oxide/RTV-602
Dimethyl Silicone Binder (S- ~~ 13)
One of the coatings which looked promising as a thermal -control mate-
rial was developed by the I llinois I nstitute of Technology Research I nstitute.
It consi sts of a high-purity zinc oxide (New J ersey Zinc Company, SP 500) in
a dimethyl silicone binder (General Electric, RTV-602), with SCR-05 (GE)
catalyst. Earlier tests had indicated that the (S-13) coating could be expected
to have good stability when exposed to UV radi ati on. However, space tests
showed that the coating did not have the expected stability. Further investi-
gation showed that the coating was affected by UV in vacuum, but that it
quickly recovered or bleached in the near-I R region when exposed to air.
Thus, the tests in which optical properties were measured in air after vac-
uum irradiation had been misleading. I t was deemed necessary, therefore,
to measure optical properties of thermal-control coatings in situ, that is,
while in a vacuum and before being reexposed to air.
Confirmation of this "bleaching" effect may be seen in tests conducted
in support of the Lunar Orbi ter proj ect. ( 16) The reflectances of coatings
were measured (1) in air, (2) in vacuum before UV irradiation, (3) in vacuum
after various intervals of i rradi ati on, ( 4) in vacuum 'at varying time periods
after i rradi ati on, (5) i n an argon atmosphere after vacuum i rradi ati on, (6) in
ai r under reduced pressure after vacuum i rradi ati on, and (7) i n air at atmo-
spheri c pressure after vacuum i rradi ati on. One of the coatings used in these
tests was B-1056 produced by the Boeing Company and based on the S-13
formulation.
I n two of the tests, argon was bled into the chamber prior to admitting
ai r. ( 16) I n neither experiment did the B-1056 coating bleach. The maximum
exposure to argon was 30 minutes at 0. 5 torr. Upon admi ssi on of ai r, two
samples "bleached", showing no permanent change in solar absorptance.
Two sampl es retai ned a t 1 percent change. This increase resulted from non-
bleachable damage in the visible-wavelength region near the absorption edge
(0. 4-0. 5 mi crons).
28
I
Fi gure B- 1 shows the relative reflectance of sampl es of the B-1056
coating before UV exposure, after 350 ESH in vacuum, and after air was let
into the system. A similar effect was reported at I I TRI and is shown in
Fi gure B-2. A refl ectance decrease of about 35 percent at a 2-micron
wavelength was noted after approximately 800 ESH in vacuum. Recovery
when exposed to the atmosphere was al most total after 2 mi nutes. (l 7) Maj or
damage occurred at wavel engths greater than 1 mi cron and was maximum at
about 2 mi crons (see Fi gure B- 1). The damage bleached out upon exposure
to ai r. I t was noted also that no gross bleaching occurred when air pressure
was l ess than torr.(l 6)
Pegasus reported data on the degradati on of S-13 for at l east 1800 sun
hours. As i s shown i n Fi gure B-3, there was good agreement between the
laboratory (vacuum) data and that obtained on space flights of both Orbiter I
and Pegasus I . Data from OSO-I11 showed a trend with S- 13 coating of con-
tinuous change with exposure to sunlight. ( 1 3 ) The resul ts compared favor-
ably with data from Pegasus I and OSO-11, both near-earth experi ments.
Changes in as measured in the near-earth space environment generally were
much l ess than those measured i n i nterpl anetary space.
Resul ts from the Mari ner V experiment, which was continuously ex-
posed tc the solar wind are shown in Figures B-4 and B-5. This flight was
launched on J une 14, 1967, encountered Venus on October 19, 1967, and
obtained information on interplanetary space. The TCR (temperature con-
trol reference) assembl i es were conti nuousl y sunl i t, and normal to i nci dent
solar radiation to within less than f 1/2 degree. ( I 8) Data on apparent solar
absorptance versus mi ssi on durati on were obtai ned for the fi rst 48 days of
flight, at which time the temperature reached the upper limit of the sensor
range and no further data were obtai ned (Fi gure B-5). Si nce it was the
change in temperature which was monitored, solar absorptance was obtained
by ass1.lming a constant emi ttance of 0. 86 and a solar intensity of 126.4 W/ft2
at 1 AU (this value was indicated by earl y resul ts from the bl ack TCR).
Absorptance changed from about 0. 23 (l ess than 1 hour after sun acquisition)
to approxi matel y 0.41. Thi s degradati on was more rapi d than was expected
based on l aboratory tests. ( 18)
The S-13 coati ng was al so tested on the ATS-I fl i ght and, agai n, degra-
dati on was more rapi d than was expected. ('97 20) Data are shown in
Figure B-6.
Work has shown that the sensitivity of the S-13 coating to UV i ncreases
very rapi dl y as the wavelength of i rradi ati on decreases bel ow 300 mp. (21)
29
See Tabl e B-1 and Fi gures B-7 and B-8. During UV i rradi ati on i n vacuum
S-13 i ncreases i n spectral absorptance near the absorpti on edge of ZnO. I n
addition, it increases considerably in spectral absorptance in the I R region
which, as stated above, bleaches out when the sample is returned to the at-
mosphere. As seen i n Fi gure B-9, IR absorption is wavelength sensitive.
For approximately the same degradation near the absorption edge, the short-
wavelength UV (250 mp) is more effective in producing the near IR degrada-
tion than is the longer wavelength UV (350 mp) .
Effect of UV and Electron Exposure
An S-13 coating was subjected to four types of exposure: UV only,
electron only, UV followed by electron, and simultaneous UV and electron
exposure. (3) All UV exposures were 18 ESH and all electron exposures
were 5 x 1014 e/cm2. Sampl es recei vi ng sequenti al exposure remai ned
i n si tu between exposures. Al l refl ectance measurements were made i n si tu.
Table B-2 shows the spectral-reflectance changes after the four types of ex-
posure. I t may be seen that initial UV exposure preconditions the S-13 coat-
ing so that l ater el ectron exposure l eaves i t l ess degraded i n refl ectance than
an electron-only exposure dose. (3) The extent of degradation also appears
to depend on the ratio of exposure rates of electron and UV radiation.
Effect of UV and Proton Exposure
An S-13 coating was subjected to UV, 10 keV proton, and combined
(sequential) UV and proton exposure at room temperature (298 K ) and
torr. (22) The effects of proton radiation are shown in Figures B- 10 and
B- 11. The characteristic curve for zinc oxide susceptibility to proton dam-
age may be seen. There appears to be no rate effect. Also shown in
Figure B-10 is the fact that the coating showed a bleaching in the IR after
remaining in the vacuum chamber for approximately 74 hours. I ncreasi ng
the dose from 1015 to 1016 p/crn2 almost doubled the peak change in absorp-
tance with approximately 5 percent greater damage i n the IR range. The
effect of ultraviolet radiation (750 sun hours) was slight. There was a slight
absorptance peak near 0.4p and less change in the IR than had been found
with the zinc oxide/potassium silicate coating. See Figure B-12.
The effects of the combined (sequential) environment are shown in
Figures B-13 to B-16.(") After a dose of 1015 p/cm2, there is little dif-
ference between the SUM of the individual environments and the combined en-
vironments except in the I R, where the effect of the sum i s greater than the
30
effect of the combined environments. Figure B-15 shows that the absorp-
tance peak around 0.4p was consi derabl y greater for the l ow dose rate than
for the higher dose rate with approximately the same damage in the IR range.
Zinc Oxide [SP-500] Coated Wi th
Potassium Silicate/RTV-602 Silicone (S- 13G)
I llinois I nstitute of Technology Research I nsititute (LITRI) developed a
formulation using a potassi um si l i cate protected ZnO in RTV-602 silicone
binder and designated the coating as S-13G. This is more resi stant to UV
i n a vacuum than the S- 13. The coating, catalyzed with GE's SRC-05
catal yst at a 0. 4 percent by weight level based on the RTV-602 solids, cures
to the touch in 4 to 6 hours and can be handled in 16 hours. The uncured
pai nt possesses a shelf life in excess of 3 months. An 8-mi l film of S- 13G
has an as of 0. 19 0. 02 and an emittance of 0. 88 * 0. 05. Aas is 0. 03 for
1000 ESH employing i n si tu postexposure refl ecti ve measurements and
AH-6 l amp i rradi ati on. ( 17)
An S-13G specimen employing a sifted pigment that was not dry ground
prior to a 3-hour paint-grinding operation exhibited an increase in solar ab-
sorptance of 0. 01 in 1400 ESH of i rradi ati on. (23) A specimen employing pig-
ment that was first hand mulled and then wet ground for 3 hours exhibited a
A aS of 0. 05; a specimen prepared from hand-mulled pigment that was wet
ground 5-1/2 hours exhibited a &xs of 0. 06 in 1400 ESH. Since sifting as a
method of insuring sufficiently deagglomerated particles is highly inefficient,
a compromise method is employed consisting of wet grinding unsifted, un-
ground silicate-treated pigment for 7 hours in the RTV-602 vehicle. A coat-
ing prepared in this way exhibited a Aa s of 0.02 in the 1400 ESH test. (23) A
grinding period of 4 to 5 hours i s usually required to produce a sati sfactory
coati ng. The presence of potassi um si l i cate on the zi nc oxi de severel y re-
tards the formati on of I R absorption bands (2. 12 mi crons). However, i n pro-
cessi ng this materi al , consi derabl e col or center si tes are formed l eadi ng to
damage under UV i rradi ati on in the visible-wavelength region. ( 16) Thi s il-
l ustrates the i mportance of the methods used for prepari ng the coati ng.
There has been al most a continual development of S-13G regarding its
manufacture and mechani cal treatment i n its manufacture. The formul a for
this paint as reported at the 3rd AIM Thermophysics conference, was: ( 24)
31
Components Weight, lbs
Si l i cate-treated SP500 ZnO 25
RTV-602 silicone resin (GE) 12
S- 13G mixed thinner 14
(Compri si ng, percent)
Toluene 40
Xylene 20
n- butanol 15
I sopropanol 20
Butyl acetate 5
The treatment of the ZnO involved a reaction of the pigment, SP-500
ZnO (New J ersey Zi nc Go. ), with PS-7 potassium silicate (Sylvania Electric
Go . ) at a temperature of 165 F. After the reaction, the filtered cake was
wrapped in Mylar and allowed to “sweat” for 18 hours. The pigment aggre-
gates were deliberately kept large, around 80 mesh, to prevent damage to
the optical properties of the pi gment and (for the same reason) a mi ni mum
of grinding was used in preparing the paint. (24)
Fi gure B- 17 shows the spectral reflectance of the S-13G coating before.
exposure, after exposure to UV while still in a vacuum, and after air was
admitted to the chamber. ( 16) The effect of UV exposure to S-13G may be
seen also in Figure B-18. Decreases in reflectance in the UV visible, and
I R wavelength regions after UV i rradi ati on were as fol l ows:( 2 5’)
UV Expo sur e,
ESH
135
2 50
49 0
7 70
1130
Decrease (I ncrease) i n Refl ectance, AR =Ri-Rf (70)
~~
250 mp 425 mp
~- ~
2100 mp
10
14
19
23
25
6
8
8
Fi gure B-19 shows the laboratory data and those obtained from Lunar
Orbi ter I1 flight. I t will be noted that there was not good agreement for the
S-13G coating between laboratory-test and flight data. The reported labora-
tory tests were conducted near 70 F. Lunar Orbi ter I1 deck temperature
experienced considerable thermal cycling due to the orbit of the spacecraft.
The orbit about the moon was 3- 1 / 2 hours, with about 30 percent of the time
in the dark. I t was believed that this changing thermal input might have
32
caused fai l ure of the adherence or cracki ng i n the top coat. In either case,
the thermal properties would change. Another reason for the discrepancy
between the flight and laboratory data is the fact that the latter did not in-
clude the effects of particulate radiation. Figure B-19 also shows the in-
crease i n Aa s for the s- 13 coating (Boeing B- 1056) which occurred on Lunar
Orbi ter I so that a compari son may be made of the behavior in space of the
two coatings, S-13 and S-13G. ( 16)
Coating S-13G was also tested on Lunar Orbiter I V and tested over
B-1056 (Boeing) on both Lunar Orbiters I V and V. The latter coatings were
used as a reference because the equipment-mount decks (EMD) of these two
spacecraft were painted with S-13G over B-1056 and it was desi red to have
a test coupon of the same coati ng system as the EMD. (26) The S-13G coat-
ing was 10 mils in thickness and had an absorptance value, as =0. 184. With
the S-13G over the B-1056, the undercoat was 10 mils, while the S-13 ti over-
coat was 2 mils. I nitial absportance was as = 0. 19 1. I nitial reflectance ver-
sus wavelength is given in Figures B-20 and B-21. Also in Table B-3 are
the initial absorptance/emittance ratios from flight measurements. Figures
B-22 and B-23 show the changes in a s / € of these coatings during the Lunar
Orbi ters I V and V flights.
Figure B-24 shows the degradation of test coatings on Lunar Orbiter I V
and the comparative test on Lunar Orbiter V for S-13G/B-1056. Figure B-25
shows the degradation of coatings on Lunar Orbiters I , 11, and V. A com-
pari son of these figures will show:
(1) Differences between Orbiter V test coupon and EMD's on
Orbi ters I and I1 are no greater than differences between
the Orbi ter I V and Orbi ter V coupons.
(2) S-13G coating over B- 1056 lessened degradation experienced
by B- 1056 alone up to about 800 sun hours. After that ti me
the S-13G/B-1056 curve for Orbiter I1 merged with the
B-1056 curve for Orbiter I .
( 3) The cal ori metri c UV test predi cted much l ess degradati on
on B-1056 than was experienced in flight. I t is suggested
that temperature of the paint during exposure may be par-
tially responsible for this disparity. The specimen
temperature i n the cal ori metri c test was from 9 to 30 F,
whereas Lunar Orbi ter deck temperatures ranged from
40 to over 100 F.
33
Compari ng the resul ts of the S-13G coatings tested on the Mariner V
with those obtained from Lunar Orbiter IV (see Fi gure B-26), it will be
seen that the i ncrease i n sol ar absorptance for each coati ng was approxi -
mately equal. The solar absorptance of the S-13G on the Lunar Orbiter
was initially lower than that on the Mariner. ( 14)
Prel i mi nary resul ts of the OSO-I11 flight experiment indicated only a
0.04 i ncrease i n sol ar absorptance i n 1000 ESH. When compared to the
0. 12 i ncrease for the same exposure ti me on the Lunar Orbi ter, a substan-
tial difference in the results of these two flight experiments is cl earl y
shown. (14) The OS0 experiments were in a near-earth envi ronment, be-
low the earth's Van Allen belt, and therefore exposed primarily to UV
radiation and micrometeoroids. The Mariner and Lunar Orbiter experiments
passed through the Van Allen radiation belts and thus were exposed to all the
listed environmental parameters. Although there were variations in the pro-
cessing parameters among the versions of S-13G prepared for testing on the
three flight experiments, a consideration of these variations does not show a
significant reason why the OS0 experiments should record much lower de-
gradation rates; therefore the change must be attributed to the environmental
parameters. (14) There appears to be a definite difference in the degradation
rate of thermal -control coati ngs between the near-earth orbi tal envi ronment
and the interplanetary or lunar environment.
Effect of Electron Bombardment
When irradiated with 50-keV electrons at 22 C, zinc oxide-, ethyl
silicone sample types (S-13, S-13G, and a zinc oxide-Dow Corning Q92-016
methyl silicone coatings) had their greatest reflectance losses in the IR
region. These showed the greatest loss of reflectance in the IR region of
the various coatings tested. The S-13G appears to be the most sensitive of
the ZnO-methyl silicone specimens. However, the loss of reflectance in
the visible region was much less than that of many other sampl e types. (3)
Fi gure B-27 shows the effect of 50-keV el ectrons on an earl y formul ati on of
S-13G coating after electron bombardment. (25) The decrease i n refl ectance
was 11 percent at 590 mp after 6 x 1014 e/cm2, and 20 percent at 2100 mp
after the same dose. I nitially a rapi d decrease of reflectance in the I R
region occurred, which eventually tended to saturate. However, in the
visible region, the buildup of damage was slow at first and then more rapi d
at high expo sur e. ( 5,
Coatings S-13, S-13G, and Goddard 101-7 (treated ZnO/methyl sili-
cone) were exposed to 20-keV, 5O-keV, and 80-keV electrons separately to
34
doses of 10l 6 e/cm . ( 2 7 ) It may be seen in Figures -B-28 to B-30 that these
coati ngs are suscepti bl e to el ectron damage, parti cul arl y at the higher
energy l evel s. It was found that after exposure to 20-keV electrons, sam-
ples (maintained in a vacuum and not exposed to light) partially recovered in
reflectance values. However, exposures to the same dose had the same re-
fl ectance val ues regardl ess of whether or not exposure was continuous. ( 2 7 )
Proton Damage
The S-13G coating was exposed to proton bombardment (E= 20 keV) and
sustained threshold degradation at 1014 p/cm2, moderate degradation at
1015 p/cm2. and severe damage at 1016 p/cm2. ( 3) I t was also exposed to
10-keV proton, UV, and combined (sequential) proton and UV(22) at room
temperature and torr. The effect of proton radi ati on on thi s materi al
is shown in Figure B-3 1. The coating showed the characteristic damage
curve for ZnO with about the same affects as the S-13 irradiated with con-
tinuous low current. The effect of UV only i s shown in Figure B-32. The
change in solar absorptance is greater (around 0. 4 micron) than for the S-13
or the ZnO/K2Si03 with virtually no damage in the IR range. The effect of
combined (sequential) environment simulation is shown in Figure B-33.
Bleaching of the proton damage in the LR range has apparentl y occurred.
The S-13G coating was tested for the effects of thermal cycling. Test
cycle consisted of hol di ng at test temperature, 395 K or 533 K , for 1/2 hour,
cooling to near-liquid-nitrogen temperature for 6 hours, and then letting the
sample slowly increase to ambient temperature (300 K ) over a period of
17. 5 hours. Coati ngs were thermal l y cycl ed 4 times before examination.
No evidence of cracking or spalling of the coatings was observed by the un-
aided eye or at lOOX magnification. (28)
B- 1060
A modification of the S-13G is B- 1060 produced by the Boeing Company.
According to their work, the sensitivity of their B-1056 paint to damage
under UV vacuum exposure was dependent upon catalyst concentration and
differed from batch to batch. Boeing then developed a paint using the silicate-
treated zinc oxide, RTV-602 (GE silicone binder), and 1, 1,3,3-tetramethyl
guanidine (TMG) as catal yst. ( 26) The formulation follows:
Pi gment ZnO (potassi um si l i cate-treated SP- 500)
Resin RTV-602 (GE)
Catalyst 0. 2 percent 1, l Y 3,3-tetramethyl guani di ne (TMG)
35
The stability of the pai nt to ul travi ol et is indicated i n the following
data:(26)
I nitial absorptance 0. 194
nas after 0. 55 ESH UV 0. 003
nas after 2. 2 ESH UV 0.005
AaS after 8. 8 ESH UV 0. 007
Aa, after 125 ESH UV 0.028
AaS after l OI 4 50-keV el ectrons/cm 0. 007
Reflectance curves showing the wavelength at which damage occurs are
shown in Figures B-34 and B-35.
I nitial absorptance/emittance of flight coupons carried on Lunar
Orbi ter I V are given in Table B-3. The increase in absorptance on exposure
to the sun during flight i s shown in Figure B-24. Laboratory in situ degra-
dation of B-1060 is also shown in Figure B-24. I n this case, the laboratory
data indicated greater degradation than was experienced in flight. Most of
the change in absorptance (Aa, = 0.028) experienced by the B-1060 in the
laboratory was due to increase in absorptance in the short-wavelength region
around 400 mp, and not due to the zinc oxide "IR anomaly".
The coatings tested on Lunar Orbiters IV and V are l i sted below i n
order of increasing degradation experienced in 1000 equivalent full sun hours
of flight:( 26)
Aa , After
Coating 1000 Sun Hours
2-93 (McDonnell) SP-500 ZnO di spersed 0. 049
PS- 7 potassi um si l i cate
Silicone Over Aluminum RTV-602 over aluminum foil, 0.081
(Boeing) 0. 15% TMG
Hughes I norganic H-2 Ti 02 i n PS-7 0. 089
B- 1060 (Boeing) Modification of S-13 paint 0.091
Hughes Organic H- 10 Calcined china clay dispersed 0.120
in RTV-602
S-13G (IITRI) -- 0. 123
S- 13G B- 1056 " 0. 168
Flight data for these coatings are given in Fi gures B-22 and B-23.
3 6
Titanium Dioxide-Silicone Coatings
(Thermatrol White Paint)
.~ ~ ~~
~ -~ ~
Based on the properties of the ZnO-silicone coatings, it would be antic-
ipated that work would also be directed toward the development of a titanium
dioxide-silicone coating. Such has been the case. However, difficulty has
been encountered in obtaining a coating stable to UV and/or ascent heati ng.(9)
In general, these coatings show good stability in the UV and IR wavelengths
of the solar spectrum, but when subjected to UV radiation, their reflectance
in the visible wavelengths is considerably decreased. They are resistant to
electron bombardment up to 1015 e/cm2, but are susceptible to proton de-
gradation. The pigment is very susceptible to proton damage. ( 2 2 ) The
coating is resistant to nuclear radiation ( l o8 rads) and to a combined nuclear
and UV environment.
Lockheed developed a coating known as Thermatrol 2A-100 which con-
si sted of a 1:l weight ratio of Titanox RA-NC pigment and Dow Corning
Q92009 silicone binder. This binder is a polymethyl vinyl silicone and the
pigment is a rutile Ti02 which has been given a surface treatment. The pig-
ment consi sts of 94 percent Ti 02, 1. 8 to 2.4 percent A1203, 0. 6 to 2. 0 per-
cent Si 02, and 0. 5 to 1. 4 percent ZnO. ( 2 8 , 297 30) The a s / € ratio of the paint
i s 0. 19. I t can be applied as a paint and cured at room temperature or used
as a precured tape wi th a pressure-sensi ti ve si l i cone adhesi ve.
Several modifications have been made to improve the coating, and
some of the data which follow are for earl i er formul ati ons. However, on the
basi s of available information, it is believed that the conclusions are applic-
abl e to the current commerci al product. I t is known that the surface treat-
ment of the pigment is important to the UV stability of the paint, and one of
the problems is to incorporate the pigrnent into the binder without affecting
the surface of the pigment particles.
Thermatrol 2A-100 was exposed to a xenon source (AH-6 lamp) at a
l -sun l evel (0. 20 to 0.40 p) for 500 hours in a vacuum at a temperature of
395 K (122 C). I n situ values of before and after exposure were as =0. 18
and 0. 32, respecti vel y. (z7) The total hemi spheri cal emi ttance remai ned
essentially constant at 0. 85 f 0. 003 for the two samples tested. The change
i n sol ar absorptance appeared to reach a saturation value of 0. 14 after
300 to 400 hours of exposure at thi s temperature. ( 2 8 )
I n another test, only slight damage was found when a Ti 02 /si l i cone
(Ti Pure R-960 in RTV 602 silicone) coating was subjected to 190 sun hours
UV at room temperature and torr. (22) See Fi gure B-36.
37
A ruti l e Ti 02/methyl si l i cone (GE RTV 602) coating was found to offer
the best stability of the white diffuse coatings to an el ectron envi ronment
(20 keV, 50 keV, and 80 keV), providing a dose above l o1 e/cm2 was not en-
countered. (27) However, at 10l 6 e/cm2 (E=80 keV) catastrophic degradation
occurred. An anatase Ti02/methyl silicone (Q92009) degraded more at lower
fluences, but did not degrade to as great an extent at 1016 e/cm 2 . Compare
Fi gures B-37 and B-38. Titanium dioxide-methyl silicones were found to be
l ess sensi ti ve to a reflectance change in the IR region than the zinc oxide-
methyl silicone samples when exposed in situ to 50-keV electrons. They
suffered more significant reflectance loss in the visible region, however.(3)
The most radi ati on resi stant of this type coating were the rutile titanium
dioxide-GE RTV 602 methyl silicone and rutile Ti02-Dow Corning XR
6-3488 methyl silicone coatings. However, the TiO2GE RTV 602 appeared
to craze when subjected to 1015 p/cm2 at 22 C. Fi gure B-39 shows the
effect of proton radiation on the Ti-Pure R-960/RTV 602 silicone coating.
At 3 x p/cm2, the spectral curve has the characteri sti c peak of ZnO
but does not return to near zero in the visible range as does the ZnO. (22)
An anatase titanium dioxide-methyl phenyl silicone (OAO Pyromark
Standard White) coating was subjected to four types of exposure: UV only,
electron only, UV followed by electron, and simultaneous UV and el ectron
exposure. All UV exposures were 18 ESH and all el ectron exposures were
5 x e/cm2 (E 50 keV). Samples receiving sequential exposure re-
mai ned i n si tu between exposures. Al l refl ectance measurements were
made i n si tu.
As may be seen in Table B-4, reflectance changes from combined ex-
posures are l ess than addi ti ve,wi th consecuti ve exposure (UV fol l owed by
electron) causing significantly less damage than simultaneous exposure. I n
much of the wavelength region measured, simultaneous exposure resulted in
less degradation than electron-only exposure. ( 3 )
The effect of UV radiation only on this coating i s shown in Figure B-40.
Changes after 1130 ESH for this coating were 3 percent at 250 mp, 67 percent
at 425 mp, and 2 percent at 2100 mp (UV, visible, and IR wavelengths). (25)
This coating when subjected to 20-keV protons reached threshol d damage
at 1014 p/cm2, moderate damage at 1015 p/cm2, and sustained severe de-
gradation at 1016 p/cm2. ( 3 )
Thermatrol 2A- 100 was exposed to nucl ear radi ati on, 1.3 x l o8 rads
(C), 1.9 x 1013 n/crn2 (E<0.48 ev), and 5.6 x l O14n/cm2 (E>2.9 MeV).
38
No change in solar absorptance was noted, the value remaining at 0. 16. Also
there was no change in hemispherical emittance. (31)
A titanium dioxide-silicone white paint which is used on the outer shell
of the service-module fuel-cell bay of the Apollo spacecraft was mounted on
the service module and command module of Apollo 9. (32) During the extra-
vehicular activity period, the astronauts removed the samples along with
samples of ZnO/K2Si03 and chromic acid anodized aluminum. These speci-
mens were the fi rst to be returned to earth from space unaffected by reentry
conditions. Exposure to space was approximately 73 hours.
The sources of contamination to which these samples were exposed
included:(32)
Plume impingement
Boost heating effects
Outgassing products of abl ati ve materi al s
Pyrotechnic discharge products
The natural space environment.
Degradation of the titanium dioxide-silicone coating resulted in a 42 to
67 percent i n absorptance i ncrease, and i n a sl i ght i ncrease i n emi ttance.
Absorptance i ncreased from 0. 24 to between 0. 34 and 0. 40. Emittance in-
creased from 0. 86 to 0. 88. Although degradation occurred, the absolute
values were well within acceptable limits for the Apollo lunar-landing
mi ssi ons. ( 3 2 ) I t should be noted, however, that samples were not brought
back to earth in vacuum and therefore the effect of solar exposure in space
may not be accurately reflected in the above figures.
An anatase Ti 02 (Ti tanox AMO) in Dow Corning Q92-090, a methyl
silicone, was tested on the ATS-I satellite. (l 9, 20) I n thi s fl i ght, a / € for thi s
coating increased over 200 percent. See Figure B-41. This was more than
had been anti ci pated from l aboratory measurements.
Hughes Organic White Paint (H-10)
This coating is made with a calcined china clay (Plasm0 clay, which is
pri mari l y al umi num si l i cate) di spersed i n General El ectri c RTV-602 si l i cone
resi n. I ni ti al sol ar absorptance as a function of wavelength is shown in
Fi gure B-42. I t was tested on the Lunar Orbi ter V and found to be equivalent
39
to the S-13G coating. I nitial absorptance/emittance values are given in
Table B-3. Solar absorptance, as, obtained in the laboratory was 0. 147 and,
after 1000 sun hours of flight on the Lunar Orbiter V. A a S = 0. 120. (26)
Changes in a/ E during the Lunar Orbiter V flignt are shown in
Figure B-23. ( 14)
Leafing Aluminum/Phenvlated Silicone
Leafing aluminum in a phenylated silicone binder showed moderate
10s ses i n refl ectance after exposure to 1017 p/cm2 (E = 20 keV). Exposure
was at 22 C. The losses were confined to wavelengths shorter than 0. 7
mi crons. On the other hand, reflectance as measured in situ increased at
wavelengths longer than 0. 7 mi crons. Thus a determi nati on of solar absorp-
tance would show little change due to proton exposure. (3)
This coating was also subjected to 10l6 e/cm2 (E = 20 keV and E =
80 keV) and found to be extremel y resi stant to refl ectance change. (27) See
Figures B-43 and B-44.
Exposed to 50-keV electrons, this coating underwent practically no
reflectance changes throughout the measured region to a dose of 8 x 1014
e/cm2 and only small changes were observed after 8 x 1015 e/cm2. At
2100 mp, refl ectance decreased 3 percent after exposure to 6 x e/cm ,
2
and 8 percent after 8 x 1015 e/cm2.
Exposure to UV resul ted i n the fol l owi ng decreases i n refl e~tance:(~)
Exposure, Decrease (I ncrease) i n Refl ectance, percent
ESH 250 mp 425 mp 2100 mp
135
2 50
49 0
770
1130
10
13
17
”
24
Silicone Over Aluminum
Lunar Orbi ter V carri ed a specimen of 1/4-mil 1145-0 aluminum-
alloy foil over which was applied 3. 8 mi l s of RTV-602 silicone catalyzed
40
with 0. 15 percent TMG (1, 173,3-tetramethyl guani di ne). Fi gure B-45 shows
the reflectance of the foil substrate as a function of wavelength and the initial
reflectance of the silicone-aluminum composite as a function of wavelength.
Evaluation of UV stability, in situ, was made on a film of RTV-602
silicone. (26) The film was 2. 6 mils thick over 2024 clad aluminum and was
catalyzed with 0. 15 percent TMG. Figure B-46 shows the reflectance of the
silicone-aluminum composite unexposed, and after 336 and 1141-ESH UV ex-
posure measured i n si tu. The data show no measurable degradation of the
silicone after 336 ESH of UV. The 1141-ESH exposure resulted in an in-
crease i n absorptance below 540 millimicrons and a decrease i n absorptance
above 540 millimicrons, with a net A a of 0.012. Laboratory i n si tu degrada-
tion of the silicone-aluminum coating is plotted in Figure B-47. I t may be
noted that there is a large disparity between the in situ value and the flight
values obtained from Orbiter V. However, the silicone over aluminum has
about the same stability as Hughes inorganic coating and as B-1060, but it
i s l ess costl y to appl y than any of the other coatings tested on Lunar
Orbi ters I V and V. The change in absorptance, Ass, after 1000 sun hours
in flight was 0. 08 1, which was surpassed only by the 2-93 coating. Flight
data for Orbi ter V are shown in Figure B-23.
Silicone-Alkyd-Modified Paints
Fuller Gloss White
Fuller Gloss White is a Ti02-pigmented silicone-modified alkyd coat-
ing in production use that requires a 465 F cure. I ts initial solar absorp-
tance is 0. 25 while its initial hemispherical emittance is 0. 90. I t has fair
optical stability in an UV environment, but good optical stability in electron,
gamma, and neutron environments. It degraded more than the al gebrai c
Sums of the two individual environments in sequential exposure (UV followed
by el ectron).
Lockheed found that absorptance changed by 0.09 f 0.05 after 2000 sun
hours. Tested for thermal -cycl i ng resi stance, the coati ng cracked and
showed a l oss of adhesion after 170 cycl es of -240 to 70 F, taking 18 minutes
per cycle. (33)
Ascent temperature i s l i mi ted to 650 F. (33) The effect of ascent
heating is shown in Figure B-47. ( 9 )
41
Fuller Gloss White showed excellent stability when irradiated (gamma
and neutron) to 108 rads (C) in vacuum at 100 F. ( 33) Solar absorptance
before and after irradiation was 0. 26. Hemispherical emittance, 0. 84, was
unaffected. ( 3 ')
An exposure of 850 sun hours i n vacuum caused a change of solar ab-
sorptance from approxi matel y 0. 25 to 0.32. (See Figure B-48). 0 ti cal -
property degradation was marginal in the UV-only environment. ( 3 1P
PV- 100 (Ti 07 i n a Silicone Alkyd Vehicle)
General Dynamics tested PV-100 coating, manufactured by Vi ta-Var
Paint Company, and found that it was degraded by 10l 6 p/cm2 (E=3 keV) in
the visible and I R regions. (34) See Figure B-49. Spectral reflectance
al so decreased i n these regi ons when the coati ng was subj ected to el ectron
irradiation (145 keV). See Figure B-50. Damage is not proportional to
dose, but approaches a saturation level at a dose not much greater than
4 x 1016 e/cm2 (145 keV). (34)
Acrylic Paints
The best known acryl i c pai nt used as a thermal -control materi al is
White Kemacryl , a Ti02-pigmented acrylic flat paint manufactured by
Sherwin-Williams. The paint is cured at room temperature and has an
initial solar absorptance of 0. 24. I nitial total hemispherical emittance is
0. 86. I t has good optical stability in an electron environment, but poor
optical stability in an UV environment. (35) Some mechanical damage was
observed after this coating had been subjected to an electron environment.
When exposed to electron and then UV i rradi ati on, the pai nt degraded more
than the results of the two environments separately would predict. Small
blisters were formed on the Kemacryl coating. I t was believed that these
were most l i kel y caused by electron-induced decompositon products. I t
was concluded that these surface alterations had no detrimental effect on the
mechanical integrity of the coating. I t was also estimated that the blisters
had no measurable effect on solar absorptance.
Lockheed exposed the coating to 100 and 850 sun hours of UV and re-
ported as/ € as i ncreasi ng from 0. 30 to 0. 35 after 100 hours and 0.40 after
850 sun hours, respectively. The maximum allowable ascent temperature
was given as 450 F providing alterations in surface finish, and solar absorp-
tance due to bubbling can be tolerated. Otherwise the maximum temperature
42
I
encountered must be l ess than 200 F. (9) See Figure B-51 for the effect of
ascent heating on solar absorptance.
Tinted white Kemacryl lacquer (Sherwin-Williams M49WC17, room-
temperature cured) was subj ected to nucl ear radi ati on i n vacuum. (25)
Emittance did not change. Data shown in Figure B-52 indicate an increase
i n as from 0.28 to 0.32 after an exposure of 5 x 107 rads (C), but no fur-
ther change at 2. 5 x 108 rads (C). (3 l ) However, degradation of optical prop-
erti es was consi dered unsati sfactory after l o8 rads.
UV exposure of 1000 sun hours i ncreased as from approxi matel y 0. 26
to approxi matel y 0.38. (31) See Figure B-48. In combined nuclear and UV
radiation, this paint turned brown and bubbled. ( 31) Exposure was 920 sun
hours of UV and 7. 1 x n/cm2 (E< 0.48 eV), 4.6 x 1014 n/cm2 (E >
2. 9 MeV), and 1. 1 x 108 rads (C) gamma. Temperature was 180 F.
A MgO/Acrylic coating supplied to General Dynamics by Wright-
Patterson Ai r Force Base was subj ected to 10l 6 p/cm 2 (E=3 keV), and some
loss in reflectance was noted in the UV and visible regions. (34) See
Figure B-53.
Polyvinyl Butyral
Butvar (polyvinyl butyral) has been considered for use as a thermal -
control finish because of i ts excel l ent fi l m-formi ng characteri sti cs and good
UV stability. ( 3 6 ) It surpasses the acryl i c pol ymers i n adhesi on and fl exi -
bility, but its stability to the heat which may be encountered during ascent
conditions rules it out as a good candidate for a surface coati ng for outer
space use. I ts softening point is approximately 125 C. A further limitation
i s the exi stence of two moderatel y strong absorpti on bands at 1. 7 and 2.3
microns which tend to make the solar absorptance. dependent on thickness
as wel l as the emittance. The change in solar absorptance and emittance
with film thickness on an aluminum backing is shown in Table B-5.
Epoxy Coatings
White Skyspar
White skyspar is an enamel consisting of a Ti02-pigmented epoxy-base
paint which is in commercial production (Andrew Brown Co. ). I t cures at
43
room temperature and has an i ni ti al sol ar absorptance of 0. 25 and an i ni ti al
total hemispherical emittance of 0.9 1. I (37) It i s stabl e to el ectron bombard-
ment, but degrades under UV i rradi ati on. Lockheed reports i ni ti al as / €
as 0. 24; change in absorptance ( b a s ) is reported as 0.35 f 0. 06 after
2000 sun hours. (9) The maxi mum al l owabl e ascent temperature is 450 F. (9)
Skyspar was flown aboard OSO-I and OSO-I1 Satel l i tes. Agreement be-
tween laboratory tests and flight tests was extremely poor, varying several
orders of magnitude. However, agreement between the OSO-I and OSO-I1
data was excellent. (21) The mai n cause of coating degradation during near-
earth satel l i te experi ments can be attri buted to absorbed sol ar-UV radi ati on
since low-energy solar-wind protons are effectively shielded from the orbits
of the satel l i tes, OSO-I and -11and Pegasus I , 11, and 111, by the earth's
magnetosphere. I t is believed that inadequate simulation of sol ar-UV radi a-
ti on i s the mai n factor i n the presentl y observed di screpancy between fl i ght
and laboratory data. Another factor is the lack of temperature control in the
l aboratory tests.
The threshold wavelength for degrading the reflectance of TiOZ/epoxy
coatings is between 260 and 290 mp (4. 7 and 4. 2 eV)('l). Olson, McKellar,
and Stewart reported that photons with energies less than 4. 2 eV resulted in
increased absorption primarily in the visible and I R, whereas photons of
greater energy produced damage pri mari l y near the UV absorption edge. (38)
Fi gure B-54 shows the absorptance changes due to irradiation with a band
centered at 260 mp and with a band centered at 350 mp. The two curves
have been normalized to equal change in solar absorptance. It will be noted
that with the 260-mp irradiation, the induced solar absorptance occurred
primarily near the absorption edge of TiO2, and the degraded sample had a
yellow appearance. For the 350-mp incident radiation, the induced absorp-
tance extended through the visible and near-I R regions, and the sample ex-
hibited a grayer appearance. The absorption edge of the epoxy binder i s
located at about 290 mp. Thus the high absorptance and poor stability of the
epoxy resin undoubtedly have a strong effect on the sensitivity to wavelengths
shorter than 300 mp.
Skyspar enamel was subjected to nuclear radiation in a vacuum. As
seen i n Fi gures B-48 and B-52, this coating showed poor stability to UV and
only fair stability to nuclear radiation. It was tested for nuclear-radiation
stability at temperatures of -100, 0, 100, and 200 F to an exposure dose of
2. 2 x l o6 rads (C), 0. 6 x 1013 n/cm2 (E <0.48 eV), 1 x 1014 n/cm2 (E >
2.9 MeV). Changes in as are shown in Table B-6. The greatest increase
was Acx, = 0.06 at 200 F. At 0 and -100 F, there was no change, There was
no change in hemispherical emittance. ( 3 '1
44
At a dose of 5 x l o7 rads (C), as of this materi al changed from 0 . 23 to
0.30 and at a dose of 2 x 108 rads (C), as changed to 0.35. Temperature
was about 100 F. ( 3 l )
Epoxy Flat Black ("Cat-a-lac")
Another epoxy coating is "Cat-a-Lac" flat black which consists of a
carbon pigment in an epoxy binder. It is widely used as a spacecraft black
coating. I ts reflectance does not vary with wavelength, thus the coating
is i nsensi ti ve to spectral di screpanci es between the sun and a solar simu-
l ator. ( 18) I t was one of the test surfaces on the Mariner I V absorptivity
standard, and data indicated good coating stability in the space environment.
On the Mariner V flight, this coating showed an unexpected apparent bleach-
ing of approximately 4 percent. I t was significantly larger than anything
observed in the laboratory. Simulation testing indicated a change of the
order of 1 percent in solar absorptance for equivalent exposure. This
bleaching is unexplained. Although it probably is not seri ous from a thermal -
control standpoint, it adds to the discrepancies found between laboratory and
flight data. ( 8,
Polvurethane Coatings
A Magna-Larninac X-500 polyurethane flat chromium reen paint has
thermal properties similar to the flight-type solar cells. (397 Their optical
properti es are as fol l ows:
Coating Absorptance ( a) Emittance ( E) a / €
Flight-type solar cell 0. 71 0. 82 0.865
X-500 polyurethane paint
0. 71 0. 85 0. 835
No information was reported on its stability in a space environment.
45
I
INORGANIC AND COMPOSITE COATINGS
I norganic coatings in general are more resistant to space radiation
than are organic coatings. However, they generally are not as convenient to
apply, and in many cases require an elevated-temperature cure.
Silicates
Probably the inorganic binder most frequently used for coatings i s so-
dium silicate. Of these silicate coatings the most important has been lithium
aluminum silicate paint.
Lithium Aluminum Silicate Paint
(Lithaf rax)
This coating consists of commerci al l i thi um al umi num si l i cate (Li tha-
f rax 2123) i n a silicate binder (sodium silicate D). I t requires a 390 F cure
and has the composition 4(Li20. Al203.8Si02)Na2Si03. I nitial absorptance
and emittance values are reported as 0. 15 and 0.87, respectively. (37)
Spraying gives excellent coatings, but brushing or dipping results in
poor adhesion and poor coverage. Minute amounts of contamination seriously
alter both the initial a s / € ratio and the UV resi stance of the paint. I n addi-
tion, the paint cannot be adequately cleaned once it i s contaminated or soiled
after application. Consequently, extreme care must be taken to prevent con-
tamination of both the paint itself prior to application and the painted surface
'after application. After application, the resultant surface should be treated
as an optical surface with protection provided from dirt and contamination.
The surface should be handled only with clean, white cloth gloves.
The method of application, temperature of cure, and susceptibility to
soiling limits the use of this paint. However, its UV resi stance is good,
having an initial absorption of 0. 13 f 0. 03; as = 0. 19 f 0. 03 after exposure
to 600 sun hours of UV i rradi ati on. I t wi l l survi ve a 230 C ascent heating
environment with no change in optical properties.
Although Lithafrax i s stable under UV-vacuum radiation, it degrades
severely under electron-vacuum bombardment (E = 0.80 MeV). (37)
46
The Lithafrax coating bleached when exposed to UV after being exposed
to electron bombardment, and as after the sequential exposure of el ectron
and UV was less than the sum of the separate effects of el ectron bombard-
ment and UV radiation.
A Li thafrax/sodi um si l i cate coati ng was subj ected to nucl ear radi ati on
and to a combination of UV and nuclear radiation while in a vacuum, I rradi -
ated to a dose of 5 x l o7 rads, this coating changed in a, f rom 0. 14 to 0.20.
At a dose of 2 x l o8 rads, as was equal to 0.28. (31) Hemi spheri cal emi t-
tance, Eh, did not change. Figures B-48 and B-52 show that the Lithafrax/
silicate coating i s relatively stable in an UV environment, but it degrades
severel y i n a nuclear environment. I t was found that there was no isotope
dependence in optical degradation. ( 31) Fi gure C- 1 shows a compari son of
the separate effects of UV and nucl ear i rradi ati on wi th the effect of concur-
rent i rradi ati on for the Lithafrax/sodium silicate system. Although the
exposure doses were not given, based on rel ated data, it i s probably that the
nuclear exposure was 1.5 x 1013 n/cm2 (E <0.48 eV), 4. 3 x 1014 n/cm 2
(E >2.9 MeV), and 1.4 x l o8 rads (C) gamma. The UV exposure was 500
to 640 sun hours. The combined UV and nuclear radiation consisted of 920
sun hours and 7. 1 x 1013 n/cm2 (E <0.48 eV), 4.6 x 1014 n/cm2 (E >2.9
MeV), and 1. 1 x l o8 rads (C) gamma. (31) These curves show a strong
interdependence of the effects of ultraviolet and nuclear radiations and,
more importantly, they show that the degradation sustained in separate i r-
radiations cannot be used to predict degradation when the two radi ati ons are
concurrent.
Synthetic Li/Al/SiOq Coating. Lockheed reported a research coati ng
that contained synthetic Li/Al/SiOq and cured at room temperature. (37)
I nitial solar absorptance was 0. 16, and initial total hemispherical emittance
was 0.87. I n general there was not much difference between this coating
and the commercial Lithafrax coating. Its advantage l i es i n i ts room-
temperature cure.
The effect of nuclear radiation in vacuum on the synthetic Li/Al/SiOq/
sodi um si l i cate system was similar to that on Lithafrax. A dose of 1. 3 x 108
rads (C) gamma, 8.2 x 10l 2 n/cm2 (E <0.48 eV), and 5.3 x 1014 n/cm2
(E > 2.9 MeV) changed as for the synthetic pigment from 0. 14 to 0.23. For
Lithafrax, the change was 0. 16 to 0.26. (31)
47
Hughes Inorganic White Coating
(A1 -SiOq/K 2Si03)
The prime white finish used in Surveyor I( 16) consisted of naturally
occurring China Clay (Plasm0 clay), which is pri mari l al umi num si l i cate,
in Sylvania PS-7 electronic-grade potassium silicate. The pigment con-
tains approximately 3. 0 percent impurities consisting of 0.42 titanium, 0. 05
calcium, 1. 28 magnesium, 0.42 sodium, and 0. 11 potassium. The clay is
calcined at 1275 C, then ball milled for 12 hours with water. The coating i s
appl i ed wi th an ai r brush; the first two coati ngs are each baked for 1 hour
at 225, and the third coating baked for 1 hour at 260 F.
As tested by Lockheed, solar absorptance for this coating was 0. 14 f
0. 02 (Gary spectrometer) or 0. 14 f 0. 01 (Gi er-Dunkl e spectrometer) and
emittance was 0. 89 f 0.04. (30) The coatings were thermally cycled 4 ti mes
from 533 K to 83 K. There was no evidence of cracking or spallation. How-
ever, several areas of a slightly brown color appeared. The increase in
solar absorptance, Oa,, was between 0.04 and 0. 07. ( I 6) After 540 sol ar
hours in vacuum, solar absorptance of a 6.4-mi l sampl e i ncreased from
0. 18 to 0.22, and exposure to the same number of hours i n ai r gave a sol ar
absorptance of 0. 21. (16). Figure C-2 shows the reflectance of the coating
before and after UV exposure in vacuum. Minimum damage was noted in
the I R region. (16) The spectral damage found in this test corresponds to that
found i n normal measurement tests i n ai r. ( 16)
Aluminum Oxide -Potassium Silicate
-
Aluminum oxide/potassium silicate coatings were subjected to 20-keV
and to 80-keV electrons. The visible-region absorption band was deeper and
more sharply defined after 80-keV exposure than after 20-keV exposure. I n
contrast, damage in the near UV was greater after 20-keV electron exposure. (27)
See Figure C-3.
Another aluminum oxide-potassium silicate coating was exposed in situ
to particulate radiation (protons alone or protons plus electrons) and to com-
bined electromagnetic and particulate radiation (UV with protons alone or
UV t protons t el ectrons). (40) Test conditions are given in Table C- 1 and
data are shown in Figure C-4. I n this work there were no significant differ-
ences found between ambient and in situ measurements. A predominant
reflectance change was observed between 0.30 and 0.40 microns. Protons
and UV had the effect of coloring this region, and electrons had the effect of
48
bleaching it. As with zinc oxide, the pattern was that the addition of el ec-
trons enhanced the stability of reflectance.
The 0.4-micron region in aluminum o ~d e i s not at the band gap. The
reflectance change has the characteri sti cs of a col or center i n that the mag-
nitude of change i s an apparent function of radiation. I t could be either a
I 'physics'' color center, i. e., belonging to the general F or V center cl assi fi -
cati on, or a "chemical" color center, i. e., a function of the appearance of a
new chemi cal i mpuri ty formed as a resul t of ionization, oxidation, or migra-
tion of an ori gi nal i mpuri ty i n the materi al . Thus i n an al umi num oxi de
{dielectric) pigmented potassium silicate coating, the major effect of the
addition of thermal electrons to proton and UV exposure is bleaching of what
is probably a col or center i n the near UV.
Three coatings, A1203/K2Si03 , (Ti 02 t A1203)/K2Si03 , and
(ZnO t Ti 02 t A1203)/K2Si 03 were tested f or stability to space environment
on the ATS-I satellite. Absorptance increased considerably; much more than
was anticipated from laboratory tests. (l 9, 20) Data are shown i n Fi gures C -5
to c-10.
Zirconium Silicate Paints
Lockheed produces a zirconium silicate coating (LPlOA) having a
pigment-binder ratio of 3. 5: 1 by weight. The pigment i s Metal s and Thermi t
Corp. 1000 W grade, "Ultrox" zirconium silicate, acid leached and calcined
by Lockheed. The binder is potassium silicate. The coating is applied by
standard spray-gun techniques and cures at room temperature in approxi-
mately 12 hours. (30) The original coating has a solar absorptance of 0. 14 f
0. 02 (Gary) or 0. 14 f 0. 01 (Gier Dunkle) and a hemi spheri cal emi ttance of
0. 89 f 0.03 according to Smith and Grammer. (30)
Sampl es to be tested for UV and electron stability had an initial as = 0. 24
and E = 0.87. The coating remained optically stable when subjected to either
el ectron bombardment or UV radiation. (37) I t should be noted, however,
that this work was not done in situ and therefore is on1 indicative of the sta-
bility of thi s coati ng, After an exposure of 1016 e/cmz, as = 0. 26; and when
exposed to 10l6 e/cm2 followed by 485 sun hours in vacuum, as = 0.30.
A Zr02- Si02 pigment has been synthesized by Lockheed and has been
optimized with respect to calcination conditions, purification, and grind
properties. Radiation stability of this pigment combined with potassium
49
silicate has been claimed to be excellent under exposures to laboratory simu-
lated solar UV, solar-wind protons, and combined UV and 230-keV protons,
Van de Graaff protons, and 1-MeV electrons. I t has also demonstrated resis-
tance to neutron/gamma radiation. (41)
Zinc Oxide in Potassium Silicate (2-93)
This coating is very stable in the UV and electron environment, (42) but
is damaged by proton bombardment. ( 13) I ts use wi th satel l i tes has been
limited because of difficulties encountered in its application and to the di ffi -
culty of keeping it clean during preflight construction and activities. (42)
However, it i s used where surfaces are i rregul ar, and on nuts and bolts and
other hardware on which it i s difficult to apply coatings other than paint, Al -
though it soils easily it can be touched up.
Experiments in OSO-11, OSO-111, and Pegasus I1 have shown no measur-
able damage to this coating after over 3000 hours of solar exposure. (13, 21)
Laboratory tests also indicate high stability although there are indications of
i ncreases i n sol ar absorptance after 3000 ESH. Fl i ght data from OSO-111
indicated that the coating showed marked stability over the 1580 ESH for
which data were analyzed. (13) A change in a, of about 0. 005 was noted after
1580 ESH. This i s i n good agreement with the data obtained from the OSO-I1
and the Pegasus 11. The temperature of all three of the coatings was less
than 0 C.
Data from Mariner IV and Lunar Orbiter V showed that the 2-93 coatings
suffered greater degradation on these interplanetary flights than on those in
the near earth environment. The cause of the increased degradation was
apparently the solar wind. (13) Both spacecraft were exposed to the solar
wind continuously. Data from the Mariner IV and Lunar Orbiter V are shown
i n Fi gure C-11. The initial solar absorptance as a function of wavelength i s
shown in Figure C-12, and initial absorptance/emittance values are given in
Table B-3. For this paint, as was 0. 184. After 1000 sun hours in flight on
the Lunar Orbiter V, Aa, was 0. 049, the lowest value obtained in the Lunar
Orbiter I V and V flights. Absorptance/emittance ratios, a,/Eh, as a func-
tion of sun exposure are shown in Figure C-13. Orbi ter V flight data are
shown in Figure B-23.
Specimens of a ZnO/K2Si03 coating along with two ther coatings (Ti02/
K2Si03 and a chromic acid-anodized aluminum) were retrieved from their
mountings by astronauts during their extravehicular -activity period on
5 0
Apollo 9. (32) The samples had received approximately 73 hours of space
exposure and were the first to be returned to earth from space unaffected by
reentry conditions. Samples were subjected to the following sources of con-
tamination:
Plume impingement from the tower jettison and Saturn I1
retromotors and from the servi ce-modul e and l unar-modul e
reaction-control-system engines
Boost heating effects
Outgassing products of abl ati ve materi al s
Pyrotechnic discharge products
The natural space environment.
A comparison of preflight and postflight results show that the degrada-
tion of the ZnO/KzSi03 coating ranged from 25 to 40 percent i ncrease i n
absorptance. Absorptance, as i ncreased from 0. 20 to 0.25 - 0. 28. See
Table C-2. No appreciable change in emittance was evidenced. Although
degradation occurred, the absolute values were well within acceptable limits
for the Apollo lunar-landing missions. (32) I t should be noted, however, that
the retrieved samples were not returned under vacuum conditions and there-
fore degradation under solar exposure may not be entirely reflected in the
measurements obtained.
Using a xenon lamp (which has a smooth continum between 200 and
400 mp) and a short-wavelength cut-off technique, the effect of vari ous re-
gions of the UV on the solar absorptance of 2-93 coating was determined. (21)
Table C-3 and Figure C-14 show the changes in Aas caused by the various
regions of UV radiation. As i s the case for many coatings, wavelengths
shorter than 300 mp were relatively much more damaging to 2-93 than those
longer than 300 mp.
Stability to Proton Bombardment. The 2-93 coating was exposed to
8-keV protons along with the S- 13 (ZnO/ silicone) and a barri er -l ayer anodi zed
aluminum coating. (43) A plot of the change in solar absorptance versus
integrated proton f l ux of 8-keV protons is shown i n Fi gure C- 15. I t may be
noted that the 2-93 coating was more susceptible to damage by the 8-keV
protons than were the other two coatings. The threshold of significant
51
damage for the white coatings (a chan e i n sol ar absorptance greater than
0.01) was i n the order of 3 to 7 x 1O1j p/cm .
2
I n another experiment, the coating was exposed in situ to particulate
exposure (protons al one or protons pl us el ectrons) and to combi ned el ectro-
magnetic and articulate exposure (UV wi th protons or UV with protons and
el ectrons). (46 Test conditions are given in Table C-1 and data are shown in
Figures C-16 and C-17. The reflectance changes occurring with the coating
varied considerably with wavelength. An i ncrease i n refl ectance bel ow the
band gap was noted. Protons alone produced coloration at all wavelengths
except below the band gap. The addition of electrons to the proton beam
i ncreased col orati on at the band gap, but it also bleached the visible and near
I R. The same general tendency was observed in the combined-environment
exposures. However, specimen overheating was suspected in the test where
electrons were added in the combined-environment test. I n these tests, the
addition of el ectrons was seen to cause less change in reflectance than when
the particulate radiation was all protons.
There i s evidence that the rate at which protons are applied to ZnO/
K2Si03 coatings has a definite effect on the amount of damage to the material,
especially in the I R portion of the spectrum. (22).
I n the proton-only environment, damage to the silicate-coated zinc
oxide i s both temperature and ener y dependent, with the greatest damage
occurring with the lower energy. (4%
A comparison of individual proton, UV and combined irradiations of
equal exposure conditions and fluxes i s shown in Figures C-18 to C-20 for
temperatures of 233 K (-40 F), 298 K (77 F), and 422 K (300F). (45) The
induced absorption for the combined exposures at 233 K and 298 K exhibits
less changes in absorptance than the sum of the individually produced absorp-
tion changes. However, at 422 K , the sum of the individual environment
exposures is approximately the same as the value obtained by the combined-
environment exposure. A compari son of the proton-only spectral changes
at 422 K with the combined environment changes at 298 K shows almost
identical changes. Apparently, the temperature annealing produces an effect
similar to that of the UV radiation to reduce the induced absorption of the
proton radiation.
The changes in spectral absorptance for combined 750 ESH of sol ar
radiation and an integrated exposure of 2 x 1015 p/cm2 (E = 10 keV) at the
three temperahre- are shown in Figure C-21. (45) The dominating influence
52
of the ultraviolet radiation at el evated temperatures resul ts i n the greatest
change in absorptance for the specimen exposed at 422 K (300 F).
The degradation, as, of the ZnO/K2Si03 coating is about 25 percent
less when simultaneously exposed to 10-keV protons and simulated solar-UV
radiation than when exposed to protons only at 298 K ( 77 F).
Douglas White I norganic Paint (2-93 Type). This was coated 5 mils
thick on 0~. 016-inch 6061 aluminum sheet. After 200 hours UV (compact-arc
xenon source, irradiation intensity of 1 ESH) in vacuum, solar absorptance
i ncreased 10 percent. No change was observed when air was introduced. (46)
" _ .~ .
Titanium Dioxide in Potassium Silicate
Hughes I norganic White (H-2) i s made with Cabot RF- 1 titanium dioxide
dispersed in Sylvania PS-7 potassium silicate. I nitial solar absorptance as
a function of wavelength i s shown i n Fi gure C-22. I t was tested on Lunar
Orbi ter I V and was found to be about equivalent to the silicone-aluminum and
B-1060 coatings. (26) I nitial absorptance and emittance values, both labora-
tory and flight values, are given in Table B-3. Absorptance, as, was 0. 178
(laboratory value) and after 1000 sun hours (flight), Aas = 0. 089. Only two
coatings had lower Aas values after 1000 sun hours' exposure on the Lunar
Orbiter I V and V flights. (See page 3 6 . ) Flight data for Lunar Orbiter I V
are given in Figure B-22.
- - . -. - -
Lanthanum Oxide in Potassium Silicate
This coating i s susceptible to UV damage, but i s less susceptible to
proton damage. I ncreasing the total proton exposure by a factor of 5 did not
increase the damage, indicating a very good resistance to proton damage.
In contrast to the ZnO/K2Si03, the La203/K2Si03 shows a definite damage
effect, principally due to UV exposure. Combined environment tests in-
cluding both proton and UV radiation roduced comparable damage to the
sum of the individual environments. (f2) However, so drasti c i s the UV-
only degradation that it completely dominates the combined environments
picture. (44)
53
Oxide Coatings
Rokide C
Rokide C is essentially chromic oxide (85 percent Cr203) flame sprayed
by Norton Abrasive Company(9) at room temperature, as = 0.90 and E = 0.85.
The green coating i s extremel y hard and i s very inert chemically. There is
no degradation of opti cal properti es resul ti ng from UV exposure.
However, because of differential thermal expansion between the oxide
coating and metal substrates, adhesion i s a problem during rapid changes of
temperature. One method of overcoming this difficulty i s the use of a ni -
chrome undercoat on Renk 41 nickel alloy. This Rene 41 -nichrome-Rokide C
combination thermal-control system has been checked for thermal- shock
damage. Heating complex shapes to 1640 F .within 5 minutes followed by a
5-minute cooling period has resulted in no coating failures.
The bonding between the substrate material, nichrome, and Rokide C
is believed to be purely mechanical. Rokide C may be used on other metal -
lic substrates; however, thermal-shock stability should always be checked
experimentally for any new substrate. Because of the mechanical bonding,
all substrates must be grit blasted prior to coating application. (9)
Bright Anodized Coatings
Aluminum i s an excellent reflecting material f or radiation in all parts
of the spectrum while continuous films of aluminum oxide are transparent to
radiation in the visible region and "black" in the I R. Therefore, polished
aluminum which has been anodized is expected to have a double surface ef-
fect because the polished aluminum reflects the solar radiation which is per-
mitted to penetrate the aluminum oxide coating. (5) An oxide coating of suffi-
cient thickness i s opaque in the long-wavelength I R region. Figure C-23
shows the optical properties of polished aluminum which has been anodized.
Figure C-24 shows the effect of temperature on the total hemispherical emit-
tance. Emittance appears to be highest in the cryogenic-temperature range.
Vacuum-thermal exposure produces two maj or resul ts. Water present
in the oxide i s partially driven out as i s evidenced by the reduction of the ab-
sorption band at 3 mi crons. A decrease in the reflectance in the visible
spectrum was the most pronounced effect. (5) See Fi gures C-25 and C-26.
54
Since the distribution of energy of a 65 C surface (based on black-body
radiation) peaks at approxi matel y 8.4 mi crons, the reduction of the water-
absorpti on band has very l i ttl e effect on the emi ttance of the anodized-
aluminum coating used at this temperature.
The optical properties of the bright anodized-aluminum system were
only slightly,altered by UV radi ati on i n air. (5) However, the combined
vacuum-UV radiation was very detrimental to the solar absorptance of bright
anodized coatings prepared by the usual methods. The color centers formed
during exposure caused a gradual increase in yellowing up to 120 hours' ex-
posure. There appears to be a leveling-off beyond the 120 hours. Thi s yel -
lowing causes the ratios to double (0. 19 to 0.42) after exposures up to
120 hours. Tabl e C- 4 and Figures C-27 and C-28 show the effect of vacuum-
UV on 0.5-mi l sheet.
Prel i mi nary data i ndi cate there i s only a slight change in the optical
properti es of bright anodized aluminum when exposed to 3 x 108 rads (C) of
nuclear radiation. (5) Table C-5 shows the changes in absorption and emit-
tance for various coating thicknesses after irradiation.
Anodized aluminum was unaffected by a dose of 1016 p/cm2 (E = 3 keV)
and unaffected by electron exposure as far as spectral reflectance at a dose
of 4 x 1016 e/cm2 (E = 145 keV).(34)
The synergistic effects of simultaneous 145-keV electron and UV radia-
tion on the spectral reflectance of barri er-anodi zed al umi num and sul furi c
acid-anodized aluminum along with aluminum oxide-potassium silicate thermal-
control coatings were investigated at 77 K . (4) Damage to the sulfuric acid-
anodi zed al umi num speci mens was produced pri mari l y i n the wavel ength
region below 0. 7 microns, with only small changes evident at longer wave-
lengths. An i ncrease i n as of 40 percent was induced by 350 ESH of UV,
while 5.8 x 1015 e/cm2 produced no change i n as. Simultaneous irradiation
to approxi matel y the same doses resul ted i n a 35 percent i ncrease i n as ,
Barrier-anodized aluminum was found to be very resistant to both UV
and el ectron radi ati ons. (4) An i ncrease of 12 percent i n as was produced by
350 sun hours of UV, while 5.8 x 1015 e/cm2 resul ted i n an 18 percent i n-
crease i n as. These changes were again exhibited primarily in the wave-
length region less than 0. 7 mi cron.
The effects of electron and UV radi ati ons on these materi al s are shown
i n Tabl e C-6. Sampl es were prepared on 10-mi l 1199 al umi num substrates.
55
Charged-parti cl e and gamma-radi ati on tests were run on barri er -l ayer
anodized aluminum having emittances up to 0. 31. (43) It was found that charged-
particle radiation (proton and alpha particle) exposures up to 1 x 10l6
parti cl es/cm2 and cobal t-60 gamma-radi ati on doses up to 1. 3 x 106 rads (C)
did not degrade the anodized aluminum surfaces. Following are the energy
levels employed and the changes in absorptance which occurred:
I ntegrated AaS at
Type of
Energy, Flux, Dose,
Maximum
Radiation
MeV
parti cl es/cm2 roentgens Exposure
-
Protons 1- 9x 10
-3 14 16
10 - 10 0.005
Protons 2.5 7 x 10 to " 0. 0
2 x 1015
12
Alphas
2 - 16 x - 10
16
" 0. 03 1
5.0 Alphas 10 - 4 x 10 " 0. 0
Gamma 1. 17 and 1. 33 " 1.3 x 10 0. 0
13 14
6
(CO-60)
The barrier-layer anodized aluminum was found stable to abrasion, salt-
spray, weatherometer, and UV. (43)
Alzak, the result of an anodic oxidation of aluminum sheets that have
been electrobrightened, i s produced commercially by the Aluminum Company
of America. The thick, porous oxide layer i s formed by an extensive dis-
solution of al umi num i n a fluoboric acid solution and is then sealed in an
oxide hydration using deionized water. I ts resultant a s / € depends on the
thickness and purity of the A1203 layer, and values comparable to a white
paint may be achieved. The quality of this coating i s dependent on the purity
of the components used in the various stages of processing. Since it i s pro-
duced commercially in large quantities, variation in UV stabi l i ty from sheet
to sheet has been observed and the initial optic.al properties are not yet pre-
dictable. This coating has been considered for the Orbiting Astronomical
Observatory satellite program. The coating forms the entire outer shell of
the spacecraft and therefore its stability i s of cri ti cal i mportance. (47)
The coating was tested on the ATS-3 and it was found that most of the
damage was caused by UV i rradi ati on (X > 160 mp). The loss in reflectance
56
I
was restri cted to wavel engths l ess than 1200 mp, and laboratory testing has
shown that thi s i s caused by an i ncrease i n the absorptance of the A1203 film
which begins in the near UV and progresses toward longer wavelengths with
'i ncreased exposure. See Fi gures C-29, C-30, and C-31. The original
values of as and E: were 0. 15 and 0. 77, respectively (7. 7-pm-thick coating).
As the stab,ility of this commercially produced coating varies from batch to
batch, these resul ts are not general l y appl i cabl e, but they serve as a good
indication of what may be expected of thi s materi al . (47)
Alzak coatings were subjected to 20 and 80-keV-electron radiation. I t
was found that it sustained more degradation from 20-keV electrons than from
80-keV electrons. Reflectance losses were chiefly in the UV region. (27)
See Figure C-32.
The effect of UV i rradi ati on on a 0.29- mi l anodized aluminum (Alzak)
i s shown in Figure C-33. Changes in the UV, visible, and I R portions of the
spectrum wi th i rradi ati on are as fol l ows:(25)
Decrease (I ncrease) i n Refl ectance, percent
with UV Exposure (AR = Ri-%)
Expo sur e
ESH 250 mp 425 mp 2100 mp
135 51
20 (1)
25 0 54 27 1
49 0 59 32 1
770 -- 35 "
1130 60 38 1
"
Anodized aluminum was tested in the OSO-111 flight experiment. (13)
The 1199 aluminum alloy substrate was chemically brightened, electro-
polished in a solution of fluoboric acid, and anodized in a solution of ammon-
i um tartrate. This coating showed no change in as i n 1580 ESH.
Chromic acid-anodized aluminum was exposed to space radiation on
Apollo 9 spacecraft. Samples were retrieved in space for postflight tests.
Absorptance i ncreased from 0. 70 to 0.73, an increase of 4 percent. Emi t-
tance decreased from 0.73 to 0.70. (32) (Note: samples exposed to air be-
fore changes i n absorptance determi ned. )
57
Chromate Coatings (Alodine)
Alodine A-1 and A-2, two chromate finishes on aluminum, were sub-
jected to ion bombardment from plasma bombardment systems in an effort to
simulate solar-wind damage. (48) Peak bombardment potentials were close
to 1 keV. The Alodines showed absorptance decreases of 0.01 to 0.04 over
the entire 0. 26 to 2. 6- p range. The conditions of high vacuum and plasma
caused changes in the coating because of volatile constituents such as water.
The changes did not follow definite patterns.
The total normal emittance, cn, for I R radiation changed a maximum of
7 percent with hydrogen-ion bombardment. (48) I t should be pointed out, how-
ever, that the data obtained were not in situ.
Composite Coatings
-
Several composite systems show promise as thermal-control coatings.
I n general, these consist of a reflecting substrate coated with a semi trans-
parent dielectric film. The reflectance of the metal substrate control s the
solar absorptance, and the thickness of the transparent or semi transparent
dielectric film governs the emittance. ( 3 6 ) These films are frequentl y pre-
pared as tapes whi ch are bonded to the surface of the space vehicle by means
of a pressure-sensitive adhesive.
Second-Surface Mirrors
Transparent or semi transparent films with a refl ecti ng substrate are
known as second-surface mi rrors. Some are cerami c mirrors having dimen-
sions about 1 x 1 x 0.008 inch and are applied to the substrate with an ad-
hesive. Others are flexible films with a reflective metal backing which has
been applied to the film by vapor deposition. Following are di scussi ons of
several types of second-surface mi rrors.
Seri es-Emi ttance Thermal -Control Coati ngs. General El ectri c devel op-
ed a series of such coatings. ( 3 6 ) The films suggested include Teflon, a vinyl
silicone (GE 391 - 15 - 170, formerl y known as PJ 113), and Butvar (poly-
vinyl butyrai). Metals examined for the reflective surfaces were aluminum,
58
silver, gold, and copper. These metals were applied to the films by vapor
deposition or the dielectric was coated on the metal foil. The adhesive which
passed the ascent-heating-simulation test satisfactorily was General Electric's
SR 527 (a silicone adhesive). However, two other adhesives also have been
eval uated and appear to have meri t. These are Dow Corning's D.C 281 silicone
adhesive and Minnesota Mining's Y9050U. The l atter i s a double-faced
pressure-sensi ti ve tape. I t is essentially a silicone-impregnated fiber-glass
cloth which is laminated to the metal surface. (36) These l atter two adhesives
failed not in shear, but by peeling as a leading edge was raised when sub-
jected to a simulated ascent heating.
According to Linder it is theoretically possible to achieve any as / € ra-
tio between 0. 05 and 5. 0 with this system, although practical limitations on
minimum coating thickness and lack of complete transparency to the solar
spectrum somewhat limit this selection. (36)
Additional advantages of this type of system include (1) the ability to
select coatings having lower emittances with the same as / € rati o wi l l mi ni -
mi ze the radi ant-heat l oss from the vehi cl e and therefore wi l l reduce the
power requirement and (2) an improved UV stability of the Teflon-metal and
silicone-metal systems which makes this type coating very attractive for use
on long-life missions.
Table C -7 and Fi gure C -34 show the variation in total normal emit-
tance with the thickness of Teflon over vapor-deposited aluminum while
Table B-5 shows similar information for Butvar on aluminum. Spectral
absorptance of silver-coated Teflon is given in Figure C-35. The reflec-
tance curves for 0. 5-mil Mylar metallized with silver, aluminum, gold,
and copper are shown in Figure C-36.
The experimental vinyl silicone, GE 39 1 - 15- 170, has been shown to be
extremel y resi stant to UV degradation. A program to develop a technique
for applying this material in controlled thicknesses to a metal foil i s being
developed. I t is anticipated that emittance values between 0. 15 and 0.90
may be obtained, depending on the thickness of the silicone coating.
Teflon and vinyl silicone (GE 391-15-170) have been exposed to the
combined effects of UV and X-rays. No significant changes in solar absorp-
tance of ei ther of these systems were observed wi th exposures up to 1000 ESH
and 100 megarads (C). There are i ndi cati ons, however, that as exposure i s
continued, the absorption edge of the dielectric tends to shift to longer wave
lengths. A typical curve of UV refl ectance after exposure to UV and X-rays
59
for Butvar and GE 391-15-170 (PJ 113) i s shown in Figures c-37 and C-38.
A summary of data obtained on UV and high-energy exposure is shown i n
Table C-8.
Silver - and Aluminum-Coated Teflon. These have shown excellent
stability to UV and to particulate radiation. Generally, FEP Teflon is used
because its radiation stability in air i s better than that of TFE Teflon. I n
vzcuum, FEP i s only slightly better than TFE, but both are stable to approxi-
mately 106 rads (C) when not exposed to air or oxygen,
Six Teflon-based coatings were subjected to 80-keV electrons. (27) These
included 2-, 5-, and 10-mil aluminized Teflon and 2-, 5-, and 10-mil si l vered
Teflon. After exposure to 1015 e/cm2 (E = 80 keV), the exposed surfaces
still retained a specular appearance and, except at the shortest wavelengths
measured, sustained only minor reflectance degradation. Exposure to 1016
e/cm2, however, left each Teflon coating significantly altered. The plastic
assumed a light gray appearance so that the vapor-deposited metal was
masked. Some crazing and a considerable amount of mottling of each Teflon
surface was also evident. (27)
Similar samples and also silvered samples were subjected to proton
bombardment. (49) No change in solar absorptance ( as ) was detected until
after a dose of 3 x 1015 p/cm2 (E = 40 keV). At the maximum doses, 1. 2
to 1.8 x 10l6 p/cm2, changes in absorptance (na,) averaged 0.04 for the
silvered Teflon and 0.06 for the aluminized Teflon. See Table C-9. The
temperature of the Teflon coating substrates throughout the test period was
10 f 1 C, based on water-exi t temperature from the chamber. Vacuum l evel s
during the exposures were 1 to 2x 10-7 torr. Magnetic analysis of the proton
beam eliminated masses >1 from the beam before it entered the exposure
chamber. Exposure rates were between 1 and 4 x 101O p/(crn2-s).
Aluminized Teflon was used as the outer portion of a thermal shi el d on
Mariner I1 and Mariner V. The thermal shield consisted of 18 l ayers of
aluminized Mylar and was attached to the sunlit surface of the spacecraft to
reduce the influence of increasing solar intensity during the mission. The
outer layer was aluminized 1-mil FEP Teflon and was used as a second-
surface mi rror wi th a / € = 0. 13/0. 55 = 0. 24. The shield for Mariner I1 was
similar except that it utilized 5-mil Teflon. With the Mariner V, a tempera-
ture transducer was taped to the bottom si de of the aluminized Teflon. The
reported data were assumed to be the measured temperature of the sunlit
FEP Teflon sheet. This assumption appeared to be supported by the data
obtained.
60
Earl y mi ssi on data shown in Figure C-39 show that the FEP Teflon de-
gradation followed a typi cal rate characteri sti c of low U/ E materi al s, wi th an
i ni ti al rel ati vel y hi gh rate, decreasi ng as degradati on progressed. However,
'approximately 45 days after launch, the rate began to increase again as can
be seen in the shape of the curve i n Fi gure C-39. The beginning of this in-
crease i n rate was coi nci dent wi th a Class-2 solar flare, the radiation pro-
ducts of which were seen at the spacecraft. However, a second flare did not
produce any increase in degradation rate. The increase in rate following the
first flare could not be attributed directly to radiation damage since the rate
increased gradually and the higher rate persisted too long. (18)
A 5-mi l silvered Teflon sample was flown on the OGO-VI (approxi-
mately 400 to 1100-km polar orbit). Prior to launch, as measured as
0. 085. After approximately 4600 hours of sol ar exposure, no i ncrease i n
as was detectable. ( 49)
Polyimide /Aluminum. Kapton H-film (polyimide) with an aluminum
backing was also tested for use similarly to aluminized Teflon. This ma-
teri al has excel l ent hi gh-temperature properti es, good radi ati on resi stance,
but i t i s affected by UV. Although this film shows some reflectance loss in
the UV, i ts moderate refl ectance changes, both i ncreases and decreases,
in the visible and I R regions when exposed to UV radiation in vacuum are
considered important. See Figure C-40 Exposed to UV in situ for 20,000
hours, as changed from 0. 305 to 0.41. ( GO)
Aluminized Kapton was subjected to 20 and 80-keV-electron radiation.
With the 20-keV exposure, reflectance changes were minimal at fluences
below 1015 e/cm2. The largest reflectance changes at 1016 e/cm2 were i n
the UV wavelengths just longer than the visible-region absorption band.
Decreases were much more severe than those after exposure to the 20-keV
electrons. See Figure C-41. Reflectance damage after exposure to 10l6
e/cm2 (E = 80 keV) was considered I 'catastrophic". (27)
In another experiment, a 2-mil Kapton H-film over a thin aluminum
coating on an aluminum substrate was subjected to 50-keV electrons. The
greatest l osses were i n the vi si bl e and near-I R regi ons. Decreases i n
refl ectance were as fol l ows: (25)
61
Decrease in Reflectance, percent
(AR =Ri - Rf )
Dose, e/cm
2
590 mp
1 x 1013 0
2 x 1014 4
6 x 1014 13
8 x 1015 60
2100 mp
"
0
0
--
When subjected to UV radi ati on al one (i n si tu), decreases i n the
reflectance changed as follows: (25)
Decrease (I ncrease) in Reflectance, percent
Exposure
ESH
135 3 (2 1 (2 )
250 5 (2 1 2
490 6 (2 ) 2
770
1130 7 (2 1 1
( AR = Ri - Rf )
-
250 mp 425 mp 2 100 m p
"
(2 )
"
Kapton showed no change in properties when exposed to 750 F for
30 seconds in vacuum. Above 900 F, it visibly darkened. (50)
Polyimide film has al so been used as a backing for a second-surface
mi rror, Si 0 on aluminum. This composite consists of a 10,500 A Si 0 over-
coat on 1200 A aluminum vapor deposited on 1. 5-mil Kapton (polyimide), an
experimental film supplied by G. T. Schjeldahl Company, Northfield,
Minnesota. I t was subjected to proton and electron radiation, exhibiting
little change in reflectance in the UV and visible regions after receiving a
dose of 1016 p/cm2 (E = 3 keV).(34) (See Fi gure C-42, ) There was a
slight reduction in spectral reflectance in the UV when exposed to 1.3 x
10l 6 e/cm (E = 145 keV). I t i s badly degraded in UV i rradi ati on, appeari ng
slightly yellow-brown. (34) (See Figure C-43. )
Silicon monoxide coatings are more susceptible to 320 ESH of UV
radiation than to either 1. 3 x 10l 6 e/cm2 (E = 145 keV) or 1 x 10l 6 p/cm 2
62
(E = 3 keV). This type coating is being used in the Apollo program and i s
also being considered for Air Force satellites. (5 1)
Coated, Vapor -Deposited Aluminum. Vacuum-deposited aluminum
coatedwi th surface l ayers of dielectric materials gives highly reflecting and
protected mirror surfaces which have been successfully used for controlling
the temperature of many satellites. Coatings generally used over the alumi-
num are silicon oxide (SiO,), silicon dioxide (SiOz), aluminum oxide (A1203))
and magnesium fluoride (MgFZ).
Silicon Oxide (SiOx). The most frequently used surface film f or con-
trolling the temperature of satellites has been silicon oxide (SiO,) produced
by evaporation of silicon monoxide in the presence of oxygen or air. Re-
commended deposi ti on parameters are rates of 3 to 5 A/sec at about 8 x
10- 5 torr of oxygen or 1 to 2 A/sec at 1 x torr of ai r. Films of this
materi al show rather high absorptance in the near and far UV. However,
-
this undesired absorptance i s claimed to be eliminated by UV i rradi ati on i n
air. (52) 53)
By increasing the thickness of reactively deposited silicon oxide (SiO,)
on al umi num from zero to 32 quarter-wavelengths ( X/ 4) , E i ncreases from
0. 017 to 0.53 and a / € can be varied from about 5 to 0. 2.(53) Exposure to
UV i n ai r vi rtual l y el i mi nates the i ni ti al l y hi gh UV absorptance of this coat-
ing without changing the I R reflectance appreciably. The total emissivity of
this coating i s unchanged by the UV treatment. With this treatment, a will
decrease. After 18 hours of UV i rradi ati on i n ai r, a was found to change
from 0. 128 to 0. 110. These coatings have been used as temperature-control
surfaces on many satel l i tes, and there are ampl e l aboratory and fl i ght data
to show their high stability in space environment. (53)
Temperature data from Expl orer XXI I I over a 3-1/2 year period have
indicated no significant degradation of its SiO, coating. (53) However, a
1200-mp SiOx coating tested on the ATS-3 proved to be very unstable. (47)
It was believed that the SiOx coating tested on the ATS-3 was not typical of
these coatings. Vapor-deposited SiO, (1. 5~) over opaque evapcjrated alumi-
num showed excellent stability when tested on the ATS-I. Initial a/€ was
0.48. Changes in a/€ which occurred in flight on the ATS-I are shown in
Fi gure C-44. This coating was about equivalent with the A1203/Al coating
and was one of the more stabl e materi al s.
The thermal-control coatings for the surfaces of the Vanguard satel-
l i tes are based on the same principle. The exterior thermal-control surface
6 3
consisted of evaporated aluminum covered with a 0.65-1.1 film of silicon
monoxide. (8) The film i s essenti al l y transparent to sol ar radi ati on but has
a strong absorption band at about lop. By controlling the film thickness of
thi s system, one exercises control over I R emittance independently of
solar absorptance. The a s / € ratio can be varied from about 4.0 to about
0.5. For the system employed in Vanguard, a s / € = 1.3.
This system, however, i f not properly prepared, has been shown to be
subject to severe degradation by solar UV exposure. (2) I t appears that the
degradation is related to the change in stoichiometry of the silicone oxide
film under irradiation. The dielectric film is produced by evaporation of
SI 0 in an oxidizing atmosphere or by subsequent oxidation of an evaporated
Si 0 l ayer. Upon i rradi ati on the transparent SiO, film l oses oxygen and
reverts to the straw-col ored Si 0 wi th resul ti ng i ncrease i n sol ar absorp-
tance.
Silicon Dioxide (Si02). Si02 films have strong absorption bands in
the I R region with maxima in the 8.5 to 9. 5-p and the 23 to 25-p regions.
Si02 films of thicknesses up to about 0.2 ' p have, even in the 8. 5 to 9. 5- p
wavelength region, very little effect on the normal incidence reflectance of
aluminum. However, i f thicker films of Si02 are applied to aluminum, very
l arge refl ectance decreases can be observed i n the I R regi on. Fi gure C-45
shows the I R reflectance from 5 to 40 ,ufor aluminum coated with 0.40, 0.97,
and 2.59-p films of SiO2.
Fi gure C-46 shows that interference effects produce a maxi mum a of
0. 13 with Si02 films that are effectively one-quarter wavelength thick at
X = 550 mp, and that for thicker films, a becomes essentially independent
of the Si02 thickness and has a value of 0. 111 f 0.04 in a thickness range
of 0. 36 to 1.9 p . In addition, the a values of Si02/Al coatings determined
i n ai r were found to be identical with those measured in vacuum. (52)
For the temperature control of satel l i tes, films of aluminum coated
with about 6 to 14 X/4 of SiQ2 are most frequentl y used ( X = 550 mp). For
this range of Si02 thickness, E and 6, (normal emi ssi vi ty) of SiO2/A1 in-
crease wi th i ncreasi ng temperature i n the temperature range measured,
Thi s i s a very desi rabl e property for a temperature-controlling coating
si nce i t provi des a certai n amount of self-regulation of the satel l i te temper-
ature. For a satellite coated with A1 and 6 X/4 of SiO2, an increase of the
shel l temperature from 10 to 20 C may be predi cted to occur duri ng 1400
hours of exposure to sunlight. (52)
64
I
Aluminum coated with various thicknesses of Si02 were exposed to
1-Mev electrons using a dose of 1 x 1015 e/cm2. No changes in the optical
properti es from the UV to the far I R were observed. It appears that UV
i rradi ati on i s the mai n cause for the degradation of SiO2-coated aluminum
films in outer space. Si02 over aluminum was exposed to 20 and 80-keV
electrons in situ and was found to be very resistant to reflectance change. (27)
See Figures C-47 and C-48. This coating undergoes significant improvement
in reflectance in the 0.25 to 0.3-p-wavelength region during electron irradi-
ati on, si mi l arl y to that observed wi th UV i rradi ati on.
SiO2-coated aluminum samples were subjected to UV i rradi ati on i n
vacuum. Figure C-49 shows the decrease in reflectance experienced by
two SiO2-coated samples subjected to xenon arc lamp in a vacuum of 1 x
torr. The films were 6.2 and 13.4 X/4 thick, and the irradiation was per-
formed in two stages usi ng fi rst one and then five times the equivalent solar
energy. Reflectance values were determined while the samples were kept
in vacuum at about 1 x torr. For both sampl es, the refl ectance de-
crease was most pronounced at shorter wavelengths and became negligible
for wavelengths longer than 700 mp, but the damage suffered by the thicker
coating was approximately twice that experienced by the thinner one. The
I R reflectance and E: of the Si02-coated aluminum were found to be unaffected ,
by UV i rradi ati on.
Si02- and A1203-coated aluminum samples tested on the ATS-3 were
more stable than the other dielectric coatings, although their degradation
was more severe than that observed in the laboratory. (47) UV radiation was
responsible for most of the damage although a significant degradation was
caused by other factors acting in combination.
A technique for producing UV transparent films of A1203 and Si02
by evaporation with an electron gun has been developed. Because of their
hardness, chemi cal stabi l i ty, and excel l ent adherence, these t wo film
materi al s are sui tabl e as protecti ve l ayers for al umi num, front-surface
mi rrors, especi al l y i f high reflectance in the UV i s requi red. (52) The
fact that the optical properties of vacuum-deposited A1203 and Si 02 are
less dependent on the preparation conditions than those of Si 02 prepared
from Si 0 makes these film materi al s more sui tabl e for many opti cal
applications.
Aluminum Oxide (A1203). Aluminum overcoated with A1203 degrades
l ess than that with Si02 under identical UV i rradi ati ons. (52) Aluminum
oxide over aluminum was also exposed to electrons (E = 20-keV and
6 5
Vapor-deposited aluminum oxide (1 1,000 A) on 1000 A of aluminum
evaporated onto a buffed, chemically cleaned, and glow-discharge cleaned
substrate, and silicon dioxide deposited in vacuum onto a buffed and de-
greased aluminum substrate exhibited only small changes in reflectance
from 0.25 to 2.5 p for exposures as great as 1017 e/cm2. (3) Exposure was
to 20-keV electrons at 22 C.
Vapor deposited A1203 (1. 1 p ) on opaque evaporated aluminum was
tested for UV stability in the laboratory and on the ATS-I . The initial
a s / € was 0. 54 as measured i n the l aboratory, and 0.59, measured 48 hours
after launch. (l 9) The changes which occurred in flight on the ATS-I are
shown i n Fi gure C-52. This coating along with SiOx on aluminum was the
most stable of those tested on this flight.
Magnesium Fluoride Over Evaporated Silver. This material i s not
used as a thermal-control coating, but i s a potential surface coating for a
solar concentrator mirror. The thin (2 x X / 4 at 550 mp) overcoat of MgF2
serves to protect the si l ver from atmospheri c contami nants. I t was i n-
cluded in the ATS-3 tests. The substantial loss in reflectance that occurred
in the 300 to 650-mp region can be attributed to both a broadening of the
interference minimum band and a decrease at the i nterference maxi mum
position due to substantial damage taking place within the body of the MgF2
film. (47) The relative stability of the shielded sample (fused-silica shield)
indicated that most of the damage to the unshielded sample was caused by
low-wavelength (160 mp) UV and electron or proton irradiation acting in com-
bination.
The ATS-3 data have shown that MgF2-coated silver i s not the best
choice for a solar-concentrator-mirror coating. However, it will continue
to be used as both a protective and reflectance-increasing flim for front-
surface al umi num mi rrors used i n far UV, orbiting telescopes. Therefore
it is important that the correlation between preparation techniques and en-
vironmental stability of MgFZ be thoroughly defined. (47)
Uncoated Aluminum. The uncoated aluminum samples tested on the
ATS-3 were least susceptible to damage by UV (X > 160 mp) i rradi ati on as
indicated by the shielded-sample data. (47) The unshielded samples, how-
ever, degraded severely, and the loss in reflectance increased with de-
creasing wavelength. The change showed no signs of saturating after l year
66
I
I
i n orbi t and may be i ncreasi ng as time goes on. These results did not agree
with earlier findings of the OSO-I11 Thermal Control Coatings Experiment
which showed aluminum to be very stable. Differences in the orbital en-
vironment may explain some of the disagreement.
Optical Solar Reflector. Two versi ons of the optical solar reflector
have been developed at Lockheed Missiles and Space Go. (2) The first con-
sists of vapor-deposited silver on Corning 7940 fused silica with an over-
coating of vapor-deposited I nconel. The second is vapor-deposited aluminum
on Corning 7940 fused silica with an overcoating of vapor-deposited silicon
monoxide. The front surface of these mi rrors consi sts of the high-purity
fused silica, the second or reflecting surface is the silver or aluminum
which has been vapor-deposited on the fused silica. The silver or aluminum
coating i s protected from corrosion or damage while being handled with the
vapor-deposited I nconel or silicon monoxide. These mirrors, 1 x 1 x 0.008
inch thick, are applied to the substrate with RTV-615 silicone adhesive. (2, 9)
The adhesive requires a mi ni mum cure of 14 days at room temperature to
mi ni mi ze outgassi ng duri ng ascent. Refl ecti ve properti es are as fol l 0ws:(9,5~)
Optical Solar Sample
Reflector
- Temperature, R
as
€ as / E
Silver 325-530 0.050 f 0.005 0. 81 0. 062
26 0 0.744 f 0.01
36 0 0.800 f 0.01
46 0 0.807 f 0.015
56 0 0.795 f 0.02
66 0 0.790 f 0.02
Aluminum 325-530 0. 100 f 0.005 0. 81 0. 124
26 0 0.744 f 0.01
36 0 0.800 f 0.01
46 0 0.807 f 0.015
56 0 0.795 f 0.02
66 0 0.790 f 0.02
67
These opti cal sol ar refl ectors (OSR) are fragi l e and shoul d be pro-
tected from mechanical damage during storage and shipping. Surface con-
tamination, including fingerprints, oil, dust, and atmospheric weathering,
does not cause permanent degradation after application. However, con-
taminants must be removed prior to launch. Panels with OSR applied to
them have successfully passed sinusoidal and random-vibration tests.
There has been no measurable change in a / € due to near UV, and
these coatings have been stable for extended missions up to 2 years i n al l
charged-particle environment and combined environments of space. These
coatings have been extensively investigated and have never been dam-
aged. ( 2 , 9 , 13) (See Table C-10. ) Also, data from the OSO-111 flight showed
no change in a s of the OSR (vapor-deposited silver on fused silica and
I nconel overcoat) in 1580 ESH. ( 1 3 )
Sol ar-Thermoel ectri c Systems
Another composi te i s the sol ar-thermoel ectri c system reported by
Schmidt and Park at Honeywell, I nc. (54) These multilayer coatings consist
of transparent molybdenum films between nominally quarter -wavelength-
thi ck di el ectri c spacers of such materi al s as magnesium fluoride (MgF2)
and aluminum oxide (A1203). The solar absorbers are prepared by evapor-
ating the multilayer optical coatings on highly reflective substrates,
The pri mary cri teri a for materi al sel ecti on are:
Substrate - high reflectance in the I R, high melting tem-
perature, low vapor pressure, low el ectrochemi cal po-
tential to provide chemical stability with the dielectric
l ayers
Di el ectri c fi l ms - high transmission in the I R, high
mel ti ng temperature, low vapor pressures, and high
electrochemical potential
Metal films - high transmission in the I R, high melting
temperature, low vapor pressure, and low electro-
chemical potential. Selective absorption in the solar
spectrum is often advantageous.
68
One of the best samples reported was prepared with depositions of
CeO2, molybdenum, and MgF2 (magnesium fluoride). This sample demon-
strated very good high-temperature stability up to 538 C in vacuum. Another
sample showed excellent high-temperature, high-vacuum, and UV stability.
All the films passed the Scoth tape test for adhesion. They do not possess
hi gh abrasi on resi stance; however, they can be washed i n acetone or al cohol . (54)
Unfortunately, there has been difficulty in reproducing these materials,
Miscellaneous Coatings
Several coatings were reported for which available information is very
meager. I n many cases only the solar absorptance and hemispherical emis-
sivity were given. Composition of some of these was not available. The re-
ported information on such coatings follows.
3M 202-A- 10
A Minnesota Mining and Manufacturing Co. coating (202-A-10) was
subjected to proton and electron irradiation in a vacuum. I t was degraded
by 10l 6 p/cm2 (E = 3 keV) in the visible and I R spectral regions (Figure C-53).
Spectral reflectance in these regions decreased as a result of el ectron i rra-
diation. Damage a proached a saturation level at doses not much greater
than 4 x 10l 6 e/cm 5 (E = 145 keV). (See Figure C-54.) Specimens appeared
somewhat darker after el ectron i rradi ati on. (34)
Aluminized Mylar
Mylar, 5 mils thick, with 2 x inch of aluminum on both surfaces
(available from Hastings & Co. , Inc. , Philadelphia, Pa. ) was unaffected by
a dose of 1016 p/cm2 (E = 3 keV) and 4 x 10l 6 e/cm2 (E = 145 keV). The
specimen blistered during irradiation, but blistering was believed to be due
to out assing of the epoxy used to attach the film to the stainless steel
disk. ( 54)
69
Cameo Aluminum 2082 Porcel ai n Enamel
Type 6061 aluminum sheet, 16 mils thick, coated with 1.5 mils porce-
l ai n enamel , i ncreased i n sol ar absorptance onl y 4 percent after 200 ESH of
uv in vacuum. (46)
Bismuch Sulfide (Bi~S3)-Dyed
Anodized Aluminum [ 1100 (2-S)AlI
-
The Bi~S3-dyed anodized aluminum was somewhat unstable. It had
relatively low absorptance values and was somewhat undesirable as a high
absorber for space applications. (55)
Cobalt Sulfide (COS)-Dyed
Anodized Aluminurn r 1100(2-S)A11
The Cos-dyed anodized aluminum was stable with relatively high absorp-
tance values over the entire wavelength region considered. (55) (See Fi gures
C-55 and C-56.)
Nickel Sulfide (NiS)-Dyed
Anodized Aluminum [ 1100(2-S)Al]
NiS-dyed anodized aluminum was stable with relatively high absorp-
tance values over the entire wavelength region considered. (55) (See Fi gures
C-57 and C-58. )
Lead Sulfide (PbS)-Dyed Anodized Aluminum, .
Sandoz Black BK -Dyed Anodizedxluminum,
and Sandoz Black OA-Dyed Anodized . . . Aluminum . . . .. . . .
These dyes on [ 1100(2-S)] aluminum had relatively low sol ar absorp-
tance and showed slight changes of solar absorptance when exposed to simu-
lated space environment. They would have limited usefulness as thermal -
control coatings. (55)
7 0
Black Nickel Plate on Aluminum [ 1100(2-S)Al]
~~
Black nickel plate on aluminum was very stable over the solar region
of the spectrum for exposures to a simulated space environment of simul-
taneous high vacuum and UV radiation of 3800 ESH plus electron radiation
of 1015 e/cm2 (E = 1 MeV), and showed no significant change of sol ar
absorptance from the i ni ti al hi gh val ue of 0.959. However, the room-
temperature emittance at the longer wavelengths (from 3 to 25 mp) was
relatively low, 0.686, and was reduced even further to 0. 598 by exposure
to the simulated space environment. This 12 percent change of thermal
emittance was the largest of any of the black coatings tested. (55) (See
Figures C-59 and C-60. )
Du-Lite-3-D on TvDe 304 SS (Grit Blasted)
Du-Lite-3-D on Type 304 SS i s a good flat absorber in the solar spec-
tral regi on. Sol ar absorptance i s rel ati vel y hi gh and thermal emi ttance i s
relatively low. I t was stable to simulated space environment. Thermal
emittance changed 4.1 percent. (55) (See Figures C-61 and C-62.)
Westinghouse Black on I nconel, Sodium
Dichromate-Blackened SS (Tvpe 347).
Sodium Dichromate-Blackened I nconel,
and Sodium Dichromate -Blackened I nconel X
Various other combinations of "blackened" metals are good flat ab-
sorbers i n the sol ar spectral regi on. Sol ar absorptance of these i s rel a-
ti vel y hi gh, whi l e thermal emi ttance i s rel ati vel y low. They are stabl e to
simulated space environment. The major disadvantage to these may be the
hi gh temperatures requi red duri ng the coati ng process. The thermal emi t-
tance of sodium dichromate-blackened I nconel changed only 2.7 percent
after being subjected to 4770 solar hours in vacuum and 1015 e/ cm . Sodium
dichromate-blackened I nconel X showed negligible change after 2560 sol ar
hours in vacuum plus 1015 e/cm2. (55) See Fi gures C-63 to C-70. Chemi-
cally blackened I nconel and beryllium with us and E greater than 0.80 were
used on the Gemini spacecraft for maintaining lower temperatures during
reentry. (5 1)
2
71
Pyromark Black Refractory Paint on
Aluminum 1 1 lOO(Z-S)Al] and Pyromark
Black Refractorv Paint on Inconel
These cannot be considered as flat reflectors because solar absorp-
tance and emittance are relatively high. However, the paints are unaffected
by prolonged exposure to simulated space environment. (55) See Fi gures
C- 71 to C-74.
72
PIGMENTS
Because of the convenience of painting a surface, parti cul arl y an
irregular structure, efforts have continued to develop a paint which would
be stable to ,space environment. The major task in developing low-solar-
absorptance, pigmented, thermal-control coatings has been to effect a
stability to UV radiation and to charged particles. The approach to this
probl em at the present ti me is to determine mechanisms of UV degrada-
tion in specific materials, particularly pigments. Knowing the mecha-
nism of degradation, methods of protection from such degradation can
then be developed. (56) In connection with this approach, efforts have been
made to determine the effect of particle size on reflectance. I t has been
found, for example, that the contribution of voids (between discrete par-
ticles and between agglomerates) is an important factor because voids in-
crease spectral reflectance and yet tend to mitigate the absorption effect
of i ntri nsi c absorbers. (56) Also, studies have been conducted to charac-
teri ze degradati on i n terms of sol i d-state parameters. Efforts have been
made to detect and identify the defect centers produced by UV irradiation.
Considerable effort has been made to determine the reasons for the insta-
bility of pigments to UV radiation and to develop methods of improving
their stability.
Zinc Oxide
Probably the major studies have centered on zinc oxide (ZnO), not
only because of the results of previous coating studies, but also because
it has lended itself for study and analyses. Several models have been
offered to describe the degradation of zinc oxide that manifests itself by
an increase in the optical-absorption coefficient in two spectral regi ons,
the 0. 39 to 0. 8 and the 1. 0 to 2.4-p range.
One general model that has been advanced to describe the degrada-
tion of zinc oxide is as follows. (57) UV photons, which are absorbed near
the surface, produce free electrons and holes. The photoproduced holes
that diffuse to the surface recombine with electrons at surface oxygen,
thereby neutralizing the surface oxygen. The neutralized surface oxygen
is then evolved from the zinc oxide surface i f the ZnO is in a vacuum
environment. The first oxygen to be evolved is chemisorbed oxygen, but
as the irradiation is continued, surface lattice oxygen is also evolved.
73
The evolution of oxygen leaves the surface zinc rich, and the excess zi nc
diffuses into the bulk of the zinc oxide. Thus, the net result of the UV
i rradi ati on i s the generati on of excess zi nc and an i ncrease i n the concen-
trati on of free el ectrons.
The mechanisms by which the above actions cause the increased
visible- and I R-region absorption are not clearly defined. (57) Some be-
lieve that the enhanced I R absorption is a resul t of addi ti onal free-carri er
absorption which is caused by the increase in the free-electron concentra-
tion. Others believe that the enhanced IR absorption is a resul t of an in-
crease in the density and population of defect levels lying near the conduc-
tion band.
The increased visible absorption is likewise not clearly understood.
It has been explained by some workers that this is the resul t of the excess
zinc precipitating out at dislocations, causing severe lattice strain in the
neighborhood of the dislocation. (57) Such strain could result in a decrease
in the separation between the conduction- and valence-band extrema and,
in effect, decrease the band gap in the neighborhood of the precipitation.
This would produce a low-energy tail on the fundamental absorption edge,
similar to the visible degradation observed. Another explanation to the
increased visible absorption is that it is a resul t of defect centers whose
energy levels lie just above the valence band.
A seri es of experiments involved studies of changes in electrical
properti es of thin films and of crystals with UV irradiation, and studies on
the effect of radiation on electron paramagnetic resonance, magnetic sus-
ceptibility, and luminescence . ( 5 7 ) These studies have shown that UV i rra-
diation of ZnO results in the production and population of defect centers
with energy levels near the conduction band and that these centers are sen-
sitive to IR radiation. UV i rradi ati on al so i ncreases the free-el ectron
concentration to such a densi ty that free-carri er absorpti on i n the near IR
region should become appreciable. The luminescence studies demonstrated
that luminescent defect levels were present in untreated SP-500 ZnO and
that UV irradiation enhanced the population and density of those levels.
These photoproduced holes and electrons can undergo chemical re-
action. (58) Such chemical reactions change the structure of the coating,
leading eventually to coloration. One approach to prevent optical degrada-
tion is to find surface additives that act as recombination centers, alter-
nately capturing the holes and electrons and thus removing the photopro-
duced carri ers wi th no net chemical change. In studies with ZnO,
74
single-crystal measurements have shown improvement up to a factor of 106
i n rate of conductivity degradation, and powder measurements have shown
photodamage protection from monolayers of additive. ( 58)
In these studi es, it was concluded that suitable surface additives,
acting as electron-hole recombination centers, could prevent degradation
of thermal -control coati ngs by preventi ng i rreversi bl e chemi cal reacti ons
at the surface of the pigment grains. It was indicated that the surface
additive will be effective i f it has the following properties: (1) it must be
nonvolatile and chemically inert toward its environment and toward photoly-
si s, (2) it must exi st i n two stable oxidation states separated by one elec-
tron, ( 3 ) the energy level occupied by this electron should be just below
the bottom of the conduction band of the pigment in order that both the hole
and el ectron-capture cross secti ons be hi gh, ( 4) the additive must be pres-
ent i n both oxidation states, and (5) it must uniformly cover the surface of
each grai n of pi gment materi al .
The material showing the most promise with ZnO was the redox
couple, a 1: 1 ferrocyanide-ferricyanide combination. (59) Tests of this
additive have been made using two test procedures. These were (1) mon-
itoring vacuum photolysis of ZnO by measurement of the increase in dark
conductance of the ZnO crystal s and (2) monitoring of vacuum photolysis
by el ectron-spi n resonance (ESR) of a signal at g - 1. 96 associ ated i n-
directly with donors in ZnO. (58) This latter method is applicable to pow-
dered ZnO.
More work needs to be done before satisfactory results may be
achieved with thermal-control coatings. However, a promising approach
has been made and theoretical considerations have been advanced which
should lead to the development of stabilized pigments for thermal-control
paints.
Two principal optical effects are found with ZnO. One, induced by
UV i n vacuum (only), appears as an increasing IR absorption which in-
creases wi th i ncreasi ng i rradi ati on. The other effect, i nduced onl y by
mechani cal and thermal treatments appears as an absorption band very
near the opti cal absorpti on edge. (6 6)
I t has been found that solar radiation-induced degradation of parti c-
ulate ZnO refl ectance occurs i n two spectral regi ons - the visible adjacent
to the band-edge and the near IR between 0.8 and 2.8 p. Visible degrada-
tion is most effectively produced by photohs of wavelength less than 0 . 3 p .
75
. "
It i s not certain, but probable, that the occurrence of IR degradation is a
necessary precondition for production of visible degradation. The kinetics
of IR degradation are strongly dependent on the irradiation intensity as well
as the total irradiation. (6 The visible degradation is primarily dependent
on the total irradiation. One of the aspects noted was that the glow di s-
charge which accompanies start-up of an electronic vacuum (VacI on) pump
may cause significant IR degradation, but none in the visible wavelengths of
si ntered ZnO.
Titanium Dioxide
Some preliminary fundamental studies have been initiated with rutile
titanium dioxide pigments containing various impurity levels in an effort to
determine damage mechanisms when the pigment is exposed to solar radi-
ation, electron irradiation, or combined environments. (62) El ectri cal -
conductivity measurements and gas -evolution experiments under exposure
to UV excitation were conducted to investigate the role of the surface of the
pigment particles,
In the course of the work, the effect of exposure to UV from an un-
filtered xenon arc (Spectralab X-25 solar-spectrum-simulation source of
4 suns) was determined. See Figure C-75. The pigment was the high-
purity rutile which had been dry pressed to a density of 1.5 g/cm3. Sam-
ples were also exposed to electron radiation (Figures C-76 and C-77) and
to simultaneous UV and electron irradiation (Figures C-78 and C-79).
76
The conclusions reached were: ( 6 2 )
The diffuse reflectance spectra of al l i rradi ated
specimens degraded.
UV irradiation produced significantly more degrada-
tion in the visible than in the IR region, while electron
irradiation produced a relatively uniform degradation
across the spectrum,
The saturated magnitudes of the UV and electron
degradations were about the same.
All the damaged samples showed recovery at room
temperature in vacuum (about torr). The UV-
damage recovery tended to destroy all the defect
centers, whereas the el ectron-damage recovery
i s more rapi d i n the IR and small in the visible
region. In both, recovery essentially ceased in
about 4 to 6 hours.
Renewed irradiation with electrons following re-
covery produced new absorbing centers in the
visible region, but the I R reflectance degradation
for the second irradiation was about the same as for
the fi rst.
Simultaneous UV and electron irradiation resulted
in saturation behavior only near 1 micron, indicating
a synergistic effect in the IR
Recovery from simultaneous UV and electron bom-
bardment lead to almost complete recovery in the I R
within a day, whereas little recovery in the visible
was observed at this stage.
Recovery after exposure to ai r 53 days later was
essentially complete to the preirradiation vacuum
characteri sti c for al l speci mens.
77
Titanates
Zinc orthotitanate (Zn2Ti04) is a spinel that is formed from 2 mol es
of ZnO and 1 mol e of anatase TiO2. The most stable product to date is
formed at 1050 C. The extraordi nari l y hard product requi res consi derabl e
energy to grind into a suitable powder. I t is believed that the grinding is
l argel y responsi bl e for the random i nstabi l i ty that has been observed i n
space-simulation tests employing in situ reflectance measurements. (23)
Zinc orthotitanate exhibits bleachable degradation in the 0.4 to 1. 5- p
region, with the damage centered at about 0.9 p.
The extraction of all residual, unreacted zinc oxide with acetic acid
has been found to be necessary for the elimination of a strong absorption
in zinc orthotitanate at 3500 A wavelength. Unextracted zinc oxide and
excess titania are believed to be in part responsible for the bleachable I R
damage observed. (23) This pigment appears promising as a stabl e mate-
ri al when properl y prepared. Work is continuing on developing methods
for producing a stabl e materi al . ( 6 3 , 64) Other ti tanates such as i ron
titanate are also being investigated.
Zirconium Silicate
A seri es of zirconium silicates (Zr02. Si02) have been synthesized
and examined for use as pigments in thermal control coatings. ( 8 ) Calcina-
tion temperature, purification, and grinding conditions are important for
stability in a space environment. A thermal-control coating consisting of
Zr020SiO2 in potassium silicate (K2Si03) has shown excellent stability
when subjected to 485 sun hours in vacuum. A aS for one coating was 0. 04.
The coating has shown excellent stability to proton and combined UV-
proton environments. After exposure to 2 x 108 rads (C), gamma, and
4 x 1014 nfvt, neutron, ACL, was 0. 03. ( 8 ) Work is continuing on the devel-
opment of this pigment.
78
BINDERS
Silicone Binders
Pol ydi methyl si l oxanes are the most stabl e pol ymers avai l abl e i n
terms of UV irradiation in vacuum. Both elastomeric and rigid cross-
l i nked si l i cone pol ymers are stabl e. Si nce they are essenti al l y trans- .
parent to UV, thei r stabi l i ty i s pri mari l y a function of their purity; thus
the amount of ami ne catal yst used to cure the l i near pol ymers greatl y
influences the stability of the system..(6)
General Electric methyl silicone RTV-602 coated over 1199 al umi -
num reflector sheet was tested as part of the Lunar Orbiter V flight ex-
peri ment. The i ncrease i n of this coating can be considered to
indicate the "true stability" of the binder. This was the degradation of
an unprotected binder, and therefore the damage incurred by the RTV-602
can be considered a maximum degradati on for thi s materi al . The ad-
dition of a pigment to this binder would generally lower the quantity of
solar-UV radiation that the binder would be exposed to and, as a resul t,
lower the degree of binder damage. Figure C-80 shows the change in
sol ar absorptance of a thermal-control coating, Hughes H- 10 [ calcined
(mono 90) clay/RTV-6021 and the RTV-602 over 1199 aluminum. Since
the H- 10 contained a relatively stable pigment, and with the change in
absorptance of the RTV-602 as shown in Figure C-80, it is considered that
a significant portion of the damage to the H- 10 coating can be attributed to
the degradation of the binder. There was, of course, some attenuation of
the binder damage due to the presence of the pigment. (I 4)
Phenylmethyl silicones undergo considerably greater optical damage
when irradiated with similar doses of UV i n a vacuum. The difference
between aromatic and aliphatic silicones is believed to be due principally
to the relative degree to which they absorb near-UV radiation. The phenyl
groups absorb UV preferenti al l y, whereas the enti re methyl si l i cone mol e-
cul e i s comparati vel y transparent. The predomi nant mechani sm i s thought
to be dehydrogenation, whether it be methyl or phenyl segments that are
affected.
79
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(21) Arvesen, J . C., "Spectral Dependence of Ultraviolet-I nduced Degrada-
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82
(22) Holland, W. R., "Stability of Thermal Control Coatings Exposed to
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I (23) Zerl aut, G. A., Noble, G., and Rogers, F. O. , "Development of
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I nstitute, George C. Marshall Space Flight Center, NASA, Huntsville,
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(24) Zerl aut, G. A. , Rogers, F. 0. , and Noble, G. , "The Development
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3rd Thermophysics Conference, Los Angeles, California, J une 24-26,
1968. Avail: AIAA, Paper No. 68-790. Progress in Astronautics and
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and Entry Bodies, J . T. Bevans, editor, Academic Press, New York,
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(25) Brown, R. R. , Fogdall, L. B., and Cannaday, S. S., "Electron-
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83
(28) Smith, F. J ., and Grammer, J . G., "Emissivity Coatings for Low-
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(36) Linder, B. , "Series Emittance Thermal Control Coatings", Paper
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(38) Olson, R. L. , McKellar, L. A. , and Stewart, J . V. , "The Effects
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(39) Glenn, E. E., and Munoz-Mellowes, A., "Thermal Desi gn and Test-
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(40) Farnsworth, D., "Exploratory Experimental Study on Neutral Charge
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(41) Bailin, L. J . , "Effects of Combined Space Radiation on Some Mate-
rials of Low Solar Absorptance", Materials Sciences Laboratory,
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(42) Slensky, A. F. , MacMillan, H. F. , and Greenberg, S. A. , "Solar-
Radiation-I nduced Damage to Optical Properties of ZnO-Type Pig-
ments", Lockheed Palo Alto Research Laboratory, Lockheed Missiles
and Space Company, Palo Alto, California, LMSC-4- 17-68- 1, NASA-
CR-98174, February, 1968. Avail: NASA, N69-13059 and CFSTI.
(43) Cl arke, D. R., Gi l l ette, R. B., and Beck, T. R., "Development of a
Barri er-Layer Anodic Coating for Reflective Aluminum in Space",
The Boeing Company, Seattle, Washington. Paper presented at the
AIAA/ASME 8th Structures, Structural Dynamics and Materials Con-
ference, Palm Springs, California, March 29-31, 1967, Progress in
Astronautics and Aeronautics, Volume 20, "Thermophysics of Space-
craft and Planetary Bodies", G. B. Hel l er, edi tor, Academi c Press,
1967, pp 315-328.
(44) McCargo, M., Greenberg, S. A., and Breuch, R. A., "Study of
Environmental Effects Upon Particulate Radiation I nduced Absorp-
tion Bands in Spacecraft Thermal Control Coating Pigments",
Lockheed Palo Alto Research Laboratory, Palo Alto, California,
LMSC-6-78-68-45, NASA-CR-73289, J anuary, 1969. Avail: NASA,
N69- 16868 and CFSTI.
(45) Streed, E. R., "An Experimental Study of the Combined Space Environ-
mental Effects on a Zinc-Oxide/Potassium-Silicate Coating", Ames
Research Center, Moffett Field, California, Paper presented at the
AIAA Thermophysics Specialist Conference, New Orleans, Louisiana,
Apri l 17-20, 1967. Avail: AIAA, Paper No. 67-339, Progress i n
Astronautics and Aeronautics, Volume 20, "Thermophysics of Space-
craft and Planetary Bodies", G. B. Hel l er, edi tor, Academi c Press,
1967, pp. 237-264,
(46) Rawuka, A. C., "In Situ Solar Absorptance of Ultraviolet Degraded
I norganic Coatings", Materials and Process Engineering Labora-
tory Report, Seri al No. MP 50, 749, Catalog No. RD 28700,
October 5, 1967.
(47) Heaney, J ames B., "Resul ts From the ATS-3 Refl ectometer Experi -
ment", NASA Goddard Space Flight Center, Greenbelt, Maryland,
Paper presented at the A I M 4th Thermophysics Conference, San
Francisco, California, J une 16-18, 1969. Avail: AIAA No. 69-644.
86
(48) J orgenson, G. V., Wenner, G. K . , KenKnight, C. E., Eckert,
E. R. G. , Sparrow, E. M., and Torrance, K . E., "Solar-Wind
Damage to Spacecraft Thermal Control Coatings ' I , Surface Physics
Laboratory of the Applied Science Division of Litton Systems, I nc. ,
Report No. 2842, Summary Report, October 20, 1965.
(49) Personal Communication from A. L. Fitzkee, NASA Goddard Space
Flight Center, Greenbelt, Maryland, J une 3, 1970. Proton irradia-
tion performed by The Boeing Company, Aerospace Group, Seattle,
Washington, under the direction of L. B. Fogdall, R. R. Brown,
and R. S. Caldwell.
(50) Luedke, E. E . , and Miller, W. D. , "Kapton Base Thermal Control
Coatings 'I, Thermophysics Section, TRW Systems Group, Redondo
Beach, California, Paper given at Symposium on Coatings in Space,
Cosponsored by ASTM E- 10 Sub VI on Space Radiation Effects and
NASA, in Cooperation with .ASTM E- 21 on Space Simulation,
Cincinnati, Ohio, December 11-12, 1969.
(5 1) Borson, E. N. , "System Requirements for Thermal Control Coat-
ings", Aerospace Corporation, El Segundo, California, SAMSO-
TR-67-63, September 1967, J une 1967-August 1967, F04695-67-
C-0158, 30pp. Avail: DDC, AD 661963.
(52) Hass, G. , Ramsey, J . B. , Heaney, J . B. , and Tri ol o, J . J . ,
"Reflectance, Solar Absorptivity, and Thermal Emi ssi vi ty of Si 02-
Coated Aluminum", Applied Optics, - 8 (2), 275-281 (February, 1969).
(53) Bradford, A. p., Hass, G. , Heaney, J . B., and Tri ol o, J . J . ,
"Solar Absorptivity and Thermal Emissivity of Aluminum Coated
with Silicon Oxide Films Prepared by Evaporation of Silicon
Monoxide", Applied Optics, - 9 (2), 339-344 (February, 1970).
(54) Schmidt, R. N. , and Park, K . C., "High-Temperature Space-Stable
Selective Solar Absorber Coatings ' I , Applied Optics, 4 ( 8 ) , 9 17- 925
(August, 1965).
-
(55) Wade, W. R. , and Progar, D. J ., "Effects of a Simulated Space
Environment on Thermal Radiation Characteristics of Selected Black
Coatings", Langley Research Center, Langley Station, Hampton,
Virginia, NASA TN D-4116, National Aeronautics and Space Admin-
istration, Washington, D. C., September, 1967.
87
I I I11111l 1111111
(56) Gilligan, J . E., and Brzuskiewicz, J ., "A Theoretical and Experi-
mental Study of Light Scattering in Thermal Control Materials",
I I T Research I nstitute, Chicago, I llinois, Paper presented at the
AIAA 5th Thermophysics Conference, Los Angeles, California,
J une 29-J uly 1, 1970. Avail: AIAA, Paper No. 70-831.
(57) Kroes, R. L ., Kulshreshtha, A. P., Wegner, U. E . , Mookherji,
T . , and Hayes, J . D., "Effects of Ultraviolet I rradiation on Zinc
Oxide", NASA Marshall Space Flight Center and Brown Engineering
Co. , Huntsville, Alabama, Paper presented at the AIAA 5th Thermo-
physics Conference, Los Angeles, California, J une 29-J uly 1, 1970.
Avail: AIAA, Paper No. 70-829.
(58) Morrison, S. R. , and Sanci er, K . M., "Effect of Environment on
Thermal Control Coatings ' I , Stanford Research I nstitute, Final Report
SRI Project PAD-6146, October 15, 1969.
(60) Gilligan, J . E., "The Optical Properties I nducible in Zinc Oxide",
I I T Research I nstitute, Chicago, I llinois. Paper presented at the
AIAA 5th Aerospace Sciences Meeting, New York, New York, J anu-
ary 23-26, 1967, Avail: AIAA, Paper No. 67-214, Progress i n
Astronautics and Aeronautics, Volume 20, G. B. Heller, editor,
"Thermophysics of Spacecraft and Pl anetary Bodi es", Academi c Press,
1967, pp. 329-347,
(61) Greenberg, S. A., and Cuff, D. F., "Solar-Radiation-I nduced
Damage to Optical Properties of ZnO-Type Pigments", Lockheed
Palo Alto Research Laboratory, Lockheed Missiles and Space
Corporation, Technical Summary Report for Period 27 J une 1966
to 27 March 1967, NAS 8- 18114, L-92-67-1, J une 1967.
(62) Fi rl e, T. E., and Flanagan, T. M., "Mechanisms of Degradation of
Pol ymeri c Thermal Control Coati ngs. Part 11. Effects of Radiation
on Selected Pigments", Gulf General Atomic I ncorporated, AFML-
TR-68-334, Part 11, March, 1970.
88
(63) Zerl aut, G. A . , and Ashford, N. , "Development of Space-Stable
Thermal-Control Coatings", IIT Research I nst., IITRI-U6002-73,
J anuary 31, 1969.
(64) Campbell, W. B. , Cochran, J . K. , Hinton, J . W. , Randall, J . W. ,
Versi c, R. J . , and Burroughs, J . E. , "Preparati on of Pigments for
Space-Stable Thermal Control Coatings", The Ohio State University
Research Foundation, J uly, 1969.
(65) "Advanced Papers of the ASM 1962 Golden Gate Metals Conference
on Materials Science and Technology for Advanced Applications
1962 Golden Gate Metals Conference, San Francisco, California,
February 15-17, 1962.
89
I NDEX
3M202-A-10 Coating 12,69, C33
1100 Aluminum 70-72, B14
11 99 Aluminum 55,57,79, C4, C45
2024 Aluminum 41, Al, A7
6061 Aluminum 53,70, A1
Absorptance - Use Solar Absorptance
Absorptance to Emi ttance Rati o 1,
2,17,18,33,36,37,39,40,42,44-46,
50,55, 56,59-61,63, 64,67, 68,79,
Al-A8, B2, B6, B14, B25, C3, C10-8
C14, C27, C30, C32
Acrylic Resin 8,42,43, A6, B29, B3 1
Acti ve Temperature Control 17
Adhesion 54, A3, A4, B30
Adhesives 59,67,69, Al, A2, A4
Air 3,5,19,28,29,32,53, C9
Alodine 12,58
Alpha Particles 2,4,22,23,25,27,56
Aluminized Mylar 60, 69, A2
Aluminized Polyimide 14, 61, A5, C29
Aluminized Teflon 5,14, 60, A5, C5,
Aluminum 3-6,8,12,14,16,18,36,
C6, C27
39-41,50,51,53-67, 69-72,79,Al,
A2,A4,A5,A7, B2, B3, B26, B27, C5,
C32, C36, C42
C14, C19-C21, C23, C26, C27, C30-
Aluminum Acrylic Paint A6
Al umi num Foi l Al , A2, C 14
Aluminum Oxide 4, 10,14,48,49,54-
56,63,65,66,68,A5,A7, C1, C4, C9-
C13, C19-C21, C23, C32
Aluminum Silicate 6, 16,36,39,40,
Aluminum Silicone Paint 18,36,41,53
Alzak C23, C24
Anodized Aluminum 4,12,39,50,51,
Apollo 15,16,39,51,57,63, C2
Ascent Force A2
48, B3
54-57,70, C2-C4, C15, C22, C34, C35
Ascent Temperature 43,44,46,59,
ATS-I 7, 11, 15,29,39,49, 66, B6,
Al , A4, A5, B28
B25, C10-C13, C30, C32
ATS-IU: 13,56,63,65,66
Auroral Radiation 2,20,24,27
B-1056 Coating 6,28,36, B4-B6,
B-1060 Coating 35,36,41,53, B2,
Beryllium A2, A3
Bi nders 3,6,8,44-46,79
Bismuth Sulfide Dye 70
Bleaching 28-30,35,45,47,49,78
Blistering 9,42,43, 69, A4, A6, B30
Butvar 12,43,58-60, B3, C5, C26
Cameo Aluminum 2082 Porcel ai n
B14, B15, C14
B14, B20, B21, C14
Enamel 70
Carbon Bl ack Pi gment 45,A3
Cat-a-Lac Coating 45
Ceri um Oxi de 69
Cermet A3
Chromate Coatings 58, A2
Chromium Oxide 54, A3
Cobalt Sulfide Dye 70, C34
Color Centers 48,49, 52,55, 62, 69
Copper 59, C26
Corning 7940 Fused Silica - Use
Silicon Oxide
Cosmic Radiation 20,26,27
Cracking 33,41, A4
Crazing 38, 60
Cryogeni c Temperature 4,11,35,
Damage Threshold 38,52
Defect Centers 74,75
Di el ectri c Materi al s 63, 65, 66,
Dimethyl Siloxane - Use Methyl
54,55, B3
68, A5
Silicones
90
Douglas I norganic White l o, 53
DOW-15 A2
D0w-J. 7 A3, B28
Du-Lite-3-D 71, C37
Electrical Conductivity 75,76
Electromagnetic Radiation 2,19, 27
El ectron I rradi ati on 2-4,7,9,11,13,
15,20-24,27,30,34,35,37,38,40,
41,46-50,52,55,57,60-62,65,66,
69, 71,76,77, B1, B2, B15-B18,B20,
B22, B23, B26, B30, C1, C4, C7, C9,
C 10, C 16, C24, C28, C3 1 -C45
Electron I soflux Contours A14
El ectron Paramagneti c Resonance
El ectrostati c A5
Emittance 1,6,8,10, 12-14, 16,31,
74,75
37,39,42-49,51,53-55,57-59, 67,
71,72,Al-A8, B2, B3, C2-C5, C19,
C20, C25, C34-C43
Engine Heat Shield A2
Epoxy Resins 8,43 -45,69, B29, B31
Equipment-Mount Decks 33, B15
Ethyl Silicone 34
Expl orer XXIII 15,16, 63
Fasson Foi l A1
Ferrocyanide-Ferricyanide 75
Flat Absorbers 1,17,18,71,A3,A9
Flat Refl ectors 1, 17, 18, 72,A6,A9
Fluorescent Lights A4
Fuller Aluminum Silicone Paint A6
Fuller Black Silicone Paint A3
Fuller Gloss White Silicone Paint 8,
Galactic Radiation 2,4
Gemini 71
Goddard 101-7 Coating 34,B18
Gold 18,59, A2, A5, CZ6
Hanovia Gold 651 8 A2
High-Altitude Nuclear Detonation
Hughes I norganic White 10,36,41,
41,42, A4, B28, B29, B31
5,24
48,79, B2, B14, C9, C14, C19
Hughes Organic White Coating 6,
16,36,39,40, B2, B14, B26, C14,
c45
I nconel 67, 68,71,72, A2-A4, C38,
C40, C43
I nconel X A2, C41
I nfrared Wavelengths 1,3,4,18,
19, 27, 28, 30, 31, 34, 35, 37, 38, 40,
42,44,52,54,57, 61, 62,64, 65,68,
69,74-78,A3,A4, B1, B2, B6-Bl3,
B16-B24, B26, B27, B29, B31, C8-
C10, C15, C19, ‘221, C22, C24-C26,
C28-C45
In Vacuum - Use Vacuum
I ron Titanate 78
Kapton 14,61,62, A5, C28, C29
Kemacryl Coating 8,18,42,43, A3,
Lanthanum Oxide 53, B29, B31
Lead Sulfide Dye 70
Lithafrax 10,46,47, C8
Lithium Aluminum Silicate 10,46,
47, A5, B29, B31
Lockspray Gold A8
Luminescence 74
Lunar Orbi ter I 7,33, B5, B12, B15
Lunar Orbi ter I1 7,32,33, B12, B15
Lunar Orbi ter I V 7,11,24,33,34,
Lunar Orbi ter V 5,7,11,16,24,33,
A4, B30
36,41,53,B13,B14,C19
36,39-41,50,53, B13-Bl5, B26,
B27, C13
Magna-Larninac X-500 45
Magnesium A2-A5, B28
Magnesium Fluoride 12,63,66,68,
Magnesium Oxide 43, B31
Magnetic Susceptibility 74
Mari ner I1 60
Mariner I V 5,11,45,50, C13
Mari ner V 5,7, 15,16,24,29,34,
Mechanical Fastening A2
69
45, 60, B5, B6, B14
91
Methyl Silicones 3,6,16,28-41,51,
76,79,A5, Bl-B25, B27, C2, (214,
C15, C45
Micobond Paint 18, A3, A8
Micrometeoroids 2,34
Mirrors 5,12,1(5,58,62,63,66, 67
Models 73 -75
Molybdenum 12,68,69, A2
Mylar 59,60, 69, C26
Mystik 7402 A2
Neutron Environment 25
Nichrome 54, A3
Nickel Plate 71, A2, C36
Nickel Sulfide Dye 70, C35
Nuclear Radiation 6,8, 10, 12,37,38,
41,43-45,47,50,55,56,78, B3, B31,
C4, C8, C26
OGO-VI 5,15,61
oso-I 5, 9,44
OSO-I1 9, 11,29,44,50, C13
OSO-111 11,13,24,29,34,50,57,
67,68
OSR A4,A5
Outgassing 67,69,73,76, Al, A4, A5
Passive Temperature Control 17
Pegasus-I 7,29,44, B5
Pegasus -11 5,11,44,50, C 13
Pegasus -111 44
Phenylated Silicone 6,38,40,79, B2,
B24-, B26, C27
Pl ati num A3
Platinum Black A3
Polyimide 14, 62, C28, C29
Polyurethane 45
Polyvinyl Butyral 12,43, 58-60, B3,
Porcel ai n Enamel 70, A5
Potassi um Silicate 3,4, 5, 10,30-36,
C5, C26
39,48-53,55,78,B3, B29, B31,Cl-
C4, C9-Cl 6
Proton I rradi ati on 2,4,7,9,11,13,
15,20-27,30,35,37,38,40,42,43,
49-53,55,56,58,60,62,66,69,78,
B5, B8-Bl l , B19, B20, B24, B29,
C1, C6, C7, C10, C13, C15-Cl7,
C29, C33
Proton I soflux Contour A10-Al2
PV- 100 8,42, B29, B30
Pyromark Bl ack Refractory Paint
Pyromark Ti 02 Si l i cone B24
QMV Beryllium A2,A3
Quilted I nconel Foil A2
Reflectance Degradation 3,5, 7,
72, C42, C43
28-30,32-34,36,38,40-43,48,49,
52,54,56,57,60-62,65-67, 69,75,
77,Bl ,B2,B4,B6,B12, B13,B15-
B18, B20-B24, B26, B27, B29-B31,
C3, C9, C10, C14, C16, C19, C21-
(324, C26-C45
Ren& 41 54,A2,A3
Reynol ds Wrap Foi l A8
Rokide A A7
Rokide C 12,54, A7
S-13 Coating 6, 16,28-36,40, 51,
B1, B2, B4-B7, B11-B17, B19, B20,
C15
Sandoz Black Dye 70
Series -Emittance Coatings 58, C5
Sherwin Williams M49BC12 A3,
Sherwin Williams M49WC17 A4,
Silicone Adhesive 59, 67, A2
Silicone-Alkyd 8,41,42
Silicone Tape A7
Silicon Oxide 5 , 12, 14,16,62-68,
Silver 12,16,59,66-68,A4,A5, C26
B29
B3 1
A4, A5, C2, C29-C31
92
Silvered Teflon 5,14, 60,61, C6, C25
Skyspar SA 91 85 A4
Sodium Dichromate 71, C39-C41
Sodium Silicate 10,46,47, B3, B29,
Sol ar Absorbers 1,17,18,68, Al ,
Solar Absorptance 1,5-16,28-31,33,
B31, C8
A2, A9
35-37,39-53,55-58,60,61,63,67,
68,70-74,78,Al -A8, B1-B3, B5-
B12, B14, B15, B19-B21,B24, B27-
B31, C2-C8,C13-C15, C17, C18,
C20, C22, C25, C27, C30, C34-C43,
c45
Solar Concentrator 5,66
Solar Flares 2,20,23, 27, 61
Solar Opacity A3, A4
Solar Radiation 18,36,52, 64, 78, A4,
B5, B6,B12,B14,B24,B25,Cl O,Cl l ,
Solar Reflectors 1-3,5,12,16-18,20,
Solar -Thermoelectric Systems 68, 69
Sol ar Wind 2,4, 5,20,23-27,50,58, C7
Stainless Steel 71, A2, A4, A7, C37, C39
Superalloys A4
Surveyor I 11,48
Synergistic Effects 7, 9, 11, 13, 15,23,
Tantalum A2
Teflon 5,14,58-61, C5, C6, C25, C27
Temperature Effects 7,11,15,52
Thermal Cycling Resistance A3, A4
Thermal Shock A3
Thermal Stability A3
Thermatrol 2A-100 6,16,37,38,A5
Titanium A2, A4
Titanium Oxide 10, 16,36-39,41-44,
C13, C23, C24, C27, C32, C34-C43
67,68,79,A4, A5,A9, C7, C45
24,30,38,48,55, B20, C17, C18
50,53,76,77,A5, B2, B21-B25, B29,
B31,C2,Cl l -C13,C44,C45
Ultraviolet Radiation 3-6,8, 10,12,
14,19,20,24,25,27-32,34-38,
40-44,46-53,55-57,59-63,65,66,
68-71,73-77,79,Al-A8, B1, B2,
B4, B6, B7, B9-Bl l , B19-B21, B27,
B29,B31, C1, C3-C5, C7-Cl0, C15-
C18, C22, C28, C29, C31, C44, C45
Ultraviolet Wavelengths 1,3,18, .
19,30,37,38,43,44,57,61,62,65,
77, B8-Bl3, B16-B24, B26,B27,
B29-B31, C8-ClO, C13, C16, C24-
C29, C31 -C33
Vacuum 5,6, 8,10, 12,14,18,19,
28-32,35,37,41-43,46-49,53-55,
61-63,65,69-71,73,75,77-79,Al ,
B3, B4, B9-Bl1, B19-B2l, B27,
B29-B31, C3, C4, C7, C9, ClO, C16-
C18, C21, C22, C29, C3 1
Van Allen Radiation Belts 2,4, 20-
Vanguard 13,63, 64
Vinyl Phenolic Paint A3
Vinyl Silicones 37,58- 60
Visible Wavelengths 1,3, 18,19,
27,31,37,38,40,42-44,48, 54,56,
61, 62, 65, 69,74-78, B1, B2, B6-
B13, B16-B24, B26, B27, B29-B31,
C8-Cl0, C14, C16, C19, C21, C22,
C24-C26, C28, C29, C31-C45
22,26,27,34, AlO-Al5, C7
Westingh0us.e Black 71, C38
White Paints 3, 6,8, 18,20,37,43,
White Skyspar 8,43,44, A4, B3,
X-Ray Radiation 13,15,19,25,27,
2-93 Coating 5,10,36,41,50-53,
Zinc Orthotitanate 78
Zinc Oxide 5,6,10,16,28-36,39,
44, A4,A5,A7, B3, B29-B31
B29, B31
59, c5
B2, B14, C3, C13-Cl5
40,49-53,73-76, Bl-B21, B29,
B31,Cl -C3,Cl l ,Cl 3-C16
Zirconium. Silicate 10,49,78, B3,
B29, B31
93
APPENDIX A
THERMAL CONTROL MATERIALS FOR SOLAR AND
FLAT ABSORBERS AND REFLECTORS
and
CONTOURS OF CONSTANT FLUX ELECTRONS AND PROTONS
TABLE A-1. THERMAL-CONTROL MATERIALS FOR SOLAR
I ABSORBERdg~33* 65)
Note: Unlemm 0Lherwi.c indicated, t be8e material. show no mignificant change
in absorptance or emittance in penetrating nuclear radiation in vacuum.
Ascent
Absorptance and Temperature Ultraviolet Cycling
Thermal-
Material Subatrate a,/€ Emittance, 70 F L hi tm, F Resimtance Re8istance Remark8
6061 Aluminum,
chemically
cleaned
6061 Aluminum,
chemically
cleaned
6061 Aluminum,
chemically
cleaned
2024 Aluminum,
chemically
cleaned (non-
cl ad)
2024 Aluminum,
sheet (clad)
Aluminum
Aluminum
Aluminum,
(I20 size grit1
sandblasted
Aluminum foil,
dry-annealed
Alumlnum f ot l .
dull side
Aluminum f oi l .
bright aide
Aluminum foil,
shiny side
Aluminum foil type
Aluminum foil,
plain
(MIL-A-I481
Fanson Foil
adhcaive backed
(Rubber-baaed
bright aluminum
foil. Type 1 has
a clear protec-
tive coating.
Type I1 ia base
only. I
_.
As-rolled 2.7t0.05 a. =0.16t0.04
c =0.07+0.03
Sheet 2.7 a, = 0 . 1610. 05
E =0.06tO. 03 aanded
belo re
proccseing
Forging
3.2tO. 08 as = D.29t0. D6
Weld area 2.6tO. 08 as =0.26t0.06
E E 0.0910.06
L =0.10f0.06
As-rol l ed. 3 , 7t0.06 a. = 0. Z Ot O. 05
hand
sanded
Not appli-
cable
Any clean
rigid
surface
1 4 . 3 5
4.28
I . 50
7.43
6. 81
5.33
5.54
= 0.06t0.03
a, =0.2210.05
E = 0. 0619. 03
as =0.387
E =0,027
a s = 0.218
t =0. 051
a, = 0.600
E = 0.410
a s = 0. 12+0 04
L : 0. 04t0.02
as = 0 . 2 2 3
E 2 0.030
a, i 0. 218
E =0.032
a, =0.192
E =0.036
0. = 0.238
L =0.043
3.0t0.05
a, =0. lZfO.04
-'. O4
E =0.05t0.02
3. 0:;: :i a. =0. 12t O. 04
c =0. 05t 0. 02
Structural
l i mi ts only
Structural
l i mi ts only
Structural
l i mi ts only
Structural
limits only
Structural
l i mi ts only
375
No effect
No effect
No effect
No effect
No effect
No effect
No effect The surface ie
very mumccptable
a, and E cauaed
to increase. in
by contamination.
No effect Ditto
No effect
No effect The surface char-
acterlaticm of the
sheet material.
are subject to
variationa de-
pending on fabri -
cations operations.
No effect Subject to degrrd-
ation from pre-
launch environ-
ment. Adhemivc
imlimiting factor
ment.
in apace environ-
No infor- Muat not be mxtcer-
mation nal during aacmnt.
Foil ahould be
perforated ( 1132-
in. di m. on 112-
prevent lifting due
in. centers) to
to ea. cvolutlon
in vacuum.
A- 1
TABLE A-1. (Continued)
Absorptance and Tempenbure Ultraviolet Cycling
Ascent Thermal-
Material Substrate a , / € Emittance, 70 F Limits, F Resistance Resistance Remarks
My6tlk 7402,
adhesive backed
silicone basad
aluminum foil
(luilted Inconel
Foil (H. 1. Thom-
pson Specificatlon
No. TPS 0101B)
MIL-N- 6840
Inconel X Foi l ,
MIL-N-7786
QMV Beryllium,
polished
chemically
Hanovia Gold 6518
on Rend 41
Gold, plated
on stainless
steel
Gold over
titanium with
resin undercoat
Gold, vacuum
deposited
Molybdenum,
slug
Chrome-
Myl ar
alummized
El ectrol ess
nickel
Pure tantalum
R e d 41, vapor
honed and buffed
Production Dow 15
on HM2lA
magnesium
Not appli- 3 . 17L0. 07 as c 0. 3 8 f 0 . 0 5
cable E =0. I2+0.05
Not appli- 4.4010. 10 as =0. 66f0.09
cable € =0. 15f0.05
Not appli- 5.0010.08 x s =0.50L0.06
cable c =0.10a0.06
Re n 6 41 6.0aO.08 os :: 0.53a0.06
c = O.OS+O. 06
Stainless LO. 77
Steel
Tltanium 9. 10
8.29
3.94
2.90
2 . 6 0
5 46
3 . 8 6
HM2lA 11.98
magne-
s ium
e =0,028
=
0.301
n s = 0.300
€ = 0.033
as i 0.282
c 10.034
as =0.480
€ : 0. I22
n S 10.247
e 10.085
o s : 0.450
c = 0.170
as z 0,442
E = 0,081
ilg 10.398
c =0. 103
a, = 0,359
E =0.030
750
2200
1500
1700 (test
maxlrnum)
900 ( " 0
change1
No effect
No effect
No effect
No effect
No effect
No infor-
mation
No effect
No effect
No effect
No effect
If applied external-
l y , the tape should
have mechanical
faatenmg on both
ends to prevent as-
peeling t he tape
cent forces from
from substrate.
Subject to handling
degradation.
Very susceptible to
and by fingerprints
i ncrease in a,
prelaunch envbron-
and oxidation in
ment. Pri mari l y
for engine heat
shield usage.
Subject to handling
degradation.
High ascent tempera-
ture has no effect
on as or c i f at
pressure of 0.05
torr or less.
May be suitable for
other substrates.
At 1700 F. values
changed t o a s =
0.8t0.06
c E 0. 4010. 10.
A- 2
TABLE A-2. THERMAL-CONTROL MATERIALS FOR FLAT
ABSORBERS(g* 33n 65)
~___
Ascent
Absorptance and Temperature Ul travi ol et Cycl i ng
Thermal -
Materi al Substrate n , l t Emi ttance, 70 F L i mi ts, F
Bl ack Kemacryl
L acquer (Sherwi n
Wi l l i ams M49BC
cure
12.1, room- temp
Ful l er Bl ack
Si l i cone Pai nt
517-B-2)
(W. P. Ful l er
Rokide C (chromi c
oxi de, fl ame
Abrasl ve Go.,
sprayed by Norton
85% Cr2031
Pl ati num Bl ack
l deposi t of
finely dl vl drd
OMV bervl l t uml
pl ati num on
Dow 17
(Anodi zed on HM
ZI A Magnesi um
Al l oy)
Dul l Bl ack Mi co-
bond (Mi dl and
I ndustri al
Fi ni shes)
Dull Bl ack Mi co-
bond, vinyl
(phenol i c) Pai nt
Carbon-Bl ack
Pi gment
Cermet (cerami c
contai ni ng
si ntered metal )
-~ " -.
_ _ _ _ ~_ -
Any cl ean I . 0610. 04 as =0.9310.03 No ef f ect at
ri gi d E =0.8810. 03 450
substrate.
pri mer
requi red
HMZI A-T8 1.0110.07 a , = 0.89aO.05 No ef f ect at
MR. FI m L = 0,8810.05 1070
ZI A- 0
Mg. AI ,
l e as steel s.
Ti , stai n-
super-al l oys,
and other ri gi d
substrates cap-
abl e of wi thstand-
i ng cure cycl e
Reni 41 I . Oba0.06 l g = 0.90+0.04 No ef f ect at
wi th a 2- 6 = 0.8510.04 I 660
mi l coat-
ing of
Ni chrome
QMV I . 11+0.08 , 5 = 0.94a0.03 No ei f cct at
berylllWl7 L = 0,8530.07 1200
HM2lA Mg 1. 11+0. 10 ' 5 =0.7830.08 No cf f ecl at
Al l oy L = 0.7010.06 500
I . I 1 ? s = 0.9310.04
t = 0.8930. 04
I . 10 as = 0.930
L = 0.840
Resi stance Resi stance Remarks
A , g<O. 05 No f ai l ure I . 5 - mi l dry f i l m
af ter 600 in 385 thi ckness requi red
sun hr UV cycl es for sol ar and i n-
-150 to frared opackty.
70 F, 18-
mi n cycl es
A1~<0.05 Cracki ng I - mi l dry f i l m
af ter 600 and losm of thi ckness requl red
sun hr UV adhesi on for sol ar and I n-
in 170 c y - frared opacLty,
cles - 240 peak cure-cycl c
t o 70 F. temperature,
cycl es
18-mi n 465 F.
No ef f ect
No ei i ect
Nu effect
No f atl ure: The bondl ng betwecn
70 to Rokldu C and the
I 600 F
substratc L S purcl y
In 5 mt n- mechani cal and
Ut e s thermal shuck 15 a
pol cntl al prubl cm.
No I nf orma- Possesses stabl e
tl on, prob- hl gh- temperaturc
abl y no ern~ttanct'.
ef f cct
NCI ef f ect Proprtctary process
of Dow Chem. Co. :
thermal stabl l l ty
>500 F doubtful .
I . 16 as =0.908
L = 0.780
I . 10 as = 0.650
L = 0. 580
A- 3
TABLE A-3. THERMAL-CONTROL MATERIALS FOR SOLAR
REFLECTOR^^, 33,36,49,50,65)
. "~ .. ~. ~
Ascent Thermal -
Absorptance and Temperature Ul travi ol et Cycl l ng
Materi al Substrate Emi ttance, 70 F L i mi ts, F Resi stance Resi stance Remarks
Ti nted Whi te
K emacryl
wi n Wi l l i ams
L acquer I Sher-
M49WC17),
room-temD cured
Ful l r Gl os s Whi te
Si .i cone Pai nt
at 165 F
( 5 1 7 - W- I ) , cured
Whi te Epoxy Pai nt
(A. Brown Sky-
spar SA 9185)
Opti cal Sol ar
vapor-deposi ted
Ref l ector IOSR),
si l ver on Corni ng
7940 fused si l i ca
wi th an overcoati ng
of vapor-deposi ted
I nconel
Any cl ean, 0. 33+0.05 as =0.28+0.04
ri gi d to. 03
=0.89-0, o6
surf ace,
requi red
pri mer
HM2I A- 0.28f:: :; X S =0.25+0.03
-0.06
T8 Mg.
Hm2I A-
= 0. got0. O3
0 Mg, AI ,
Ti, SS,
super-
al l oys,
and other
ri gi d sub-
strate cap-
abl e of
wi thstandi ng
cure cycl e
Any ri gi d 0. 24- t : q' : : O s = 0. 91". O3
E = 0.22*0. 04
-0. 06
surf ace
0. 062 o s =0.50f0. 005
E =0. 7?5+0.02
(-135 to t70 F)
450
650
450
200 to
450 F:a,
by 0. 04
i ncreases
(constant]
maxi mum
al l owed
500
Aa, =
af ter 2000
0.18+0.04
sun hr
No f ai l ure 5- mi l dry f i l m
in 385
cycl es
thi ckness requi red
for opaci ty to
-150 to sol ar; I - mi l thi ck-
70 F,
18-mi n opaci ty in I R.
ness suf f l ci ent for
cycl es Requi res 14 days
temperature cure
at room-
to mi ni mi ze bl i s-
teri ng duri ng
ascent heati ng.
mum ascent tern-.
Used where maxi -
perature L S ~450.
If no change i n sur-
f ace can be tol er-
perature <ZOO F.
ated. max tem-
A i s = 0. 09 Cracki ng 5-mi l dry film thi ck-
+O. 05
af ter 2000 adhesi on opaci ty to sol ar;
and l oss of ness requi red f or
sun hr In 170 cy- I - mtl thdckness
cl es -240 for opaci ty in I R.
to 70 F.
cycl es
18-mi n
Aa2 =0. 3 5 No f ai l ure a, hi ghl y suscepti bl e
+O. 06
af ter 2000 cl es -150 prel aunch sun-
in 385 cy- to change from
sun hr to 70 F, l i ght and fl uores-
18-mi n cent l i ghts. Not
cycl es recommended
where a,/t i s
cri ti cal .
4- mi l dry fl l m,
mi ni mi ze outgas-
14-day cure to
duri ng ascent.
si ng of adhesi ve
500 F l i mi t due to
adhesi ve.
A- 4
I
TABLE A- 3. (Continued)
. ~ .- ~. . . ". ~
Absorptance and Temperature Ul travi ol et Cycl i ng
Ascent Thermal -
Materi al Substrate Emi ttance, 70 F L i mi ts, F Resi stance Resi stance Remarks
ODti cal Sol ar Refl ector 0. 124 os = 0. 100+0. 005 500
E = 0.795+0. 02
0. 73
0 3 1
0. 19
0 . 2 5
0.21
1). 17
0 . I b
c = 0.700
* =0.510
10. 256
L = 0.828
m s = 0 . 16+0.03 650
L = 0. 95+0. 03
14- day cure to
mi ni mi ze out-
gassi ng duri ng
ascent.
Surface i s soft and
rubbery. Materi al
i s el ectrostati c.
24- hr cure at room
temperature re-
qui red.
L 10.830
: 3. 210
.- 0. n7o
- 0 180
', = 0.13+0 01 600
,. = 0.85fU 04
?a, = 0. 04 No el f ect Cured at 400 F.
af ter 2000
sun hr
af ter 2000
sun hr
= 0 . I 4 700 Am, = 0.03 No effect
L = 0 . 8 6
as = 0. 05*0.02
CIS = 0.14*0.02
I s = 0.20*0.02
(gol d)
(si l ver)
(al umi num)
L = 0. 03 (500 angstrom
di el ectri c overl ay)
i =66 (60,000 angstrom
dtel ectri c overl ay)
a = 0. 13 to 0. 16
= 0. 2b to 0. 89
t o
a = 0. 07-0. 09
c%cpondcnt on
aa = 0. 44
thicknesa
c =0.78
A- 5
TABLE A-4. THERMAL-CONTROL MATERIALS FOR t’LAT REFLECTORS(’#33* 65)
Ascent Thermal -
Absorptance and Temperature Ul travi ol et Cycl i ng
Materi al Substrate CI S / € Emi ttance, 70 F L i mi ts, F Resi stance Resi stance Remarks
Ful l er Al umi num
Si l i cone Pai nt
(172-A-1)
*
I Ful l er Al umi num
Si l i cone Pai nt
(171-A-152)
Ful l er Al umi num
Si l i cone Pai nt
(not identified)
Nonl eafi ng Al umi num
Acryl i c Pai nt
0. 89* 0. 10 as =0.25*0.07
E =0.28*0.07
0.92*0.08 as = 0.22*0.04
E =0.24+0.04
1. 2 as = 0.230
€ = 0.200
47.s i ncreases
by 0.09*0.04
af ter 600 sun
hr, E i s
unaffected
4rrs i ncreases
by 0.09*0.04
after 600 sun
hr, E is
unaffected
0. 85*0. 08 as = 0.41*0.03 650 where bub-
t =0.48*0.05 bl i ng can be
tol erated, other-
wi se 240 F
maxi mum
Baked at 465 F.
No change ob-
served at 885 F.
No change to
880 F.
Requi res 14-day
cure to mi ni -
mi ze bl i steri ng.
I
TABLE A-5. MISCELLANEOUS THERMAL-CONTROL
Materi al
LMSC Si l i cone
Tape ( 1 A48)
Roki de A, al umi -
num oxl de, [l ame
sprayed by Norton
Abrasi ve Co ,
San J ose, Cal i f ,
Absorptance and Temperature Ul travi ol et Cycl i ng
A scent Thermal -
Substrate a,/€ Emi ttance, 70 F L i mi ts, F Resi stance Resi stance Remarks
. .. - ~~
Any ri gi d 0. I 8 as = 0. 16 700 Aa, =0.04 No effect
substrate t =0. 66 af ter 2000
sun hr
Any 0. 36+0. 05 a, = 0.27t0. 04
metal l i c L = 0.75*0.03
substrate
Stai nl ess Steel Not 0. 88 'Is = 0.75
c =0.85 AIS1 410,
sandbl asted
applicable
Al uml num (2024), AI al l oy 2. 0
sandbl asted
'Is = 0.42
(2024) t = 0. 21
LMSC Whi te
Si l i cone Ai r
Dry Pai nt
No i nf or-
mati on
No i nf or-
matl on
Any ri gi d 0. 16 a, =0. 14 700 Aa, * 0.03 No effect
substrate E.= 0.86 af ter 2000
sun hr
Thi s materi al wan
used on Expl orers
Ti ros 2. Total area
I , 3, and 7 and
covered by thi s
materi al smal l :
actual perf ormance
not be eval uated.
of materi al can-
mi tred 1 yr, Ex-
Ti ros 2 trans-
pl orer 7 trans-
mi tted about 2 yr.
Thl s materl al wl th
Rokl de A strLpes
was prl mary
thermal - control
surf ace 01 Expl or-
er s I , J . and 4.
Materl al used In
Expl orer 7 as
cel l s and as stl f -
support f or sol ar
f ener ri ng between
gl ass rel nf orced
pol yester conl cal
secti ons of space-
craf t structure.
Thermal desi gn
was 0 to 60 C.
ments i n space-
Whi l e i n orbi t i n-
craf t were never
hi gher than 41 C.
l ower than 16 C or
Transmi tted f rom
8/ 24/ 61.
10/13/59 to
a
A- 7
TABLE A-5. (Continued)
Ascent
~ . .~" ~ _ .
T hermal
Absorptance and Temperature Ul travi ol et Cycl i ng
____
Materi al Substrate as/€ Emi ttance, 70 F L i mi ts, F Resi stance Resi stance Remarks
Bl al k I l r ~ o - Any metal 1 . 11+0.05 O s =0.93*0.04 No
bund I L I ~ XQCZ I surf ace
Mi dl and
I ndustri al
Fi ni shes Co. ,
Waukegan, I l l .
No ef f ect No i nf or-
€ =0.84*0. 03 i nf ormati on af ter 500 mati on
sun hf
Reynol ds Wrap Not appl i - Dul l si de as =0.20 Structural No ef f ect No ef f ect
Foi l , smooth cabl e 5.0: E =0.04
shi ny as = 0 . I 9
l i mi ts onl y
si de
6 . 3
E =0. 03
L ockspray Anodi zed 7.3 to 4.8 =0.22 to
Gold Mg or 0. 24
AI al l oys € =6. 03 to
coated 0. 05
wi th cl ear
or whi te,
gl ossy or
matte epoxy
No effect No i nf or- No ef f ect Materi al used as
to 400 F mati on coati ng on vi sor
of f ace pl ate on
hel met duri ng
Astronaut Whi te's
acti vi ty in the
extra- vehi cul ar
used as coati ng on
Gemi ni 4 mi ssi on;
i nteri or of Gemi ni
5 adapter secti on
wl th substrate of
whi te epoxy on
al l oy HK31A-H24.
Dow 17 treated Mg
A- 8
Polished aluminum al loy
I
2 10 20
Wavelength, microns
Fl at absorber
2
I
10 20
Wavelength, microns
!?
0 Ideal
e-
5 : r
2 ‘
-
‘ I
t e
\ J
a
Solar ref lector
”“~o-----
c
v ”
Q)
Cnd
Or 2 10 20
Wavelength, microns
t
0
a,
a
Cn
C
Fl at reflector
1A; ; num paint
“”-=“”-- “”- “ 0”
Ideal
2 IO 20
Wavelength, microns
FIGURE A-2. PROTON ISOFLUX CONTOURS (E >4 MeV)
Contours are labeled i n uni ts of protons/
cm2 -sec, RE =3440 nm. (lo,
I L
0.4 0.8 1.2 1.8 2. 0 2.4 2.8 3.2 3.6 4.0
.EARTH RADII
FIGURE A-3. PROTON ISOFLUX CONTOURS (E >15 MeV)
Contours are labeled in units of protons/
cm2-sec, RE =3440 nm. (I1)
A-10
0 0 . 2 0 4 0 G 0 8 1. 0 1 . 2 1.1 1 . G 1 . 8 7.0 2 . 2 2 . 4 2 G 2 8 3 . 0 3 2 3 . 4
I.. I I A . I I .I I I . I I I- 1 -
EARTH RADI I
FIGURE A- 4. PROTON ISOFLUX CONTOURS (E >34 MeV)
Contours are labeled in units of protons/
cm2- sec, radial distance is in earth radii,
RE =3440 nm. (Io*
" .. -
0.4 0. 8 1. 2 1.6 2. 0 2. 4 2. 8 3. 2 2
EARTH RADII
FIGURE A-5. PROTON ISOFLUX CONTOURS (E >50 MeV)
Contours are labeled in units of protons/
cm2-sec, RE =3440 nm. (I1)
G
A-11
2. 0
1.0
El
3
x
E
&
s
1. a
2. c
FIGURE A-6. PROTON ISOFLUX CONTOURS (E >0.4 MeV)
Contours are labeled in units of protons/
cm2 -sec. (10)
R
L =2.8
2.8
lo2 I I I I 1 I l l
1 2 3 4 5 6 8 1 0 20 30 40 50
I I l l
PROTON ENERGY (MeV)
FIGURE A-I . INNER ZONE PROTON SPECTRA(^')
\
\
PROTON ENERGY (MeV)
FIGURE A-8. OUTER ZONE PROTON SPECTRA
(10)
2.0
1.0
C
c
p:
EC
n
$
w
EARTH RADII
FIGURE A-9. TRAPPED ELECTRON ISOFLUX CONTOURS (E >0.5 MeV) AS OF AUGUST 1964
Contours are labeled i n units of electrons/cm2-sec.
FIGURE A-10. TRAPPED ELECTRON
SPECTRA(~O)
"' ,, ,1111 J ",, ,I ,., ,,,,, .I,./
,I 111, 1)). mni ,
FIGURE A-11. ELECTRON FLUX PER
DAY ENCOUNTERED
IN CIRCULAR ORBITS
FOR DECEMBER 196d' O)
ALTITUDE (nml
FIGURE A-12. PROTON FLUX PERDAY
ENCOUNTERED IN CIR-
CULAR OFBITS(~O)
APPENDI X B
TABLES AND FIGURES FOR ORGANIC
THERMAL-CONTROL COATINGS
TABLE B-1. EFFECT OF WAVELENGTH OF ULTRAVIOLET ON SPECTRAL
ABSORPTANCE OF s-13 COATING(^^)
- .
. "~~
Peak Energy Absorbed
I rradi ati on by Sampl e, lo6 @A, 10-8
Wavel ength, r n p j oul es/m' A a, ( a) j oul es/m2
-~ ". ..
255 (4.86 eV)
0 . 035 0. 48
273 (4.54 eV) 14.6 0.038 0.26
293 (4. 23 eV) 21.7 0.026 0. 12
350 (3. 54 eV) 60. 0 0.015 0. 03
~.
7.3
. "
- - ~- . . . ". ~-
. ._ _. -
( a) l nl l ~al a, 11. 200
TABLE 8-2. DECREASE I N REFLECTANCE IN S-13 (TYPE B)(3)
- .
~ ~~ - ~.
. ~- - - "
~- .~- I "_
c
Measured Af ter
A R =R i - Rf("C) at Selected Wavelengths
Exposure to: 425 mu 590 IW 950 mu 1,200 ~TW 1,550 mu 2,100 mu 2,500 mu
"~ .~ ~ ~ . _ _ _ _
~ =. __ -
UV only 1 1 3 6 10 22 14
Electrons only 0 2 6 11 20 37 26
Arithmetic 1 3 9 17 30 59 40
Sum of above
Consecutive 0 2 4 7 15 30 19
exposure io
UV, then to
electrons
Simultaneous 0 2 I 12 24 43 30
UV-electron
exposure
." . . -
UV exposure =18 ESH.
Electron exposure =lOI4 e/cm2.
~ ~ - ~ ~~
~ . ~~ ~ ". ~ -
~ ~ ~ __ .. ".
. "_
"
B- 1
TABLE B-3. INITIAL ABSORPTANCE/EMITTANCE OF
FLIGHT COUPONS(26)
Coati ng
S-13-G over B-1056 0. 191 0.860 0.222 0.200 0.022
(L. 0. I V)
S-13-G over B-1056 0. 191 0.860 0.222 0. 187 0.035
(L. 0. V)
S-13-G
B-1060
0. 184 0.879 0.209 0.203 0.006
0. 178 0.855 0.208 0. 193 0. 015
Hughes I norgani c (H-2)
0. 178 0.876 0.203 0.216 0.013
Hughes Organi c (H-10) 0 . 147 0.860 0. 171 0 . 162 0.009
Si l i cone-over-Al umi num 0. I 97 0. 800 0.246 0.239 0.007
2 -93 (McDonnel l ) 0. 184 0.880 0.209 0. 183 0. 026
-~
- -.
TABLE 8-4. DECREASE IN REFLECTANCE IN Ti 02 - METHYL PHENYL SILICONE(3)
Measured After
AR =Ri - Rf (70) at Selected Wavelengths
Exposure to: 425 mu 500 mu 590 mu 950 mlJ 1,200 mu 1,550 mu 2,100 n- &~ 2,500 mu
UV only 36 17 8 4 3 2 2 2
Electrons only 9 10 12 18 19 17 12 6
Arithmetic 45 27 20 22 22 19 14 8
sum of above
Consecutrve 36 19 9 5 4 3 2 1
exposure to
Uv, then to
electrons
Simultaneous 40 22 15 16 16 14 13 6
UV-electron
exposure
W exposure =18 ESH.
Electron exposure =5 x lOI4 e/cm2.
.. ,
TABLE B-5. RADIATIVE PROPERTIES OF BUTVAR ON
ALUMINUM(36)
Thi ckness, Sol ar
mils Absorptance Emi ttance
0.75 0.18 0.45
3 . 2 0. 22 0. a5
6. 5 0.22 0 . aa
TABLE B -6. EFFECT OF SAMPLE TEMPERATURE DURING NUCLEAR IRRADIATION
ON THE OPTICAL PROPERTIES OF THERMAL-CONTROL COATINGS(31)
Materi al
. " - - . " ".
Skyspar epoxy-based coati ng
"_ .
~ -. .
. .
Temperature
Duri ng
I rradi ati on,
F f 10
-100
0
t l O O
t200
U S
I ni ti al Fi nal Dose
0. 22 0. 22 2. 2 x l o6 rads ( C )
0.22 0.22 0.6 x 1013n/cm2, E<0.48 eV
0.22 0. 23 1 x 1014n/cm2, E>2.9 MeV
0. 22 0.28
i n vacuum
ZrSi 04--K~O/Si 02 70 0. 11 0. 13 2. 2 x l o6 rads (C)
-320 0. 11 0. 22 2.26 x 1014~/ ~m2, E<O. 48 eV
4. 72 x 1014n/cm2, E>2.9
MeV i n vacuum
Na20. AI 203- 4,502 70 0. 17 0.24
- NazO/Si Oz -320 0. 17 0. 34
"
.. , ~- , . ~ .
~- ~
B- 3
FIGURE B-1. SPECTRAL REFLECTANCE OF ~1056 COATING(^^)
Wavelength, mlcrons
FIGURE B- 2. EFFECT OF UV I N VACUUM ON S-13 C0ATI NG(l7)
B -4
o.20r
. ”
I
1 Legend 1
0 Laboratory data
h Lunar Orbiter I
Peaosus I
i”.$ ”
IO’
1
I I I l l
IO’ IO4
Equivalent Solar Hours
FIGURE B-3. CHANGE IN SOLAR ABSORPTANCE OF B1056 COATING;
LABORATORY DATA AND FLIGHT DATA(^^)
0.25
m
0.20
0. 15
0. I 0
0.05
0
I
0 2.8 x 10l6 2keV protons/cm2
/
I
FI GURE B -4.
IO 100 1000
Time in Sunlight, ESH
ZINC OXIDE IN SILICONE (S-13)
10,000
B-5
FI GURE B-6. ATS-1 FLI GHT DATA FOR S-13 COATING(20)
Eqvi~llenl Solar Hours. ESH
FI GURE B-7. REFLECTANCE CHANGE OF B1056 AS A FUNCTION OF
uv EXPOSURE AT TWO WAVELENGTH^^^)
B -6
200 250 300 3 50 4 00
lrrodlation Wavelength, mp
FIGURE B-8. EFFECT OF IRRADIATION WAVELENGTH ON SPECTRAL
SENSITIVITY OF s-13 COATING(^^)
0.12
x
4
c g
2 0.08
6 0.10
a
e
-
0.06
v)
0
c
-
6 0 . 0 4
e
=0.02
'0 400 800 1200 1600 2000 2400
Wavel enegt h. rnp
FIGURE B-9. EFFECT OF WAVELENGTH ON SPECTRAL ABSORPTANCE
OF s-13 COATING(^^)
B- 7
35 - I I I I I I I I
I I
f
" Continuous current 7.3 X lo9 p/cm2/sec
-" Accelerated current 5.5 X IO" p/cm2/sec
5 30-
-
2
a 25-
Total proton flux 2xIOl 5 p/cm2
Totol proton flux 2~l O' ~p/ crn~
to vacuum for 74 hours
a3
-
W
0
" Accelerated current sample after exposure
-
VI
-
-
m e-""
._ c 5
0' 0- -
-
a,
0,
c
V
-8.2 0:4 016 018 1.b 1.; 1. ; 1. ; 1. ; 210 212 2.4
Wavelength, microns
FIGURE B-10. RATE AND VACUUM EFFECT OF PROTON RADIATION
ONLY - Z~O/ SI L I CONE(~~)
70, I I I I I I I I I I I
c
W
c
a,
a
2 60
6 50
-
-
5 40-
2 30-
e
0
c
0
2
-
c
!i 2 0 -
a
m
c
a,
c
CT
._
10
-
V
2 0 -
n2 I
-101 I I I I I I I I I I
0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2. 2 24
Wavelength, microns
FI GURE B-11. EFFECT OF INCREASING TOTAL PROTON FLUX FROM
z x 1015 P / CM~ TO 1 x 1ol 6 P / CM~ - Z~O/SILICONEW)
B -8
I
35 I , 1 I - I
I I I I I I 1
E t ---
8 30 - 750 sun hours near and vacuum UV
a i
W
25
SI
a 15
n
I
-5
I I I I I I I I I I
0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4
Wavelength,microns
FI GURE B-12. EFFECT OF UV RADIATION ONLY - ZI I O/SI LI CONE(~~)
I I I 1 I I 1 I I I
Combrned environment Z3x IO9 p/cm2/sec
Total proton flux ~ x I O ' ~ p/cm2
750 sun hours near ond vacuum UV
Sum of indivlduol envlronments
~
-
-
-
-
//""
-
0 0 /I' - -
-
-5 I I I I I I I I I I I I
0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4
Wavelength, microns
FIGURE E-13. COMBINED EFFECTS VERSUS SUM OF INDIVIDUAL
EFFECTS. CONTINUOUS LOW'CURRENT -
Z~O/SI I J CONE(~~)
E-9
c
35
c
!?
x =
25
0
c
!?
n
g 20
a
- 15
e
c
0
cn
x IO
.-
c
a,
IT
c
5
E o
0
- 1
I o n m e n t 5.6 x 1011 p/cr#/sec
- Total proton flux 2 x 1015p/cm2 -
- Sum of individual environments -
I
75C sun hours near and vacuum UV.
""
-
-
-
- -
///-
-// 7 -
-
t-
-5 r I
0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4
Wavelength, microns
FI GURE B-14. COMBI NED EFFECTS VERSUS SUM OF INDIVIDUAL
EFFECTS. ACCELERATED CURRENT -
Z ~O / SILICONE(^^)
35
c
c
a,
30
a
8 25
c
0
c
E- 20
Li
s
a
- 15
e
w
a IO
c
0
.-
c
a,
c
IT
0
5
G o
I I I
cbntinudus l o; curr'ent 7.3 x 10' p/Az/sec
I
- Total proton flux 2 x IOl5 p/cm2 -
"" Accelerated current 5.5 x IO" p/cm2/sec
-
Total proton flux 2 x IOl5 p/cm2
-
- -
- -
- -
-
-
A"-""= ""
- -
-5 I I I I I I I I I
I I I
0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4
Wavelength, microns
FIGURE B-15. COMBINED EFFECTS WITH CONTINUOUS CURRENT
VERSUS COMBINED EFFECTS WITH ACCELERATED
CURRENT - Z~O/SI L I CONE(~~)
B-10
30 35F
c
Q)
a
V c 0 25t
I I I I I I I
Immediately after accelerated proton
radiation. 5.5~ IO" p/cm2/sec.
Total proton flux 2 X IOl5 p/cm2
"- After 750 sun hours near and vacuumUV
6 25
-
V
c
0
5 20 -
51 f\
2 15-
e
t 10-
c 5 -
I \
a,
a
v)
Q)
0
1
d
E 0 - a
f
0
-5
I I I I I I I
0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4
Wavelength, microns
I I I I I I I
0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4
Wavelength, microns
FIGURE B-16. EFFECT OF COMBINED ENVIRONMENT IMMEDIATELY
AFTERACCEL ERATEDPROTONEXPOSUREANDAT
END OF TEST - Z~O/SI L I CONE(~~)
I O .
"_ ~~. ~
09
~ -~
0.2 0.4 0.6 0.8 1.0 1.2 1.4 I .6 1.8 2.0 2.2 2.4 2.6
Wavelength, microns
FIGURE B-17. SPECTRAL REFLECTANCE OF S-UG COATING(^^)
B-11
FIGURE B-18. REFLECTANCE CHANGES IN AN EARLY FORMULATION OF S-13G(25)
Lunar Orblier I
I 100 10
Eauivalent Solar Hours
FIGURE B-19. CHANGE I N SOLAR ABSORPTANCE OF S-13G COATING: LABORATORY
DATA AND FLIGHT DATAW)
B-12
Wavel ength. microns
,- ..I:
FIGURE B-20. INITIAL REFLECTANCE S-13G USED ON
LUNAR ORBITER I V(26)
FIGURE B-21. INITIAL REFLECTANCE S-13G OVER 8-1056 USED
ON LUNAR ORBITERS IV AND V(26)
B-13
.36
-
. 2 0 L L L - . I 60 ~L . -~.I- -L_--I _ _ J
200 400 600 000 1000 1200 1400
EOUIVALENT SOLAR HOURS
L I
0 4 0 0 000 1200 1600
1 I " "~ J
FLIGHT HOURS
a h
42 -
.40
.36
-
/
/'
0 '
-
' 1 6 t ; ' 200 4bO ' 6& 060' IdOO' 1200' 1 4 % 1606I 600
I
EQUIVALENT SOLAR HOURS
0 400 000 1200 1600 2000 2400
- 1 I I 1. J
FLIGHT HOURS
FIGURE B-22. RESULTS OF THE THERMAL CON- FIGURE B-23. RESULTS OF THE THERMAL CONTROL
TROL COATING FLIGHT EXPERI- COATING FLIGHT EXPERIMENT ON
MENT ON LUNAR ORBITER 1v(W LUNAR ORBITER dl4)
Equwalent Full- Sun Exposure, hours
FIGURE B-24. DEGRADATION OF COUPONS ON LUNAR ORBITER IV WITH
COMPARISONS TO LUNAR ORBITER v(26)
B- 14
I
'I4[ .I2
0 18
9
r
"
0 06
0 4
I
I -
t
I
'herrnol
i - 1 3 - G
nent mount deck
. .. .
* 1200 1600 2000 2400 2800 3200
FIGURE 6-25. DEGRADATION OF COATINGS ON LUNAR
ORBITERS I, 11, AND v(26)
LUNAR ORBITER
,021 .
I I I , I ,
EQUIVALENT SOLAR HOURS
0 200 400 600 800 IO00 1 2 0 0 I400 I
50
- "_._.
y)
- - n X 1015
0 . 3 0. 5 0. 7 0. V 1. 1 1 . 3 1. 5 1. 7 1.9 2. 1 2. 3 2. 5
WAVELLNGTH, A(mi crom)
FIGURE B-26. COMPARISON OF THE CHANGE FIGURE B-27. IN SITU REFLECTANCE LOSS I N TREATED
I N SOLAR ABSORPTANCE OF
ZI NC OXIDE-METHYL SILICONE FOL-
S-13G COATINGS I N TWO LOWING EXPOSURE TO 50 KEV
FLIGHT EXPERIMENTS(14) ELECTRONS(25)
B-15
1
W
z
u
<
WAVELENGTH, MI C R ONS
FIGURE B-28. DEPENDENCE OF REFLECTANCE DEGRADATION IN S-13 UPON ELECTRON ENERGY(27)
FIGURE B-29. DEPENDENCE OF REFLECTANCE DEGRADATION IN S-13G UPON ELECTRON ENERGY(27)
1
w
I
m
c
FIGURE B-30. DEPENDENCE OF REFLECTANCE DEGRADATION I N TREATED ZINC OXIDE-METHYL SILICONE
(GODDARD SERIES 101-7 -1) UPON ELECTRON ENERGY(27)
I
""
c 3
= - ~
c
aI
I".~, ~ 1" -I!-.
I I 1 I I
V 2 x loi5 p/cm2 at zs x 109 p/cm2/sec
25
-
A
-
..
g 20
- -
0
t
0
*
15
- -
n
a - 10-
2
w 5 -
c
V
9.
m
.- I=
0 - 1
w
0
c
c
-
0 -5
- 1- I I I " I I I I I I
0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4
Wavelength, microns
FIGURE B-31. EFFECT OF PROTON RADIATION ONLY (S-13G)(22)
L
E 30
~ 25
w
Q
L
w-
2 20
0
c
h
L -
0
a
* 15
c
g o
0
C
f
-5
I .-T -~1 I I I 1 I I I
750 sun hours near and vacuum UV
-
1 I I I I I I I I I I I
0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4
Wavelength, microns
FIGURE B-32. EFFECT OF uv RADIATION ONLY (s- 13~)(22)
B-19
35
$ 30
$ 25
t
c
a,
a
0
a
t
$ 20
n
a
-
15
t
V
a,
0
Q IO
c
.-
8 5
c
0
c
0 0
-7
I
- Combined environment 2 x
p/cm2
at 7.3 X lo9 p/cm2/sec
750 sun hours near and vacuum UV
-
-
"- Sum of individual environment
I
I
I
I
I
I
I
I
-
-
-
I I I I I I I I I I I
? 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4
Wavelength, microns
FIGURE B-33. COMBINED EFFECT VERSUS SUM OF INDIVIDUAL
EFFECTS (S-13G)(22)
Wovelength. microns
FI GURE B-34. B-1060 (10.1 MI LS), DEGRADATION FROM
ULTRAVIOLET, MEASURED IN SITU(^^)
B-20
I .c
0.8
E O6
-
0
aJ
c
-
d
0.4
02
0-
0.2
1
(Aa=0.007)
06 10
. ~ ~~
Af t er IOl4 50 keV e/crn2
at dose rate of 10'krn2/sec
a =0.180
J
-
,
Wavelength, rnlcrons
FIGURE B-35. B-1060 ( 9. 4 MILS), DEGRADATION FROM 50-keV
ELECTRONS, IN SITU MEASUREMENTS(~~)
30
.~~
c
2
17 7
190 sun hours UV and vacuum UV -
25-
a,
c
Q)
u
20-
c
-
2
a
0
n
IJI 15
- -
-
10-
u
a,
(1
-
5-
-
.-
C
a, 0,
0 " -
t
0
c
-5-i
I I I I I I I I I I
0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4
Wavelength, microns
FIGURE B-36. EFFECT OF UV RADIATION ONLY (Ti02 SI LI CONE)(22)
B-21
td
I
N
N
J
"0 . 2 . 4 . 6 . 8 1 . 0 1.2 1 . 4 1 . 6 1 . 8 2 . 0 2 . 2 2 . 4 2 . 6 2 . 8 3 . 0
HA VEL ENGTH, MI CRONS
FIGURE B-37. DEPENDENCE OF REFLECTANCE DEGRADATION IN RUTILE Ti 02"ETHY L SILICONE UPON ELECTRON ENERGY(27)
FIGURE B-38. DEPENDENCE OF REFLECTANCE DEGRADATION IN ANATASE Ti02-METHYL SILICONE UPON ELECTRON ENERGY(27)
3 x 10' ~ p/crn2 at 5.5 x IO" p/rn2/sec
I I I I I I I I I 1
? 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2
Wavelength, microns
FIGURE B-39. EFFECT OF PROTON RADIATION ONLY (Ti 02 SILICONE)(22)
T s 0 2 - METHYL PHENYL SI LI CCI NE
SAMPLE TYPE P Y QOMAQK Y i
18 E S H ........_
53ESH _ _ _
250 ESC __
135 ESH .-._._
dPO ESH -
I130 ESH - -
0. 3 9.5 0.' 0.9 !.I 1.1 1. 5 1.7 1.9 ?.I 2 . 3 2. 45
-
4
:,AVELENCTH v s ~r o n , ) .
FIGURE B-40. REFLECTANCE CHANGES FOR SAMPLE TYPE PYROMARK(25)
B-24
2.6
2.4
2.2
2 .o
I .e
1.6
1.4
1.2
I .c
0.E
0. E
0. 4
0.2
C
0
I I I I 1 I I I I 1 I
l o ' I
0
-
-
l -
-
TiO, /methyl silicone
l -
I -
0 0
0
P -
)-
I I 1 I t I I 1 1 I I I ,
IO 1 0 0 1000 IO/
Equivalent Sun Hours
FIGURE B-41. ATS-1 FLIGHT DATA FOR Ti 02/METHY L
SILICONE COATI NG(~O)
B-25
0.4 I
I I I . I " I
0.2 0.6 I .o I .4 !.8 2.2
Wovelength, microns
FIGURE 8-42. INITIAL REFLECTANCE H-10 HUGHES ORGANIC COATING
USED ON LUNAR ORBITER V(26)
I "
0 .2 .4 .6 .8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0
WAVELENGTH, MICRONS
FIGURE B-43. REFLECTANCE CHANGES I N LEAFING ALUMINUM-SILICONE DUE TO
20-keV ELECTRON EXPOSURE(27)
K~=initial reflectance
~f =reflectance after irradiation
E
IO
-
AFTER 1615 AND
I
1016 E K M ~
L y o
"- I I
.-
E
-! E/C,M 5 , x 1013 I
-10
0 .2 .4 .6 .8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0
WAVELENGTH, MICRONS
FIGURE B-44. REFLECTANCE CHANGES I N LEAFING ALUMINUM-SILICONE DUE
T O 80 -keV ELECTRON EXPOSURE(27)
=initial reflectance
Rf =reflectance after irradiation
B-26
Aluminum foil substrate-
a =0.103
\
' "t
\/ -\- k
_"" ~"""
- Silicone over aluminum f ai l
a.0.197
I
I .4
Wovelegth. microns
""""
""""
e
\
2.2 2.6
FIGURE B-45. INITIAL REFLECTANCE RTV-602 SILICONE (3.8 MILS)
OVER ALUMINUM FOIL USED ON LUNAR ORBITER V(26)
~~
"""
/
No exposure
and after 336 ESH
(Aa = O )
a =0.327
1.8 2.2 26
Wavelength , rnlcrons
FIGURE B-46. RTV-602 SILICONE (2.6 MILS) OVER CLAD ALUMINUM;
DEGRADATION FROM ULTRAVIOLET, MEASURED
IN SITU(^^)
B-27
0 800 900
FIGURE 847. EFFECT OF ASCENT HEATING ON SOLAR ABSORPTANCE OF FULLER (S17-W-1) GLOSS WHITE PAINT
ON DOW 17 OR HM21A MAGNESIUM(9)
I
0.5
- --
""_" +"""
Ti02piqmented epoxy base point
(Whi t e Skyspar Enamel )
(Sherwin-Willioms M49WC17
White acrylic f l at paint I
0 500 1000 1500 2000 2500
Exposure, sun hours
FIGURE 8-48. EFFECT OF NEAR-ULTRAVIOLET RADIATION I N VACUUM ON
THE SOLAR ABSORPTANCE OF SELECTED SOLAR
REFLECTOR COATINGS(31)
-1
--------- After IO" p/cm2(3 keV)
- . -. - After phm'
-a_-.. - After IO6 p/cm2
Prelrrodlotlon
1.0 1.2 1.4 1.6 1.8 2 0 22 24
Wavelength, microns
FIGURE B49. SPECTRAL REFLECTANCE OF
PV-100 (9-2) I N VACUO(34)
B-29
I .c
0.8
~ 0.6
0
c
0
c
:
0.4
In
0.2
a
1.0
0.9
0.8
0.7
0)
0.6
-
u
% 0.5
-
[L
0.2 _" -"""
""_
0.3
0.2
0. I
0 0.2 0.4 0.6 08 IO 1.2 I 4 I 6 1.8 2.0 22
Wavelength, microns
FIGURE B-50. SPECTRAL REFLECTANCE OF PV-100
(8 -2) I N V A C U ~~~)
- 1
"
Not e: Bl ock ar ea denot es maxi mum changes
of sol ar absor Dt ance due to bubbl i na.
.
I- /
I I I I I
1 0 0 200 300 400 500 600 700 0
Maxi mum Ascent Temper at ur e, F
0
FIGURE B-51. EFFECT OF ASCENT HEATING OR SOLAR ABSORPTANCE OF SHERWIN WILLIAMS
WHITE KEMACRYL PAIN?Ig)
B-30
Whi t e ocryl i c flat pai nt
""_
Best fl t to dot a
O L I I
0 0 5
I I
10 15 2 0 2 5
Gommo Dose, IO r ods(C)/g
I O
09
0.8
07
a
0.6
-
0
W
-
-
w 0 5
U
0.4
0 3
0 2
"
0 02 04 06 0.8 I O 12 1.4 16 1.8 2.0 2.2 2.4
Wovel ength. rntcrons
FIGURE B-53. SPECTRAL REFLECTANCE OF MgO/
ACRYLIC (9 -4) I N VACUO(34)
FIGURE B- 54. EFFECT OF TWO UV WAVE-
LENGTHS ON THE SPECTRAL
ABSORPTANCE OF SKYSPAR
COATL NG(~~)
B- 3 1
APPENDIX C
TABLES AND FIGURES FOR INORGANIC
THERMAL CONTROL COATINGS
TABLE C-1. ENVIRONMENTAL CONDITIONS(40)
Exposure Test Number:
Pi gment/Bi ndeda)
Specimen Position:(b)
. __-___
Radiation Environment
Flux Density
Fluence
(x1010 particles/cm2. s)
(x1015 particles/cm2)
Approximate Neutralization,
Proton Specie
Irradiation Level
Total Sun Irradiance/Hour
UN Sun Irradiance/Hour
Energy
percent
I rradiance
Total Sun Hour Equivalents
Total Ultraviolet Sun Hour
Equivalent
Vacuum During Measurement
Vacuum During Exposure
Specimen Temperature Based
on Substrate Measurement
and Substrate Control
1 2 3 4
ZnO/KaSiOg ZnO/K2SiO3 A1203/K2Si03 A1203/K+i03
A B C D A B C D A B C D A B C D
- UV H+ H+ - UV H+ H+ - UV H+ H+ - UV H+ H+
- ~ _ _ _ -~
e- e- e- e- e- e- e- e-
uv uv uv uv
2.4 1.2 2.4 1.2 2.3 1.1 4.0 0.9
4.0 2.0 4.0 2.0 6.1 2.9 11.0 2 2
55 100 55 100 30 100 30 100
H+
6
4
450
300
1 x 10-8 Torr
8 x Torr
294 K f 5 except for Test Number 1, position B and D, where
higher temperatures are suspected based on speci men
appearance after completion of the test.
(a) ZnO New J ersey Zinc Co., SP-500, 99.970 pure; 0.25-0.35 p particle. Pigment/Binder Ratio =5.2.
Pigment ball milled with K2Si03 for 4 hrs, sprayed 6 coats, overnight dry at 20 C. oven cured
1 hr at 150 C. 6-mil coating.
Pigment ball milled with K2Si03 for 2 hrs, oven cured 1 hr at 150 C, 5-mil coating.
A1203(cl) Linde Division, Union Carbide Co., 99.9870 pure, 1.0 !J particle. Pigment/Binder Ratio =2.0.
K2Si03 Sylvania Electronic Products (3570 solids) PS-7.
Position B Electromagnetic radiation exposure.
Position C Particulate radiation exposure (protons alone or protons plus electrons).
Position D Combined electromagnetic and particulate radiation exposure (with protons alone or protons
(b) Position A No radiation exposure.
plus electrons).
c- 1
TABLE C-2. SUMMARY OF APOLLO 9 THERMAL PROPERTY MEASUREMENTS(32)
Absorptance
Change, Emittance
Material Sample Location Preflight Postflight percent Preflight Postflight
Zinc oxide- Service module
potassium Upper left
0.20 0.28 40 0.93 0.93
silicate Upper right 0.20 0.25 25 0.93 0.93
Lower right 0.20 0.27 37 0.93 0.93
Titanium Service module
dioxide-silicone Upper left 0.25 0.37 48 0.86 0.88
Upper right 0.24 0.34 42 0.86 0.88
Lower right 0.24 0.40 67 0.86 0.87
Chromic acid - Lunar-module 0.70 0.73 4 0.73 0.70
anodized hatch area
aluminum
Fused silica - Lunar -module (a) (a) (a) ( a) (a)
filtered hatch area
(a) Approximately 2-percent decrease in transmittance.
c-2
TABLE C-3. RESULTS OF 2-93 TESTS; INITIAL a, = 0. 147(21)
Energy Absorbed
Wavelength by Sample
Region, mp j oul es/m Aa.5 (joules/rn2)-1
i
@,(a),
~~~~ ~ ~~ ~
I 3. 6 x l o8
0.021 0. 58 x 10-10
I1 1. 9 x l o8
0.003 0. 16 x
III 6. 0 x l o8
0. 003 0. 05 x 10-l'
(250-312)
(302-324)
(330-380)
increase in solar absorptance
(a) = energy dose absorbed
= Aas/Ht
H, =total energy absorbed.
TABLE C-4. OPTI CAL PROPERTI ES OF BRlGHT ANODIZED
ALUMINUM EXPOSED TO VACUUM-
ULTRAVIOLET RADIATION (0.5 mi1)(5)
_ _ _ _ _ _ _ _ . ~~ .
- .
Polishing bath: Phosphoric Acid/Nitric Acid (95/5)
Exposure, hours(a): 0 24 96 192
Total Reflectance, p
0.84 0. 72 0.66 0.65
Solar Absorption, a, 0. 16 0. 28 0.34 0.35
Emittance , CTh 65 C 0. 83 0.83 0.83 0. 83
a/ € Ratio 0. 19 0.34 0.41 0.42
- -
(a) To obtain ESH, multiply by 6.
c-3
TABLE C-5. EFFECTS OF NUCLEAR RADIATION ON THE OPTICAL
PROPERTIES OF BRIGHT ANODIZED ALUMINUM(5)
Thermal
Thi ck- Neutron Nucl ear
ness, Flux, Rads (C),
mil (0,)i (q,)f (E)i (E)f I 014 nvt 108
~~
0. 15 0.088 0. 101 0.70 0. 70 2.35 2.93
0. 4 0 . 091 0. 123 0.75 0. 75 2.35 2.93
0.5 0. 126 0. 140 0. 77 0. 78 2.35 2.93
2.59 2.71 0. 6
" 0. 129 0.80 0.80
TABL E C-6. EFFECTS OF EL ECTRON AND UV RADIATIONS
ON ANODIZED-ALUMINUM COATINGS AT
77 K (4)
as af ter as af ter
I ni ti al a , after 5. 8 x 1015 UV and El ectron
Sampl e Type as 350 ESH e/cmZ Radi ati on
Sul furi c aci d 0. 20 0. 28 0. 20 0. 27
anodi zed al umi num
( 1 199 al umi num)
Barri er anodi zed 0. 17 0. 19 0. 16 0. 20
al umi num ( 1 199 All
Al umi num oxi del 0. 11 0. 16 0. 19 0. 24
potassi um si l i cate
c-4
TABLE C-7. EMITTANCE OF TEFLON OVER VAPOR
DEPOSITED ALUMINUM(36)
Thickness, mi l s Total Normal Emi ttance
-
0. 25
__"
0. 26
n. 50 0. 43
1.00 0 . 53
2.00 n. 67
5.00 0.83
10.00 0.89
""
-
TABLE C-8. ULTRAVIOLET EXPOSURE OF SERIES
EMITTANCE COATINGS(36)
Sampl e
Descri pti on
Dosage
uv, X-Ray, Sol ar Absorptance
ESH(a) Before After
~
PJ l 13 on al umi num
3,800
" 0. 15 0. 15
PJ 1 13 on al umi num 170 10 0. 16 0. 17
PJ 1 13 on al umi num I , 720 100 0. 16 0.18
Pol yvi nyl butyral (Butvar)
100 10 0. 19 0.20
Pol yvi nyl butyral (Butvar)
1, 000 IO0 0. 18 0. 20
5 - mi l Tefl on on al umi num 1, 150 115 0.21 0.21
c-5
TABLE C-9. CHANGES IN SOLAR ABSORPTANCE (Aa s) OF ALUMINIZED AND SILVERED TEFLON
WITH PROTON BOMBARDMENT(49)
~ ~
Solar Absorptance,a
~
~ . . ~_ _ _
Pre - After I rradiation Dose, p/cmz
Coating irrad. 3 x 1012 5 x 1013 3 x 1014 8 X lOI4 3 x 1015 1 x 1016 N(a) x 1016 Aa
!-mil
- . - - ". ~ - c ~ " , . ~ - - _I _I_
aluminized
Teflon (TA-2) 0.12 0.12 0.12 0.12 0.12 0.13 0.16 0.18 (1. 8) 0.06
i -mil
aluminized
Teflon (TA -5) 0.13 0.13 0.13 0.13 0.14 0.15 0.18 0.19 (1.7) 0.06
L O -mil
aluminized
Teflon (TA -10) 0.16 0.16 0.16 0.16 0.16 0.17 0.20 0. 21 (1.4) 0.05
2 -mil
silvered
Teflon (TS-2) 0.06 0.06 0.06 0.06 0.06 0.07 0.09 0.10 (1.7) 0.04
j -mil
silvered
Teflon (TS-5) 0.07 0.07 0.07 0.07 0.07 0.08 0.10 0.11 (1.6) 0.04
LO -mil
silvered
Teflon (TS-10) 0.09 0.09 0.09 0.09 0.09 0.10 0.12 0.12 (1.2) 0.03
.~
'a) I rradiation dose given i n N x p/cm2; N indicated i n parentheses.
C- 6
TABLE C-10. ENVIRONMENTAL STABILITY OF THE OPTICAL SOLAR REFLECTOR MATERIAL(2)
Test Condi ti ons
Sample Change in
Envi ronment of Type of Radi ati on I ntegrated Pressure, Temperature, Sol ar
I nterest Radi ati on Energy Flux torr K Absorptance
Arti fi ci al El ectron El ectron 800 keV 1016 e/cmZ 210-6 290 0
Bel t El ectron 800 keV 1015 e/crnZ - <10-6 155 0
El ectron pl us
800 keV 6 x 1014 e/cmZ 51 0-6 3 00 0
si mul taneous el ectrons t plus 436 ESH
ul travi ol et (UV) 3. 1 to 6. 2 eV UV
ul travi ol et
e t UV Ditto - <10-7 77 0
e t UV
I 3 x 1015 e/ cm 2
- <10-7 300 0
plus 150 ESH
130 kcV
Van Allen Protons 130 keV
Proton Bel t 176 keV
466 keV
987 keV
500 keV
500 keV
p i uv 500 keV
p t uv 500 kcV
2 x 1015 p/cm'
25 x 1015 p/cm2
-5 x 1015 p/cm'
- 5 x 1015 p/cm2
-5 x 1015 p/cm2
-6 x 1015 p/crn2
6 x 1015 p/cm2
6 x 1015 t150 ESH
6 x 1015 $150 ESH
"
"
290
290
284
2 84
2 E4
77
280
77
300
Sol ar Wi nd Proton and Hzt 2 keV 8 x 1015 p/cmZ <I 0-7 280 0
Proton pl us 2 keV protons 5 x 1015 p/cmz <10-7 260 0
si mul taneous UV t 3. 1 t o 6. 2 eV pl us 255 ESH
LiV uv
Proton I . 4 keV
1016 pI cm2
<I O- ' 3 05 0
Proton pl us 2 keV protons
8 f 1015 p/cm2 <10- 7 320 0
si mul taneous UV t 3. 1 to 6. 2 eV tl 100 ESH UV
photons
Sol ar Ul travi ol et uv 3. 1 to 6. 2 eV 485 ESH <10-6 290 0
uv 3. 1 t o 6. 2 eV 436 ESH <10-6 300 0
uv 3. 1 t o 6. 2 eV 175 ESH <6 x 10-8 3 00 0
uv 3 . I to 6. 2 e V 2000 ESH <10-6 294 0
uv 3. I to 0 . 2 e\' 2000 ESH <10-6 533 0
0.7
0. E
0.5
0.4
0
Q)
c
0
c
9
2
a 0.3
0. i
0. I
C
I
Legend
-.-.-
n - Y
- - - Concurrent UV and n- y I
Control
1.6 I .4 1.2 1.0 0.8 0.6 0.4 0.2
Wavelength , microns
FIGURE c-1. SPECTRAL ABSORPTANCE OF IRRADIATED LITHAFRAX/SODIUM SILICATE PAINT(35)
C -8
0 2 0.4 06 0 8 I O 12 1.4 16 I 8 2 0 2. 2 2 4 2 6
Wavel engt h ,microns
FIGURE c-2. SPECTRAL REFLECTANCE OF HUGHES INORGANIC WHITE COATING(^^)
YAVELCRGI H, MICRONS
FIGURE C-3. DEPENDENCE OF REFLECTANCE DEGRADATION I N Al203-KzSi03
UPON ELECTRON ENERGu(27)
c-9
Protons, Eleclrons and Ultraviolet
(I00 % Neut ral i zat l on)
- 0.0
- -0.2
- -0.4
I
I 0.5
x (pL)
I
I .o
FIGURE C-4. CHANGE IN SPECTRAL REFLECTANCE OF A1203
IN K2Si03, MEASURED IN SITU(40)
:I
0.2 -
01 I I I l l I I I l l I I
10 100 1000
Equi vol enl Sun Hour s
FIGURE C-5. ATS-1 FLIGHT DATA FOR A1203/K~Si 03
COATING(W
c
8
14
- -
TIO,+AI,O,/K,SIO, 8
8
I 2
- a,=0170 -
10
-
0 8
--
0 6
-
@ -
0 4
-
0 2
- -
0 I I I l l I I I l l I I I I
10 1 0 3 1 0 3 0 IO.030
Sun Hours
FIGURE C-6. ATS-1 FLI GHT DATA FOR Ti02/K2Si03 COATI NG(2o)
2 0 .-
I 8
-
16
-
14 -
I 2
-
10
-
0 8
-
06
-
04
-
02
-
Zn O+T~O2+AI ZO, / KPS~OJ
a,:0170
0 -
0
FI GURE C-7. ATS-1 FLI GHT DATA FOR (ZnO +Ti 02 +A1203)/
K2Si03 COATING(2o)
c- 11
FIGURE C-8. ATS-1 FLIGHT DATA FOR A1203/K~Si 03 COATING(2o)
I .50
140
I I I I I I I I 1 I
1 I I I I I I I
-
TIO,+ AI , 0, / K2S~0,
-
120
- a , = 0 170
A
A A A A -
I I 1 I I I I
0 20 40 60 BO 100 120 1 4 0
Days In Orblt
580
FIGURE C-9. FLI GHT DATA FOR (Ti 02 +A1203)/KZSi03 COATING(20)
c-12
FIGURE C - 10. ATS- 1 FLZGHT DATA FOR (ZnO -I- Ti 02 t A1203)/
K2Si03 COATING(20)
t)
u) 0.20
Q
ai- 0.15
0
C
0
c
g 0.10
u)
m
a
k 0.05
0
v)
t
a
.-
0 0 C
c
0
-0.05
0 2 X 10'510kev protons/cm2
0 2.8 x 2 kev protons/cm2
Mariner
t
/
I
h
OSO-II and Pegasus II show little or no
deaadation to 2500 ESH
0. I I 10 100 1000
-
L
l0,Ooo
Time in Sunlight, esh
FIGURE C-11. ZINC OXIDE IN POTASSIUM SILICATE (2-93)(l 3)
C-13
Legend
.
0.2 06 I .o 14 18 2 2 2.6
Wavelength, rnlcrons
FIGURE C-12. INITIAL REFLECTANCE 2-93 USED ON
LUNAR ORBI TERP~)
Designation Paint Type Flight SIC
0.45
0.4 0
8
,p 0.35
c
c
E
W
\
C
8
0.30
:
2
u)
L
0.25
cn
0.20
0.15
S-13-G Overcoat on 8-1056 IV
S-13-G Overcoat on 8-1056 V
Hughes Organic White V
S-13-G IV
8-1060 IV
Hughes Inorganic White IV
Silicone over aluminum foil V
2-93 V
J
500 1000 1500 2000 2500
Equivalent Full-Sun Exposure, hours
FIGURE: C-13. ABSORPTANCE EMITTANCE RATIOS OF
THERMAL COUPONS(26)
-8
x
c)
I
Ir r adi at i on Wavel ength, rnp
FIGURE C-14. SPECTRAL SENSITIVITY FACTOR VERSUS
IRRADIATION WAVELENGTH FOR ZINC
OXIDE/POTASSIUM SILICATE (2-93)
COATING(^^)
I I I I I I I I I I '
Q - ZINC OXIDE/POTASSIUM SILICATE (2-93) PAINT
0 ZINC OXI DE/ LTV 602 (5-13) WNT
Q BARRIER-LAYER ANODI ZED ALUMI NUM
O.' "
-
PROTON INTEGRATED FLUX, PROTONS/CM~
FIGURE C-15. EFFECT OF 8-keV PROTONS ON BARRIER-
LAYER ANODIZED ALUMINUM AND
SPACECRAFT PAINTS(43)
ApX
.
-0. I
r Protons and Electrons
(55 ' 3%Neut ral i zat l on)
-0.0
"0. I
0 I
1-02
FIGURE C-16. CHANGE IN SPECTRAL REFLECTANCE OF ZnO I N K2SiO3 DUE TO
PROTONS AND ELECTRONS, MEASURED IN SITU(4o)
\
\
\
Protons, Electrons and Ultraviolet
( 1 0 0 % Neutmlization)
""""
Protons and Ultraviolet
t -Oel
0
I
2
FIGURE C-17. CHANGE IN SPECTRAL REFLECTANCE OF ZnO I N K2Si03 DUE TO
PROTONS, ELECTRONS, AND ULTRAVIOLET, MEASURED IN SI TV(~O)
C-16
.25
-
W-
0
5 .20
-
I-
a
m .I5
a
a
-
E
-I
lokev PROTON 2 X lOlS p/crn2
F .IO
2 0
2
-
z .05
-
AT 7.4X109 p/crn2 - SeC
V
W
ln
75 hrs uv +EUV AT IoES
a
W
U 4.0 3.0 2 .o 1.0 .5
z
ELECTRON VOLTS
I I I I I I I
.35 .40 .50 .60 .80 1.2 2.4
X, micron
FIGURE C-18. THE INCREASE IN SPECTRAL ABSORPTANCE OF SPECIMENS IRRADIATED
WITH COMBINED AND INDIVIDUAL ENVIRONMENTS AT 233 K(45)
EUV =solar vacuum ultraviolet
UV =0. 2 to 0.4 p
U
rc
2 5
-
bi
0
z
2 20
- 10kev PROTONS 2 ~1 0 ' ~
a
a
75hr UV+EUV AT IO ES
AT 7. 4x 109pk m2-
ln
0
9 .I5
-
a
IL
-I
.IO
-
W
v)
a
Z_ .05
-
W
v)
a
E O
v 4.0
z
3 .O 2.0 ID .5
ELECTRON VOLTS
p/crn2
' sec
I I I I I I
.35 .40 .50 .60 .80 1.2 2.4
X, micron
FIGURE C-19. THE INCREASE I N SPECTRAL ABSORPTANCE OF SPECIMENS IRRADIATED
WITH COMBINED AND INDIVIDUAL ENVIRONMENTS AT 298 K(45)
EUV =solar vacuum ultraviolet
UV =0.2 to 0.4 p
C-17
I "
a
a .25
W'
-
1
0
z
- COMBINED EXPOSURE (MEASLIRED)
2 . 2 0
8
-
a
a
9 .I5
-
a
J
IO kev PROTONS 2 x IOl5 p/cm2
AT 7 . 4 ~ 1 0 ~ p/cm2 -sec
E .IO
-
75hr UV+EUV AT IO ES
n
z .05
-
UJ
W
W
In
w
a
a 0 '
0 4.0
z
3.0 2.0
ELECTRON VOLTS
1.0 .5
I I I , I I I
.35 .40 .50 60 B O 1.2 2.4
X, micron
FIGURE C-20. THE INCREASE IN SPECTRAL ABSORPTANCE OF SPECIMENS IRRADIATED
WITH COMBINED AND INDIVIDUAL ENVIRONMENTS AT 422 K(45)
EUV =solar vacuum ultraviolet
UV =0.2 to 0.4 p
W
Q .25 0 422'K
W-
A
u
z
2 . 20
a
v)
0
m
a
4 .I5
5 .IO
2 ~ 1 0 ' ~ Iokev/cm2 AT 7.4xlO9p/cm2-sec
_1
a
75 hr UV +EUV AT IO ES
W
UJ
a
z . 05
W
2
W
n o
2 4.0 3.0 2 .o 1.0 0.5
ELECTRON VOLTS
I I I I I
.35 .40 .50 60 BO 1.2 2.4
x. micron
FIGURE C -21. THE INCREASE IN SPECTRAL ABSORPTANCE OF SPECIMENS IRRADIATED BY
COMBINED ENVIRONMENTS AT TEMPERATURES OF 233, 298, AND 422 K(45)
EUV =solar vacuum ultraviolet
uv =0.2 to 0.4 !.I
C-18
FIGURE C -22.
I .o
0.8
8 0.6
c
0
0
0)
.4-
+
-
#! 0.4
0.2
9
0 2 0 6 10 14 I 8 2 2 2 6
Wavelength, mlcrons
INITIAL REFLECTANCE OF H-2 HUGHES INORGANIC COATING USED
ON LUNAR ORBITER IV(26)
0
~
0.2
0.4 0)
0
c
0
-
+
.-
0.6 W
E
0.6
4
I .o
16
Wavelength, microns
FIGURE C-23. OPTICAL PROPERTIES OF POLISHED ALUMINUM COATED WITH A 1~03( ~)
C-19
i
c
w
E
L
0
Temperature, F
FIGURE C-24. TOTAL HEMISPHERICAL EMITTANCE AND ABSORPTANCE VERSUS TEMPERATURE OF THE Al-Al2O3 SYSTEM(5)
1.0
- . -
0.8 d f
/
I
g 0.6
-
c
0
0
c
*
-
d 0.4
0.2
-
0-
0
I
Legend
-
Control
5 x l d r n m Hg. 600 F
"" Vacuum-thermal exposure -
Wavelength. microns
FIGURE C-25. EFFECT OF VACUUM-THERMAL EXPOSURE ON THE WATER-
ABSORPTION BAND OF THE Al-A1203 SYSTEM(5)
0.9 ' O I I
I
d 0 , 7 m :_ Exposure, 24 hr -
5 x 10-'rnm Hg, 600 F -
"_ Exposure, 48 hr
" Exposure, 96 hr
0.6
0.5 0.6 7
Wovelength, microns
FIGURE C-26. EFFECT OF VACUUM-THERMAL EXPOSURE IN SHORT-
WAVELENGTH REGION, 25 MINUTES ANODIZE(5)
c-2 1
, . . . , _. ..._ .
0.3 0.4 0. 5 0 6 0 7 0.8 0 9 I O I I 1 2
Wavelength,mlcrons
FIGURE C-27. EFFECT OF VACUUM-ULTRAVIOLET EXPOSURE ON BRIGHT ANODIZED
ALUMINUM (0.0005 IN. )(5)
0.30
a“ 025
a o”---o 000015 in
2 0 2 0
a,
+
e
0
015
L
O
0
cn
-
g 0.10
m
0
0
6 0.05
0
Actual 12 24 48 72 96 120 1 4 4 168 192
Space
72 144 288 432 5 76 720 864 1008 1152
Time. hours
FIGURE C-28. CHANGE IN SOLAR ABSORPTANCE VERSUS TIME FOR VACUUM-
ULTRAVIOLET EXPOSURE OF BRIGHT ANODIZED COATINGS(5)
c - 22
"
0.30 unshielded S/N 16
Q 0.20
0.10
300- 300- 650- 1200- 600-
400 650 1200 3000 3000 nm
FI GURE C-29. CHANGE I N RELATI VE REFLECTANCE OF ALZAK AND
A1203/Al AFTER 2000 ESH(47)
0.40
Al zak I
I 1
OUnshi el ded S/N 14
S/N 13, .
0'30 - +Shi el ded
AI
LT
a 0.20
-
n ++#+++ ++
0. ++
o.l O,; r; f C + +
" % ++ *
n - I I
Unshi el ded S/N 14
LT
S/N 13, .
a 0.20 n 0. ++#+++ ++ T
" % ++ *
0 500 IO00 1500 2000
ESH
FI GURE C-30. RATE OF CHANGE OF RELATI VE REFLECTANCE OF
ALZAK I N THE 300-400 nm BAND AS A FUNCTION
OF ESH(47)
0.40
0.30
- 0 Un s h i el d ed S/N 14 -
Al zak I
I I
LT
+Shi el ded S/N 13
Q 0.20
- -
0.1 0
.DOooD
0. a
jp*+++'. - ++- *
O* I I I
0 500 1000 1500 2000
ESH
FIGURE C-31. RATE OF CHANGE OF RELATI VE REFLECTANCE OF
ALZAK I N THE 300-650 IUII BAND AS A FUNCTION
OF ESH(47)
C -23
FIGURE C-32. DEPENDENCE OF REFLECTANCE DEGRADATION IN 0.15-MI L
ALZAK UPON ELECTRON E NE RGY ( ~~)
FIGURE C-33. REFLECTANCE CHANGES FOR SAMPLE TYPE ALZAK (0.29 MIL)(25)
C -24
80
al
2 60
c
0
0
ln
40
20
0 I 2 3 4 5 6 7 8 9 10
Thickness of FEP Teflon, mils
FIGURE C-34. THICKNESS OF FEP TEFLON VERSUS EMITTANCE(36)
0.5 0.055
- 1.0 0.059
2.0 0.059
5.0 0.090
AI
5 mi l s
0.5, I ,2 mils
Wavelength, microns
FIGURE C-35. SPECTRAL ABSORPTANCE OF SILVER-COATED TEFLON(36)
C-25
Aluminum 0.1E
Wavelength, microns
FIGURE C-36. REFLECTANCE OF 0.5-MIL-METALLIZED MYLAR(36)
I .c
0.E
O f
c
U
0
+
L
-
d
0.4
0.:
5
T E ef o r e exposure I
gqq?
After IOOOESH +IO8 rads
28 0.30 0.32 0.34 0.36 0
Wavelength, microns
_=
I O 14
FIGURE C-37. EFFECT OF IRRADIATION ON ULTRAVIOLET REFLECTANCE OF BUTVAR SAMPLE 8-4(36)
C- 26
o,30b4T 6 6-1 -2 100 IOESH ESH IO I Mr ad Mr od
164 1000 ESH 100Mr ad
0 IO
0.28 0.x) 0.32 0.34 0.36 0 38 040
Wavel engt h, microns
FIGURE C-38. EFFECT OF IRRADIATION ON THE ULTRAVIOLET REFLECTANCE OF
SILICONE GE 391-15-170 ON ALUMINUM(36)
0.34"- , - T
~ -7- I I I I I
- 0.05
0.33 -
0.32 -
0.04
0.31 -
UI 0.30
-
\
-OD3 e
e a
E 0.29- E
2 B
:: 0.28
a
-
-
0.02 ;
- 0.01
I I I I I I I I I I
0.24-
Equivalent Sun, hours
-0
0 5 0 0 K H x ) - I s 2000 2500 3000 3500 4000 4500 5000 5500
FIGURE C-39. APPARENT ~1 /E AND Aa OF ALUMINIZED 1-MIL FEP TEFLON(18)
C-27
FIGURE C-40. SPECTRAL REFLECTANCE CHANGES IN KAPTON H FILM, FOLLOWING
EXPOSURE TO ULTRAVIOLET RADIATION(3)
YAVEL ENCTH, MICRONS
FIGURE C-41. DEPENDENCE OF REFLECTANCE DEGRADATION IN KAPTON H
FILM UPON ELECTRON ENERGY(27)
C-28
I
Preirradiation
"" ""_ - After O" p/crn2 (3 k
0.2
- I
0.1
0.2 0.3 0.4 0.5 0.6 07 0.8 0.9 1.0 I I 12
Wovelength, microns
FIGURE C-42. SPECTRAL REFLECTANCE OF SiO-A1-KAPTON (1-3) IN VACUO(34)
0. I
0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 I . I 1.2
Wovelength, mlcrons
FIGURE C-43. SPECTRAL REFLECTANCE OF SiO-A1-KAPTON (2-1) IN VACUO(34)
C- 29
i
Si Ox/AI
Q~ =0.146
oJQ/41ioht
0
0
0.4 t -1 FIGURE C-44. ATS-1 FLIGHT DATA
1 0 0
Sun Hours
WAVELENGTH IN MICRONS
THICKNESS IN MICRONS
0 0174 03630551 0739 0928 1116 1305 i 493 1681 1.870
. - ~ ~ "" "T"-7-.
7"
FIGURE C-45. INFRARED REFLECTANCE
OF A1 AND A1 COATED WITH 0.40 p,
0.97 1-1, AND 2.59 1 ~ . OF s ~o , ( ~~)
FIGURE C-46. MEASURED SOLAR
ABSORPTIVITY OF A1 COATED
WITH si0,(52)
C -30
HAVELENGTH I MI CRONS I
FIGURE C-47. REFLECTANCE CHANGES I N Si 02 OVER A1 DUE TO 20-keV ELECTRON EXPOSUFd27)
I- Y A V f L t N C T H I Ml CRONS t
FIGURE C -48. REFLECTANCE CHANGES I N Si 02 OVER A1 DUE TO 80 -keV ELECTRON EXPOSURE(27)
100
90
80
z 70
2
Y 100
90
80
70
60
0
W
u
LL
w
z
W
W
LL
53
I
6.2 X/4 I
-
'1488 HOURS (0 z.120)
*
_-
13.4 X/4
I
I
I
D 400 500 600 700
l
WAVELENGTH IN MILLIMICRONS
FIGURE C-49. EFFECT OF UV IRRADIATION I N
OIL-FREE HIGH VACUUM ON THE REFLECTANCE
OF A1 COATED WITH 6.2 AND 13.4 QUARTER-
WAVELENGTH-THICK FILMS OF sio2(52)
C - 3 1
YAVEL ENGTH I M l C R O N S I
FIGURE C-50. REFLECTANCE CHANGES IN A1203 OVER A1 DUE TO 20-keV ELECTRON EXPOSURE(27)
"0 .2 . 4 . 6 . e 1. 0 1. 2 1 . 4 1 6 1 . 8 2 0 2.2 2 . 4
~~
Y A V CL E HCT H IMICRONS I
FIGURE C-51. REFLECTANCE CHANGES IN A1203 OVER A1 DUE TO 80-keV ELECTRON EXPOSURE(27)
FIGURE C-52. ATS-1 FLIGHT DATA ON A1203/Al COATING(2o)
C-32
0.8
03
0.2
01
O (
""""" After IO* p/crn2 (3 keV). -
-.-. -.- After 1015p/crn2
- . . - .. - After 10'6p/crn2
IL ~
04 0.6 08 I O 12 14 16 18 2.0 22 I
Wovelength, mlcrans
FIGURE C-53. SPECTRAL REFLECTANCE OF 3M202-A-10 (8-1) I N VACUO(34)
0.4
-. -. - After I ~xI O' ~ e/cm2
--. -. . - After 4x10" e/crn'
03
0.2
- ~ . "~
0.1
0 0.2 0.4 0.6 0.8 1.0 12 14 1.6 1.8 20 2.2 24
Wovelength, r n~cr cms
FIGURE C-54. SPECTRAL REFLECTANCE OF 3M202-A-10 (7 -1) I N VACUO(34)
c - 3 3
0.5 I
Legend
Solar Absorptance
0.4
0. I
0.5
0.6
0.9
0
0 0.4 0.8 1.2 I .6 2 .o 2.4
I .o
Wavelength, mlcrons
FIGURE C-55. SOLAR ABSORPTANCE OF COS-DYED ANODIZED ALUMINUM(55)
0.5
0.4
-
z 0.2
W
(0
a
0. I
0
I
Legend
-
Total Emittance
3760 ESH and
0.5
0.6
W
C
L
W
0.7 0
E
e
a
-
0.8 5
cn
0.9
0 4 8 12 16 20 24
Wavelength, mlcrons
FIGURE C-56. EMITTANCE OF COS-DYED ANODIZED ALUMINUM(55)
c - 34
FIGURE C-57. SOLAR ABSORPTANCE OF NiS-DYED ANODIZED ALUMINUM(55)
Unexposed
3540 ESH
FIGURE C-58. EMITTANCE OF NiS-DYED ANODIZED ALUMINUM(55)
c - 35
Wavelength, rnlcrons
FIGURE C-59. SOLAR ABSORPTANCE OF BLACK NICKEL PLATE ON ALUMINUM(55)
Wavelength, rnlcrm
FIGURE C-60. EMITTANCE GF BLACK NICKEL PLATE ON ALUMINUM(55)
C- 36
0.5
.0.4
W
c
Z 0.3
-
u-
d
5 0.2
-
0
0)
v)
a
0. I
0
Legend
-
Solar Absorptance
I
-
Unexposed 0.952
2130 ESH exposure
3800 ESH t ot al exposure 0.949
0.953
3800 ESH and
1015e / c d exposure 0.945
"-
-
0.5
0.6
rn
e
E
0.7 g
s
0.8 g
u)
-
e
a
e
v)
0.3
I .o
0 0.4 0.8 1.2 0.6 2.0 2.4 2.8
Wovelength, mlcrons
FIGURE C-61. SOLAR ABSORPTANCE OF DU-LITE 3-D ON GRIT-BLASTED
TYPE 3-4 STAINLESS STEEL(55)
W
c
0
c
G
I?
-
e
c
0
v)
a
0.a
0.7
0.6
0.5
0.4
0.3
0.2
0.1
Total Emittance
3800 ESH and
1 0 ' ~ e/cm2 exposure 0.626
I I I I I I
0.2
0.3
0.4
0.5
8
.-
t
0.6
E
e
c
0.7
v)
0.8
0.3
I .o
0 4 8 12 16 20 24 28 32 36 40
Wavelength, microns
FIGURE C-62. EMITTANCE OF DU-LITE 3-D ON GRIT-BLASTED TYPE 3-4.STAINLESS STEEL(55)
c-37
FIGURE C
Wavelength, microns
-63. SOLAR ABSORPTANCE OF WESTINGHOUSE BLACK ON INCONEL(55)
0
0.
aJ
C
-
go.
-
L
W
LL
-
e
&
go.
v)
a
0.
4 e 12 16 20 1
Wavelength ,microns
3.5
3.6
0
C
3.7 g
E
e
0.8 0
W
-
c
v)
n
3.9
1.0
.. .. .
FIGURE C-64. EMITTANCE OF WESTINGHOUSE BLACK ON INCONEL(55)
C- 3 8
0. 5
0.6
3
0
c
0.7 e
::
5
0.8 5
e
::
D
0.9
0 0 4 0.8 I 2 1.6 2.0 2.4 2.8
I .o
Wavelength ,ml crans
FIGURE C-65. SOLAR ABSORPTANCE OF SODIUM DICHROMATE-BLACKENED TYPE 347
STAINLESS STEEL(55)
Wavel engt h,mi crons
FIGURE C -66. EMITTANCE OF SODIUM DICHROMATE-BLACKENED TYPE 347
STAINLESS STEEL(55)
c - 3 9
0.5
4770 ESH total exposure 0.96 I 0.6
al
C
0.7 p
s
::
e
0.8 E
-
a
v,
0.9
0.0 0.4 0.13 1.2 1.6 2.0 2.4 2.8
I .o
Wavel engt h, microns
FIGURE C-67. ABSORPTANCE OF SODIUM DICHROMATE-BLACKENED INCONEL(55)
Total Emittance
0.040
0.4
""
4770 ESH and Id5 ek m2
exposure
0 4 8 12
Wavelength ,mi cr ons
0.5
0.6
al
C
3.7 2
E
e
c
.-
W
-
38 p
I 2
m
3.9
I O
FIGURE C-68. EMITTANCE OF SODIUM DICHROMATE-BLACKENED INCONEL(55)
C -40
Wavel ength .microns
FIGURE C-69. SOLAR ABSORPTANCE OF SODIUM DICHROMATE-BLACKENED INCONEL x(55)
Wavel engt h, mi crons
FIGURE C-70. EMITTANCE OF SODIUM DICHROMATE-BLACKENED INCONEL X(55)
C-41
0 0.4 0.8 I .2 I .6 2.0 2
Wavel engt h,rni crons
FIGURE C -71. SOLAR ABSORPTANCE OF PYROMARK BLACK ON ALUMINUM(55)
FIGURE C-72. EMITTANCE OF PYROMARK BLACK ON ALUMINUM(55)
C -42
I
0.5
I ' Legend' r
0. 5
- Solor Absorptance
Unexposed 0.906
I760 ESH exposure 0.900
3440 ESH t ot al exposure 0.906
3440 ESH and IOl5 e/crn2
C 0
exposure 0.906
m
P
n
a
e
0.8 5
n
0.6
-
.~~
0.7 2
-
r
-
v)
m
v)
0 1 ~ ~ 0.9
OO 0 4 0.8 1.2 I . 6 2 . 0 2. 4 2. 8
10
Wavel engt h, mc r o n s
FIGURE C-73. SOLAR ABSORPTANCE OF PYROMARK BLACK ON INCONEL(55)
1 I
Total Ernlttona
t 3
- Unexposed 0 842
0.845
3440 ESH and ekm2
"
.- . " .
- 1
0 . 4 0 . 8 1.2 I .6 2 0 2. 4
Wavel engl h, rnlcrons
FIGURE C-74. EMITTANCE OF PYROMARK BLACK ON INCONEL(55)
c - 43
oi . 1
0 5
:::I
10
-
10
-
FIGURE C-75. EFFECT OF EXPOSURE TO
UV AND RECOVERY (TiOX-024-G2,
NO BINDER)(^^)
FIGURE C-76. EFFECT OF ELECTRON
IRRADIATION ON DRY -PRESSED
BINDERLESS SPECIMEN (TiOx-028-G2)(62)
FIGURE C-77. EFFECT OF FURTHER ELECTRON
IRRADIATION ON DRY -PRESSED BINDERLESS
SPECIMEN (TiOx-028-G2)(62)
c -44
FIGURE C-79. RECOVERY AFTER SIMULTANEOUS
UV AND ELECTRON IRRADIATION OF DRY -PRESSED
BINDERLESS SPECIMEN (TiOx-026-G2)(62)
/
/'
/
/
/
/
CHANGE IN SOLAR
ABSORPTANCE .oO
.06
.04
FIGURE C-80. CHANGE IN SOLAR ABSORPTANCE
RTV- 602 OF H-10 AND RTV-602 OVER 1199 ALUMINUM
1199 AI REFLECTOR SHEET(14)
I l l I I I I I I I , , I , , ,
0 200 400 600 000 1000 1200 1400
EOUIVALENT SOLAR HOURS
c -45
N A S A C O N T R A C T O R
R E P O R T
RADIATION EFFECTS DESIGN HANDBOOK
Section 3. Electrical Insulating Materials
and Capacitors
by C. L. Hunks and D. J. Hunzmun
Prepared by
RADIATION EFFECTS INFORMATION CENTER
BATTELLE MEMORIAL INSTITUTE
Columbus, Ohio 43201
for
NA TI ONA L A ERONA UTI CS A ND SPA CE A DMI NI STRA TI ON WA SHI NGTON, D. C. JULY 1971
TECH LIBRARY KAFB, NM
-___. -
1. Report No. 3. Recipient's Catalog No. 2. Government Accession No.
NASA CR-1787
- ~~
4. Title and Subtitle I 5. Report Date
RADIATION EFFECTS DESIGN HANDBOOK
SECTION 3. ELECTRICAL INSULATING MATERIALS AND
CAPACITORS
July 1971
6. Performing Organization Code
" ~ ~~ ~ ~~~~ ~
7. Author(s) 8. Performing Organkation Report No.
C. L. Hanks and D. J . Hamman
10. Work Unit No.
9. Performing Organization Name and Address
RADIATION EFFECTS INFORMATION CENTER
Battel l e Memori al I nsti tute
Col umbus L aboratori es
Columbus, Ohio 43201 13. Type of Report and Period Covered
11. Contract or Grant No.
NASW-1568
12. Sponsoring Agency Name and Address
Contractor Report
Nati onal Aeronauti cs and Space Admi ni strati on
Washi ngton, D.C. 20546
14. Sponsoring Agency Code
15. Supplementary Notes
T hi s document contai ns summari zed i nf ormati on rel ati ng to steady- state
radi ati on ef f ects on el ectri cal i nsul ati ng materi al s and capaci tors. The i nf or-
mati on i s presented i n both tabul ar and graphi cal f orm wi th text di scussi on.
The radi ati on consi dered i ncl udes neutrons, gamma rays, and charged parti cl es.
The i nformati on i s usef ul to desi gn engi neers responsi bl e f or choosi ng candi date
materi al s or devi ces f or use i n a radi ati on envi ronment.
.. ~ ~- .- ~
17. KeGWords (Suggested by Authoris)) 18. Distribution Statement
Radi ati on Ef f ects, El ectri cal I nsul ators,
Capaci tors, Radi ati on Damage
Uncl assi f i ed-Unl i mi ted
19. Security Classif. (of this report)
- . - - . . .
20. Security Classif. (of this page) 22. Rice' 21. NO. of Pages
Uncl assi f i ed $3.00
88
Uncl assi f i ed
For sale by the National Technical Information Service, Springfield, Virginia 22151
PREFACE
This document is the third section of a Radiation Effects Design
Handbook designed to aid engineers in the design of equipment for operation
in the radiation environments to be found in space, be they natural or arti-
ficial. This Handbook will provide the general background and information
necessary to enable the designers to choose suitable types of materi al s or
cl asses of devices.
Other sections of the Handbook wi l l di scuss such subj ects as transi s-
tors, sol ar cel l s, thermal -control coati ngs, structural metal s, and i nter-
actions of radiation.
iii
ACKNOWLEDGMENTS
The Radiation Effects I nformation Center owes thanks to several
individuals for their cornments and suggestions during the preparation of
this document. The effort was monitored and funded by the Space Vehicles
Division and the Power and Electric Propulsion Division of the Office of
Advanced Research and Technology, NASA Headquarters, Washington,
D. C. , and the AEC-NASA Space Nuclear Propulsion Office, Germantown,
Maryland. Also, we are indebted to the following for their technical re-
view and valuable comments on this section:
Mr. F. N. Coppage, Sandia Corp.
Mr. R. H. Dickhaut, Braddock, Dum and McDonald, I nc.
Dr. T. M. Flanagan, Gulf Radiation Technology
Mr. F. Frankovsky, IBM
Mr. D. H. Habing, Sandia Corp.
Mr. A. Reetz, J r. , NASA Hq.
Dr. V. A. J . VanLint, Gulf Radiation Technology
V
TABLE OF CONTENTS
SECTION 3 . ELECTRI CAL INSULATING MATERTALS
AND CAPACITORS
ELECTRI CAL INSULATING MATERIALS . . . . . . . . . . 1
INTRODUCTION . . . . . . . . . . . . . . . . . 1
RADIATION EFFECTS ON ORGANIC MATERIALS . . . . . 2
RADIATION EFFECTS ON INORGANIC MATERIALS . . . . 10
RADIATION EFFECTS ON SPECI FI C BULK. SHEET.
AND FI LM INSULATORS . . . . . . . . . . . 11
Pol ytetrafl uoroethyl ene (PTFE) . . . . . . . . . 12
Polychlorotrifluoroethylene (Kel -F) . . . . . . . . 16
Polyethylene . . . . . . . . . . . . . . . . 18
Pol ystyrene . . . . . . . . . . . . . . . . 19
Polyethylene Terephthalate . . . . . . . . . . . 20
Polyamide . . . . . . . . . . . . . . . . . 20
Diallyl Phthalate . . . . . . . . . . . . . . 21
Polypropylene . . . . . . . . . . . . . . . 22
Polyurethane . . . . . . . . . . . . . . . . 22
Polyvinylidene Fluoride . . . . . . . . . . . . 23
Polyimide . . . . . . . . . . . . . . . . . 24
Pol yi mi dazopyrrol one (Pyrrone) . . . . . . . . . 24
Epoxy Laminates . . . . . . . . . . . . . . 25
Cerami c . . . . . . . . . . . . . . . . . . 26
Mi ca . . . . . . . . . . . . . . . . . . 29
Mi scel l aneous Organi cs . . . . . . . . . . . . 26
RADIATION EFFECTS ON SPECI FI C WI RE
AND CABLE INSULATION . . . . . . . . . . . . 29
Pol ytetrafl uoroethyl ene (PTFE) . . . . . . . . . 30
Polyethylene . . . . . . . . . . . . . . . . 31
Silicone Rubber . . . . . . . . . . . . . . . 32
Polyimide'. . . . . . . . . . . . . . . . . 33
I rradiation-Modified Polyolefin . . . . . . . . . . 33
Miscellaneous Organics . . . . . . . . . . . . 34
vii
. ..
" . . 1 1 1 1 " 1 1 - I ..-. _I"." , . -.-. ..................................... .-
TABLE OF CONTENTS
(Continued)
Page
C er amic . . . . . . . . . . . . . . . . . 35
Miscellaneous I norganics . . . . . . . . . . . . 36
RADIATION EFFECTS ON ENCAPSULATING
COMPOUNDS . . . . . . . . . . . . . . . . . 36
RADIATION EFFECTS ON CONNECTORS
AND TERMINALS . . . . . . . . . . . . . . . . 40
CAPACITORS . . . . . . . . . . . . . . . . . . . 46
INTRODUCTION . . . . . . . . . . . . . . . . . 46
Gl ass- and Porcel ai n-Di el ectri c Capaci tors . . . . . 48
Mica-Dielectric Capacitors . . . . . . . . . . . 50
Cerami c-Di el ectri c Capaci tors . . . . . . . . . . 51
Paper- and Paper/Plastic-Dielectric Capaci tors . . . . 52
Pl asti c-Di el ectri c Capaci tors . . . . . . . . . . 60
Electrolytic Capacitors . . . . . . . . . . . . 64
REFERENCES . . . . . . . . . . . . . . . . . 71
INDEX . . . . . . . . . . . . . . . . . . . 79
vi i i
SECTION 3 . ELECTRI CAL INSULATING
MATERIALS AND CAPACITORS
ELECTRI CAL INSULATING MATERIALS
INTRODUCTION
Dielectric and insulating materials as applied to electronic circuitry
are second only to semiconductor devices, such as integrated circuits,
transistors, diodes, in sensitivity to radiation. Consideration of this sen-
sitivity and what effects might occur as a resul t are of pri mary i mportance
to the circuit designer and application engineer in designing a system that
includes radiation as an environmental condition. The purpose of this
report i s to assi st i n provi di ng i nformati on regardi ng the radi ati on tol -
erance of various insulating materials and the degradation of thei r el ectri -
cal properties. Deglladation of mechanical properties, however, is also
a consideration to the extent that in many applications the mechanical fail-
ure of an insulator or dielectric will adversely affect its el ectri cal char-
acteri sti cs. If the reader's i nterest i s such that he requi res more
information than is presented herein concerning changes in the basic
mechani cal characteri sti cs of organi c i nsul ati ng materi al s or the damage
mechanisms involved, he is directed to the elastomeric and plastic com-
ponents and materials section of this handbook.
I t is impractical to attempt to compile within this document the
detailed information that would be directly applicable to all ci rcui t requi re-
ments and environmental conditions. Often the damage experienced by an
insulating or dielectric material is dependent upon environmental condi-
tions present in addition to the radiation, such as temperature and humidity.
The fabrication method used by the manufacturer can also be a factor in
determining the amount of damage that mi ght occur. For these reasons,
this report is limited to generalized "ballpark" type information which is
applicable to early design considerations. Where information on a materi al
i s insufficient for "ballpark" generalization, however, details of specific
i rradi ati ons are presented.
The effects of radiation as presented i n thi s report are often i denti -
fied as damage threshol d and/or 25 percent damage dose. These terms
relate to changes in one or more physi cal properti es, i. e. , tensile strength,
1
elongation, etc., with damage threshold being the dose where the change is
first detected. The 25 percent damage dose is that where a 25 percent
change i n property occurs.
The scope of thi s report has been l i mi ted to the effects of steady-
state and space radiation and excludes information concerning transient
radi ati on or pul se-radi ati on effects wi th the excepti on of the next few pages
where transi ent effects are used for i l l ustrati on. The i nformati on presented
i s separated by the configuration of the test item, i. e. , bulk or sheet
materials, wire and cable insulation, encapsulating compounds, connectors
and terminals, and capacitors. I ntroductory paragraphs on organic and
i norgani c i nsul ators di scuss the effects of radi ati on i n general terms on
these two basi c categori es of insulating materials. Also, the information
on the effects of radiation on bulk or sheet-type specimens is considered
applicable to toher configurations of the same materi al , keepi ng i n mi nd
what effect the different configuration may have in regard to the type of
damage that occurs.
Conversion factors for converting electron fluences to rads, and pro-
cedures to c.alculate ionization due to neutrons and protons are available
in the handbook section entitled "Radiations in Space and Their I nteraction
with Matter".
RADIATION EFFECTS ON ORGANIC MATERIALS
Organic insulating and dielectric materials experience both tempo-
rary and permanent changes i n characteri sti cs when subj ected to a radi a-
tion environment such as that found in space or the fields of a nuclear
reactor or radi oi sotope source. Data i ndi cate that the temporary effects
are general l y rate sensi ti ve wi th a saturation of the effect at the higher
radiation levels. The enhancement of the electrical conductivity is the
most i mportant of the temporary effects; i ncreases of several orders of
magni tude are observed. The magni tude of the i ncrease i s dependent
upon several factors i ncl udi ng the materi al bei ng i rradi ated, ambi ent
temperature, and the radiation rate.
Absorption of energy, excitation of charge carri ers fron nonconduc:
ting to conducting states, and the return of these carri ers fron conducti ng
to nonconducting states are considered responsible for the induced conduc-
tivity. S. E. Harri son, et al, (l ) have demonstrated that, with steady-
state gamma irradiation between and l o4 rads (HZO)/s, the excess
2
conductivity has di sti nct characteri sti cs i n three ti me i nterval s whi ch are
denoted as A, B, and C i n Fi gure 1. The conductivity increases exponen-
ti al l y i n response to a step i ncrease i n gamma dose rate, y, during I nter-
val A and is characteri zed by
where
uo =initial conductivity
u = conductivity at ti me t
A =empi ri cal constant
T o =k o j - p =time constant of the response as a function of
gamma dose, gamma equivalent ionizing dose, or
dose rate ko and p being empirical constants
(see Fi gure 2 ) .
During I nterval B, the induced conductivity is at equilibrium, and
its value is determi ned by the rate of exposure and temperature for a
speci fi c materi al . Thi s condi ti on i s characteri zed to a good approxima-
tion by
(u-u,) =A j'
Y
7 ( 2 )
where
A,, and 6 = empi ri cal constants (see Tabl e 1) and
i, = gamma or gamma equivalent (ionizing)
exposure rate i n rads (H20)/s.
The equi l i bri um or saturati on of the radiation induced conductivity is attri-
buted to two conditions: (1) equal rates of free-carri er generati on and car-
rier annihilation through recombination, and (2) the rate of f ree-carri er
capture in trapping states equals that of trapped-carri er decay.
The induced conductivity gradually decreases following the termina-
tion of the i rradi ati on. The measured conducti vi ty of I nterval C has been
characteri zed for several organi c materials by
3
I
9
""
I
I
I
I
I
00 I
I
I I
I I
I I
a b
Time, t, s
FI GURE 1. TYPICAL BEHAVIOR OF CONDUCTIVITY I N
RESPONSE TO A RECTANGULAR PULSE OF
GAMMA-RAY DOSE RATE(^)
4
5
4
3
2
I
0
5
4
cn
c
c
3
2
I
-
c
0
5
4
3
2
I
I
- EPOXY 1478 - I
-
-
- Below I .7 rads (H,O) /s
- No photoconductivity is measured
-3 -2 - I 0 I 2 3 4 5 6 7 a 9
i n p, rads (H,O)/s
FI GURE 2. LOGARITHM OF TIME CONSTANT VERSUS LOGARITHM
OF GAMMA-RAY DOSE RATE FOR POLYETHYLENE,
POLYSTYRENE, AND EPOXY 1478-1 AT 38 C( '1
5
I !
TABLE 1. MEASUED VALUES OF 4, AND 6 FOR EIGHT MATERIAL5 AS DEFINED BY (0-ir o) =pt; da)
Temperature(c),
Material@) C 6 Range of; , rads (H20)/s
Polystyrene
Polyethylene
Epoxy 1478 -1
38
49
60
38
49
60
38
49
60
0.97 4. o X 10-17 1.7 X 10-2 to 5. 0 X 103
0.97 4. o x 10-l7 1.7 x 10'2 to 5. 0 x 103
0.97 4.0 X 10-17 1.7 X 10-2 to 5. o X 103
0.74 5.2 x 10-16 8.3 x 10-2 to 1.7 x l o3
0.74 6.3 x 8.3 x 10'2 to 1.7 x l o3
0.74 1.6 x 8.3 x 10'2 to 1.7 x l o3
No measurable photoconductivity below f =1.7
1.0 3.3 x 10-17 1.7 to 4.2 X 103
No measurable photoconductivity below p =9.0
1. 0 3.3 X 10-17 9. o to 4.2 X 103
No measurable photoconductivity below; =7.5 x 101
1.0 3.8 x 10-17 7.5 X 101 to 4.2 X 103
, Polypropylene 38 0.88 3.8 x 10-17 1.8 x to 6.0 x l o3
H-film 38 1.1 5.8 x 1.8 X 10-3 to 6. o x 103
Teflon 38 1.0 1.2 x 10-16 1.8 X 10-3 to 6.0 X 103
Nylon 38 No measurable photoconductivity below =8.0
1.3 2.8 x 10-18 8.0 to 6.0 x l o3
Diallylphthalate 38 0.30 2.1 x 10-16 1. E( x 10-3 to 3.0 x 102
1.7 8.0 x 10-20 3.0 x 102 to 6.0 x l o3
(a) Data taken under steady state conditions after 1.8 x 103 seconds of electrification.
(b) Temperature is f 1C.
(c) Fifteen samples of polyethylene, polystyrene, and Epoxy 1478-1 and three samples of the other materials
were measured.
6
where
Oeq =Do t A y 6 =equilibrium conductivity
Y
n =number of discrete decay-time constants in. the
recovery process
~i =decay-time constants of the recovery
ki =weighting factors associated with the icTi. (2)
A generalized expression for conductivity in insulating materials
utilizing the "unit-step function", U( t), was combined with the three basi c
characteri zati ons presented above for I nterval s A, B, and C by S. E.
Harri son, et al( I ), to yield an equation which has been modified(2) to
o(t,y) =[ V(t) - U(t-b)o(t-b)] oo + [ U(t-a) t U(t-b)o(t-b)]
The cumul ati ve resul ts of the temporary effects pertaining to the
el ectri cal parameters of i nsul ati ng materi al s are a reduction in breakdown
and flashover voltages as well as an i ncrease i n l eakage current or conduc-
tance - the latter also being identified as a decrease i n the materi al s i n-
sulation resistance. However, these temporary changes in electrical
characteristics are often not large enough to prevent the use of organic
insulators and dielectrics in a radiation environment. This is especially
true i f the designer considers these changes and makes allowances to
mi ni mi ze thei r effects. Howver, where the desi gner is under severe
space limitations or the application includes a high radiation-exposure rate,
it may be necessary to limit insulating-material considerations to the
inorganics since tney tend to have a l arger dose tol erance than organi cs
for the same ionizing rate.
Permanent effects of radiation on organic insulating and dielectric
materi al s are normal l y associ ated wi th a chemical change in the material.
Most important among these chemical reactions that occur are mol ecul ar
sci ssi on and crossl i nkage. These chemi cal reacti ons or changes modi fy
the physical properties of the materi al . A softening of the materi al , de-
creases i n tensi l e strength and mel ti ng poi nt, and a greater solubility could
be the resul t of chain scission. Crosslinking leads to hardening, an in-
crease i n strength and mel ti ng poi nt, a decrease i n sol ubi l i ty, and an
i ncrease i n densi ty. Thus, the permanent effects of radiation on organic
materi al s i s predominantly a change in the physical properties. This
7
.. ...
I
physical degradation, however, may also be disastrous to the electrical
characteri sti cs of a component part such as pri nted ci rcui t boards, wi re i n-
sulation, and connector s. Radiation-induced embrittlement of insulating
structures, such as these, where the i nsul ati on cracks or fl akes, i n turn,
could, cause a circuit to fail electrically through an "open" or "short" cir-
cuit. This is often the case when an insulator or dielectric material fails
i n a radiation environment, i. e. , physical degradation followed by fai l ure
of el ectri cal properti es. Changes i n di el ectri c l oss or di ssi pati on factor
and insulation resistance have also been recorded as permanent effects
from exposure to a radi ati on envi ronment. These changes, however, are
often quite small, and it would be an uncommon application where they
would offer any problem.
A comparison of the rel ati ve resi stance of organic insulating mate-
rials to permanent effects is presented i n Fi gure 3 . Another reaction that
may occur when an organi c i nsul ator or di el ectri c i s i rradi ated i s gas
evolution. Gas evolution from the solid organic polymers is l ess than
that for liquids because of a greater possibility of recombination and
limited diffusion. It is unlikely, therefore, that the volume of gas would
be of seri ous concern except for organi c fl ui ds when suffi ci ent pressure
may be produced to di stort or rupture a sealed enclosure. Another prob-
l em wi th some evol ved-gas speci es i s that they are corrosi ve. Thi s i s
true of the gases produced during the irradiation of halogenated hydro-
carbons such as polytetrafluoroethylene (Teflon) and Kel-F. Although
fai l ure from other .causes is likely to occur before the corrosion would
become a probl em, some consi derati on i n thi s area may be advi sabl e when
selecting sealed parts - l i ke mi ni ature rel ays - that contain electrical
contacts.
Environmental conditions other than radiation contribute to the
degradation of organi c i nsul ators and di el ectri cs. Temperature and/or
humidity may be important for some materials, and the gaseous content
of the ambient atmosphere is of seri ous i mport to others. For exampl e,
the absence of oxygen is known to increase the tolerance of tetrafluoro-
ethylene to radiation by one to two orders of magnitude. This could be
an important factor when considering its possible use in a radiation
application.
8
Damage Utility of Organic
- Incipient to mild Nearly always usable
- Moderate to severe Limited use
Mild to moderate Often satisfactory
Phenolic, glass laminate I
Phendic asbestos filled
Phendi4 unfilled
Epoxy, aromatic-type curing agent I
Polyurethane
I
I r , l / l l l -
Polyester, gl ass filled
Polyester, mlneral filled
Diallyl Phthalate, mineral filled
Polyester, unfilled
Mylar
Sillcone, minerol filled
SI Ilcone, glass fllled
Sillcone, unfilled
Urea-formaldehyde
Melamine- formeldehyde
Aniline-formaldehyde
Polystyrene
Polyimide
Acryl onl t ri l e/but odi ene/st yrene (ABS)
Polyvmyl chloride
Polyethylene
Polyvlnylldene chloride
Polyvinyl formal
Polycarbonate
Kel-F Poly trlfluorochloroethylene
Pol vlnyl butyral
CelLose ocetote
Polymeth I methacrylate
PolyomlJ e
Vinyl chlorlde-ocetote
Teflon (FEP)
Teflon (TFE)
Notural rubber
Styrene- butodiene (SBR)
Neoprene rubber
Silicone rubber
Polyprop lene
Polyvinyridene fluoride (Kynor 400)
lo4 to5 106 10' 108 lo9 1010
Gamma Dose, rads(C)
I I I I I I I
loi3 1014 1015 1016 1017 IO^' 1019
Neutron Fluence, n/cm2(E>0.1 Mev)(O)
(0) Approxlmate fluence (I rod(C) = 4 x IO' n/cm2)
FI GURE 3. RELATIVE RADIATION RESISTANCE OF ORGANIC
INSULATING MATERIALS BASED UPON CHANGES
IN PHYSICAL PROPERTIES
9
RADIATION EFFECTS ON INORGANIC MATERIALS
I norgani c i nsul ati ng and di el ectri c materi al s are, i n general , more
resi stant to radi ati on damage than are the organi c i nsul ators. Atomi c di s-
pl acements are responsi bl e for nearl y all of the permanent damage that
occurs in inorganic insulators, but constitutes only a small part of the
damage in organic insulators. No new bond formati ons are produced by the
i rradi ati on of the i norgani c i nsul ati ng materi al s, and they are l eft unal tered
chemically.
A l arge part of the energy of incident radiation is absorbed through
electronic excitation and ionization which produce a strong photoconductive
effect in inorganic ceramics. A higher mobility of charge carri ers i n the
inorganic compounds and the excitation-produced quasi-free electrons are
responsible for this photoconductive effect. The generalized expression
for conductivity in insulating materias, Equation (4), is applicable to the
i norgani c materi al s as well as the organics. The value of 6 i s al most
always 1 for inorganics and Ay is approximately <Ay < 10- 18. (2)
Atomic displacements lead to permanent changes in crystalline
inorganic insulators which are manifested as changes in density, strength,
and el ectri cal properti es. The densi ty of crystal l i ne i nsul ators decreases
from exposure to fast neutrons. Amorphous i nsul ators, such as fused
quartz and gl ass, experi ence a breakdown of their bonds Change in re-
sistivity is the predominant effect on electrical properties; little or no
change occurs i n a-c characteri sti cs.
A comparison of the rel ati ve radi ati on resi stance of inorganic insu-
l ators to permanent damage i s presented i n Fi gure 4.
10
Magnesium oxide
Al umi num oxi de
Qu ar t z
Gl ass (hard)(<l 0I6n
Gl ass (boron f ree)
Sapphi r e
For st er i t e
Spi nel
Ber yl l i um oxi de
Damage Ut i l i t y of I nor gani c
- I nc i pi ent t o mi l d Near l y al ways usabl e
DZZZZZl Mi l d t o moder at e Of t en sat i sf act or y
- Moder at e to severe Li mi t ed use
Gamma Dose, rods(Cf b)
( 0) Unsat i sf act or y at n/cm2
(b) Approxi mate gamma dose (4 x IOe n/cm2 = I r ad (C))
IC) Var i es gr eat l y with t emper at ur e
FIGURE 4. RELATI VE RADIATION RESI STANCE(C) OF
INORGANIC INSULATING MATERIALS
Based upon changes in physical properties
RADIATION ~~ EFFECTS ON SPECIFIC BULK,
SHEET. -AND FI LM INSULATIONS
"
El ectri cal i nsul ati ons of the bulk, sheet, and film type have been
investigated as to the effect of radiation on their physical and electrical
properti es by a number of experi menters. Thi s secti on of the report
summari zed the resul ts of these i nvesti gati ons.
11
Pol vtetrafl uoroethvl ene (PTFE)
Polytetrafluoroethylene (commonly identified as Teflon TFE, but also
including the trades names Halon TFE, Tetran, Fluon, Polyflon and Algo-
flon) has demonstrated a rather high susceptibility to radiation damage,
which is quite apparent from the degradation of physical properties when it
i s i rradi ated. The rapi d degradati on of these properti es by ionizing radia-
ti on i s pri mari l y attri buted to a prevalence of main-chain scission by li-
berated fluorine atoms and the production of entrapped fl uorocarbon gases.
Tensi l e sgrength and ul ti mate el ongati on decrease, and the materi al be-
comes embrittled through the main- chain scission. The embrittlement
becomes severe with extended irradiation [ l o7 rads (C)] and the polytetra-
fl uoroethyl ene crumbl es and/or powders. The approxi mate danage thres -
hold and the 25 percent damage dose are 1. 7 x l o4 rads ( C ) and 3.4 x l o4
rads ( C) , respectively.
There. is evidence that the damage observed when polytetrafluoro-
ethyl ene i s i rradi ated i s a function of several factors. These i ncl ude the
various types of pol ytetrafl uoroethyl ene such as TFE and the copol ymer
FEP, the ambient atmosphere, and the test temperature. I t had been
demonstrated that Tefl on-FEP i s more radi ati on resi stant than TFE. In
vacuum, 10-mi l -thi ck FEP has retai ned its elongation properties for a
factor-of-10 higher radiation exposure than similar TFE-7 film. ( 3 ) In air,
there was a factor.-of-.l6 difference between the doses at which FEP and
TFE-7 Teflon retained equivalent elongation properties. These differences
are i l l ustrated i n Fi gures 5, 6, and 7 which also give a comparison between
the effects of i rradi ati on i n vacuum and ai r at room temperature for vari ous
sampl e thi cknesses. The absence of air or oxygen improves the radiation
resi stance of Teflon. These data al so show a trend in the damage-thickness
relationship.
The effect of elevated temperature in combination with irradiation is
to accelerate the degradation of the polytetrafluoroethylene's physical prop-
erties. For example, in one study only negligible damage was observed
at -65 F after a dose of 2. 6 x 105 rads (C), while the tensile strength de-
creased 40 and 6.0 percent after si mi l ar doses at 73 and 350 F. (4)
Polytetrafluoroethylene also experiences changes in electrical prop-
erti es when it is. subjected to a radiation environment. The electrical
parameters that have shown a sensitivity to radiation include dissipation
factor or loss tangent, volume resistivity, dielectric constant, and dielec-
tri c strength. The changes observed are often i nsi gni fi cant i n many
12
10.
FIGURE 5. COMPARISON OF ULTIMATE ELONGATION VALUES OF
VARIOUS THI CKNESSES OF TEFLON TFE-7 I RRADI ATED
IN VACUUM(3)
i
FI GURE 6. COMPARISON OF ULTIMATE ELONGATION VALUES OF
VARIOUS THICKNESSES OF TEFLON TFE-7 IRRADIATED
T
I
FI GURE 7. COMPARISON OF ULTIMATE ELONGATION VALUES OF
VARlOUS THICKNESSES OF TEFLON FEP IRRADIATED
IN VACUUM AND AIR(^)
13
practical applications as long as the materials mechani cal i ntegri ty is mai n-
tained. Therefore, even though changes in electrical properties do occur,
the degradation of physi cal properti es i s the cri teri a often used i n deter-
mining the acceptability of thi s materi al for use i n a specific application.
The volume resistivity of polytetrafluoroethylene decreases two or
three orders of magnitude from initial values between 5 x 1017 and
1 x 1018 ohm- cm or greater when irradiated under vacuum conditions to
total doses of 10 6 rads (C) and higher. The degradation may continue after
the radiation exposure is terminated with an additional decrease of one or
two orders of magnitude over a period of several days. Recovery may
also occur with the volume resistivity approaching its prei rradi ati on val ue
several weeks after the i rradi ati on.
Di el ectri c-constant measurements of polytetrafluoroethylene during
and following exposure to a radiation environment have shown increases of
l ess than 15 percent when irradiation in air or vacuum to respective doses
of 8 x l o6 and l o8 rads (C). Recovery i s essentially complete within a day
or two after the i rradi ati on. Si mi l ar resul ts have al so been obtai ned under
vacuum conditions at cryogeni c temperatures to a dose of 7 x l o6
rads ( C ) . ( 3 ) However, when thi s test was termi nated at 9. 5 x l o7 rads (C),
the greatest value for the dielectric constant during exposure was approxi-
matel y 22 percent hi gher than the i ni ti al cryotemperature val ue. Recovery
to within 0. 4 percent of the initial value occurred after the irradiation
was terminated.
Significant increases of between two and three orders of magnitude
occur in the low-frequency dissipation factor (60-100 Hz) or l oss tangent
of Tefl on TFE when i rradi ated. Thi s is true for i rradi ati ons at normal
atmospheric conditions (ai r) and in vacuum at room temperature as
i l l ustrated by the example shown in Figure 8. Exposure to radiation in
an air envi ronment resul ts i n an i ncrease to a maximum value which is
then maintained during the irradiation. I rradiation in a vacuum environ-
ment produces a si mi l ar i ncrease i n di ssi pati on factor; however, upon
reaching a maxi mum val ue, thi s di ssi pati on factor gradual l y decreases.
The absorbed dose at which the maximum occurs appears to be a function of
the exposure rate i n that the beak occurs at a higher total dose with an in-
crease i n the rate of exposure.
The recovery characteri sti cs of the dissipation factor of Teflon
i rradi ated i n air and vacuum are qui te di fferent. That of vacuum i rradi ated
Teflon recovers rapidly and is essentially complete as long as it remai ns
14
I
I .O
0. I
0.0 I
0.001
Ai r
I
I
I
I
I
I
I-
0 I 2 3 4 5 6 7 a 9
Absorbed Dose, IO6 r ads (Ag)
FI GURE 8. EFFECT OF X-RAY IRRADIATION ON TFE-6(5)
15
in the vacuum environment, while the dissipation factor of Tefl on i rradi ated
in a normal atmosphere recovers gradual l y over several days or weeks.
If the vacuum-irradiated Teflon is exposed to air or ni trogen after i ts re-
covery under vacuum conditions the dissipation factor increases sharply.
Following this i ncrease, there i s a more gradual recovery. Exampl es of
these recovery characteri sti cs are presented i n Fi gure 9 after the ex-
po sure shown i n Fi gure 8.
Limited information on the effect of radiation on the dissipation factor
of different Teflon types indicate a difference in sensitivity in radiation.
The a-c l oss characteri sti cs of the copolymer Teflon FEP- 100 did not
change si nificantly when this material was irradiated to a total dose of
3. 08 x 10 % rads (Ag). (6) It has been assumed that thi s dose and that i n
Fi gure 8 are i n rads si l ver si nce the cal ori meter target used i n measuri ng
the dose was silver and .no other materi al i s menti oned i n the documents
in describing the radiation environment. Similar radiation exposure
caused substantial increases to 0.408 and 0. 169 in the dissipation factors
for TFE-6 (extrusi on resi n) and TFE-7 (mol di ng resi n), respecti vel y, i n
this same study.
Dielectric breakdowns induced in Teflon F EP by el ectron i rradi ati on
to a given fluence are both flux and temperature sensitive. (7) An i ncrease
i n temperature or a decrease i n el ectron fl ux tends to decrease the number
of breakdowns observed. Approximately twice as many breakdowns were
observed for a fluence of iO13 e/cm2 (Ek =40 keV) and a f l ux of 10
e/(cm2. s) than for a similar fluence and a flux of 10 l o e/(cm2. s), and the
number of breakdowns at liquid nitrogen temperature was seven to eight
ti mes greater than at room temperature.
Similar exposures of Teflon. TFE to a proton environment including
a flux range of 1 x 109 to 2 x l o1 p/(cm2. s), and a proton fluence of up
to 5 x 1014 p/crn2 did not result in dielectric breakdown at the test tempera-
tures of -134 C or 27 C. (8) A large recombination of trapped charges
appears to take place in this and other materials with proton energies of
0. 4 to 2. 15 MeV at these fluxes and fluences and thus eliminates the di-
electric breakdown effect observed with electron irradiation.
Pol ychl orotri fl uoroethyl ene (Kel -F)
Polychlorotrifluoroethylene, another fluoroethylene polymer, also
experiences severe degradation of its physical properties when exposed to a
radiation environment. I t is reported to have a damage threshold of
16
I .o
0. I
L
+
0
0
z
.- 0 0.01
a
c
t
0
v,
v,
.-
c)
.-
0.001
0.0001
0
4"4
vacuum
I I I I I I
~~
5 IO 15 20 25 30 35
Recover y Ti me, days
FIGURE 9. RECOVERY CHARACTERISTICS OF TFE-6 SPECIMENS
AFTER X-RAY IRRADIATION AS SHOWN IN FI GURE 8(5)
17
1.3 x 106 rads (C) and a 25 percent damage dose of 2 x l o7 rads (C)(4).
The elongation of this materi al i ncreased 47 percent and the impact strength
decreased 16 percent when it was subjected to a total dose of approximately
2.4 x l o7 rads (C). (9) The ultimate tensile strength was unaffected.
El ectron i rradi ati on wi th a total of 3. 67 x 10l 6 e/cm2 (E = 1. 0 MeV)
at 60 C so seri ousl y degraded a speci men of polychlorotrifluorethylene
that it could not be measured as to its physi cal and el ectri cal properti es.
The degradation of the el ectri cal properti es of polychlorotrifluoro-
ethylene from exposure to radiation includes a reduction in volume and
surface resi sti vi ty. Decreases of between one and two orders of magnitude
have been observed in both of these parameters duri ng X-ray i rradi ati on
to a total dose of 2. 1 x l o7 rads (Ag) in a vacuum environment.(6) Essen-
tially, no recovery was observed following the i rradi ati on.
Measurements of dissipation factor during and following the irradia-
tion of thi s materi al has actual l y shown decreases or i mprovement i n thi s
characteri sti c. Low values of 0. 001 after 1920 hours of recovery in air
were observed. (6)
A Russian study that included a total bremsstrahl ung dose of 5.3 x
l o7 rads (C) produced similar reductions in volume resistivity. (10)
Polvethvlene
I n some respects, polyethylene improves with exposure to radiation
in that its softening-point temperature increases for exposures of l ess than
l o7 rads (C). I n addition, the tensile strength also increases until approxi-
matel y l o8 rads (C), after which it decreases and is 25 percent below the
initial value at approximately 1O1O rads (C). (4) The damage threshold is
greater than l o7 rads (C).
There are some di fferences i n the resul ts obtai ned from the ir-
radiation of polyethylene; thinner films degrade at lower radiation doses
than thicker films. This difference in behavior i s attributed, at l east i n
part, to the oxidation of the polyethylene when it is i rradi ated. Other
factors that contribute to differing results are the various densities in
which this material is produced and the addition of fillers.
A study where polyethylene of low and high densities and another
which was carbon-black filled were exposed to an electron dose of
18
5.8 x 10l 6 e/cm2 (E = 1. 0 MeV) at 60 C i l l ustrates the di fferences these
factors make. ( l ) The hardness and sti ffness i n fl exure of the high-density
materi al decreased as a resul t of the irradiation, and the low-density and
carbon-fi l l ed materi al s experi enced i ncreases i n these properti es. The
high-density polyethylene also increased in tensile strength and the others
decreased.
The el ectri cal properti es of polyethylene also degrade when it is
exposed to a radiation environment. Measurements of the insulating qual-
ities such as vol ume resi sti vi ty, surface resi sti vi ty, and i nsul ati on-re-
sistance indicate that a decrease of up to three orders of magnitude occurs
i n these parameters duri ng i rradi ati on wi th permanent decreases of one
order of magnitude when subject to a total dose of 5. 8 x 10l 6 e/cm2
(E = 1. 0 MeV). The dissipation factor at 1 KHz i ncreases one to two
orders of magnitude as a resul t of irradiation, and the dielectric con-
stant changes less than *5 percent.
Electron-radiation-induced dielectric breakdown in polyethylene
is sensitive to the f l ux to which the polyethylene i s exposed; the number
of observed breakdowns i ncreases wi th an i ncrease i n el ectron f l ux. ( 7 )
Exposure to a flux of 1 x 10l 1 e/ (cm2. s ) resul ted i n 20 breakdowns for
a fluence of 2 x 1013 e/cm2 (Ek =30 keV) while only 12 breakdowns were
observed for a similar fluence at 5 x l ol o e/(cm2.s) and none at 1 x l ol o
e/(cm2* s ) .
Proton i rradi ati on of polyethylene over a flux range of lO9to 10
10
p/(cm2. s ) for a fluence of 1013 p/crn2 at each rate with energies of 1. 15
and 1. 65 MeV produced no breakdowns in the material. (8)
Pol vstvrene
I rradi ati on studi es of polystyrene have shown it to be one of the most
radiation-resistance plastics among those used for insulating purposes
i n el ectroni c ci rcui try. It has a damage threshold of l o8 rads (C) and does
not experience 25 percent damage to its physical properties below 4 x 109
rads (C). Pol ystyrene is subject to postirradiation oxidation that continues
for several weeks, however, oxidation plays little or no part in the radia-
tion damage that occurs.
Electron irradiation to a fluence of 5. 8 x 10l 6 e/cm2 ,(E = 1. 0 MeV)
at 60 C has resul ted i n decreases of approximately 50 percent in the tensile
strength and ultimate elongation. (11) The hardness and the stiffness in
19
fl exure al so decreased 1 percent and 13 percent, respectively, during this
same study. These resul ts i ndi cate pol ystyrene becomes more fl exi bl e and
softer as a resul t of the i rradi ati on.
The insulating quality of polystyrene appears to be the only electrical
property that is affected by exposure to radi ati on. Permanent decreases of
one and two orders of magni tude have been observed i n the vol ume resi s-
tivity and insulation resistance of this material following doses as low as
4. 5 x l o6 rads (C) and as high as 1 x l o8 rads (C). Other electrical para-
meters, such as di el ectri c constant and di ssi pati on factor, have shown
l i ttl e or no change from exposure to a radiation environment within this
range of total dose.
Polvethvlene TereDhthalate
Polyethylene terephthalate (Mylar) has shown improvement in its
physical properties when exposed to limited radiation doses with very little
degradation in electrical properties. There is, however, some di sagree-
ment concerning the dose at which the trend toward improved physical
properti es is reversed and degradation begins. Based upon available in-
formation, the best estimate for the dose at whi ch thi s reversal occurs is
l o6 to 107 rads (C) for X-ray and reactor irradiation. Radiation exposure
to doses of 108 rads (C) and above causes severe embri ttl ement of poly-
ethylene terephthalate to a degree that properti es are unmeasurabl e.
Degradation of the el ectri cal properti es of polyethylene terephthalate
with the doses described above, 106 to l o7 rads (C), is insignificant.
Changes in the insulation resistance, volume resistivity, and surface re-
sistivity as a resul t of i rradi ati on are l i mi ted to approxi matel y one decade.
The dielectric constant and dissipation factor remain, essentially,
unchanged.
Exposure to a proton fluence of lOI3 p/.cm2 at various energies
between 0. 8 and 3. 25 MeV and f l ux of 109 to l ol o p/(cmZ. s) did not induce
adi el ectri c breakdown i n Myl ar at temperatures of -134 C and 27 C. (8)
Polyamide
Polyamide (nylon) sheet or film insulation changes in both physical
and electrical properties when subjected to a radiation environment. This
20
material experi ences threshol d damage at a dose of 8.6 x l o5 rads (C) and
25 percent damage at 4.7 x l o6 rads (C). These doses are based upon
losses in ultimate elongation and impact strength. Another property of poly-
ami de that deteri orates from radi ati on exposure i s stiffness in flexure,
which has increased between 52 and 181 percent, depending upon the nylon
type, after exposure to an electron dose of 5.8 x 1016 e/cm2 (E = 1.0 MeV)
at 60 C( l l ). This same exposure improved the tensi l e strength by 49 to
107 percent. These resul ts agree wi th other radi ati on studi es whi ch have
shown increases in tensile strength of 25 percent for doses over 109
rads (C).
I nformation on the effects of radiation on the electrical properties of
polyamide is limited to results of the electron irradiation mentioned above.
Exposure to this radiation environment produced an increase of approxi-
mately one order of magnitude in the insulation resistance and a decrease
of l ess than an order of magnitude for the dissipation factor. A decrease
in dielectric constant was insignificant at 1 MHz and varied between 5 and
3 2 percent at 1 KHz, depending on the polyamide type.
Diallvl Phthalate
Diallyl phthalate with various fillers such as glass or Orlon has
shown exceptional radiation tolerance for a plastic insulating material.
Little or no permanent degradation of physical or electrical properties have
been observed with radiation exposures to doses of between 108 and 1010
rads (C). I nsignificant changes are observed in the hardness and flexibility
of this material when irradiated to these total doses. The ultimate elonga-
tion and tensile strength of Orlon-filled diallyl phthalate actually increased
or improved with exposure to an electron dose of 5.8 x 10l 6 e/cm2
(E = 1.0 MeV) at 60 C.
The el ectri cal properti es of diallyl phthalate such as dielectric con-
stant, di ssi pati on factor, and i nsul ati on resi stance are affected by exposure
to a radiation environment such as described above. The amount of degra-
dati on or change i n these parameters because of this exposure i s of little
practical significance. Permanent changes in dielectric constant were
less than 6 percent while the dissipation factor recovered to below the
initial value. I ncreases in insulation resistance during exposure are fol-
lowed by complete recovery within approximately 1 hour after the i rradi -
ati on i s termi nated.
21
Polypropylene
Polyprolylene i s subject to a severe l oss in physical properties when
exposed to a radiation environment. Above a total dose of 1 x l o7 rads (C)
thi s material becomes embri ttl ed and exTeri ences decreases i n tensi l e and
i mpact strengths that approach 60 and 75 percent, respectively, at a dose
of 5 x l o7 rads (C). An electron fluence of 5. 8 x 10l 6 e/cm2 (E = 1.0 MeV)
at 60 C resul ted i n decreases of 87 to 96 percent in utlimate elongation and
tensile strength. (11) This electron fluence also produced a decrease i n
hardness of 25 percent which is i n agreement wi th resul ts from other
studies where polypropylene became increasingly softer and more flexible
with doses of between 2.6 x l o8 and 8.7 x l o8 rads (C) when lower doses
caused embri ttl ement of the materi al . ( 12) The suggested mechanism for
this reversal in the effect of radiation is that at higher doses some of the
polypropylene chains have become low in molecular weight from chain
cleavage and this lower molecular weight material pl asti ci zed the re-
mander of the polymer.
The permanent degradation or change in electrical properties that
occurs when polypropylene is irradiated to the above doses is of l i ttl e or
no practical significance. The dielectric constant decreases slightly and
the i nsul ati on resi stance decreases l ess than an order of magnitude.
Measurements of a-c l oss such as power factor and dissipation factor at
1 KHz to 1 MHz have vari ed from no observable change to an increase
from between 0. 0005 and 0.0008 to between 0. 002 and 0.003. No informa-
tion concerning temporary changes that might occur during irradiation is
available.
Electron-irradiation-induced dielectric breakdown of polypropylene
appears to be sensitive to the electron f l ux to which it is exposed for a
specific fluence. (7) The maxi mum number of breakdowns observed at
room temperature wi th a f l ux of 1 x 10l 1 e/(cm2. s) for a total fluence of
5 x 1013 e/cm2 (Ek =30 keV) was 40, while that for a flux of 1 x 1010
e/cm2 was 8 for a similar fluence and temperature.
Polvur ethane
Polyurethane has shown good stability in both physical and electri-
cal properties when exposed to a radiation environment. I rradiation to
doses up to 7 x 108 rads (C) has caused very little change in flexure
strength or modulus. ( 13) A weight loss of 1 percent (a physical change)
22
between this dose and 1. 75 x l o8 rads (C) indicates the possibility of
approaching a damage threshold. No information is available above this
dose, with exception of the resul ts from an el ectron fl uence of 5. 8 x' 1016
e/cm2 (E = 1. 0 MeV) at 60 C.( ') Serious deterioration of physical prop-
erti es occurred from thi s radi ati on exposure and i ncl uded a 67 and 176 per-
cent i ncrease i n hardness and sti ffness i n fl exure, respecti vel y. A 59 per-
cent decrease i n tensi l e strength and a 99 percent decrease i n ul ti mate
elongation were also noted following irradiation to this electron fluence.
I nformation concerning the effect of radi ati on on the el ectri cal prop-
erti es of polyurethane is l i mi ted to resul ts from two radiation studies:
the electron irradiation mentioned above and a reactor exposure to a neu-
tron fluence of 1. 2 x 1014 n/cm2 (E >0. 5 MeV) and gamma dose of
1.4 x l o6 rads (C) at 16 C to 29 C. (14) I nsignificant permanent changes in
the insulating properties, volume resistivity, or insulation resistance of
l ess than one order of magnitude were observed as a resul t of these two
studies. The dissipation factor at 1 MHz was essentially unchanged while
that at 1 KHz increased approximately 30 percent in the reactor study
(-6. 0 to 7.4) and doubled in the electron irradiation study (0. 02 to 0.04).
The onl y di sagreement i n the resul ts of the two studies was the dielectric
constant which decreased 6-1/4 percent at 1 KHz from the el ectron i rradi a-
tion and increased approximately 16 percent from the reactor exposure.
Polyvinylidene Fluoride
Polyvinylidene fluoride (Kynar 400) has shown higher radiation toler-
ance than other fluorocarbons such as Teflon and Kel-F. I t has demon-
strated an ability to withstand irradiation to a dose of l o7 rads (C) i n air
or vacuum with no indication of degradation in physical properties except
color change. An order-of-magni tude i ncrease i n the radiation dose to 108
rads (C) and above causes embri ttl ement and l oss of flexibility and tensile
strength. Low temperature, however, increases the radiation tolerance of
polyvinylidene fluoride in that doses of this magnitude, l o8 rads (C), at
cryogeni c temperatures do not reach damage threshol d.
Changes in the electrical properties of polyvinylidene fluoride in-
cl ude decreases of between two and three orders of magnitude in volume
resistivity during and after irradiation to doses up to 2. 1 x l o7 and 6. 6 x
10 7 rads (C) i n an air and a vacuum-cryotemperature envi ronment, re-
spectively. ( 3) A decrease of approxi matel y fi ve orders of magnitude
occurred with a dose of 2. 1 x 108 rads (C) i n the air atmosphere. Di ssi pa-
ti on factor i ncreased l ess than one decade, and the di el ectri c constant was
essentially unaffected by the i rradi ati on.
23
Polvimide
Polyimide (Kapton) has shown little or no change in either its physical
or el ectri cal properti es to gamma doses (Co 60) of up to 109 rads (C). (15)
Tensi l e strength remai ned essenti al l y constant when exposed to a total dose
of this magnitude but decreased to approximately one-half its initial value
between 1 x 109 and 6 x 109 rads (C). The el ectri cal resi sti vi ty remai ned
at 1 x 1019 ohm-cm or above and only decreased to 3 x 10l 8 ohm-cm at a
total dose of 1 x 101o rads ( C) , Thi s same dose l eft the di el ectri c constant
essentially unchanged and decreased the breakdown voltage to approximately
75 percent of its initial value.
Dielectric breakdown induced in polyimide (Kapton) by el ectron i rra-
diation has been shown to be sensitive to both flux and temperature. (7) A
total of eight breakdowns on two sampl es were observed at room tempera-
ture for a f l ux of 1011 e/(cm2. s) and a fluence of 1013 e/cm2 (Ek =30 keV) -
a factor of four greater than the number observed at a similar fluence and
a flux of 101o e/(cm2. s). The effect of temperature on the number of di-
electric breakdowns is illustrated by the resul ts at liquid nitrogen and room
temperature. Fifteen and 35 breakdowns were observed, respectively, for
the two specimens irradiated to a fluence of 2 x iO13 e/cm2 (Ek =30 keV)
at room temperature whi l e 75 and 120 breakdowns occurred with the speci-
mens i rradi ated to a similar fluence at the temperature of liquid nitrogen.
No dielectric breakdowns were observed in polyimide (Kapton) that
was subjected to proton irradiation that included fluences to 5 x 1014
p/cm2 with a flux range of 109 to 2 x 10l 1 p/(cm2. s ) . ( ~ ) The energy range
of the protons was between 0.4 and 2. 5 MeV and the test temperatures
were -134 C and 27 C.
Polvimidazopvrrolone (Pvrrone)
Pol yi mi dazopyrrol one pol ymers (Pyrrone) have been subj ected to
various radiation environments including electron, proton, and gamma
(Co 60). Exposure to high doses of electron radiation, 1 x l ol o rads (C)
( E = 1 MeV) and 5 x 109 rads (C) (E =2 MeV) resulted in insignificant
degradation in the mechanical and electrical properties of Pyrrone.( 16, 17)
The yield strength of specimens irradiated to a fluence of 1 x 1O1O rads ( C)
was approximately 70 percent greater than that of noni rradi ated Pyrrone,
the tensile strength was essentially unchanged, and elongation was reduced
by two-thirds. Little or no difference was noted in the dielectric constant
24
and dissipation factors of nonirradiated specimens and those exposed to a
fluence of 5 x 109 e/cm2 (E = 2 MeV). However, this fluence caused an
i ncrease i n dark current by a factor of 5 i n Pyrrone made up of benzophe-
none tetracarboxylic acid dianhydride (BTDA) and diaminobenzidine (DAB)
while the dark current of a Pyrrone composed of pyromellitic dianhydride
(PMDA) and diaminobenzidine (DAB) increased approximately two orders
of magnitude.
Dielectric breakdown induced in Pyrrone by el ectron i rradi ati on to a
given fluence is sensitive to both flux and temperature; the number of break-
downs that occur tends to increase with flux and decrease with tempera-
ture. (7) An order of magni tude i ncrease i n el ectron fl ux, from 109
e/(cm2. s) to 101o e/(cm2. s ) , resulted in twice as many breakdowns for
similar fluences of e/crn2 (Ek =30 keV) at room temperature. Al so,
the number of breakdowns recorded at liquid nitrogen temperature was
more than twi ce that observed at room temperature for a flux of either
1010 or 1011 e/(cm2. s ) .
No dielectric breakdowns occurred in Pyrrone specimens irradiated
to a proton fluence of iO13 p/cm2 (Ek = 1.0 and 1. 5 MeV) at temperatures
of -134 C and 27 C. ( 8 ) Dose rates were 109 and 1O1O p/(cm2. s ) with speci-
mens subjzcted to each rate for the total fluence.
The exposure of Pyrrone, both PMDA-DAB and BTDA-DAB, to a
g a ma dose rate of 10 to 1000 rads/mi n ( Co 60) produced current densi ti es
of 1 x to 6 x ampere cm-2 in the PMDA-DAB and 2 x to
2 x 10-11 ampere cm-2 in PTDA-DAB. (17) The currents are attributed to
the motion of free radi ati on-i nduced charge carri ers mi grati ng i n the
el ectri c fi el d.
EDOXV Laminates
Epoxy-glass laminates have shown little or no degradation in mechani-
cal and/or el ectri cal properti es from reactor i rradi ati on to 2 x 1013 n/crn2
( E >0. 1 MeV) and 1 x l o8 rads ( C) or cobalt-60 gamma irradiation to
1 x 107 rads (C) . ( 3 7 15) Variations in breakdown voltage have been observed
at gamma doses below this level, however, with decreases of 15 to 30 per-
cent from prei rradi ati on val ues at 1 x 107 rads (C) and 50 to 70 percent at
1 x 109 rads (C). Other el ectri cal properti es such as resi sti vi ty, di el ectri c
constant, and dissipation factor are not degraded significantly at this total
dose.
25
The tensi l e strength of epoxy-glass laminates remains unchanged to a
gamma dose of 1 x l o7 rads (C) but decreases to l ess than 20 percent of the
initial value at 1 x 109 rads (C). Compressive strength does not change
significantly. A total gamma dose of 101o rads (C) wi l l cause an epoxy-
gl ass l ami nate to become bri ttl e and weak or to l ose most of the resi n
binder.
Miscellaneous Organics
Radiation-effects information is available on organic bulk, sheet,
and/or film materi al s other than those di scussed on the precedi ng pages.
The information, however, is limited to results from only one radiation-
effects test of each materi al . Therefore, these resul ts are l i mi ted to the
tabular presentations of Tabl es 2 and 3 . Tabl e 2 is a listing of materi al s
that were s o seri ousl y degraded by the indicated radiation dose that their
physical and electrical properties could not be tested or measured. This
is not to imply that these materials are all unsatisfactory in some radia-
tion environments; it indicates only that they did not survive the indicated
electron fluence. The listing in Table 3 consi sts of those materi al s that
survived exposure to the radiation environment and includes some of the
particulars concerning changes observed in their physical and electrical
properti es.
Cerami cs
Cerami c i nsul ati ng materi al s, such as si l i ca, Steati te, Al si mag,
Alox, and Pyroceram, in sheet and other basic physical configurations
have shown virtually no change in a-c properties (dissipation factors and
dielectric constant) with X-ray irradiation to doses up to l o7 rads (C).
Si mi l ar resul ts have al so been observed wi th reactor i rradi ati on to doses
as hi gh as 1017 n/cm2 (E >0. 1 MeV) and l o9 rads (C). Permanent de-
creases of between one and tow orders of magnitude will occur in the
volume and surface resistivity of cerami c i nsul ati ng materi al s at these
doses. However, Steatite in combination with phosphate-bonded inorganic
cements and chrome-plated copper conductors has shown little or no
change in conductor-to-ground insulation resistance with neutron fluences
of 2. 2 x 1019 n/cm2 (E >0. 1 MeV) and 9. 0 x 1010 rads (C) gamma. (20)
Also, Lucalox, a high-purity alumina, did not experience a change in
resistivity when subjected to a neutron fluence of 1.6 x 1020 n/cm2
(E >MeV) with temperatures of 800 to 1000 C. (‘l)
26
TABLE 2. MISCELLANEOUS ORGANIC BULK, SHEET, AND/OR FILM MATERIALS WHICH
LIMITED INFORMATION INDICATE AS UNSATISFACTORY AT THE RADIATION
EXPOSURE I NDI CATEDW)
~ .. ~~~ " . - .~
" - "_ - - .. . ~ ~~ - - -
.~-
Total Electron Fluence at 60 C
Material I dentification (E =1.0 MeV)
" - ~ .. -. " - . ~
Acetal resin 1.22 x e/cm2 (3.8 x 108 rads)
Acrylic plastic, molding grade (rubber modified) 5.80 x 1016 e/cm2 (1.8 x l o9 rads)
Allyl carbonate plastic, cast 4.10 x 1016 e/cm2 ( 1. 3 x l o9 rads)
Cellulose acetate 5.80 x 1016 e/cm2 (1.8 x l o9 rads)
Cellulose butyrate 4.10 x 10l 6 e/cm2 (1.3 x l o9 rads)
Cellulose propionate 4.10 x e/cm2 (1.3 x 109 rads)
Chlorinated polyether
Polycarbonate
2.90 x 1016 e/cm2 (9 x l o8 rads)
5.80 x 1016 e/cm2 (1.8 x l o9 rads)
Polyfluoroethylenepropylene, Teflon FEP (copolymer) 3.67 x 1OI6 e/cm2 (1.1 x l o9 rads)
Polymethyl methacrylate, cast 1.22 x e/cm2 (3.8 x 108 rads)
Polymethyl methacrylate, molding grade 4.10 x 1OI6 e/cm2 (1. 3 x 109 rads)
Styrene acrylic copolymer 2.90 x 1016 e/cm2 (9 x 108 rads)
Polyvinyl chloride, DOP plasticized 3.67 x 1016 e/cm2 (1.1 x l o9 rads)
Polyvinyl chloride, rigid 4.10 x 1016 e/cm2 (1.3 x 109 rads)
. _-
"~ -. " - " - ~-
-~ "~ - _ _ _
27
TABLE 3. FL4DJATION.EFFECTS ON MISCELLANEOUS ORGANIC BULK, SHEET, AND/OR FILM
MATERIALS WHERE ONLY LIMITED INFORMATION IS AVAILABLE
~~ - ~~
~ ~ _ _ -" "
- - -. . -. , - " ""
Material I dentification Total I ntegrated Exposure Remarks
Acrylonitrile-butadiene- 5.8 x 1016 e/cm2 (E =1.0 MeV) Hardness increased 13 percent; flexibility, ten-
styrene
Styrene-acrylonitrile
copolymer
Styrene-butadiene
(high-impact styrene)
Styrene-divinylbenzene
Polyvinyl chloride
acetate
Polyvinylfluoride
Polyester/glass
laminate
91 -LD Resin/l81 -Volan
A laminates (copper
clad)
Silicone/glass
laminate
at 60 C sile strength, and ultimate elongation decreased
49, 58, and 93 percent, respectively. Dielec-
tric constant increased <1. 5 percent and DF
decreased slightly. IR increased. (11)
5.8 x 1016 e/cm2 (E =1.0 MeV) Tensile strength and ultimate elongation de-
at 60 C creased 34 and 47 percent, respectively.
Hardness was unchanged and flexibility in-
creased 5 percent. Dielectric constant in-
creased 4 to 6 percent. DF increased to
0.01 at 1 KHz and 0.40 at 1 MHz. I Rde-
creased one decade. (11)
5.8 x 1016 e/cm2 (E =1.0 MeVj Flexibility and ultimate elongation decreased
at 60 C more than 90 percent and tensile strength de-
creased 35 percent. Hardness increased.
Dielectric constant ipcreased slightly while
DF increased -50 percent. IR increased. (11)
5.8 x 1016 e/cm2 (E =1.0 MeV) Changes in physical properties were of no
at 60 C practical significance. (11)
5.8 x 1016 e/cm2 (E =1.0 MeV) Insignificant changes in hardness, tensile
at 60 C strength, dielectric constant, and dissipation
factor. Insulation resistance decrease two
decades. Flexibility increased 30 percent. (11)
5.8 x 1016 e/cm2 (E =1.0 MeV) Serious degradation prevented measurement of
at 60 C physical degradation. Dielectric constant de-
creased 7 percent and dissipation factor in-
creased one decade. Insulation resistance did
not change. (11)
Volume and surface resistivity decreased three
decades. Dissipation factor increased from
0.003 and 0.006 to 0.019 and 0.010. No
change in dielectric constant. (6)
2.5 x l o6 rads (C)
2.5 x 1015 n/cm2 (E >2.9 MeV) No degradation in physical properties.(l8)
at 55 C
5.0 x 1013 n/cm2 (E >2.9 MeV) 49 percent loss in flexure strength, slight change
1.0 x 108 rads (C)
at 200 C in color, thickness, and weight. (19)
A change or darkeni ng i n col or i s the only observable change in the
cerami cs' physi cal properti es at the above doses. However, investigations
of physical damage to doses of 1019 - 1020 n/crn2 ( E >0. 1 MeV) have
shown dimensional and density changes. The latter varying from 1 to 17
percent depending upon the material tested.
Mica
Mica is the only inorganic insulating material other than ceramics
on whi ch there are radi ati on effects data for sheet or other basi c physi cal
forms of the material. These data include the evaluation of physical
damage in a reactor environment for total doses up to 5 x 1013 n/cm2
( E >2. 9 MeV) and 1 x l o8 rads at 200 C and of changes in both physical
and electrical properties in a cobalt-60 gamma environment to 1 x 1010
rads (C).( 15, l 9) No significant effect has been observed other than color
darkening for most forms of mica including flexible mica paper and flake
and rigid-mica mat. A rigid, inorganic, bonded amber mica, however,
experienced a 29 percent decrease i n fl exure strength at the above reactor
environment.
A glass -bonded mica experienced no change in compressive strength
to a total dose of 1 x 1O1O rads (C) gamma: the tensile strength decreased
approximately 50 percent with no decrease for doses up to 1 x l o7
rads (C). The resi sti vi ty was unchanged and the di el ectri c constant i n-
creased l ess than 10 percent for the same total dose of 1 x 1010 rads (C)
(Co 60). Variations in voltage breakdown ranged from 95 to 120 percent
of the initial value to a gamma dose of 1 x 109 rads (C) and decreased to
70 percent at 1 x 1O1O rads (C).
RADIATION EFFECTS ON SPECI FI C WIRE
AND CABLE INSULATION
Both organic and inorganic wire insulations have been tested and
evaluated as to their radiation resistance. A seri ous deteri orati on of
physi cal properti es as a resul t of irradiation has occurred with some
organi cs, and others, demonstrati ng a high level of radi ati on tol erance,
have survived doses of up to 1 x l o8 rads (C). Special cables and wires
insulated with inorganic materials have shown similar radi ati on resi stance
29
I ..
to doses of 8.8 x 109 and 8.8 x l ol l rads (C). Changes in the electrical
properti es of wi re havi ng ei ther organi c or i norgani c i nsul ati on are gener-
ally of little practical significance and include both temporary and perma-
nent effects. The insulation resistance may decrease several orders of
magnitude during irradiation and then completely recover or recover to
within one order of magnitude of the initial value when the radiation ex-
posure is termi nated. Permanent decreases i n di el ectri c strength have
also been observed following exposure to radiation as have i ncreases i n
dissipation factor and the attenuation of coaxial cables. Details concerning
these and other effects of radi ati on are di scussed i n the fol l owi ng para-
graphs as they pertai n to speci fi c wi re and cabl e i nsul ati on.
Pol ytetrafl uoroethyl ene (PTFE)
Polytetrafluorethylene (Teflon) wire insulation has shown severe
degradati on i n physi cal properti es as a resul t of exposure to a radiation
environment. The extent of the damage that occurs is sensitive to total
dose and vari es from a noticeable decrease in wire flexibility to the com-
plete disintegration of the materi al .
The lowest total dose at which information on changes in physical
charscteri sti cs is available is 10 rads (C) with a 5 psia oxygen atmosphere
and ambient temperature of 90 C as other enivronmental conditions.(22, 2 3 )
A decrease in flexibility was noted for a wire specimen having TFE Teflon
insulation with an ML (polyimide resin) coating after exposure to these
conditions. Wire insulated with the copolymer Teflon FEP and having this
same outer coating, however, showed no loss in flexibility, nor did a
Type-E TFE-insulated wire per MI L-W-1687D. Similar results also
occurred for a dose of 6 x 10 rads (C) with a vacuum of l oe6 torr and
a temperature of 150 C. These resul ts i ndi cate two possi bi l i ti es: the TFE
Teflon (polytetrafluoroethylene) insulated wire with the ML coating has a
lower radiation tolerance and/or the l o3 to 6 x l o4 rads (C) total dose is
the threshol d area for damage to polytetrafluoroethylene-insulated wire and
damage to the other wire insulations was not yet apparent.
3
4
The change in the physical properties of polytetrafluoroethylene-
insulated wire and cable continues with increasing dose, and complete de-
teri orati on has been reported after total exposures of l o7 and l o8 rads (C).
The damage is such that the inner core of a Teflon-insulated coaxial cable
wi l l appear sound, but will powder and crumble when stressed mechanically
through handling or testing. Failure of this type in a coaxial cable could be
expected to include shorting between conductors and/or between conductors
30
and the outer sheath or shield when radiation environments reach these dose
levels. This should be of special concern in applications that include vibra-
ti on or other mechani cal stresses as a part of the intended environment.
The i rradi ati on of polytetrafluoroethylene-insulated wi re al so re-
sul ts i n the degradation of electrical properties. I nsulation resistance
measurements performed before and after i rradi ati on have shown l i ttl e or
no significant change in this parameter. Breakdown voltage has decreased
as much as 50 percent .between twisted pairs of wire having initial break-
down at voltages as high as 15.8 to 28. 2 kV.(22, 23) The posttest range
was 9. 1 to 14. 2 Kv. Several el ectri cal characteri sti cs of coaxial cables
have shown the effects of degradation. The attenuation of a 10-foot length
of RG-225/U at 400 MHz i ncreased 0 . 20 db while the change for a similar
sampl e of RG 142/U was so great it could not be measured after a total ex-
posure of 3 x 10l 6 n/cm2 (E >0 . 1 MeV) and 2.3 x l o8 rads (C). (24) The
RG 142/U cable also experienced larger increases in other measured para-
meters including VS WR (1. 19: 1 to 2. 4: l ), apparent change in electrical
length (0. 224 wavelength), and phase shift (between 0 and t 15 degrees).
Polyethylene
The physi cal and el ectri cal properti es of wire and cable that in-
corporate polyethylene as the insulating media have shown little or no deg-
radation for total doses up to 107 and l o8 rads (C) at temperatures of from
15 C to 100 C. Thi s i s a comparatively high radiation tolerance for plastic
insulated wire. Some degradation is apparent in the physical properties
after a dose of 9. 6 x l o7 rads (C) with the darkening of the polyethylene,
but it still remai ns resi l i ent wi th no indication of sti ffness. I t i s esti -
mated that threshol d damage occurs at approxi matel y 4.4 x l o8 rads (C).
Loss of flexibility has been observed, however, after cable insulated
with polyethylene and having outer jackets of ei ther Estane or Al athon
received a total dose of 8. 8 x l o8 rads (C). (25) The polyethylene of both
cables was brown and brittle and broken on the wire. The Estane jacket
on the one cable was very pliable while the Alathon jacket on the other
was very brittle. This embrittlement of the outer jacket material of a
cable can offer a problem, particularly with a coaxi al or shi el ded type, i n
that some materi al s used for this purpose become brittle at lower doses
than the polyethylene. Therefore, the outer jacket can be the limiting
factor in the application of a cable rather than the insulating material
used on the wire the jacket encloses.
31
The el ectri cal properti es of polyethylene-insulated wire and cable
have shown some degradation during and following exposure to a radiation
environment. I nsulation resistance is both rate and dose sensi ti ve wi th
changes of one to three orders of magnitude observed during exposure. Re-
covery is essentially complete following the termination of the i rradi ati on.
The characteri sti c i mpedance of coaxial cables has shown some variation
as a resul t of radiation exposure but the extent of these variations is of
little significance (0. 5 to -10 percent). Li mi ted data on other coaxi al -
cabl e parameters i ndi cate that l i ttl e or no change occurs in attenuation,
VSWR, or apparent el ectri cal l ength when these cabl es are i rradi ated.
An induced current is al so an el ectri cal characteri sti c that has been
observed i n el ectri cal cabl e of various insulations. The only steady-
state-radiation data concerning this effect are limited to polyethylene-
insulated coaxial cable.(26) Currents of the order of 10-8 amperes were
observed duri ng the cabl e's exposure to the radi ati on whi ch i ncl uded
1. 2 x 10l 2 n/(cm2.s) (E >2. 9 MeV) and 6. 6 x l o7 rads (C) r / hr gama
at a reactor power of 1 megawatt.
Silicone Rubber
Silicone rubber wire insulation does not experience noticeable de-
gradiation of its physical properties at doses up to 8. 8 x l o5 rads (C). A
slight change or lightening in color with a barely perceptible loss in
resi l i ence or fl exi bi l i ty has been observed i n fl at-ri bbon mul ti conductor
wire insulated with this material after an exposure of 8. 8 x 10 6
rads ( C) . ( 27) Seri ous deteri orati on of the wi re's mechani cal qual i ti es
occurs with a total dose of 8. 8 x l o7 rads (C) and above. There i s a
definite loss in flexibility, and the silicone rubber insulation will crack
and/or crumble when the wire is stressed mechani cal l y.
The i nsul ati on resi stance of wire insulated with silicon rubber
decreases one or two orders of magnitude during irradiation with recovery
to within one order of magnitude when the exposure is termi nated. If the
environmental conditions also include moisture and/or elevated tempera-
ture the combined effect can decrease the insulation resistance even
further. The breakdown voltage of silicon wire insulation has shown some
variation between - and posti rradi ati on measurements after doses of
1 x l o3 and 4 x 10 rads (C). ( 2 2 , 23) These changes in breakdown voltage,
however, i ncl ude both i ncreases and decreases and are of little significance.
r e
32
Polyimide
Pol yi mi de resi n film, ML, wire insulation has shown no indication
of deteri orati on i n physi cal or el ectri cal properti es up to a dose of 1 . 5 x
l o8 rads (C) and 4 . 4 x 1017 n/cm2 (E >0. 1 MeV). Flexibility and strip-
pi ng characteri sti cs are unaffected wi th no vi si bl e di fference between wi re
that has been irradiated and that which has not. Measurements of el ectri -
cal parameters such as insulation resistance, capacitance, and dissipation
factor have shown no significant difference between pre- and postirradia-
tion values. Wires with a combination of gl ass brai d and pol yi mi de resi n
film insulation exhibited a breakdown voltage of approximately 1000 wi res
before and after receiving the total exposure indicated above. (27)
The absence of degradation at doses up to 1. 5 x l o8 rads (C) demon-
strates a high level of radi ati on resi stance for thi s wi re i nsul ati on wi th a
possibility of satisfactory performance at even higher doses.
I rradiation-Modified Polvolefin
I rradiation-modified polyolefin+-insulated wire has experienced no
serious degradation in physical or electrical properties when irradiated to
a total dose of 5 x l o8 rads (C). The insulation may change somewhat in
color, but it remains flexible and has some degree of compressibility.
Wire specimens insulated with this polyolefin have successfully met stan-
dard military bend tests using a 10-D Mandrel following an electron dose
of 5 x 108 rads (C) at 23 C. (28) A test to determine the corrosiveness of
any gas evolved from the polyolefin on copper- and aluminum-surface mir-
rors was al so i ncl uded i n thi s same study. No corrosive effect was
observed.
I nformation on the effect of radiation on the electrical properties of
irradiation-modified polyolefin-insulated wire is limited to comparisons of
pre- and posttest measurements. However, as a precautionary procedure,
the designer should allow for a decrease of one to three orders of magni-
tude in insulation resistance during irradiation. No significant changes of a
permanent nature occurred in the only study that included measurements of
insulation resistance and breakdown voltage on irradiation-modified
polyolefin-insulated wire.(22, 23) The two environmental combinations
* Unidentified as to whether polyethylene or polypropylene.
33
used i n thi s study were (1) an X-ray dose of 6 x l o4 rads (C) with a vacuum
of torr and temperature of 150 C and ( 2) an X-ray dose of 1 x 10
rads (C) wi th a 5-psi oxygen atmosphere and a temperature of 90 C. The
stability of the insulating qualities of thi s materi al when i rradi ated was al so
demonstrated in another study when wire insulated with this material com-
pleted a wet di el ectri c-strength test of 2. 5 kV after a radiation dose of 5 x
l o8 rads (C). ( 2 8 )
3
Coaxial cable insulated with irradiation-modified polyolefin (poly-
ethylene) experienced an increase in attenuation of 0. 30 and 0. 40 db in a
cable length of 10 feet when exposed to a total dose of 2. 9 x l o8 rads (C)
and 3.0 x 10l 6 n/cm-2 (E >0. 1 MeV).(24) At the same ti me there was
little change in VSWR and the apparent change in electrical length was
0. 08 and 0. 106 wavelength.
I rradiation-modified polyolefin-insulated wire and cable has demon-
strated a high tolerance for radiation when compared to that of other
organic insulations and should be suitable for many applications that in-.
clude radiation as an environmental condition.
Miscellaneous Organics
Radiation-effects information is available on five organic wire
insulations other than those discussed above. This information, however,
is limited to results from only one radiation-effects test of each. There-
fore, with one exception, this radiation effects information is confined to
the tabular presentation of Table 4.
The single exception is the resul ts of a study of el ectron i rradi ati on
of polyethylene terephthalate-insulated ribbon wire. ( 2 9 ) The purpose of
the study was to determine the effects of shunt capacitance on temporary
effects of the electron irradiation. Results of this study indicate that a
voltage pulse observed during irradiation at 3 . 1 x l ol o e/(cm2. s) (E >60
keV) at room temperature vari ed i nversel y wi th the total capaci tance i n
the system. The average pulse height decreased from 5. 1 volts at 1. 1 x
resi stance from 3 kohms to 300 kohms increased the maximum pulse height
to 35 volts and 0. 2 volt, respectively, for the minimum and maximum
capacitance values mentioned above. After irradiation to a total dose of
1. 1 x 1014 e/cm2 (E >60 keV), el ectron-di scharge patterns (Li chtenberg
fi gures) were found in the insulation. Rough calculations indicated that
farad to l ess than 0. 01 volt at 1. 0 x farad. I ncreasing the load
34
I
the power density along the discharge path is adequate to produce the
physical damage observed. The actual pulse height of the di scharges were
possibly as high as 11,000 volts, and power densities of 3 x 101o watts/
cm2 were i ndi cated i f a di scharge ti me of 0.01 mi crosecond is acceptable.
The data support a postulate that a portion of the incident electrons are
stopped and stored within the dielectric. This charge increases with
i rradi ati on, and at some point in time it is rel eased and transported to the
conductor and is observed as a voltage pulse. A surface i rregul ari ty or
pin pri ck i ni ti ates the release mechanism. Such pulses could be damaging
to sensitive electronic circuits.
TABLE 4. RADIATION EFFECTS ON MISCELLANEOUS ORGAMC WIRE INSULATIONS
~ ___ -
- ~~ - - ~
-
"
Total Integrated
Material I dentification Exposure(a)
". ~ _, - ~~ ~ - _
Alkanex 4.6 x l o7 rads (C), Co-60
Silicon-alkyd 4.6 x lo7 rads (C), Co-60
Polypropylene 7.1 x lo7 rads (C), Co-60
XE-9003A 4.08 x n/cm2
(E >0.5 MeV)
Gamma dose unknown
SE-975 4.08 x 1016 n/c&
(E >0.5 MeV)
Gamma dose unknown
Remarks
Satisfactory performance, 150 C (encapsulated in rigid
epoxy and semirigid silicone). (30)
Satisfactory performance, 150 C (encapsulated in rigid
epoxy and semirigid silicone). (30)
Unsatisfactory, becomes brittle and crumbles (15 C,
55 C, and 100 C).(31)
Ambient temperature. Unsatisfactory, insulation
too brittle and cracked for postirradiation
testing. (32)
Ambient temperature. Unsatisfactory, insulation
cracked and too brittle for postirradiation
testing. (32)
"
~_ _ _ I _ - ~ -~ "-
_ c _ - ~
(a) These exposures are not to be interpreted as indicating superiority in radiation tolerance of any material.
They are the limits to which the wires or cables have been subjected and are not damage thresholds.
Cerami c
Magnet wire, insulated with ceramic enamel (Ceramicite and Ceraml-
temp), has demonstrated a high tolerance for radiation for total doses up
to 1. 5 x 108 rads (C) and 4.4 x 1017 n/cm2 (E >0. 1 MeV) at room tempera-
ture. A tendency to powder during stripping tests is the only indication of
deteri orati on of physical properties. The stability of el ectri cal properti es
has also been satisfactory with some loss in dielectric strength and insula-
tion resistance being observed. A decrease of approximately 16 percent
occurred in breakdown voltage or dielectric strength between pre- and
posti rradi ati on measurements i n one study.(27) Resul ts of other studies
3 5
have shown a definite difference between the dielectric strength of i rradi a-
ted and-control speci mens. These di fferences coul d be termed i nsi gni fi -
cant with one exception where the results of a study shows a breakdown
voltage of 60 to 160 volts for irradiated specimens, and 140 to 500 volts
for control speci mens. ( l 9) Considerable difficulty due to the hygroscopic
property of the ceramic insulation was encountered with these measure-
ments and may have contri buted to some of the difference. Changes in the
i nsul ati on resi stance as a resul t of exposure to a radiation environment
have been insignificant.
Miscellaneous I norganics
Radiation-effects information on seven inorganic wire insulations
other than the cerami c di scussed above i s l i mi ted to si ngl e eval uati ons of
the radi ati on resi stance of each wire or cable. Of the seven wires and
cabl es tested, four are standard products and three are speci al or non-
producti on i tems. Because of the limited information available, informa-
tion concerning the radiation resistance of these wi res and cabl es are
presented i n the tabul ar format of Table 5.
RADIATION EFFECTS ON ENCAPSULATING COMPOUNDS
Encapsulating compounds that have been evaluated as to their radi-
ation resistance include epoxy resins, silicone resins, polyurethane, and
aninorganic, calcium aluminate. These materials, generally experienced
insignificant changes in their physical and electrical characteristics from
the radiation exposures to which they were subjected. An exceptions are
discussed in the following paragraphs along with details concerning the
effects experienced by all materi al s tested and the radi ati on envi ronment
to which they were exposed.
19
of
Si l i cone resi n encapsul ati ng materi al s, such as RTV-501 and Syl gard
2 and 183, have not been seriously degraded at radiation exposure doses
2 x 1013 to 1. 5 x 1015 n/cm2 (E >0. 1 MeV) and 1.8 x l o6 to 8.8 x 108
rads (C). Degradati on of the physical properties has been limited to a
slight but insignificant weight loss of less than 1 per cent. I nsul ati on re-
si stance dat.a show permanent decreases of 40 to 50 percent with the
mi ni mum resi stance of approximately 1 x 10l 2 ohms after a total exposure
36
I
TABLE 5. RADIATION EFFECTS ON MISCELLANEOUS INORGANIC WIRE INSULATION
Material I dentification
~. ~~~
Silica-glass (39001 -1 -16)
double shielded coax
Quartz (39Q02-3-26)
multiconductor coax
Asbestos and fiber (Phosroc
111, RSS -5 -203) lead
wire
Mica paper-fiberglass
(Mica-Temp, RSS-
5 -304)
S-994 Fiberglass
Ceramic Kaowool and
Refrasil (power cable)
Magnesium oxide
(Rhodium conductor
and platinum sheating)
Total I ntegrated
Exposure(a) Remarks
1.5 x 108 rads (C)
4.4 x 107 n/cm2
(E >0.1 MeV)
1.5 x 108 rads (C)
4.4 x 1017 n/cm2
(E >0.1 MeV)
9.8 x l o7 rads (C)
4.1 x 1013 n/cm2
(E >2.9 MeV)
1.1 x 108 rads (C)
4.5 x 1013 n/cm2
(E >2.9 MeV)
6.5 x 1O1O rads (C)
I. 5 x 1019 n/cm2
(E >0.1 MeV)
Room temperature. No visible signs of degradation. No
electrical tests.(27)
Room temperature. No visible signs of degradation. No
el ectri cal tests. (27)
200 C. No breaking, cracking, or spalling was evident
when subjected to a bend test. Weight loss <0.2 per-
cent. No el ectri cal tests. Slightly darker in color.(lg)
200 C. No breaking, cracking, or spalling was evident
when subjected to a bend test. Weight loss ~0. 15 per-
cent. Slightly darker in color. (19)
Environment also included a temperature of 1200 F. In
Duration of test 2300 hours. The in-pile insulation
resistance was within 1/2 decade of nonnuclear results
in almost all cases. Temperature was the over-
whelming factor in determining level of insulation
resistance (-107 ohms). (33934)
8.8 x lo9-8. 8 x 1010 Cable met 1200 volt rms dielectric breakdown require-
rads (C) (Estimated) ment. Also, withstood 2000 volt rms between con-
3 x 1019 n/cm2 ductor and ground for 5 minutes. (35)
(Energy unknown)
5 x 107 rads (C) Met dielectric strength requirement of 1200 volts rms
1.0 x 1015 n/cm2 for 30 seconds. Insulation resistance decreased as
(fission) much as four orders of magnitude between pre- and
postirradiation measurements. (36)
- "
(a) These exposures are not to be interpreted as indicating superiority in radiation tolerance of any material.
They are the limits to which the wires or cables have been subjected and are not damage thresholds.
37
of 1. 5 X n/cm2 (E >0.1 MeV) and 1.8 x l o6 rads (C) gamma. I n
the onl y study where measurements were performed duri ng i rradi ati on, the
i nsul ati on resi stance decreased by something in excess of one order of
magnitude (>2 x 10l 2 ohms to 1 x 10l 1 ohms) when the reactor was at its
maximurn power level of 30 kW. (37) An esti mate of the neutron and gamma
rate at this level is 1. 5 x 10l 1 n/cm2. s) (E >0. 1 MeV) and 6 x l o4 rads
(C)/hour, respecti vel y.
Limited information on a polyurethane foam encapsulant indicates
that thi s materi al may be more sensi ti ve to radi ati on exposure than other
encapsul ati ng materi al s. Decreases i n i nsul ati on resi stance have
approached three orders of magnitude during exposure to approximately
1. 5 x 10l 1 n/cm2.s) (E >0. 1 MeV) and 6 x 104 rads (C) hour. Ful l
recovery occurred, however, within 3 days after the irradiation was termi-
nated with a total dose of 1. 5 x 1015 n/cm2 (E >0. 1 MeV) and 1.8 x l o6
rads (C) gamma. (38)
Several , but not necessari l y all epoxy resin encapsulants have shown
a radi ati on resi stance that is above average for plastics. Polyfunctional
epoxy resin and polyfunctional epoxy novolac resin with,anhydride or
aromati c ami ne hardeners appear to be the most resi stant. Epoxi es have
withstood neutron and gamma doses up to 1. 1 x 10l 6 n/cm2 (E >0. 5 MeV)
and 1 x l o9 rads (C) from a reactor source without serious deterioration.
Si mi l arl y, el ectron i rradi ati on to a total exposure of 5. 8 x 10l 6 e/cm2
(E = 1.0 MeV) at 60 C and cobalt-60 irradiation to 1 x 108 rads (C) pro-
duced only limited degradation of an epoxy's physical and electrical prop-
erties. Epoxies that have shown a satisfactory radiation tolerance within
the limits to which they were tested are listed in Table 6.
I nformation concerning the degradation of an epoxy encapsulant's
physical properties indicate that a noticeable darkening in color and a
sl i ght l oss i n wei ght occurs when these materi al s are i rradi ated. Other
changes that have also been reported for the radiation doses mentioned
above include increases in hardness ( 2 percent), stiffness in flexure
(4 percent), and tensi l e strength (8 percent), and decreases i n ul ti mate
elongation ( 6 percent). These changes in physical properties should not be
of serious concern in the use of epoxies as encapsulants for electronic
components and equipment. However, gamma doses from a cobalt-60
source i n excess of 10 rads (C) may resul t i n fai l ure i n some appl i cati ons
where the epoxy i s under stress. The ul ti mate tensi l e strength of epoxies
has decreased to between 43 and 24 percent of the initial value at 109
rads (C).(15) Compressi ve strength was essenti al l y unaffected to 1O1O
rads (C).
8
38
TABLE 6. EPOXIES EXHIBITING SATISFACTORY RADIATION
TOLERANCE AT THE EXPOSJRES INDICATED
Epoxy Identification Total Integrated Exposure(a)
.~.. _ _ _ ~_ ~- . ~.
Bisphenol A
Eccobond 182
Epocast 17B
Epon 828
Maraset 622-E
Novalak
Scotchcast 5
Scotchcast 212
Stycast 1095
Stycast 2651 MM
12-007
412"
420 -A
1126A/B
CF-8793
CF-8794
8.8 x l o7 rads (C) gamma
3.6 x n/cm2 (E >0.1 MeV)
1 x 108 rads (C) gamma
2 x n/cm2 (E >0.1 MeV)
8.8 x l o7 rads (C) gamma
4.0 x 1013 n/cm2 (E >0.1 MeV)
4.4 x 106 rads (C) gamma
3.3 x 1015 n/cm2 (E >0.1 MeV)
1 x l o9 rads (C) gamma
1.1 x 1016 n/cm2 (E >0.5 MeV)
8.8 x l o7 rads (C) gamma
4.0 x 1013 n/cm2 (E >0.1 MeV)
1 x l o9 rads (C) gamma
1.1 x n/cm2 (E >0.5 MeV)
1 x 109 rads (C) gamma
1.1 x n/cm2 (E >0.5 MeV)
1 x l o8 rads (C) gamma
2 x 1013 nl cm2 (E >0.1 MeV)
4.4 x 106 rads (C) gamma
3.3 x 1015 n/cm2 (E >0.1 MeV)
1.8 x 106 rads (C) gamma
1.5 x n/cm2 (E >0.1 MeV)
1 x l o9 rads (C) gamma
1.1 x 1016 n/cm2 (E >0.5 MeV)
1 x l o9 rads (C) gamma
1.1 x 1016 n/cm2 (E >0.5 MeV)
1.8 x l o6 rads (C) gamma
1.5 x 1015 n/cm2 (E >0.1 MeV)
9.4 x l o7 rads (C) gamma
3.8 x 1013 n/cm2 (E >0.1 MeV)
1.0 x 108 rads (C) gamma
4.0 x 1013 n/cmf! (E >0.1 MeV)
Unidentified (Mineral filled) 5.8 x 1016 e/cm2 (E =1.0 MeV)
(a) These exposures are not to be interpreted as indicating superiority in
radiation tolerance of any material. They are the limits to which the
materials have been subjected and are not damage thresholds.
39
The el ectri cal properti es of epoxy encapsulants show some variation
i n radi ati on tol erance but are general l y of adequate stability for use in
most el ectroni c ci rcui ts. The i nsul ati on resi stance has decreased by as
much as two orders of magnitude during irradiation with a mi ni mum of
1. 7 x 1010 ohms being reported. Recovery to near initial value normally
occurs within 2 to 4 hours after the irradiation is terminated. Changes in
dielectric constant, capacitance, and dissipation factor are insignificant;
the l atter shows the greatest sensi ti vi ty to radi ati on by increasing approxi-
mately one order of magnitude. Polyfunctional epoxy resin and poly-
functional epoxy novolac resin with anhydride or aromatic amine hardeners
have retained 90 percent of their initial dielectric strength at 1 x l o9
rads ( C).(37) Diglycidylethers of bisphenol A araldite epoxy with an
al i phati c ami ne hardener retai ned 84 percent of its i ni ti al di el ectri c
strength at 6. 8 x 108 rads (C), but was severl y damaged physi cal l y at
109 rads (C) so that the di el ectri c strength coul d not be measured.
The above information is representati ve of the radi ati on resi stance
of several epoxy encapsulants, but the reader should be cautioned that one
type of epoxy (358-G) was considered as unsuitable following a test because
it exhibited large variations in volume resistivity during exposure. (32)
The extent of these variations is unknown and this information is included
only as precautionary information.
Calcium aluminate, an inorganic encapsulant, was eval uated as part
of one study where it was subjected to a total integrated exposure of 1 x l o8
rads (C) gamma and 4. 1 x 1013 n/cm2 (E >2. 9 MeV) at 200 C, (19) No
significant changes occurred between pre-and postirradiation measure-
ments of capacitance, dissipation factor, and insulation resistance. Di -
el ectri c strength of control and irradiated specimens was comparable fol-
lowing the radiation expo sur e.
RADIATION EFFECTS ON CONNECTORS AND TERMINALS
~~ ~.
Connectors and terminals used in electronic circuits have experienced
both permanent and temporary changes in their physical and/or electrical
properti es. These changes are associ ated wi th the i nsul ati ng materi al
rather than the metal s used i n these devi ces. The l atter requi res some
consideration, however, since metals used in connector and terminal
construction become radioactive when irradiated and, thus, offer a bio-
logical hazard to maintenance personnel.
40
I
The degradation of the insulating materials physical properties, which
may ul ti matel y l ead to el ectri cal fai l ure, is a permanent effect and a maj or
concern in selecting a connector or termi nal for use i n a radiation environ-
ment. This degradation of physical properties is manifested in the crumb-
ling or disintegration of some organics that are empl oyed as the insulating
medi a. Thus, a connector or termi nal that i ncl udes a materi al of this type
will fail through structural col l apse i n a radiation environment of sufficient
total exposure. Tetrafluoroethylene (Teflon) and similar fluorocarbon
materi al s are wel l known for their lack of radiation resistance and this
mode of fai l ure.
I norganic insulated connectors and terminals of the hermeti c seal
type, those having glass-to-metal seals, have also experienced physical
damage when exposed to a radiation environment. This damage is in the
form of cracking and chipping in the glass area immediately surrounding
the metal pi ns used as conductors (an area of hi gh stress under normal
conditions). If this type of damage i s more extensi ve than si mpl e surface
fractures, a loss in the sealing properties of the connector will result.
The changes in the electrical properties of connectors and terminals
are general l y temporary, wi th compl ete or what can essenti al l y be termed
complete recovery soon after the irradiation has been terminated. Changes
in insulation resistance breakdown voltage and corona voltages have been
reported by experi menters. The consensus i s that these parameters are
sensitive to the rate of irradiation during exposure. Data, however, lack
sufficient consistency at this time to provide an estimate of how much
change may be expected for a particular rate. Differences in environ-
mental conditions other than radiation, such as humidity and/or minor
differences in the same insulating material, may be responsible for these
inconsistencies .
Reports indicate that connectors employing rubber compounds such
as neoprene, silicone rubber, and Buna-N as the insulating material can
withstand total exposures of as much as 1015-1016 n/cm2 and (E >2. 9 MeV)
and 8. 8 x 106 rads (C) gamma at 55 C and still provide reasonable electri-
cal performance. Decreases in insulation resistance of between one and
two orders of magni tude have occurred duri ng the i rradi ati on of these con-
nectors with recovery to within one order of magnitude of the prei rradi ati on
values within minutes after the irradiation was terminated. Neoprene-
insulated connectors have shown a mi ni mum i nsul ati on resi stance of
approximately 1 x 109 o h m s during exposure to 1.5 x 10l 1 n/cm2- s)
(E >0. 1 MeV) and 6. 1 x l o4 rads (C)/hr. Buna-N-i nsul ated connectors
have exhibited minimums of less than 10 megohms for neutron fluxes and
41
g a ma dose rates of 8. 4 x 1O1O n/cmz. s ) ( E >0.9 MeV) and 6. 1 x l o4
rads (C)/hr. Resul ts from i nsul ati on-resi stance measurements on the
neoprene-i nsul ated connectors are presented i n Fi gure 10. Breakdown-
vol tage measurements on these connectors i ndi cate val ues i n excess of
500 vol ts duri ng i rradi ati on and greater than 1000 volts 3 weeks l ater.
100I I
E
40 wat t
c
0
0
-0 - I
T
I
LT
a,
C
.o 1.0
4-
0
3
-
0. I
-
10
IO" 10'2 lot3
rads(C) gamma
I I 1 1
1014 loi5 0 ' 6
Neutron Fluence, n/cm2(E >0.1 MeV)
FIGURE 10. INSULATION RESISTANCE OF NEOPRENE-
INSULATED CONNECTORS VERSUS TOTAL
EXPOSURE(38, 39)
Physi cal degradati on has resul ted i n the recommendati on that
Buna-N-insulated connectors be repl aced after a gamma exposure of
2 x 106 rads (C) at room temperature.
Pl asti c-i nsul ated connectors that have been i nvesti gated as to thei r
radiation resistance include units with phenol formaldehyde, melamine
formaldehyde, and glass-fiber filled diallyl phthalate insulation. Con-
nectors having a gl ass-i nsul ated hermeti c seal or gl ass-fi ber fi l l ed di al l yl
phthalate insulation have shown superior resistance to radiation damage
42
when compared to silicon rubber-insulated units after a total exposure of
1.67 x 1016 n/cm2 (E >2.9 MeV) and -7 x l o8 rads (C). Feedthrough
termi nal s i ncorporati ng the latter for insulating purposes have also been
tested i n a radiation environment. Degradation in the insulation resistance
of the connectors consisted of a decrease of between one and two orders of
magnitude during irradiation. Combined effects of temperature (55 to 65 C)
and radi ati on have resul ted i n decreases of four and five orders of magni-
tude.(l 8, 26) Minutes after radiation exposures of 1015-1016 n/cm2
(E >2.9 MeV) and 8.8 x 106 rads (C) gamma at 55 C, the insulation re-
sistance recovered to within one order of magnitude of the prei rradi ati on
values. Breakdown-voltage information, which is limited to the diallyl
phthalate-insulated connectors, indicate that no breakdown was observed
at 500 volts or below during exposure to a radiation environment. Three
weeks after exposure no breakdown occurred at 1000 volts. Of the three
pl asti c i nsul ators tested as connector insulation the diallyl phthalate was
least subject to mechanical degradation.
Feedthrough terminals insulated with glass-fiber filled diallyl phtha-
late that survived a total exposure of 3 . 1 x 10 l 6 n/cm2 (E >0. 5 MeV) and
9. 8 x l o8 rads (C) gamma at room temperature experi enced decreases of
f rom 2000 to 3000 volts in corona ignition and extinction voltages during
exposure at altitude equivalents of sea level to 70,000 feet. The insulation
resi stance remai ned fai rl y constant at 6-7 x l o7 ohms during irradiation
at a neutron fluence of 2 . 3 x 101o n/(cm2. s) (E >0. 5 MeV) and a gamma
rate of 2. 6 x l o5 rads (C)/hr. wi th a pretest resi stance of : 1 x 10l 2
ohms. Capacitance and dissipation factor were fairly independent of the
altitude and radiation conditions to which the terminals were subjected.
Several of the termi nal s fai l ed because of low corona voltages and insula-
tion resistance: included were all of the smaller size and 50 percent
of those cl assi fi ed as medi um and l arge si zes.
Radiation-effects information on inorganic insulated connectors in-
cl ude the gl ass hermeti c-seal type and a cerami c (al umi na)-i nsul ated AN
type connector. Si mi l ar i nformati on i s al so avai l abl e on cerami c-i nsul ated
feedthrough terminals. I nsulation resistance data indicate that both types
of connectors have a decrease of approxi matel y two orders of magnitude
during irradiation with recovery approaching preirradiation values after
total exposures of 2-10 x 1015 n/cm2 (E >0. 1 MeV) and 8. 8 x l o6 rads (C)
gamma at 55 C. Results of i nsul ati on resi stance measurements on the
cerami c-i nsul ated connectors are presented i n Fi gure 11. Combi ned
effects of radiation and temperature (156 F) have produced decreases of up
to fi ve orders of magnitude in insulation resistance during irradiation at a
neutron fluence of 1.2 x 10l 2 n/cm2. s) (E >2. 9 MeV) and a gamma rage of
43
IO''
I O'
cn
r
0
E
.-
cn
Q)
cn
LT
1o9
I oa
0
I
Al l remaining connectors fall between
the maximum limits of Connector I and
minimum limits of Connector IO.
1.0
Neutron Exposure, n/cm2 (E>0.5MeV) x IOl5
2.0
FI GURE 11. INSULATION RESISTANCE OF CERAMC-
INSULATED CONNECTORS(32)
44
6. 6 x l o7 rads (C)/hr. (26) Recovery following irradiation was within one
or two orders of magnitude of the i ni ti al val ues. The gl ass hermeti c-seal ,~
type connectors exhibited breakdown voltage characteristics in excess of
500 vol ts duri ng i rradi ati on and greater than 1000 volts 3 weeks after the
radiation exposure was terminated. Corona voltage data on the ceramic-
insulated AN connector s show a range of 1.2- 1.8 kV for all but two con-
nectors. One connector exhibited a distinct failure when the corona ignition
voltage or a voltage breakdown of one pin was observed to occur at approxi-
matel y 100 volts while a second connector experienced a decrease to
between 600 and 800 volts in corona ignition voltage.
A radiation study of several types of ceramic-insulated feedthrough
terminals indicate that these units experience insignificant degradation
f rom a total exposure of 4. 2 x 1013 n/cm2 (E >0. 1 MeV) and 9. 3 x l o7
rads gamma at 200 C. The insulation resistance was 1014-1015 o h m s
before and after the irradiation.
It i s recommended that the reader consul t the secti on on sheet and
bulk insulating materials for additional information on the connector insula-
tions discussed above and others that may be of interest. I n addition, the
activation of metal parts provi des a continuing source of radiation to the
connector and surrounding electronic parts even after irradiation from the
pri mary source has termi nated. I n gl ass to metal seal s, wi th materi al s
like Kovar or similar alloys, the interface between the metal and glass, a
most sensi ti ve area, is i n an area of high radiation concentration and high
physi cal stress and, thus, i s more subj ect to damage. Therefore, the
selection of a connector for use in a radiation environment must include
consideration of both the insulating material and the metal parts.
45
CAPACITORS
INTRODUCTION
Dimensional change of the interelectrode (capacitor plate) spacing is the
principal cause of capacitance changes during irradiation. This dimensional
change is most pronounced when radiation-sensitive materials, generally
organi cs, are used i n one or more parts of the capacitor's construction.
Pressure buildup from gas evolution and swelling causes physical distortion
of capacitor elements and thus changes the interelectrcde spacing. Radiation
effects on the dielectric constant of capaci tor di el ectri cs is l i mi ted as little
or no change i s shown in this property. Therefore, the effect on the dielec-
tri c constant i s second-order effect, especi al l y for i norgani c di el ectri cs.
Capacitor temperature changes by gamma heating, with resultant changes in
physical dimensions and dielectric constant, is another second-order effect
for the dose typically encountered.
I onization of the air surrounding or within the capacitor structure, deg-
radation of the dielectric and filler material, and radiation-induced tempera-
ture i ncreases may cause decreases i n the i nsul ati on resi stance. The i oni za-
tion effect is the main insulation effect observed during irradiation tests.
I nsul ati on resi stance measurements of paper-di el ectri c capaci tors exposed
to intense radiation illustrate the effects of both ionization and insulation
breakdowns within the capacitor. Upon irradiation, the insulation resistance
i mmedi atel y drops as a resul t of ionization, and then continues to decrease
with the degradation of the dielectric and filler material after some given
dose. Thermal-neutron contribution to insulation-resistance decrease must
be considered in connection with electrolytic capacitors that use borates as
the electrolyte, and fast neutrons must be considered for hydrogenous mate-
rials. Decreases i n i nsul ati on resi stance wi l l occur wi th i ncreasi ng temper-
atures; therefore, any ri se i n temperature associ ated wi th radi ati on wi l l
contribute to a decrease in the insulation resistance. Capacitors such as the
mica, glass, and ceramic types exhibit high insulation resistances and low
dissipation factors, while the electrolytic and some paper types exhibit low
insulation resistances and high dissipation factors. The relative neutron-
radiation sensitivity of capaci tors accordi ng to di el ectri c materi al i s shown
in Figure 12.
46
Cer ami c
Gl ass
Mi c a
Paper and Paper /Pl ast i c
Pl ast i c
El ect r ol yt i c
FIGURE 12.
Mi l d - to - moder at e permanent damage
Moder at e- t o -sever e per manent damage (behavi or spr ead)
Sever e per manent damage
IO l3 loi4 1015 IOi6 1017
Fast Neutron Fluence, n/cm2
I I I 1 I
~~~~ ~ ~~
l o5 IO6 lo7 IO8 lo9
Estimated I oni zi ng Dose, R
RELATIVE RADIATION SENSITIVITY
OF CAPACITORS
If the capaci tors are going to be used in a system that will operate in
a nuclear or space environment, then temporary changes that occur during
irradiation will be of i nterest. I n general, the temporary capacitance change
will be larger and more positive than the permanent change. This also seems
to be the case for the dissipation factor, while the temporary leakage resis-
tance may decrease by several orders of magni tude. I t must be remembered,
however, that the temporary effects are largely dependent on the f l ux rate,
and the permanent effects are mai nl y the resul t of total exposure. More
specific information concerning the various types of capaci tors, as cl assi fi ed
by di el ectri c material, is presented in the following sections.
I
47
Gl ass - and Porcel ai n-Di el ectri c " Capaci tors ~- ~~~ ~
The basic construction of glass -dielectric capacitors includes alternate
l ayers of gl ass ri bbon and el ectrode or pl ate (al umi num) materi al wi th an
outer covering of gl ass. These l ayers are seal ed together i nto a monolithic
bl ock by hi gh temperature and pressure. Vi treous-enamel (porcel ai n-
di el ectri c) capaci tors are of si mi l ar constructi on, wi th al ternate l ayers of
cerami c gl aze and si l ver that are fused i nto a monolithic block with an ex-
teri or of the same ceramic glaze. Applications for glass- and porcelain-
dielectric capacitors include blocking, by-pass, coupling, high-stability
beating oscillators and low-drift R-C osci l l ators. They are wel l sui ted for
cri ti cal hi gh R- F applications, within the limitations of thei r sel f-resonance
frequency, and where a mi ni mum of noi se i s requi red.
Capaci tors havi ng gl ass- or porcel ai n- (vi treous enamel ) di el ectri cs
compared to capacitors of other di el ectri c materi al s, have shown a relatively
hi gh resi stance to damage from exposure to a neutron environment. The
damage or effect of the radiation on the electrical properties of these capac-
i tors i ncl udes both permanent damage and temporary effects. The tempo-
rary effects are attri buted to i oni zati on i n the capacitor and i n the i medi ate
area surroundi ng the capaci tor and i ts l eads. Experi menters have attempted
to reduce and/or eliminate part of the ionization problem in the near vicinity
of the test specimen by potting the capacitor and its lead-connection area in
wax or other insulating material and conducting the test in a vacuum. This
encapsul ati on, however, someti mes presents more of an ionization problem
i n temporary effects because of charge equilibration.
Gl ass - and porcelain-dielectric capacitors have exhibited both tempo-
rary and permanent changes in capacitance as a resul t of irradiation.
Changes in dissipation factor and insulation resistance are generally tempo-
rary effects with recovery to near preirradiation values within a few hours
after the termi nati on of the exposure. The dissipation factor of porcelain
units, however, has sometimes experienced permanent changes after a
neutron fluence of - 1016 n/cm2 (E >2. 9 MeV).
Capaci tance measurements on gl ass -di el ectri c capaci tors duri ng i rra-
diation have shown maximum temporary changes or variations between +4.0
percent and -2,'5 percent. Permanent changes between t3. 1 and -2. 5 per-
cent have also been recorded. The radiation environment for these changes
included neutron fluences of 3.4 x 1018 and 5.7 x 1016 n/cm2 (E >2.9 MeV)
and total gamma exposures of 7.7 x 108 to 3. 0 x 109 rads (C). A maxi mum
48
change of only +O. 1 percent, wi th an average i ncrease of 0.05 percent has
been observed, however, with a neutron flux and fluence of -4 x 10l 2 n/
(cm2- s ) , E >10 keV, and 8 x 1014 n/cm2, respectively. (40) The gamma
environment included a rate of 5.4 x l o6 rads (C)/hr and a total dose of
3 x l o6 rads (C). Several factors may be responsi bl e for the di fferences
i n the resul ts reported by vari ous experi ments, such as l ack of cl ose si mi -
l ari ty i n test speci mens due to producti on changes and/or di fferences be-
tween production lots, instrumentation difficulties, and lead effects.
Maximum changes or variations in the capacitance of porcel ai n-
dielectric capacitors during irradiation include a decrease of 3. 5 percent
and an i ncrease of 2.1 percent. Permanent changes between - 4.0 and +3.5
percent have al so occurred. In many cases, however, the capaci tance
remai ns much more stabl e wi th temporary and permanent changes of l ess
than 1. 0 percent.
In general, the capacitance of gl ass- and porcel ai n-di el ectri c capaci -
tors remai ns stabl e enough i n a radi ati on envi ronment that they are sui tabl e
for many of their intended applications, with the exception of circuits involv-
ing critical tuning where precision capacitors are a necessity. Applications
i n ci rcui ts of this type require shielding to protect the capacitors against the
radiation environment.
The dissipation factor of gl ass- and porcel ai n-di el ectri c capaci tors
experi ences temporary effects from exposure to a nucl ear-radi ati on envi ron-
ment. Gl ass-di el ectri c capaci tors have shown i ncreases from i ni ti al di ssi -
pation factors of approximately 0. 015 to values between 0. 021 and 0. 078
during irradiation with complete or nearly complete recovery when it was
terminated at neutron fluences and total gamma exposures as high as 3.4 x
10l 8 n/cm2 (E =unknown) and 7.7 x l o8 rads (C), respectively. The dis-
sipation factor of porcel ai n-di el ectri c capaci tors has approached 0. 05 during
and after exposure to a nucl ear-radi ati on envi ronment. These devi ces have
shown both complete recovery to preirradiation values and additional in-
creases when the irradiation was terminated. The maximum, with the post-
i rradi ati on i ncrease, has never exceeded 0. 05, and i n several tests the di s-
sipation factor did not exceed 0. 0 1 or 1. 0 percent at the following neutron
and gamma flux and total exposure levels: 4 x 109 n/(cm2. s) (epicadmium),
2, 1 x 1015 n/cm2, 2, 1 x 108 rads (C)/hr, and 3.2 x 10l 1 rads (C).
The i nsul ati on resi stance of gl ass- and porcel ai n-di el ectri c capaci tors
decreases between two and three orders of magnitude when they are subjected
49
I
to a nucl ear-radi ati on envi ronment. Thi s effect i s temporary and the i nsul a-
ti on resi stance recovers when the i rradi ati on i s termi nated.
Mi ca-Di el ectri c Capaci tors
The i nternal constructi on of mi ca-di el ectri c capaci tors i ncl udes al ter-
nate l ayers of mi ca-di el ectri c and metal l i c el ectrodes. The el ectrodes or
capaci tor pl ates may be of metal foi l or deposi ted si l ver. The deposi ted
si l ver uni ts, because of the intimate contact between the electrode and di-
el ectri c, are used where hi gh-stabi l i ty capaci tors are requi red, such as i n
timing and frequency-determining circuits and other applications where
stabi l i ty i s of pri mary i mportance. They are not, however, recommended
for applications that may include high-humidity, high-temperature, and con-
stant d-c potentials. This is due to silver-ion migration, which is accentu-
ated by these conditions. The foil types are less stable than the deposited
si l ver (si l ver mi cas), and l arger dri fts are to be expected with these units,
parti cul arl y at el evated temperature.
The capacitance and dissipation factor of mi ca capaci tors are suscept-
i bl e to permanent damage from i rradi ati on, whi l e changes i n i nsul ati on
resi stance are general l y temporary. The permanent changes i n capaci tance
and di ssi pati on factor are possi bl y due to changes i n the physi cal structure
of the capaci tors, such as separati on of the metal el ectrode and di el ectri c
layers. Visual examination following exposure has shown severe damage in
the form of casi ng fractures as a resul t of the irradiation.
Capaci tance measurements on mica-dielectric capacitors have shown
permanent changes of approximately 6.0 percent when capacitors of this type
have been exposed to neutron fluences as high as 6 x 1015 n/cm2 (E >2.9
MeV) and 1016 n/cm2 (E >0.3 MeV) and total gamma exposures of l o8 rads
(C ).
Changes in the dissipation factor of mi ca-di el ectri c capaci tors vary
from none, or no significant effect, to increases where the dissipation
factor was as much as 0. 10 after a neutron fluence of 1 x 1016 n/cm2
(E >0. 3 MeV). The total gamma ex osure is not known; however, the rate
varies between 8.7 x lo2 to 4.4 x 10 E rads (C)/hr. (41) A si mi l ar di ssi pa-
tion factor (0. 10) was the result of a temporary i ncrease duri ng a dose-rate
test, and decreased to 0. 04 during a fluence or i ntegrated exposure test that
was a part of the same study. (42) No predominant or significant changes
50
were reported i n tests at neutron fluences of 1 x 1014 and 1 x 1015 n/cm2
-
(E >2.9 MeV), and total gamma exposures of 1 x l o7 and 1 x 108 rads
(C). ( 32343)
The insulation resistance of mi ca-di el ectri c capaci tors decreases to
values in the range of 108 and 109 ohms during their exposure to a nucl ear-
radiation environment, 109 n/(cm2* s) (E 1 0.5 MeV) and 3 x l o5 rads (C)/
hr. Recovery to near prei rradi ati on val ues, 1010 and 1011 ohms, occurs
i mmedi atel y following or soon after the i rradi ati on i s termi nated. The
decrease i n i nsul ati on resi stance is generally attributed to the ionization
within the capacitor structure and in the near vicinity of the capaci tor, as
a resul t of the radiation environment.
Cerami c-Di el ectri c CaDaci tors
Basically, a cerami c-di el ectri c capaci tor consi sts of a cerami c di -
el ectri c with a thin metallic film, such as si l ver, appl i ed to ei ther si de and
fi red at hi gh temperature. The fi red metal l i c film serves as the el ectrodes
or capaci tor pl ates of the devi ce. Cerami c capaci tors are avai l abl e as two
basi c types (general purpose and temperature compensati ng), wi th several
body designs: disk, tabular, standoff, and feedthrough. The general-
purpose units are used in applications where large capacitance changes and
hi gher l osses are not cri ti cal . Typi cal uses are for bypass, fi l ter, and non-
critical coupling circuits. The temperature-compensating units are used in
more cri ti cal appl i cati ons that make use of thei r temperature characteri sti cs
to compensate for parameter changes of other elements or components i n the
circuit, These applications include critical coupling and tuning circuits.
Ceramic capacitors have shown various degrees of sensitivity to
steady-state nucl ear -radi ati on envi ronments. The capaci tance and di ssi pa-
tion factor appear to be susceptible to both temporary and permanent effects,
while the insulation resistance suffers from temporary effects due to ioniza-
tion. The changes in capacitance for general-purpose ceramic capacitors
are negl i gi bl e when the extremel y wi de tol erances and temperature coeffi -
ci ents that are associ ated wi th these devi ces are consi dered. The capaci -
tance changes that occur may be attri buted, at l east i n part, to temperature
effects and aging. The latter results in a gradual decrease i n capaci tance
with time.
51
The capacitances of general -purpose cerami c capaci tors have de-
creased duri ng i rradi ati on with but few exceptions, when increases were
observed. These changes i n capaci tance vary from a mi ni mum of 1 or
2 percent to a maxi mum of 20 percent. Typically, however, the maximum
change is in the range of 10 to 15 percent. The permanent effect, i. e.,
change i n capaci tance, i s normal l y l ess than the temporary effect that i s
observed during the actual exposure to the radiation environment. The dif-
ference between the temporary and permanent effect on capaci tance may
possibly be attributable to temperature change, and the permanent effect
may be the result of aging. The possibility that the radiation environment
accelerates the aging process, which is a decrease i n di el ectri c constant,
i s a consideration.
I nformation on the effect of radiation on the dissipation factor of
cerami c-di el ectri c capaci tors i s l i mi ted, and there are no cl ear trends
indicated. The dissipation factor of these devi ces has i ncreased duri ng and
after i rradi ati on, remai ned rather stabl e, or even decreased. (42) The in-
creases observed usually did not exceed 0.02.
The insulation resistance of cerami c-di el ectri c capaci tors decreases
as much as two to fi ve orders of magnitude during irradiation at neutron
fluxes and gamma dose rates of -4 x 10 8 n/hr (cm2* s) (E >2.9 MeV) and
2 x l o8 rads (C), respectively. Recovery generally approaches the pre-
irradiation values when the irradiation is terminated. Results from one
reported experiment(44) show no indication of recovery within 2 days after
the discontinuation of the exposure to a neutron fl ux and fluence of up to 7. 54
x 109n/(cm2. s ) and 3. 11 x 1015 n/cm2 (E >0. 1 MeV), respectively. The
gamma environment included a dose rate of up to 4. 1 x l o5 rads (C)/hr and
a total dose of 4.67 x 108 rads (C).
PaDer- and PaDer/Plastic-Dielectric Canaci tors
The basi c physi cal structure of paper-di el ectri c capaci tors consi sts
of two metal -foi l stri ps or deposi ted metal fi l ms' separated by two or more
l ayers of paper di el ectri c. The paper i s general l y i mpregnated wi th wax,
oil, or synthetic compounds to increase its voltage breakdown and to pro-
vi de the desi red characteri sti cs. The paper/plastic-dielectric capaci tors
are similar in Construction, with the addition of l ayers of plastic film i n
the paper l ayers. Paper and paper/pl asti c capaci tors are used i n general
applications involving high voltages and currents at low frequencies, in
52
fi l ters and networks of moderate precision at audio frequencies, and in by-
pass and coupling circuits.
Radiation-effects experiments on paper and paper/plastic capacitors ,
with and without impregnation, have shown them to be more sensitive to
radiation than the inorganic types (ceramic, glass , and mica) by two and
three orders of magni tude. Pl ai n paper or paper/pl asti c i s a more sui tabl e
dielectric for applications that include nuclear radiation as an environmental
condi ti on than the same or si mi l ar di el ectri c that has been oi l i mpregnated.
Thi s i s because the oi l or other hydrocarbon used to i mpregnate the di el ec-
tri c rel eases hydrogen or hydrocarbon gases when the devi ce i s pl aced i n a
radiation environment. The pressure buildup from the evolved gases sub-
sequently causes the distortion of the capacitor element and a change in
capacitance and dissipation factor. Hermetically sealed units have actually
ruptured thei r encl osures and/or l eaked at the termi nal seal s as a resul t of
thi s pressure. The i oni zati on within the capacitor structure and the imme-
di ate surroundi ng area that occurs duri ng i rradi ati on al so contri butes to
changes i n the el ectri cal characteri sti cs of paper and paper/pl asti c capaci -
tors. These changes, 'however, are temporary and mani fest themsel ves as
a decrease in the capacitor's insulation resistance.
Measurements of capacitance on paper- and paper/plastic-dielectric
capacitors have shown both increases and decreases during and after capac-
i tor exposure to a radiation environment. The maximum changes observed
in the capacitance of units of thi s constructi on are an i ncrease of approxi-
matel y 18 percent and a decrease of 50 percent. The 18 percent i ncrease
has been observed with a capacitor type that is molded i n mi neral -fi l l ed
hi gh-temperature pl asti c. If the results of two radiation studies i n which
these extremes occurred for a sample size of two i s del eted from consi der-
ation, the range of capacitance degradation would be much l ess, +8. 5 and
-20 percent. It is readily understandable that the evolving of gas, with the
associ ated di storti on of the capacitor structure, could result in a decrease
i n capaci tance by i ncreasi ng the spaci ng between the capaci tor pl ates or
el ectrodes. The i ncrease i n capaci tance i s not as easy to explain unless
the di storti on may al so i n some i nstances i ncrease the effecti ve area of the
capaci tor pl ates.
The dissipation factor of paper- and paper/plastic-dielectric capaci-
tors i ncreases when the capaci tors are subj ected to a nucl ear-radi ati on
envi ronment. These i ncreases typi cal l y have been l ess than 1.0 percent in
all of the referenced reports. The change in dissipation factor occurred
with a neutron and gamma environment that included a neutron fl ux of 3 . 0 x
53
1011n/(cm2- s)(epi cadmi um)for a fluence of 4 x 10l 7 n/cm2 and a g a ma rate
and total dose of 8. 7 x l o5 rads (C)/hr and 3 x l o8 rads (C), respectively.
The i nsul ati on resi stance of paper- and paper/plastic-dielectric capac-
tors decreases as a resul t of i rradi ati on. The temporary decrease that
occurs i s general l y attri buted to the i oni zati on that i s produced by the radi -
ation environment. A permanent decrease in the insulation resistance may
be the result of (1) a decrease i n the vol ume resi sti vi ty of the substance
used to impregnate the device and (2) the process that resul ts i n the embri t-
tl ement of the kraft-paper di el ectri c. I ncreases due to i nterel ectrode di s-
torti on from pressure bui l dup i s al so a strong possibility.
Several programs have i ncl uded suffi ci ent quanti ti es of paper- and/or
paper/plastic-dielectric capacitors to provide statistical confidence in the
results. The following discussions of i ndi vi dual test programs are pre-
sented for this reason.
One hundred CP08AlKE 105M paper-di el ectri c capaci tors were sub-
jected to combined environments of hi gh temperature and nucl ear radi a-
tion. (45) The ambient temperature was controlled at 85 C with the reactor
power level limited to 1 megawatt duri ng the fi rst 24 hours. The reactor
power l evel was then rai sed to 10 megawatts for the duration of the experi -
ment whi l e the temperature was sti l l control l ed at 85 C. The radiation
environmental conditions for this study included a neutron fluence of 1.4 x
10l 6 n/cm2 (E >2. 9 MeV) and a total g a ma exposure of 9. 0 x 108 rads (C).
Observations of capacitance during the combined environmental con-
ditions indicated that the capacitors decreased in capacitance with increase
in radiation intensity. Most of the capacitors exceeded their lower tolerance
limit of -20 percent at approximately 8.4 x 1014 n/cm2 (E >2.9 MeV) and
3.41 x 107 rads (C). As the exposure i ncreased further, there was a gen-
eral trend for the capacitances to increase slightly, sometimes returning to
within their specified tolerance. This behavior was followed by an almost
exponential increase above the upper 20 percent tol erance l evel for several
measurements when the capaci tors fai l ed catastrophi cal l y. Fi gure 13 i s a
graphi c presentati on of the reliability indices for these units based on the
specified tolerance and the resulting catastrophic-failure occurrences. The
reliability indices are the percent surviving the specified failure criteria at
the indicated neutron fluence or gamma dose. Postirradiation examination
of the capacitors revealed that 22 units were ruptured, 59 were short-ci rcui t-
type failures, 9, although not shorted, could not be charged, and only 10 ca-
paci tors were chargeabl e. The threshol d of failure for the out-of-tolerance
54
I -
90
5 80
70
4
x 6 0
5 50
Q)
U
t
.- '=40
IO
0
I 013 l oi 4 1015 IOi 6 I 017
Average Integrated Neutron Fluence,n/cm*
(E >2.9 MeV)
I o5 I o6 I o7 I o8 I o9
Average Gamma Dose, rads (C) -----
FIGURE 13. RELIABILITY INDEX FOR PAPER CAPACITORS FOR A
96 PERCENT CONFIDENCE LEVEL, BASED ON A
SAMPLE SI ZE OF 100 UNITS CAPACITANCE AND
CATASTROPHIC FAILURE)(4 E !
and catastrophically failed units, as shown in Figure 13, was 1.04 x 1014
n/cm2 (E >2.9 MeV) and 3.92 x l o6 rads ( c) .
In another i n~esti gati on(~6) wi th a l arge sampl e si ze, a small group
of units was initially stressed in order to obtain conditions for 75 percent
failure in 1000 hours of operating-life time. It was determined that 2000
vdc and 135 C should be the stress conditions. The units being tested
were paper/Myl ar 0.1 pf, 600-~0l t, CPM08 capaci tors. The cobal t-60
source used provi ded a maximum gamma exposure of 8.77 x 104 rads (C)/hr.
I
Resul ts of this investigation which included a constant-temperature
environment and a temperature-cycled environment are given in Figure 14.
The temperature-cycl ed group was subj ected to room temperature and 135 C
55
2000 vdc
160 hr
2000 vdc
I r r adi at ed
100 hr
decrease In capaci t ance
Pr i or
;to -f ai l ur e
0. 5%
6.0 to lO.O%
Pulsed 2000 vdc
I r r ad i at ed
Pul sed 2000 vdc
6.0 to 10.0%
155 hr 275 hr
I
7 failed- l?Tm-y- 4%
I
‘2””- I
636 hr 1086 hr
a. Const ant 135 C
*Because of equipment malfunction, the units failed at 636 hr. If there had
been no tronbl e, 75 percent of the units should have failed by 1086 hr.
Pr i or -t o-f ai l ur e
decrease in capaci t ance
2 O/O 2000 vdc 15 failed”
2000 vdc
I
I
1
566 hr
Ir r adi at ed - 9 O/O
312 hr
Pulsed 2000 vdc
Ir r adi at ed 0
6 O/ o
131hr
I ~~~
Pul sed 2000 vdc -1 I 2 O/O
I
I I
9 f ai l ed 650 hr
b. Temper at ur e -Cycl ed Uni t s
1. The pulsed 2000 vdc had a maximum surge current of 30 ma
2. In all cases the sample size equals 25 units, Type CPM08
FIGURE 14. EFFECTS OF GAMMA RADIATION ON PAPER/MYLAR
CAPACITORS FOR 100 PERCENT SAMPLE-SIZE
FAI LURE(46)
56
with 30 mi nutes to stabi l i ze at each temperature. A total of 90 minutes was
requi red at each temperature to make all necessary measurements. Mea-
surements of dissipation factor and insulation resistance for both the constant-
temperature group and the temperature-cycl ed group reveal ed no trend to-
ward degradati on before fai l ure. Al l the fai l ures that are i ndi cated resul ted
from voltage breakdown. As a comparison, four units were passively irra-
diated in the gamma source for 1000 hours. These units showed the follow-
ing results:
(1) No case ruptures
( 2 ) 6 percent decreases i n capaci tance
(3) A factor of two increase in dissipation factor
(4) A factor of seven decrease in insulation resistance.
Twenty-four units were also operated at 840 vdc and 125 C (no radiation),
and were found to be functioning normally after 5, 33 1 hours.
A thi rd ~tudy( ~9) included both paper- and paper/plastic-dielectric
capacitors with deposited metal (metallized) plates or electrodes manufac-
tured about 1965. Both types were subjected to five environmental conditions
with d-c voltage applied. The paper-dielectric capacitors were also sub-
j ected to one of the environments with no voltage applied. The basic sample
size at each test condition consisted of 20 units for a total of 100 paper/
pl asti c capaci tors and 120 paper capaci tors. Each group of 20 speci mens
was subjected to one of the environmental conditions indicated in Table 7.
The sixth group of paper-di el ectri c capaci tors (Test Group VI) was
subjected to the same environmental conditions as Test Group I11 with no
voltage applied.
Fai l ure-rate computati ons at the 50,60, and 90 percent confidence
levels, as shown in Table 8 for the metal l i zed-paper capaci tors, i ndi cate
that temperature was the greatest contri butor to thei r fai l ure, si nce the
capaci tors i n Test Group V (50 C) exhibited a much l ower fai l ure rate than
that for any of the other test groups. The units subjected to normal atmo-
spheri c pressure, Test Group I, al so experi enced a fai l ure rate approxi -
matel y one-hal f that observed for uni ts i n the vacuum envi ronments, with the
exception of those in Test Group V. The no-load condition of Test Group VI
resul ted i n a l ower fai l ure rate than that for Test Group 111, which was sub-
jected to identical environmental conditions, but included the application of
a d-c voltage.
57
TABLE 7. TEST DESIGN, RATED VOLTAGE APPLI ED
Test
Temperature, Pressure,
Neutron
Group
C torr Fluence
Gamma
Dose
I 100 76 0 None None
I1 100 10-5 None None
I11(a ) 100 10-5 -1013 n/cm 2
- l o7 rads (C)
IV (b) 100 10-5 -1013 n/cm 2
- l o7 rads (C)
V ( 4 50 -1013 n/cm2
-l o7 rads (C)
(E >0. 1 MeV)
(E >0.1 MeV)
(E >0. 1 MeV)
-
(a) 10,000 hours at 3 x l o5 n/(cm2- s) and 1 x l o3 rads (C)/hr.
(b) 100 hours at 3 x 107 n/(cm2. s) and 1 x 105 rads (C)/hr followed by 10,000 hours at 100 C and l om5 torr
without radiation.
TABLE 8. FAILURE RATE FOR P323ZN105K CAPACITOR, AT 50,
60, AND 90 PERCENT CONFI DENCE LEVELS(39)
Failure Rate at I ndicated Confidence Level,
percent/ 1000 hr
Percent Recorded
Test Group 50 Percent 60 Percent 90 Percent as Failed
I 2. 09 2.35 3.58
I1 4.86 5.25 7.03
I11 5.46 5.88 7. 77
I V 4.26 4.67 6.41
V 0. 30 0.39 0.98
VI 4. 56
4.97 6.72
All test groups 3 . 19 3.32 3.87
20
50
55
40
0
45
35
58
The el ectri cal characteri sti cs of these capacitors experienced a
greater degree of degradati on from a 100 C ambient with a load voltage ap-
plied than from the radiation environment. Any radiation damage that oc-
curred, however, may have been anneal ed by the el evated temperatures.
On the basis of the above results, it was concluded that the radiation
levels involved in this study are of little concern compared to the cata-
strophic failures and degradation that resulted from the 100 C ambients.
Therefore, the application or design engineer would need to be more con-
cerned with normal degradation due to elevated temperature at 100 C than
with the radiation environment of this program in the application of these
capacitors.
No failures were observed among 100 metal l i zed/Myl ar (pl asti c)
capacitors, also manufactured about 1965, that were subjected to the vari-
ous test conditions in Table 7.
TABLE 9. FAI LURE RATE FOR 118P1059252 CAPACITOR AT 50,
60, AND 90 PERCENT CONFI DENCE LEVELS(39)
~
~- - - .
Failure Rate at Indicated Confidence Level,
Dercent/lOOO hr
Percent Recorded
Test Group 50 Percent 60 Percent 90 Percent as Fai l ed
I 0.30 0.39 0.98 0
I1 0.30
0.39
0.98 0
III 0.30
0.39 0. 98 0
IV 0.29
0.39 0.97 0
V 0.30
0.39
0.98 0
Al l test groups 0.06 0.08 0.20 0
" .
I
59
Any degradation in capacitance that was observed with these capacitors
would not be detrimental to their normal application. No significant amount
of degradation was noted in the dissipation factor. The results from the
i nsul ati on-l eakage-current measurements i ndi cated the greatest degradati on
i n thi s parameter occurred i n the 100 C vacuum environments of Test
Groups 11, 111, and IV. The maxi mum l eakage current approached 1.0 mil-
l i amperes i n al l three of these test groups,
I t was concluded from the results obtained that a radiation environ-
ment of the level used in this study is not a significant factor in the appli-
cation of these capacitors. The application engineer needs to be more con-
cerned wi th the degradati on associ ated with elevated temperature.
Pl asti c-Di el ectri c Capaci tors
Most pl asti c-di el ectri c materi al s harden and eventual l y become bri ttl e
when irradiated. This results in flaking and crumbling especially under
stress. The el ectri cal properti es of Myl ar are stabl e to an absorbed dose
of 108 rads. During irradiation, the dielectric constant and dielectric loss
undergo significant changes, but they recover on removal from the radiation
field. (4) It takes about 12 days for a 2-mil speci men to approach a quiescent
state after irradiation. Dielectric constant and dielectric l oss show no per-
manent dose-rate effect. Some properties of Mylar do exhibit a dose-rate
effect that i s general l y l ess at hi gher dose rates. For exampl e, di el ectri c
strength i s consi derabl y reduced at l ower dose rates, but at higher dose
rates the change i s not nearl y as great.
Pl asti c-di el ectri c capaci tors are si mi l ar i n constructi on to the paper
and paper/pl asti c capaci tors, wi th the excepti on that the di el ectri c i s a thin
pl asti c film rather than paper or paper and pl asti c. Materi al s commonl y
used as the di el ectri c film are polystyrene, polyethylene, polycarbonate,
and Mylar (polyethylene terephthalate). In general, low-voltage units are
manufactured without impregnation or liquid f i l l . However, for hi gher
voltages, a liquid f i l l i s requi red to reduce corona and i ncrease vol tage-
flashover limits. Applications for plastic-dielectric capacitors are the
same as those for the paper and paper/pl asti c capaci tors.
Radiation-effects testing of pl asti c-di el ectri c capaci tors has essen-
tially been limited to devices employing Mylar as the dielectric film. There-
fore, the following discussion of radiation effects on pl asti c-di el ectri c capac-
i tors i s concerned with or l i mi ted to Myl ar capaci tors.
60
Experi ments to determi ne the effect of nuclear radiation on plastic-
dielectric capacitors have shown that these organic dielectrics experience
moderate-to-severe permanent damage at a radiation fluence an order of
magni tude l ess than the i norgani cs, i. e., gl ass, cerami c, and mi ca. As in
the case for paper- and paper/plastic-dielectric capacitors, plain plastic is
a more sui tabl e di el ectri c for nucl ear-radi ati on envi ronments than the same
or si mi l ar di el ectri c i mpregnated wi th oi l or wax. I mpregnated hermeti cal l y
seal ed uni ts may even experi ence a rupture of the exteri or case or encl osure.
Thi s rupture may be the pushi ng out of the gl ass-to-metal end seal s so that
the materi al used to i mpregnate the capaci tor l eaks out, or, i f there i s a
sufficient buildup of pressure, the end seal may even be blown completely
free of the capacitor, with the capacitor element extending beyond the limits
of i ts encl osure. Such a violent rupture occurring in an actual application,
offers, i n addi ti on to el ectri cal fai l ure, a physi cal hazard to other component
parts in the vicinity of the capacitor.
The capacitance of pl asti c-di el ectri c (Myl ar) capaci tors subj ected to a
radi ati on envi ronment has both i ncreased and decreased when pre- and post-
i rradi ati on measurements are compared. In general , these changes are
within *4 percent of the preirradiation value at neutron fluences of l O15n/cm
(E 2.9 MeV) and 10l6 n/cm2 (E >0.3 MeV). However, decreases of as
much as 10 percent and as smal l as <1 percent have al so been recorded for
similar capacitors and fluences. The differences i n the sensitivity to a radi -
ation environment may possibly be the result of differences i n the Mylar and
i ts treatment before or duri ng the manufacture of the capacitors, or differ-
ences i n the materi al used to impregnate them. The evolving of gas by the
breakdown of the oil or wax used to impregnate the capacitors could be
responsible for capacitance change. Bubbles forming between the layers of
the capacitor could increase the spacing.
2
The dissipation factor of plastic-dielectric (Mylar) capacitors remains
stable with a negligible amount of change. The change, i f i t occurs, i s not
detectable because of the measurement accuracy and/or the di ssi pati on factor
of the long leads required between the test capacitors in the radiation environ-
ment and the i nstrumentati on used to measure thei r el ectri cal character-
i sti cs. The maxi mum observed i ncrease i n di ssi pati on factor i s 60 percent
of the i ni ti al val ue measured before the capaci tors were i nserted i n the re-
actor. Thi s i ncrease occurred at a neutron fluence of 6 x 1017 n/cm2
(epicadmium) and a total gamma dose of 4.4 x 108 rads (C).
The i nsul ati on resi stance of pl asti c-di el ectri c capaci tors decreases
when they are exposed to nuclear radiation. Permanent changes in the insu-
lation resistance may be due to the chemical breakdown process that occurs
61
in the oil or wax substances used to impregnate the capacitor or a change in
the pl asti c-di el ectri c-materi al s characteri sti cs. The i nsul ati on resi stance
of capacitors having a Myl ar di el ectri c decreases as much as three and four
orders of magnitude, with minimum values as low as 10 megohms. Recovery
after the i rradi ati on i s termi nated normal l y returns the i nsul ati on resi stance
to near prei rradi ati on val ues, i. e., within an order of magnitude.
Two programs have i ncl uded quanti ti es or sampl e si zes of Myl ar-
di el ectri c capaci tors to provi de a higher than usual statistical confidence in
the results. The following discussions of i ndi vi dual test programs are pre-
sented for this reason.
One hundred Hyrel Mylar capacitors, rated at 1. 0 pf, were subjected
to a combined environment of high temperature and nuclear radiation. (45)
The ambient temperature was controlled at 85 C, with the reactor power
limited to 1 megawatt duri ng the fi rst 24 hours. The reactor power was then
i ncreased to 10 megawatts for the duration of the experiment. The neutron
Average Integrated Neutron FIuence,n/cm*
(E >2.9 MeV) -
1
I o5 I o6 10’ IO* I o9
I J
Average Gamma Dose,rads(C) ----
FIGURE 15. RELIABILITY INDEX FOR MYLAR CAPACITORS FOR
A 95 PERCENT CONFI DENCE LEVEL, BASED ON A
SAMPLE SIZE OF 98 UNITS (CAPACITANCE AND
CATASTROPHIC FAILURE)(45)
62
fluence and total gamma exposures to which these Mylar capacitors were
subjected were 1.32 x 10l 6 n/cm2 (E 7 2.9 MeV.) and 8.5 x l o8 rads (C),
respectively. The capacitance values of the Mylar capacitors exhibited very
little change for an extended period of radiation; a general i ncrease was
observed toward the end of the test. At the end of the test several uni ts ex-
ceeded the 10 percent tol erance l evel speci fi ed for the capaci tor. Pri or to
these failures, the mode of failure had been essentially limited to
catastrophic-type damage. The reliability indices, shown in Figure 15,
indicate this phenomenon by comparison of catastrophic failures with out-
of-tolerance occurrence. Postirradiation examination of the Mylar capaci-
tors reveal ed that 94 units had failed catastrophically and 81 had ruptured
as a resul t of the test conditions. One capacitor that exhibited a nonshorted
condition could not be charged, and 18 units of the enti re test group were
chargeable,
The second study that included a l arge sampl e si ze of Mylar capacitors
consisted of subjecting them to the five environmental conditions listed in
Table 7 with a d-c voltage applied. Nonenergized units were included in two
of the environments (Test Groups VI and VI I ). (39) These additional test
groups were subjected to the same environmental conditions as Groups I and
111. The basic sample size at each test condition consisted of 20 units for a
total sampl e si ze of 140 Mylar capacitors manufactured about 1965.
Failure-rate computations, Table 10, show that the combination of
radiation exposure and 100 C temperature, Test Groups 111and I V, resul ted
TABLE 10. FAILURE RATE FOR 683G10592W2 CAPACITOR AT 50,
60, AND 90 PERCENT CONFI DENCE LEVELS(39)
Failure Rate at I ndicated Confidence Level,
percent/ 1000 hr
"" ______ ~. - .
' Percent Recorded
Test Group 50 Percent 60 Percent 90 Percent as Fai l ed
- . -
. ~ ~- . . . .
I 1.23 1.43
2.44 10
I1 0.30 0.39
0.98 0
III 36.70 38.85
48.38 95
IV 18.76 20.02
25.53 75
V 0.30 0.39
0.98 0
VI 0.30 0.39
0.98 0
VI1 0.30 0.39
0.98 0
All test gr,oups 2.83 2.95 3.48 25.7
.. - ~
__ ." . . " ". . "" .. ~- - .~ . . .
63
in exceptionally high failure rates. The results for the capacitors in Test
Group V, radiation and 50 C, indicate that temperature was a definite factor
i n these fai l ures, whi l e resul ts for Test Group 11, 100 C without radiation,
show a similar indication for the radiation environment. The results shown
for Test Group VI , with environmental conditions identical to those for Test
Group I11 but with no load applied, indicate that electrical load was also a
factor in the failures. This concentration of failure in the radiation environ-
ments i ndi cates that these capaci tors are qui te suscepti bl e to radi ati on
damage, even at the low levels used in this study, when in combination with
a 100 C ambi ent temperature. Therefore, it was recommended that their
application be limited to lower ambient temperatures, such as 50 C, when
nuclear radiation is an environmental consideration.
Electrolytic Capacitors
Electrolytic capacitors offer a major advantage over other capacitor
types for applications where space and weight requirements necessitate a
high level of volumetric efficiency of the capacitors used in the circuits.
The greatest capacitance -to-volume ratio (volumetric efficiency) is provided
by el ectrol yti c capaci tors, and they are general l y used i n appl i cati ons where
thi s i s of pri me concern. A maj or di sadvantage of el ectrol yti c capaci tors i s
that they are polar, and applications of nonpol ar capaci tors requi re two
electrolytic capacitors connected back-to-back or a single unit having a foil
that has been anodized on both sides. This reduces the capacitance by
50 percent, which i n turn reduces the volumetric efficiency of the el ectro-
l yti c capaci tor, whi ch as stated above i s i ts maj or advantage.
The construction of an electrolytic capacitor includes an electrode
or capaci tor pl ate of some form that has been anodized on one side to form
a di el ectri c film or insulating layer. A wet or dry el ectrol yte i s provi ded
between this anodized surface and the other terminal of the capacitor.
Tantal um and al umi num are the commonl y used metal s for the anodi zed
el ectrodes i n electrolytic capacitors, and the capacitors are identified by
whi ch materi al i s used. The tantal um el ectrol yti cs are general l y consi dered
more reliable than the aluminum electrolytics because the tantalum oxide
layer in combination with the capacitor's electrolyte is more stable than the
aluminum oxide layer and electrolyte combination. Both types, however,
experience degradation in the form of i ncreasi ng l eakage currents and de-
creasing breakdown voltages during shelf life or operation at below-rated
voltage. The .aluminum units experience greater degradation because they
64
deform (the thickness of the oxide layer is reduced) at a more rapi d rate than
that for the tantalum. Applications for electrolytic capacitors include filter-
ing and bypass circuits.
I nformation on the results of radiation-effects experiments with
tantal um- and al umi num-el ectrol yti c capaci tors i ndi cates that both types
may be capable of surviving extended exposure to intense radiation. These
results have also shown the tantalum units to be more radiation resistant;
however, they offer a biological hazard where servicing of equi pment may
be required. This is due to the activation of the tantalum when subjected to
thermal neutrons and the l ong hal f-l i fe, 112 days, associ ated wi th the re-
sulting radiation from the tantalum isotope Ta-182. This hazard is not
associated with the aluminum units because of the very short half-life of
2. 3 minutes for the aluminum isotope A1 -28. The aluminum units also have
the possibility of an isotopic reaction, A1-27 (n, a) Na-24, when exposed to
a high level of fast neutrons. The sodium isotope has a half-life of 15 hours.
The el ectri cal characteri sti cs of electrolytic capacitors have experi-
enced both temporary and permanent changes when exposed to nuclear radi-
ation. The capacitance and dissipation factor suffer from both temporary
and permanent effects. The leakage current, however, generally experiences
a temporary i ncrease wi th compl ete or nearl y compl ete recovery to pre-
irradiation values when the irradiation is terminated. Some of the el ectro-
l yti c capaci tors al so experi ence physi cal damage because of thei r construc-
ti on. These are the types that empl oy Tefl on i n the construction of the end
seal s of the capaci tor case. Tefl on i s very sensi ti ve to the nucl ear-
radiation environment, especially if oxygen is present in the atmosphere
during the irradiation. I t also suffers damage i f exposed to oxygen after
bei ng i rradi ated i n a vacuum or inert atmosphere. The Teflon end plugs of
tantalum-electrolytic capacitors have popped out because of this sensitivity
of Teflon to radiation, and the inner rubber seal protrudes.
The capacitance of tantalum- and aluminum- electrolytic capacitors
has both increased and decreased during radiation-effects experiments.
The changes in capacitance have varied between the maximums of -25 and
+20 percent for tantal um types and between the maxi mums of -2 and $65 per-
cent for al umi num. The changes are not necessari l y permanent, and the
capacitance in some studies has recovered to near the preirradiation value.
Others, however, have shown additional degradation after the irradiation was
termi nated. Temporary i ncreases i n capaci tance duri ng i rradi ati on may be
due to temperature effects from gamma heating. The permanent changes or
those that show recovery over an extended peri od of ti me would be indicative
65
The dissipation factor of tantalum and aluminum electrolytic capacitors
has shown both temporary and permanent effects from exposure to a nucl ear-
radiation environment. The dissipation factor of high-capacity aluminum-
electrolytic capacitors has increased by as much as 0.50, from preirradi-
ation values, after a rather low neutron fluence and total gamma exposure of
4.8 x 1012 n/cm2 (E >0.5 MeV) and 7.1 x l o5 rads (C), respectively. (47)
Much smal l er i ncreases have occurred wi th some smal l -capaci ty uni ts after
a much higher neutron fluence and total gamma exposure, such as 2.5 x 1017
n/cm2 (fast) and 6 x 108 rads (C). The di fference i n these resul ts i s very
likely due to the large volumetric difference in the capacitors, and should be
a consideration in what to expect in the application of si mi l ar devi ces.
The dissipation factor of tantal um-el ectrol yti c capaci tors may i ncrease
to where it exceeds 0. 50 during irradiation. These high values or large in-
creases occur when the Teflon end seals fail and there is a l oss of el ectro-
lyte. Maximum increases in dissipation factor remain below 0. 10 i f there
is no l oss of electrolyte and may not exceed 0.05 with neutron and gamma
flux and total exposure levels as high as 3 x 10l 1 n/(cm2* s ) and 6 x 1017
n/cm2 (epicadmiurn), and 8.7 x l o5 rads (C)/hr and 4.4 x 108 rads (C),
respectively.
The l eakage current of aluminum- and tantalum-electrolytic capacitors
increases during irradiation by one or two orders of magnitude at neutron
fluxes and gamma dose rates of 2.5 x 101o n/(cm2- s) E >0.5 MeV and 3.6 x
105 rads (C), respectively. It has i ncreased to val ues as hi gh as 1000 mi cro-
amperes for l arge capaci tors such as 47 mfd and 100 Vde. Smal l er capaci -
tors experience lower leakage currents since there is a di rect proporti onal i ty
between the product of capacitance, applied voltage and dose rate, and the
l eakage current. Thi s i ncrease i s normal l y a temporary effect and the l eak-
age current returns to near prei rradi ati on val ues after the radi ati on exposure
has been terminated. This recovery may not occur immediately but can re-
qui re a period of several days.
Two programs on tantalum capacitors have included sufficient quanti-
ti es of test specimens to provide a higher than usual statistical confidence
in the results obtained. The following discussions of these individual test
programs are presented for thi s reason.
66
One hundred Type TES-1M-25-20 solid-electrolytic-tantalum capaci-
tors, nominal capacitance 1.0 pf, were subjected to a combined environment
of hi gh temperature and nucl ear radi ati on i n one program. (45) The ambi ent
temperature was control l ed at 85 C with the reactor power limited to 1 mega-
watt during the first 24 hours. The reactor power was then i ncreased to
10 megawatts for the duration of the experi ment whi l e the temperature con-
tinued to be controlled at 85 C. The neutron fluence and total gamma expo-
sure to whi ch these capaci tors were subj ected i ncl uded 2. 0 x 1016 n/cm2
(E >2. 9 MeV) and 7.3 x 108 rads (C), respectively. The capacitance and
dissipation factor of the tantal um capaci tors i ncreased very earl y i n the
test, with all units exceeding the 5 percent dissipation factor tolerance when
the exposure reached 9.63 x 1014 n/crn2 (E >2.9 MeV) and 3.07 x 107 rads
(C). This change can be observed in Figure 16, where the reliability indices
I 013 I 014 l oi 5 I Ol6 I 017
Average Integrated Neutron Fiuence,n/cm2
I
(E> 2.9 MeV)- I
I
105 I06 l o7 108 to9
-~
Average Gamma Dose,rads (C)-----
FIGURE 16. RELIABILITY INDEX FOR TANTALUM CAPACITORS
FOR A 95 PERCENT CONFI DENCE LEVEL, BASED
ON A SAMPLE SIZE OF 98 UNITS (CAPACITANCE
AND DISSIPATION FACTOR)(45)
67
are plotted on the basis of both capacitance and dissipation factor. No catas-
trophi c fai l ures occurred duri ng the exposure, whi ch, wi th the capaci tance
i ncreases observed, woul d i ndi cate that tantal um capaci tors may be used i n
noncritical circuits to an integrated exposure of at l east 1.6 x 1016 n/cm2
(E >2. 9 MeV) and 5. 1 x l o8 rads (C). Posti rradi ati on exami nati on of the
tantal um capaci tors reveal ed no visual damage, and all capacitors were
chargeable.
Two types of tantalum capacitors, manufactured about 1965, wet foil
and wet slug, were included in the second ~t udy( ~9) that included statistically
significant sample sizes. Both types were subjected to the five environmental
conditions described in Table 7, with d-c voltage applied. The wet-foil
tantal um capaci tors were al so subj ected to one of the environments with no
voltage applied. These additional capacitors, Test Group (VI ), were sub-
jected to the same environmental conditions as Test Group 111, Table 7.
The basi c sampl e si ze of each test condition consisted of 20 units, for a
total of 120 of the wet-foil-type and 100 of the wet-slug-type capacitor.
No fai l ures were observed for 120 wet-foil tantalum capacitors, and no
l eakage or physi cal damage was detected duri ng the fi nal vi sual i nspecti on.
Fai l ure-rate computati ons are presented i n Tabl e 11 for these capac-
itors. The minor difference between the failure rates for Test Group I V and
TABLE 11. FAILURE RATE FOR 5K106AA6 CAPACITOR AT 50,
60, AND 90 PERCENT CONFI DENCE LEVELS(39)
Failure Rate at I ndicated Confidence Level,
percent/ 1000 hr
Percent Recorded
Test Group 50 Percent 60 Percent 90 Percent as Fai l ed
I 0.30
0.39
0.98 0
II 0.30 0.39 0. 98 0
I11 0.39
0.39 0. 98 0
IV 0.29
0.39 0.97 0
V 0.30
0.39
0. 98 0
VI 0.30
0.39 0.98 0
All test groups 0. 05 0. 06 0. 16 0
68
p-
those for the other test groups is due to the additional operating time associ-
ated with the 100 hours of high-flux radiation that these components received
pri or to the begi nni ng of the 10, 000-hour life test.
The range of capacitance remained well within the specified lirnit. A
general i ncrease was observed i n the di ssi pati on factor for all test groups,
with the exception of Test Group V (50 C, vacuum, low-flux radiation environ-
ment). This would indicate that the 100 C ambient of the other test groups was
responsi bl e for the i ncrease. No dissipation-factor degradation was apparent
in the results from the radiation environments.
The results indicate that the various environmental conditions and com-
binations thereof that were included in this study offer no parti cul ar probl em
in the application of these capaci tors.
Twenty-five failures were observed in a total sample of 100 of the wet-
slug tantalum capacitors that were subjected to the five operating conditions
of this study. Three of these failures were not confirmed by final measure-
ments. Two of the remaining 22 indicated a high leakage-current condition
(approaching short circuit), and 20 were open circuits during final measure-
ments. The visual examination when the test was terminated revealed that
the plastic covering on the capacitors in Test Group I (100 C, atmospheri c
pressure, no radiation exposure) had discolored to a dark brown and become
hard, and the capacitors showed evidence of electrolyte leakage. In addition,
all specimens in Test Group I1 (100 C, vacuum, no radiation exposure) also
showed evidence of leakage, and the solder at one end of the case had mel ted
on four capacitors.
Failure-rate computations for these units, Table 12, indicated a much
hi gher fai l ure rate for the capaci tors i n Test Groups I and I1 (nonradiation
envi ronments). The hi gher val ues for Test Group I were attributed, at l east
in part, to the fact that the plastic cover was left on the capacitors in this
test group but was removed from all others as offering a possible outgassing
problem in the vacuum-environments. The plastic covers were considered
as possibly having prevented or reduced the rate at which the heat due to
internal losses could be dissipated. However, this did not explain the high
fai l ure rate for the capaci tors i n Test Group I1 (compared to that of Test
Groups III and I V), which had their plastic covers removed.
A beneficial effect from the radiation was considered an unlikely pos-
sibility, but was given as one possible explanation of the catastrophic-failure
distribution for these capacitors , i. e. , high failure rates for the nonirradi-
ated groups.
6 9
TABLE 12. FAILURE RATE FOR HP56C50D1 CAPACITOR AT 50,
60, AND 90 PERCENT CONFI DENCE LEVELS(39)
- -~
~ .~ ~ -
~~
Fai l ure Rate at I ndicated Confidence Level,
percent/ 1000 hr
Percent Recorded
"~ - . __
Test Group 50 Percent 60 Percent 90 Percent as Fai l ed
~~ __ ~~~ ~ ~~ -
I 11.82 12. 56 15.80 85
I1 7.31 7.81 10.05 30
I11 0.30
0.39
0.98 0
IV 0.75 0.89 1.74 5
V 0.75
0.90
1.72 5
All test groups 3.25 3.39 4.02 25
The results obtained on these capaci tors show that they can survi ve the
radiation environment, but the results were somewhat inconclusive because
of the excessive number of failures that occurred in the control environments.
70
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77
I NDEX
91-LD Resin 28
Acetal Resi n 27
A-C LOSS 16, 22
Acryl i c Resi ns 27
Acrylonitrile Butadiene Rubber
41, 42
Acrylonitrile Butadiene Styrene
Rubber 9, 28
Activation 40, 6 5
Aging 51, 52
Air Environment 12- 17, 23
Alkanex 35
Al l yl Carbonate Pl asti c 27
Alox 26
Alsimag 26
Aluminum 33, 48, 64, 65
Aluminum Capacitor 64-66
Aluminum I sotope 65
Aluminum Oxide 1 1, 26, 43
Aniline Formaldehyde 9
Annealing 59
Anodized 64
Applied Voltage 66
Asbestos 37
Atomic Displacements 10
Audio Frequency 53
Beryllium Oxide 11
Biological Hazard 40, 65
Blocking 48
Borate El ectrol yte 46
Breakdown Voltage 7, 24, 25, 29,
Buna-N - Use Acrylonitrile Buta-
Calcium Aluminate 36, 40
Capacitance 33, 34, 40, 43, 46,
Capaci tor Plate 46, 50, 51, 53,
Carri er Characteri sti cs 2, 3, 10, 25
79
31-33, 35, 36, 41-43, 45, 52, 64
diene Rubber
48-54, 57, 60, 61, 63-69
64
Casi ng Fracture 50
Cellulos Acetate 9, 27
Cellulose Bytyrate 27
Cel l ul ose Propi onate 27
Cements/Bonding/ 26
Cerami c Capaci tor 46, 47, 51, 52
Cerami c Gl aze 48
Cerami ci te 3 5
Cerami temp 35
Chai n Sci ssi on 7, 12, 22
Charge Equi l i brati on 48
Chemical Breakdown 6 1
Chemical Change 66
Chlorinated Polyethers 27
Chrome-Pl ati ng 26
Circuits 48-51, 53, 65
Compressive Strength 26, 29, 33,
Conductance - See Also Conduc-
38
tivity 7
Conductivity 2-7, 10, 24, 25
Conductors 26, 41
Confidence Level 59, 62, 68, 70
Constant D-C Potenti al 50
Copper 26, 28
Corona Voltages 41, 45, 60
Corrosi on 8, 33
Cracking 8, 31, 32, 41
Crosslinking 7
Cryogeni c Temperatures 14, 16,
Damage Threshol ds 1, 2, 9, 11, 12,
Dark Current 25
Density 7, 29
Diallylphthalate 6, 9, 21, 42, 43
Dielectric Breakdowns 16, 19, 20
Dielectric Constant 12, 14, 19-26,
23-25
16, 18, 19, 21-23, 31
22, 24, 25, 37, 46
28, 29, 40, 46, 52, 60
Di el ectri c Film 64
Di el ectri c Loss -- See al so Di ssi pa-
Di el ectri c Strength 12, 30, 34-37,
Dimensional Changes 29, 46
Disintegration 12, 30, 32, 41, 60
Dissipation Factor 8, 12, 14-23, 25,
tion Factor 8, 60
40, 60
28, 30, 33, 40, 43, 46-53, 57, 60,
61, 65-69
Dose Rate Effect 3-5, 60, 66,
Electrode 46, 50, 51, 53, 54, 57
Electrolyte 46, 64-66
Electrolyte Leakage 69
Electrolytic Capacitor 46, 47, 64-70
Elongation 12, 13, 18, 19, 21-24
Embrittlement 8, 12, 20, 22, 23, 26,
Encapsulation 36, 38-40, 48, 69
Epoxy Resins 5, 6, 9, 25, 26, 35,
Failure Rate 59, 63, 68, 69
Fi bergl ass 37
Fi l l ed Pol ymers 9, 18, 21, 39, 42
Flaking - See Also Disintegration 60
Flashover Voltage 7, 60
Flexure Properties 19-23, 28-33, 38
Forsteri te 11
Fused Quartz 10
Gamma Heating 46, 65
Gas Evolution 8, 33, 46, 53, 6 1, 69
Gl.ass Capacitor 46-48
Gl asses 10, 11, 29, 33, 37, 42,
Gl ass Lami nates 9, 25, 26, 28
Gl ass-to-Metal Seal s 41, 45
Hardness 7, 19, 21-23, 28, 38,
Heat Dissipation 69
Hermetic Seal 41-43, 45
H-Fi l m - Use Polyimides
28, 38
31, 35, 54, 60
36, 38-40
43) 53
43, 48
60, 69
80
I mpact Strength 18, 21, 22
I nduced Conductivity - Use Photo-
I nsulation Resistance 7, 8, 19-23,
conductivity
26, 28, 30-33, 35-38, 40-46, 48-
54, 57, 60-62
54
I onization Effect 46, 48, 51, 53,
Kaowool 37
Kapton - Use Polyimides
Kel -F - Use Polytrifluorochloro-
ethylene
Kovar 45
Leakage Current 7, 60, 64-66, 68,
Leakage Resi stance 47
Li qui d Fi l l er 60
Low Frequency Current 52
Lucalox 26
Magnesium Oxide 11, 37
Mel ami ne Formal dehyde 9, 42
Melting 69
Melting Point 7
Mica 29, 37
Mica Capacitor 46, 47, 50, 51
Mi rrors 33
Myl ar 9, 20, 34, 60, 62
Mylar Capacitor 60-64
Natural Rubber 9
Neoprene Rubber 9, 41, 42
Network 53
Nylon 6, 9, 20
Oi l I mpregnated 52, 53, 61, 62
Open Ci rcui t Fai l ure 69
Orl on 21
Oscillators 48
Oxidation 18, 19
Paper Capacitor 46, 52-60
Paper/Myl ar Capaci tor 55-60
Paper/Pl asti c Capaci tor 47, 52-60
Phenol Formaldehyde 42
Phenol i c Resi ns 9
Phosphate-Bonded Cements 26
69
Phosroc I11 ,37
Photoconductivity 2-6, 10, 25, 32
Plastic Capacitors 47, 52.-64
Pol ycarbonates 9, 27, 60
Pol yester Resi ns 9, 28
Polyethylene 5, 6, 9, 18, 19, 31,
Pol yethyl ene Terephthal ate - Use
Polyimidazopyrrolone - Use Pyrrone
Polyimides 6, 9, 24, 30, 33
Polymethyl Methacrylate 9, 27
Polyolefins, Radiation-Modified 33, 34
Polypropylene 6, 9, 22, 35
Pol ystyrene 5, 6, 9, 19, 20, 60
Polytetrafluoroethylene - Use
Pol ytri fl uorochl oroethyl ene 8, 9,
Pol yurethanes 9, 22, 23, 36, 38
Polyvinyl Butyral 9
Polyvinyl Chloride 9, 27
Polyvinylfluoride 28
Pol yvi nyl Formal 9
Polyvinylidene Chloride 9
Polyvinylidene Fluoride 9, 23
Porcel ai n Di el ectri c Capaci tor 48, 49
Potting - Use Encapsulation
Pressure Bui l dup 46, 53, 54, 6 1
Pyroceram 26
Pyrrone 24, 25
Quartz 10, 11, 37
Recovery Characteri sti cs 14, 16- 18,
30, 32, 38, 40, 41, 43, 45, 48, 49,
51, 52
32, 34, 60
Mylar
Teflon
16, 18
Refrasi l 3 7
Reliability I ndices 54, 55, 58, 62,
Resistivity - Use Conductivity
R-F Appl i cati on 48
Rupture 54, - 6 1, 63
63, 67
Sapphi re 1 1
Seal i ng Properti es 41
Seals 41-43, 45, 53, 65, 66, 69
Shielding 49
Short Ci rcui t Fai l ure 54
Silica 26, 37
Silicone-Alkyd 3 5
Silicone Resins 9, 28, 36
Silicone Rubbers 9, 32, 35, 36, 38,
Silver 48, 50, 51
Si l ver -I on Migration 50
Sodium I sotope 65
Softeni ng Poi nt Temperature 18
Solder 69
Solubility 7
Spinel 11
Steatite 26
Stress 60
Styrene Acrylic Copolymer 27
Styrene Acrylonitrile Copolymer 28
Styrene Butadiene Rubber 9, 28
Styrene Divinylbenzene 28
Surface Resistivity 18-20, 26, 28
Swelling 46
Tantalum 64, 65
Tantalum Capacitor 64-70
Tantalum I sotope 65
Teflon 6, 8, 9, 12-17, 27, 30, 31,
Temperature Cycl i ng 55-57
Temperature Effects 12, 24, 25,
41, 43
41, 65, 66
32, 34, 46, 50-52, 54, 59, 62,
64-67
Tensile Strength 7, 12, 18, 19,
Urea Formal dehyde 9
Vacuum 12-17, 23, 30, 34
Vinyl Chloride-Acetate 9, 28
Vi treous Enamel Capacitor 48
Volume Resistivity 12, 14, 18-20,
21-24, 26, 28, 29, 38
23, 26, 28, 40
E
81
Volumetric Efficiency 64
Wax I mpregnated 48, 52, 61, 62
82
Weight Loss 22, 28, 36-38
Y ield Strength 24
NASA-Langley, 1971 - 9 CR-1787
N A S A C O N T R A C T O R
R E P O R T
RADIATION EFFECTS
DESIGN HANDBOOK
.
Section 4. Transistors
by J. E. Drenndn and D. J. Hamman
Prepared by
RADIATION EFFECTS INFORMATION CENTER
BATTELLE MEMORIAL INSTITUTE
Columbus, Ohio 43201
for
NA TI ONA L A ERONA UTI CS A ND SPA CE A DMI NI STRA TI ON WASHI NGTON, D. C. A UGUST 1971
I
. .
TECH LIBRARY KAFB, NM
1. R e m No.
4I-Title-and~Subtitle 5. Report Date
. . "" ~-~ :" " .- ~
~ ~~
2. Government Accession No. 3. Recipient's C a t a l o g No.
NASA CR-1834
~ ..
. ~~~~
-
RADIATION EFFECTS DESIGN HANDBOOK
6. Performing Organization Code
SECTION 4 . TRANSISTORS
August 1971
7. Author(s)
~~ ~
~~ ..
8. Performing Organization Report No.
J. E. Drennan and D. J. Hamman
- __ ~ ~ _ _ ~ ~
~~~ ~~ 10. Work Unit No.
9. Performing Organization Name and Address
RADIATION EFFECTS INFORMATION CENTER
Battel l e Memorial I nsti tute
Columbus, Ohio 43201
NASW-1568 Columbus Laboratori es
11. Contract or Grant No.
~
13. Type of Repor t and Period Covered
2. Sponsoring Agency Name and Address
Contractor Report
Nati onal Aeronauti cs and Space Administration
Washington, D. C. 20.546
14. Sponsoring Agency Code
5. Supplementary Notes
T hi s document contai ns summarized i nformati on rel ati ng to steady-state
radi ati on ef f ects on transi stors. The radi ati ons consi dered i ncl ude neutrons,
protons, el ectrons, and el ectromagneti c. The information i s useful to the desi gn
engi neer for esti mati ng the effects of radi ati on on transi stors.
7. KeiWords (Suggested by Authoris)) I 18. Distribution Statement
Radi ati on effects, Transi stors, Semi conductors,
Bi pol ar Transi stor, Uni j uncti on Transi stors,
JFETS, MOSFET
Unclassified-Unlimited
9. Security aasif. (of this report) 20. Security Classif. (of this page) I 21. Noi ; ' Pages I 22. Rice'
Uncl assi fi ed Uncl assi fi ed $3 .oo
.
For sale by the National Technical Information Service, Springfield, Virginia 22151
ACKNOWLEDGMENTS
L
The Radi ati on Ef f ects I nf ormati on Center owes thanks to
several i ndi vi dual s for thei r comments and suggesti ons duri ng
the preparati on of thi s document. The ef f or t was moni tored and
funded by the Space Vehi cl es Di vi si on and the Power and El ectri c
Propul si on Di vi si on of the Of f i ce of Advanced Research and
Technol ogy, NASA Headquarters, Washi ngton, D. C., and the AEC-
NASA Space Nucl ear Propul si on Offi ce, Germantown, Maryl and.
Al so, we are i ndebted to the f ol l owi ng f or thei r techni cal
revi ew and val uabl e comments on thi s secti on:
M r . R. A. Breckenri dge, NASA-Langley Research Center
Dr . A. G. Hol mes-Si edl e, RCA
M r . S. Manson, NASA Hq.
M r . D. Miller, NASA-Space Nucl ear Systems Of f i ce
M r . A. Reetz, J r., NASA Hq.
Dr. A. G. Stanl ey, Massachusetts I nsti tute of Technol ogy
M r . W. T. Whi te, NASA-Marshall Space Fl i ght Center
PREFACE
This is the fourth section of a Radiatiofi Effects Design Handbook
designed to aid engineers in the design of equipment for operation in the
radiation environments to be found in space, be they natural or arti fi ci al .
This Handbook will provide the general background and information neces-
sary to enable designers to choose suitable types of materi al s or cl asses
of devices .
Other sections of the Handbook discuss such subjects as solar cells,
thermal -control coati ngs, structural metal s, i nteracti ons of radiation,
el ectri cal i nsul ati ng materi ai s, and capaci tors.
V
SECTION 4. TRANSISTORS
INTRODUCTION
This portion of the Handbook presents information about the effects of
radiation on bipolar transistors, unijunction transistors, and field-effect
transistors (FET's). Data presentation is graphic wherever possible, con-
sisting of envelopes that enclose the data points for a particular parameter.
Where possible, representative sets of data points also are plotted.
The reader is cautioned that the intent of the presentation in the fol-
lowing paragraphs is to give a broad picture of radiation effects on general
cl asses of transi stors. If the intended application requires a radiation
fluence greater than that for which information is presented, further infor-
mation for the specific device of interest should be sought.
BIPOLAR TRANSISTORS
The two structures of bi pol ar transi stors are shown schematically
Figure 1. Both silicon and germanium bipolar transistors are available
. both of these structures.
in
in
The radiation effects of greatest significance'' in bipolar transistors
are the displacements in the semiconductor crystal lattice caused by the
incident radiation. Radiation particles lose energy primarily by elastic
collisions with the semiconductor atoms and, depending on type and energy,
may cause l arge di sordered cl usters to be formed within the material.
Electromagnetic radiation, in contrast, loses energy by creating Compton
electrons which then may cause lattice displacements. Since electrons
have such a small mass, however, they primarily cause Frenkel defects '
(vacancy-interstitial pairs) rather than clusters of defects. Lattice damage
due to electromagnetic radiation is usually of secondary importance unless
a large dose (greater than l o5 rads) is absorbed by the material.
Lattice damage degrades the electrical characteristics of bipolar
transi stors by i ncreasi ng the number of trapping, scattering, and recom-
bination centers as follows:
*At high radiation intensities such as may be experienced in a pulse environment, other effects may be
dominant.
C '
P
Emitter
2 Collector
6
Base
a. NPN Transistor Structural
Diagram
d
E
b. NPN Transistor
Schematic Symbol
C
Emitter d ~ k ~~ Collector i-4
c. .-PNP Transistor Structural d. PNP Transistor
Base
E
Diagram Schematic Symbol
FIGURE 1. STRUCTURAL DIAGRAMS AND SCHEMATIC SYMBOLS
FOR BIPOLAR TRANSISTORS
2
(1) The trapping center.s remove carriers from the conduc-
tion process. N- and P-type silicon -gradually changes
toward intrinsic material with increased radiation expo- \
sure. N-type germanium irradiated with neutrons or
protons is converted to P-type. The conductivity of
P-type germani um i ncreases or decreases monotonically
with bombardment, approaching the same limiting value
that the converted N-type reaches.
(2) The additional scattering centers reduce the mean-free
path of the free carri ers. Si nce the mobi l i ty i s di rectl y
proportional to the mean-free path, radiation exposure
reduces the mobility of charge carri ers.
( 3 ) The recombination centers decrease the minority-carrier
lifetime according to the relationship:
(See Introduction to Section l ., Semiconductor Devices. )
The dominant radiation effect for bipolar transistors is the degrada-
tion of the forward current gain (hFE, p ) resulting from the radiation-
induced decrease of mi nori ty-carri er l i feti me, 7, p is defined by:
2D
p z - 7 ,
W2
where
D = diffusion constant
W =effective base width.
Simple theory predicts a linear change in reciprocal low frequency gain,
1/p, with fluence as shown by the relation:
where
h
&, = common-emitter low frequency gain at some value
of fluence
Po = preirradiation common-emitter low frequency gain
@ = radiation fluence (particle/cm )
2
KT = minority-carrier-lifetime damage constant for the
material and type of radiation
D
f ac 0
=f (-) = alpha cutoff frequency defined as the frequency at
W2 which the magnitude of the common-base small-
signal current gain is reduced to 70.7 percent of
its initial value.
At the low fluence, 1/p does not depend linearly on fluence, an effect
attributed to surface damage. A power-law f i t of data obtained at low
A (1//3), is proportional to (@)n, where 0 <n <1. Hence, the general ex-
pression for silicon-transistor low-frequency current-gain degradation for
fluence levels sufficiently low that conductivity changes are neglible is
where
Kb
K
= bulk-damage constant = ('* 22) ( (cm 2 /parti cl e)
2n faco
KS = surface-damage constant (cm /particle)
2
n = a positive exponent greater than 0 but less than 1
[A (1//3)] sat = the saturated value of the surface-damage curve
(' 1 s at
= the fluence level at which saturation of the surface-
damage curve occurs (particles/cm 2 ).
This relation provides the basic tool for estimating the degradation of
transistor-current gain caused by radiation by means of the quantities Kb,
K,, n, and the measurabl e parameters of the device, Po and faco. The
~
4
greatest uncertainties in using this relation are the values of the damage
constants, Kb and K,, and the exponent, n. This is because the- values for
a given transistor may vary widely with current density and impu'rity vari-
ations of the base material. The values will *also depend upon the type and
energy of the bombarding particle.
At the present time, experimental values of Kb, KT, K,, and n are
extremely limited. Further, it 'must be recognized that the radiation-
induced change of the bipolar transistor current gain also will depend on
the type of semiconductor material, type of impurity (N or P), resistivity,
fabrication technique, device structure, etc., as well as injection level,
temperature, electrical bias conditions, energy spectrum of the incident
radiation, and the time since the radiation exposuke. Accordingly, the
available theory cannot be applied effectively for detailed predictions of
expected radiation effects for a specific application. However, the theory
does provide a basis for presenting generalized information useful in guid-
ing decisions about application of transistors in radiation environments.
Thus, one can estimate whether or not a radiation effects problem is likely
to exist for a specific application and i f such is the case, then steps can be
taken to obtain the necessary specific information.
The theory has been applied to approximate Kb using available experi-
mental values of A (1/P) and @ in the relation:
This approximation is larger than the theoretical 7 I alue of KF. b ~y the amount
[ A (l / p)J sat/O. Available data generally do not provide an experimental
value of [ A (1 / P ) ] sat, so only the approximate value of Kb can be calculated.
U
The calculated value of Kb is used to estimate the value of fluence,
@50, for which the theory predicts that the gain would be 50 percent of i ts
initial value :
ced d The radiation-indu
to follow:
.egradation of the beta ratio, Pn, i s shown by theory
5
where @ is the fluerice for which a beta ratio value of Pn is predicted by
the theory.
Pn
The available data for bipolar transistors have been grouped accord-
ing to the application for which each transistor was designed. The five
application groups used are: audio and general purpose, high frequency,
low-level switching, high-level switching, and power. Equations (5) and
(6) were used to estimate values of Kb and @50 for each experimental data
poini. for which meaningful degradation was observed. The maximum and
minimum values of @50 for each application group were used with
Equation (7) to generate an envelope of potentially significant radiation
damage that includes the available data.
Figures 2 through 21 present plots"' of the radiation-effects envelopes
obtained for each application for each of the radiation environments: neu-
tron, proton, electron, and electromagnetic. Points for selected sets of
bipolar transistor data are included on these plots. Table 1 l i sts the max-
imum, minimum, and median Kb values determined for each application-
environment category and the number of sets of data used to establish these
values .
In applying the plots, one should determine i f the specific environ-
ment of i nterest l i es: (1) outside the envelope i n the low-fluence region,
( 2) . within the envelope, or ( 3 ) outside the envelope in the high-fluence
region. The interpretation of these three al ternati ves i s that for Case 1
there probably is no radiation effects problem; Case 2 signifies a potential
problem with radiation effects indicating that additional information should .
be obtained; and Case 3 indicates a virtual certainty of severe radiation
effects implying a high probability that bipolar transistors will not perform
satisfactorily in this specific application.
*The low frequency common emitter current gain ratio, @n = Bo/ Bo =BF/B,, is plotted versus fluence,
The number of data sets listed on the figures i s the total number of ( fin, CP ) points available from which
those plotted were selected as representative.
6
T
"
I .o
0.8
q.f 0.6
\
qL 0.4
0.2
FI GURE 2 , NEUTRON ENVI RONMENT AUDI O AND GENERAL PURPOSE
APPLI CATI ONS, BI POLAR TRANSI STOR BETA RATI O
VERSUS FL UENCE
21 sets of data
Fluence, n/cm2
FI GURE 3. NEUTRON ENVI RONMENT HI GH-FREQUENCY APPLI CATI ONS,
BI POLAR TRANSI STOR BETA RATI O VERSUS FLUENCE . .
131 s et s of data
I .o
0.8
1 0.6
0.4
0.2
0.0
FI GURE 4. NEUTRON ENVI RONMENT LOW-LEVEL-SWI TCHI NG
APPLI CATI ONS, BI POLAR TRANSI STOR BETA RATI O
VERSUS FLUENCE
62 sets of data
Fluence, n/cm2
FI GURE 5. NEUTRON ENVI RONMENT HI GH-LEVEL-SWI TCHI NG
APPLI CATI ONS, BI POLAR TRANSI STOR BETA RATI O
VERSUS FLUENCE
73 sets of data
FI uence, n/cm2
FI GURE 6. NEUTRON ENVI RONMENT POWER APPLI CATI ONS,
BI POLAR TRANSI STOR BETA RATI O VERSUS
FL UENCE
7 2 sets of data
I .o
0.8
0.6
\
0.4
0.2
0.0
FI GURE 7. PROTON ENVI RONMENT AUDI O AND GENERAL PURPOSE
APPLI CATI ONS, BI POLAR TRANSI STOR BETA RATI O
VERSUS FL UENCE
3 sets of data
9
I .o
0.8
$ o.6
a" 0.4
0.2
0.0
. FI GURE 8. PROTON ENVI RONMENT HI GH-FREQUENCY APPLI CATI ONS,
BI POL AR TRANSI STOR BETA RATI O VERSUS FL UENCE
29 sets of data
I .o
0.8
0.2
0.0
109 IOIO IOII IO'* 1013 loi4 loi5
Fluence, p/cm2
FI GURE 9. PROTON ENVI RONMENT LOW-LEVEL-SWI TCHI NG
APPLI CATI ONS, BI POLAR TRANSLSTOR BETA RATI O
VERSUS FL UENCE
11 sets of data
10
I .o
0.8
6 0.6
& 0.4
0.2
\
0.0
FI GURE 10. PROTON ENVI RONMENT HI GH-LEVEL-SWI TCHI NG
APPLI CATI ONS, BI POLAR TRANSI STOR BETA
RATI O VERSUS FLUENCE
26 sets of data
Fluence, p/cm2
FI GURE 1 1 . PROTON ENVI RONMENT POWER APPLI CATI ONS,
BI POLAR TRANSI STOR BETA RATI O VERSUS
FL UENCE
26 sets of data
11
Fluence, e/cm2
FI GURE 12. ELECTRON ENVI RONMENT AUDI O AND GENERAL
PURPOSE APPLI CATI ONS, BI POLAR TRANSI STOR
BETA RATI O VERSUS FL UENCE
78 s e t s of data
Fluence, e/cm2
FI GURE 13. ELECTRON ENVI RONMENT HI GH-FREQUENCY APPLI CATI ONS,
BI POLAR c TRANSI STOR BETA RATI O VERSUS FLUENCE
288 sets of data
12
. . - . . ...
FIGURE 14. ELECTRON ENVIRONMENT LOW-LEVEL-
SWITCHING APPLICATIONS, BIPOLAR
TRANSISTOR BETA RATIO VERSUS FLUENCE
64 s e t s of data
0.2
0.0 0.4 L l L " -
IOIO IOII IO'* toi3 loi4 lot5 lot6
Fluence, e/cm*
FIGURE 15. ELECTRON ENVIRONMENT HIGH-LEVEL-SWITCHING
APPLICATIONS, BIPOLAR TRANSISTOR BETA RATIO
VERSUS FLUENCE
146 s e t s of data
I .o
0.8
6 0.6
@? 0.4
\
0.2
0.0
FI GURE 16. EL ECTRON ENVI RONMENT POWER APPL I CATI ONS,
BI POLAR TRANSI STOR BETA RATI O VERSUS
FL UENCE
167 sets of data
1.0
0.8
5 0.6
a" 0.4
\
0.2
0.0
101 102 103 lo4 105 106 107 to8 109 to1O
Fluence, rads (material)
FI GURE 17. ELECTROMAGNETI C ENVI RONMENT AUDI O AND GENERAL
PURPOSE APPLI CATI ONS, BI POLAR TRANSI STOR BETA
RATI O VERSUS FLUENCE
33 sets of data
14
I .o
0.8
@? 0.4
0.2
0.0
IO' IO* 103 lo4 lo5 lo6 lo7 loe lo9
Fluence, rads (material).
IO'O
FI GURE 18. ELECTROMAGNETI C ENVI RONMENT HI GH-FREQUENCY
APPLI CATI ONS, BI POLAR TRANSI STOR BETA RATI O
VERSUS FL UENCE
164 sets of data
1.0
0.8
QO 0.6
Q 0.4
\
LL
0.2
0.0
FI GURE 19. ELECTROMAGNETI C ENVI RONMENT LOW-LEVEL-SWI TCHI NG
APPLI CATI ONS, BI POLAR TRANSI STOR BETA RATI O
VERSUS FL UENCE
59 sets of data
FI GURE 20. ELECTROMAGNETI C ENVI RONMENT HI GH-LEVEL-SWI TCHI NG
APPLI CATI ONS, BI POLAR TRANSI STOR BETA RATI O VERSUS
FL UENCE
106 sets of data
FI GURE 2 1. ELECTROMAGNETI C ENVI RONMENT POWER
APPLI CATI ONS, BI POLAR TRANSI STOR BETA
RATI O VERSUS FL UENCE
120 s e t s of data
16
TABL E 1. RANGE AND MEDIAN VALUES OF' BULK DAMAGE CONSTANT, Kb,
FOR VARIOUS APPLICATION-ENVIRONMENT COMBINATIONS
I
Si ze of Data
Envi ronment Mi ni mum Kb Medi an Kb Maxi mum Kb Base(a)
Audi o and General Purpose Appl i cati ons
Neutron 3.96 X cm2/ n 3.38 x cm2/ n 2.62 x cm2/n 21
Proton 5.08 X
cm2/ p
7.00 x
cm2/ p
1.11 x 10-14 cm2/p 3
El ectron 7.38 x cm2/ e 1.72 x cm2/ e 5.63 x cm2/ e 78
El ectromagneti c
2.43 x rad- l 1.43 x rad-' 1.92 x rad-l 33
Hi gh-Frequency Appl i cati ons
Neutron 3.57 x 10- l ~ cm2/ n 4.52 x 10-16 cm /n 1.10 x 10- 14cm2/n 131
Proton 6.24 x cm2/p 1.26 x 10-14 cm /P 2. 38. ~ c m /p 29
El ectron ' 7.38 x cm2/e 3.71 x 10- 17 cm /e 6.70 X cm2/e 288
El ectromagneti c 5.85 x 10- l ' rad- l 8.10 x 10-9 rad-l 1.92 X rad-1 164
2
2 2
2
Low-Level -Swi tchi ng Appl i cati ons
Neutron 1.52 X cm2/n 3.99 x 10-16 cm /n 2.56 x cm2/n 62
Proton 1.66 X cm2/p 5.72 x 10- 15 cm /P 5.50 x cm2/ p 11
El ectron 7.38 X cm /e 1.28 x cm2/e 64 2.73 x 10- 17 cm /e
El ectromagneti c 2.10 x rad-' 1.37 X rad- l 2. 44 x rad- l 59
2
2
2 2
Hi gh-Level -Swi tchi ng Appl i cati ons
Neutron 1. 15 x cm2/n 5.46 X cm2/n 4.60 x 10-14 cm2/n 73
Proton 1.77 x 10- l ~ cm2/ p 1. 29 X cm2/p 7.00 x 10- l 4 cm /P
26
El ectron 2.22 x 10-18 cm2/e 3.94 x 10-17 cm / e
146
El ectromagneti c 5.85 x rad-l 5.95 X 10-9 rad-l 2.39 x rad- ' 106
2
2 2
5.00 x 10- 15 cm /e
Power ADDl i cati ons
Neutron 5.25 X cm /n 1.30 x cm2/n 1.21 x 10-13 cm /n
72
Proton 1.77 X cm / p 1.29 X cm2/p 7.00 x 10-14 cm2/p 26
El ectron 4.27 X crn2/e 5.87 x cm2/e 6. 70 X cm / e
167
El ectromagneti c 5.85 x rad-' 4.27 x 10-9 rad-1 2.39 x rad-' 120
2
2
2
2
(a) The si ze of the data base gi ves the number of computed val ues of Kb used to determi ne the l i sted range and
medi an val ues.
UNIJ UNCTION TRANSISTORS
The .unijunction transistor structure is shown schemati cal l y i n
Figure 22. Sometimes called a "double-base diode", this device displays
a negative resistance characteristic which results from conductivity modu-
lation of a moderatel y hi gh resi sti vi ty si l i con bar by means of injected
mi nori ty carri ers from the recti fyi ng emi tter contact. It is thus highly
sensitive to radiation-induced changes in minority-carrier lifetime and
resistivity.
6
Emitter
B2
P
b
B i
a. Unijunction Transistor Structural Diagram b. Unijunction Transistor
Schematic Symbol
FIGURE 22. STRUCTURAL DIAGRAM AND SCHEMATIC SYMBOL
FOR UNIJ UNCTION TRANSISTORS
The very limited amount of radiation-effects data that is available
for unijunction transistors verifies that these devices have a very high
sensitivity to radiation. The distance between the two ohmic base con-
tacts i s of the order of 5 x cm. Thi s corresponds to a bi pol ar tran-
si stor with an exceptionally wide base and resul ts i n the formati on of an
enormous number of trapping centers because of i rradi ati on. The el ectri -
cal effects of these trapping centers are further enhanced-by the initially
high silicon resistivity. Relatively low radiation fluences will significantly
increase the resistivity of the N-type bar and change most of the properti es
of the device. '" Ultimately most of the holes injected into the bar are
captured.
.L
The very significant changes observed in almost all of the important
unijunction transistor parameters after relatively low radiation exposures
*Stanley, A. G. , "Effect of Electron I rradiation on Electronic Devices", Technical Report 403,
Massachusetts Institute of Technology, Lincoln Laboratory, November 3, 1965.
18
I
lead to the conclusion that the use of these devices in a yadiation environ-
ment should be approached with caution, If thei r use is unavoidable, esti-
mates of expected radiation effects can be ma'de by comparison to the least
radiation tolerant of the bipolar power transistors. Thus, adverse changes
in the unijunction transistor parameters can be expected to be similar to
the radiation-induced change in beta shown by the minimum envelope bound-
ari es for power transi stors i n Fi gures 6, 11, 16, and 21.
FI ELD-EFFECT TRANSISTORS
Fi el d-effect transi stors are uni pol ar devi ces which operate by
electric-field control of maj ori ty-carri er conduction. The two basic types
of field-effect transistors are the junction-field-effect transistor (J FET)
and the insulated-gate-field-effect transistor (I GFET), discussed in the fol-
lowing paragraphs ~
J unction-Field-Effect Transistors
A P N junction is the interface between channel and gate in a J FET.
The structure i s di agrammed and the schemati c symbol shown in Figure 23
for both N-channel and P-channel J FET's. All J FET's operate in the de-
pletion mode where a reverse bias, applied between gate and source, con-
trol s the current flow. Under these conditions a depletion region surrounds
the channel of the J FET. The value of gate-to-source bias voltage (for zero
or small drain-source voltage), for which the depletion region penetrates
(from both sides) the entire thickness of the channel thus "pinching off" the
current flow, is called the "pinch-off" voltage, Vpo Wi th a zero gate-to-
source bias voltage the current flow i s a maximum.
For the N-channel J FET's, a negative gate voltage turns the device
off, whereas for the P-channel J FET's a positive gate voltage is necessary
to stop device conduction. FET's have a high input impedance relative to
that of bipolar transistors and provide a vol tage gai n measured i n terms of
transconductance, Gm, similar to vacuurn pentode tubes. A third important
parameter is the total gate leakage current, I gss, which is the current flow-
ing from gate to channel for a zero drain-to-source potential. These three
J FET parameters are the most sensitive to radiation damage.
Source
Drain
P
N
a. N- Channel J FET Structural Diagram
"0
Gate
0
Source Drain
c. P-Channel J FET Structural Diagram
Gate
+D
P
- s
b. N-Channel J FET Schematic Symbol
- D
b
+s
d. P-Channel J FET Schematic Symbol
FIGURE 23. STRUCTURAL DIAGRAMS AND SCHEMATIC SYMBOLS FOR
N- AND P-CHANNEL J UNCTION-FIELD-EFFECT
TRANSISTORS
x)
. ~ "" -
The general effects of radiation on J FET's can be summarized as
follows :
(1) The transconductance, Gm, and the "pinch-off" voltage,
wi l l decrease because of a radiation-induced change
vP,
in effective impurity concentration that increases channel
, resistivity and changes carrier mobility.
(2) I ncreases i n l eakage current, Igss, will be observed as
a resul t of radiation-induced carrier generation surface
contaminants near the junction edge and recombination-
generation in the depletion region due to the introduction
of recombination levels deep in the eneEgy gap.
Representative values' for the rati o of postirradiation to prei rradi a-
tion transconductance, Gm(F)/Gm(O), are plotted versus fluence for
P-channel J FET's i n Fi gures 24 and 25 in the neutron and the electromag-
netic environment, respectively. Available information is too limited to
permi t similar plots for other radiation environments or for N-channel
J FET's. However, based on observations for a very few part types it
appears that significant radiation-induced decreases in J FET Gm would not
be expected for fluences less than 1011 n/cm2, or 1015 e/cm2, or 105 rads
(Si) of electromagnetic radiation. No proton data for J FET I s are available.
Of course, specific device types may have superior radiation tolerance but
the information presently available permits only these generalizations.
.b
The data available showing the effects of radiation on Vp for J FET's
are too l i mi ted to permi t the presentation of trend plots. However, it
appears that the fluences producing significant reductions in the value of
thi s parameter are at l east as l arge as those producing significant reduc-
tions in Gm.
The significance of radiation-induced increases in I depends upon
the circuit usage. Where signal levels are high; i ncreased val ues of Igss
can often be tolerated without degrading circuit performance. h low-level
circuits small values of leakage current can be detrimental.
gss
The information available about radiation-induced leakage currents in
J FET's al so is very l i mi ted. Fi gure 26 shows available values for the ratio
of posti rradi ati on to prei rradi ati on P-channel J FET l eakage current,
I gss(F)/I gss(0), plotted versus neutron fluence. These data are for a single
T he values plotted fo the neutron environment are representative of 28 Sets of data available for four device
types. For the elect )magnetic environment the plotted values represent 143 sets of data available for six
device types.
-
21
c-
I .6
"i 1.21
0
W
c5 X
\
X
X
0 .o I
IO 1013 loi4 1015 10'6
Fluence, n/crn2
FI GURE 24. NEUTRON ENVI RONMENT, P-CHANNEL J UNCTI ON-FEL D-
EFFECT TRANSI STOR, RADI ATI ON EFFECT ON
TRANSCONDUCTANCE
28 sets of data
2.0
X
IO 104 lo5 IO6 lo7 IO*
Fluence, rads (material)
FI GURE 25. ELECTROMAGNETI C ENVI RONMENT, P-CHANNEL J UNCTI ON-
FI ELD-EFFECT TRANSI STOR, RADI ATI ON EFFECT ON
TRANSCONDUCTANCE
143 sets of data
22
0
-8
U
\
cz,
h
LL
Y
u)
u)
cz,
J-l
X
X
FI GURE 26. NEUTRON ENVLRONMENT, P-CHANNEL J UNCTI ON-FI ELD-
EFFECT TRANSI STOR, RADI ATI ON EFFECT ON
L EAK AGECURRENT
6 sets of data
FI GURE 2 7.
6.8 847
X
52
36
20
4
IO 6 lo7
Fluence, rads(material1
IO8
ELECTROMAGNETI C ENVI RONMENT, N-CHANNEL J UNCTI ON-
FI EL D-EFFECT TRANSI STOR, RADI ATI ON EFFECT ON
LEAKAGE CURRENT
3 s et s of data
. part type, the TIX693. The I gss(F)/I gss(0) data available for a 2N3089A
N-channel J FET at three el ectromagneti c fl uences are pl otted i n Fi gure 27.
Generalizations about the fluences for which radiation-induced leakage cur -
rents become significant cannot be made until additional experimental data
on other part types becomes available and unless usage'is known.
I nsulated-Gate-Field-Effect Transistors
The I GFET has a dielectric layer that insulates the channel from the
gate. There are several di el ectri c materi al s used for thi s l ayer, but the
most common is silicon dioxide (SiO2). An I GFET using Si02 as dielectric
is normally called a metal-oxide-semiconductor field-effect transistor
(MOSFET).
Thin-film field-effect transistors (TFT's) constitute another impor-
tant category of I GFET's. The TFT's employ geometrically controlled sur-
face films on a polycrystalline substrate. Typical semiconductor films
employed are: cadmium selenide (CdSe), cadmium sulfide (CdS), or
epitaxially deposited silicon, while the substrate m-aterial is usually glass,
cerami c, or sapphire.
Metal-Oxide-Semiconductor Field-
Effect Transi stors
MOSFET's are constructed to operate i n one or both of the depletion
or enhancement modes. In the depletion mode a reverse bias applied be-
tween gate and source produces a depletion region surrounding the channel
thereby reducing the current flow. As for the J FET's the bi as for which the
current cuts off completely, is called "pinch-off'' voltage, Vp. With zero
gate voltage, the current flow is heavy. The structural diagrams and sche-
matic syrrrbols for depletion mode MOSFET's are shown in Figure 28.
In the enhancement-mode MOSFET, the application of reverse bi as
between gate and source induces a channel, increasing or "enhancing" the
current flow. Wi th zero gate voltage, the source to drain structure looks
like two P N junctions back to back and there is no current flow. The
structural diagrams and schematic symbols for enhancement MOSFET's
are shown in Figure 29. Some MOSFET types are constructed for operation
in either the depletion mode or in the enhancement mode.
Transconductance, Gm, gate leakage current, I gss; and "pinch-off"
voltage, Vp , are i mportant parameters for depl eti on mode MOSFET's as
24
N-Channel
7 Gate r
SiO, Insulator
Source
a. N-Channel Depletion MOSFET
Structural Diagram
P- Channel Gate r SiO, Insulator
Source
c. P-C hannel Depletion MOSFET
Structural Diagram
b. N-Channel Depletion MOSFET
Schematic Symbol
- D
9
d. P-Channel Depletion MOSFET
Schematic Symbol
FIGURE 28. STRUCTURAL DIAGRAMS AND SCHEMATIC SYMBOLS FOR
N- AND P-CHANNEL DEPLETION METAL-OXIDE-
SEMICONDUCTOR FI ELD-EFFECT TRANSISTORS
N-Channel Si02 Insulator
Source
a. N-Channel Enhancement MOSFET
Structural Diagram
P- Channel SiO, Insulator
Source
c. P-Channel Enhancement MOSFET
Structural Diagram
- s
b. N-Channel Enhancement MOSFET
Schematic Symbol
- D
P
d. P-Channel Enhancement MOSFET
Schematic Symbol
FIGURE 29, STRUCTURAL DIAGRAMS AND SCHEMATIC SYMBOLS FOR
N- AND P-CHANNEL ENHANCEMENT METAL-OXIDE-
SEMICONDUCTOR FI ELD-EFFECT TRANSISTORS
they are for J .FET's. For the enhancement mode MOSFET's, the i mpor-
tant voltage parameter is the threshold voltage, Vgth, which is the voltage
from gate to source required to enhance the Lhannel and thus increase cur-
rent flow. The important leakage current for enhancement mode MOSFET's
is the drain to substrate leakage current, Idss.
The general effects of radiation on MOSFET's can be summari zed as
"
follows :
(1) The threshold voltage, Vgth, will increase because
radiation induces (by ionization) a buildup of a positive
charge in the Si02 layer that is semipermanent (months).
These changes in V,gth affect most of the other MOSFET
parameters.
(2) I ncreases in the leakage currents, I,,, or I dss, are
observed as the resul t of carri er generati on-
recombination in the depletion region and surface con-
taminants near the junction edge.
(3) Changes in channel resistivity and carrier mobility result
from radiation-induced changes in the effective impurity
concentration causing decreases in Vp and Gm.
Damage in MOSFET's is caused primarily by ionizing radiation. The
most radiation-sensitive MOSFET parameter is the threshold voltage,
Vgth, for enhancement mode devices, or the "pinch-off" voltage, Vp, for
depletion-mode devices. In general, degradation of Vgth or Vp proceeds
rapidly in the range of 103 to 104 R, but becomes more gradual above this
exposure. Complete failure i. e. , zero transconductance, has been
observed at exposures of 10 6 to 107 R.
A s previously stated, changes in Vgth in MOSFET's result from
radiation-induced surface charge at the Si-Si02 interface. These voltage
changes caused by the charge buildup have the same effect as voltage app1,ied
directly to the gate; e.,g. , the current-voltage curves for MOSFET's approx-
imately retain their shape but are translated to more negative gate biases
with radiation. Because of rapid recombination in the silicon region, no
permanent changes result from charges generated in the silicon. However,
in silicon dioxide the radiation-generated holes are relatively immobile and
are trapped or recombined before they leave the oxide. The electrons are
mobile 'and thus drift toward the positive electrode where they are removed
from the oxide. Since electrons cannot enter the oxide from the silicon be-
cause of the potential barrier at the Si-Si02 interface, a positive charge.
builds up near the interface. The charge increases and then saturates with
increasing.dose. The saturation value of the positive ch'arge depends on the
gate potential.
*
The exact dependence of the saturated value of radiation-induced
charge on the gate bias is determined by the distribution of the charges in
the oxide.. Normally, a nearly linear dependence 0-f charge-saturation
value on gate voltage is observed over a range of several volts. The charge
buildup appears to be independent of oxide thickness, indicating a dependence
on gate voltage but not on the applied field. The charge buildup is indepen-
dent of the dose rate at least for positive gate voltages. <''; Some dose-rate
dependence of the charge buildup has been observed for zero and negative
gate voltage.
.I.
. a-
Available information showing the effects of radiation on MOSFET's
i s l i mi ted to a few measurements of a few part types. The values available
for Gm(F)/Gm(0) and Vgth(F)/Vgth(0) are listed together with the fluence in
Table 2 . Representative values of vgth(F)/Vgth(0) sel ected from 22 mea-
surements for the two types of P-channel enhancement MOSFET's are
plotted versus I . 5 MeV electron fluence in Figure 30. No leakage current
data are available at this time.
Other I nsulated-Gate-Field-
Effect Transistors
Metal-insulator-semiconductor field-effect transistors (MI SFET's)
are I GFET structures that have a material other than silicon dioxide as a
gate insulator. Metal-.nitride-silicon (MNS) and metal-nitride-oxide-
silicon (MNOS) structures exemplify this class of devices. These devices
are of parti cul ar i nterest where a high radiation flux exists in the use
environment since laboratory prototype devices indicate an improved radia-
tion tolerance to flux dependent effects. No specific information is avail-
able for commercial MI SFET devices at high radiation fluences but it i s
reasonable to expect a performance comparable to that of MOSFET devices.
Wi tchel l , I. P., "Radiation-I nduced Space-Charge Buildup in MOS Structures", IEEE Transactions on
Electron Devices, ED- 14, November, 1967, p. 7'74.
-now, E. H., et al., "Radiation Study on MOS Structures", Fairchild Semiconductor, Contract AF 19(628)-
5747, J anuary, 1967.
28
FIGURE 30. ELECTRON ENVIRONMENT, P-CHANNEL MOS
FI ELD-EFFECT TRANSISTOR, RADIATION-
EFFECT ON GATE THRESHOLD VOLTAGE
Twenty-two sets of data.
Thi n-Fi l m Transi stors
As previ ousl y stated TFT's consi st essenti al l y of an FET structure
deposited on a polycrystalline substrate. Various combinations of semi -
conductor films, gate insulating materials and substrate materials may
be used. Most of the small amount of available radiation-effects informa-
ti on for TFT's is for developmental devices and its applicability to pro-
duction types is questionable. In general, it appears that TFT's can be
expected to respond to radiation similarly to MOSFET's. Estimation of
fluence levels causing significant parameter changes does not appear
warranted at this time.
W
0
TABL E 2. RADI ATI ON EFFECTS ON MOSFET PARAMETERS
TA 2330
TA 2330
TA 2330
FN 1002
X 1004GME
X 1 O04GME
X 1004GME
2N36 08
2N36 08
FI 100
FI
N
N
N
P
P
P
P
P
P
P
P
P
P
Enhancement
Enhancement
Enhancement
Enhancement
Enhancement
Enhancement
Enhancement
Enhancement
Enhancement
Enhancement
Enhancement
Enhancement
Enhancement
0. 13
0.33
"
0. 71
0. 36
0. 70
1. 00
"
"
0.81 - 0.91
"
0.89 - 0. 96
"
" 5 x 1014 n/cm2 (E> 10 keV)
" 5 x 1014 n/cm2 (E >10 keV)
0. 52 5 x 1014 n/cm2 (E> 10 keV)
0.47 5 x 1014 n/cm2 (E> 10 keV)
0. 15 5 x 10 l 4 n/ cm2 (E >10 keV)
" 5 x 1014 n/cm2 (E> 10 keV)
" 5 x l o5 rads (Si) (Co60)
1.01 2 x 10" p/ cm2 (E= 100MeV)
" 5 x 10l 2 e/ cm2 (E= 1.5MeV)
1.34 8 x 10l 1 p/ cm2 (E =140MeV)
1.0 - 2.48 1 x 10'0 - 5 x 1 0 1 ~ e/cm
2
(E= l .5MeV
" 5 x lo1' e/cm J (E= 1.5MeV)
(E =1.5 MeV)
0.95 - 5.25 1 x l ol o - 5 x 10l 2 e/cm 2
(a) See Figure 30.
BIBLIOGRAPHY
Anspaugh, B. E. , "High Energy Proton Testi ng of Mari ner r V Components",
California I nstitute of Technology, J et Propul si on Laboratori es, Pasadena,
California, J PL-TM-33-314, Tach. Memo, NAS7-100, J anuary 1, 1967.
Brown, R. R. , The Boeing Company, Seattle, Washington, "Equivalence of
Radiation Particles for Permanent Damage in Semiconductor Devices", IEEE
Transactions on Nuclear Science, NS-10 (5), November, 1963, pp 54-57.
Brucker, G. , Dennehy, W. , and Holmes-Siedle, A. , Radio Corporation of
America, Astroelectronic Division, Princeton, New J ersey, "High-Energy
Radiation Damage in Silicon Transistors", paper presented at the I EEE
Annual Conference on Nuclear and Space Radiation Effects, Ann Arbor,
Michigan, J uly 12-15, 1965.
Garrett, C. G. B. , and Brattain, W. H. , "Some Experiments on, and a
Theory of, Surface Breakdown", J ournal of Applied Physics, 27,1956, p 299.
-
Gordon, F. , J r. , and Wannemacher, H. E. , J r. , "The Effects of Space
Radiation on MOSFET Devices and Some Application I mplications of Those
Effects", NASA, Goddard Space Flight Center, Greenbelt, Maryland,
X-716 -66 -347, August, 1966.
Hofstein, S. R. , and Heiman, F. P. , "The Silicon I nsulated-Gate Field-
Effect Transi stor", Procceedi ngs of the I RE, - 51, 1963, p 1190.
Holmes-Siedle, A. G. , Radio Corporation of America, Princeton, New
J ersey, "Space Radiation: Its Influence on Satellite Design", RCA
Engineering, - 11, J une-J uly, 1965, pp 8-14.
Hughes, H. L. , and Giroux, R. R. , Naval Research Laboratory,
Washington, D. C. , "Space Radiation Effects MOSFET's, Electronics,
37 (32), December 28, 1964.
-
Kaufman, A. B. , Newhoff, H. R. , and Gaz, R. A. , "Effects of Neutron
and Gamma Ray Spectra on Flight Control Systems", Litton Systems, I nc.,
Woodland Hills, California, FDL-TDR-64-30, Feburary, 1964, Tech. Doc.
Rpt. , J anuary, 1963 - March, 1964, A F 33(657)-10584.
Lockheed Aircraft Corporation, "Components I rradiation Test No. 19 Gamma
I rradiation of 2N914, 2N198, S2N930, 2N2192, and 2N2369 Transi stors",
Lockheed Georgia Company, Marietta, Georgia, ER-8623, NASA-CR-82010,
October, 1966. Avail: NASA, N67-18545.
Measel, P. R., and Brown, R. R., The Boeing Company, Seattle,
Washington, "Low Dose Ionization-Induced Failures in Active Bipolar Tran-
si stors", paper presented at the IEEE Conference on Nuclear and Space
Radiation Effects, Missoula, Montana, J uly 15-18, 1968.
Nelson, D. L., Sweet, R. J ., and Niehaus, D. J ., "Study to Investigate
the Effects of Ionizing Radiation on Transistor Surfaces", The Bendix
Corporation, Southfield, Michigan, Bendix-R-36 99, J anuary, 1967,
Final Repo'rt, NAS 8-20 135.
Pel eti er, D. P., "The Effects of I onizing Radiation on Transistors",
The J ohns Hopkins University, Applied Physics Laboratory, Silver
Springs, Maryland, TG-937, August, 1967, Tech. Memo., NOw-62-
0604-c. Avail: DDC, AD 659295.
Radio Corporation of Ameri ca, "TOS Radiation Program Report. Analysis
and Evaluation of Test Results", Astro-Electronics Division, Princeton,
New J ersey, September, 1965.
Radio Corporation of Ameri ca, "TOS Radiation Test. Series No. 2
(February, 1965)", Astro-Electronics Division, Princeton, New J ersey,
Engineering Report, September, 196 5.
Raymond, J ., Steele, E., and Chang, W., Northrop Corporation,
Ventura Division, Newbury Park, California, "Radiation Effects in Metal-
Oxide-Semiconductor Transistors", I EEE Transactions of Nuclear Science,
NS-12 (l ), February, 1965, 11th Nuclear Science Symposium I nstrurnenta-
tion in Space and Laboratory, Philadelphia, Pennsylvania, October 28-30,
1964, pp 457-463.
Rind, E., and Bryant, F. R., NASA, Langley Research Center, I nstrument
Research Division, Hampton, Virginia, "Experimental I nvestigation of
Simulated Space Particulate Radiation Effects on Microelectronics ' I , paper
presented at the Conference on Nuclear Radiation Effects, jointly sponsored
by the I nstitute of Electrical and Electronics Engineers, the Professional
and Technical Group on Nuclear Science, and the University of Washington,
Seattle, Washington, J uly 20-23, 1964.
Roberts, C. S . , and Hoerni, J . A. , "Comparative Effects of 1 MeV
Electron I rradiation on Field Effect and I njection Transistors", Teledyne,
Inc. , Amelco Semiconductor Division, Moun$ain View, California, Tech.
Bul. No. 1, March, 1963, Field Effect Transistors Tech. Bulletin.
Robinson, M. N. , Kimble, S. G. , and Walker, .D. M. , "Low Flux Nuclear
Radiation Effects on Electrical and Electronic Components (BMI -LF-3)",
North American Aviation, I nc., Atomics I nternational Division, Canoga
Park, California, NAA-SR-9634, December 1, 1964, AT-(ll-l)-Gen-8.
Avail: NASA, N65-12642.
Sah, C. T. , "A New Semiconductor Tetrode - The Surface Potential
Controlled Transistor", Proceedings of the I RE, - 51, 1963, p 119.
Wannemacher, H. E. , "Gamma, Electron, and Proton Radiation Exposures
of P-Channel, Enhancement, Metal Oxide Semiconductor, Field Effect
Transi stors I f , NASA, Goddard Space Flight Center, Greenbelt, Maryland,
X-716-65-351, August, 1965.
33
Index
2N3089A 24
2N3608 30
Alpha Cutoff Frequency 4
Audio Transi stors 6,7,9, 12, 14,
Beta Ratio 5- 16
Bi pol ar Transi stors 1 - 19
Cadmium Selenide 24
Cadmium Sulfide 24
Carrier Mobility 21,27
Charge Buildup 28
Charge Carri ers 3,27
Cl usters 1
Compton Electrons 1
Crystal Lattice 1
Damage Constants 4-6, 17
Dielectric 24
Displacements 1
Electrical Conductivity 3, 18,21,
Electromagnetic Radiation 1,
Electron I rradiation 12- 14, 17,2 1,
FI 100 29,30
Fi el d-Effect Transi stors 19-38
F N 1002 30
Forward Current Gain .3
Frenkel Defects 1
Gamma I rradiation 30
Germanium 3
High-Frequency Transistors 6,7,
10, 12, 15, 17
Impedance 19
I mpurity Concentration 2 1,27
I nsulated-Gate-Field-Effect
17
27
14-17,2124
28-30
Transi stors 24-30
J unction-Field-Effect Transistors
Leakage Current 19,21,23,24,27
Low Frequency Common Emitter
Low-Frequency Gain 3-5
Metal-I nsulator-Semiconductor
Fi el d-Effect Transi stors 28
Effect Transi stors 28
Effect Transi stors 24-30
19-24
Current Gain Ratio - Use Beta Ratio
Metal-Nitride-Oxide-Silicon Field-
Metal-Oxide -Semiconductor Field-
Minority-Carrier Lifetime 3,4, 18
MM 2103 29,30
Neutron I rradiation 7-9, 17,21-23,
Pinch-Off Voltage 19,2 1,24
Power Transi stors 6,9, 11, 14, 16,
Prediction Equations 3-5
Proton I rradi ati on 9- 11, 17,30
Recombination Centers 1, 3,2 1,27.
Schematic Diagrams 2, 18,20,25,
Silicon 4, 18,24,27,28
Silicon Dioxide 24,27,28
Substrates 24,27,29
Surface Effects 4,27
S-witches 6,8, 19, 11, 13, 15- 17
TA 2330 30
Thin-FlTn? Transi stors 24,29
Threshol d Vdtage 27-30
TIX693 24
Tran.sconductance 19,21,22,24,28,
Unijunction Transistors 18, 19
X 1004GME 30
30
17,19
26
30
34
NASA-Langley, 1971 - 9 CR-1834
NASA CONTRACTOR
REPORT
-
RADIATION EFFECTS
DESIGN HANDBOOK
.... -.- ..
Section 5. The Radiations in Space
and Their Interactions With Matter
by M. L. Green and D. J. Hamman
Prepared by
RADIATION EFFECTS INFORMATION CENTER
BATTELLE MEMORIAL INSTITUTE
Columbus, Ohio 43201
for
NASA
CR
1785-
sect.5
c.2
NASA CR-1871
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION • WASHINGTON, D. C. • SEPTEMBER 1971
I
TECH LIBRARY KAFB, NM
11111111111I1111I .... .. - .....
0061050
I
1. Report No.
______ Accession No.
3. Recipient's oltalog No.
NASA CR-18:rl
- -
4. Title and Subtitle 5. Report Date
RADIATION EFFECTS DESIGN HANDBOOK
September 1971
SECTION 5. THE RADIATIONS IN SPACE AND 6. Performing Organization Code
THEIR INTERACTIONS WITH MATTER
-_._--------- - --- - ----- --
7. Author(s) B. Performing Organization Report No.
M. L. Green and D. J. Hamman
-
10. Work Unit No.
9. Performing Organization Name and Address
Radiation Effects Information Center
Battelle Institute
11. Contract or Grant No.
Columbus Laboratories NASW-1568
Columbus, Ohio  
---
13. Type of Report and Period Covered
12. Sponsoring Agency Name and Address
Handbook - Several Years
National Aeronautics and Space Adminis t ra t ion
14. Sponsoring Agency Code
Washington, D. C. 20546
15. Supplementary Notes
16. Abstract
This document summarizes the types and sources of radiation tha t may be
encountered in space and how they interact with matter. The detection and measurement
of these radiations also are discussed. A glossary is inc 1 uded.
17. Key' Words (Suggested by Author(s)) lB. Distribution Statement
Radiation Types, Radiation Sources, Dosimety Unclassified - Unlimited
19. Security Classif. (of this report)
1
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I
PREFACE
This document is the fifth section of a Radiation Effects Design Handbook
designed to aid engineers in the design of equipment for operation in the radia-
tion environments to be found in space, be they natural or artificial. This
Handbook will provide the general background and information necessary to
enable the designers to choose suitable types of materials or classes of
devices.
Other sections of the Handbook discuss such subjects as transistors,
solar cells, thermal-control coatings, structural metals, electrical
insulating materials, and capacitors.
v
TABLE OF CONTENTS
THE RADIATIONS IN SPACE AND THEIR INTERACTIONS
WITH MATTER. I
INTRODUCTION . 1
THE SOURCES OF RADIATION IN SPACE 1
TYPES OF RADIATION AND THEIR INTERACTION WITH MATTER. 4
Introduction. 4
Protons and Heavy Charged Particles 4
Electrons (Beta Particle s) . 7
Neutrons. 8
High-Energy Electromagnetic Radiation 9
EFFECTS OF THE INTERACTION OF RADIATION WITH MATTER 12
Ionization 12
Atomic Displacement 17
CORRELATION OF EFFECTS CREATED BY DIFFERENT
RADIA TIONS . 24
Energy Deposition 25
Displacement Effects 27
Distribution of Defects 3u
Annealing 31
DOSIMET R Y 32
Introduction. 32
Neutron Measurement . 34
Photon, Proton, and Electron Measurements 38
Dosimetry Devices 42
Spectrum Monitoring. 47
G LOSSAR Y . 49
REFERENCES. 54
vii
I
SECTION 5. THE RADIATIONS IN SPACE AND
THEIR INTERACTIONS WITH MATTER
INTRODUCTION
This section is provided as an introduction to the radiations to be
encountered in the space envirorunent, a description of these radiations, and
the microscopic manner in which they interact with matter. Also included
is a brief discussion of the correlation of the effects of different radiations,
as well as a discussion of the units and techniques of measuring radiations.
The primary purposes of this section are to serve as an introduction to
these subjects, to provide some insight into the mechanisms involved when
radiation interacts with matter, and to facilitate the understanding of sub-
jects treated elsewhere in this Handbook for those unfamiliar with radiation
physics. For a comprehensive treatment of the subjects dealt with in this
section, the reader is directed to the references at the end of this section.
Logical additions to the content of this section include a brief deocrip-
tion of the possibilities and limitations of simulating the effect of one type of
radiation with another type of radiation and a description of the instruments
used to measure radiation.
THE SOURCES OF RADIA TION IN SPACE
As stated, in this section the interactions of space radiations with
matter are dealt with. To put these radiations into perspective, the sources
of these radiations and their relative intensities are covered briefly.
Sources of radiation that may be encountered in the space environ-
ment are:
(l) The Van Allen belts are toroidal belts of charged particle s
surrounding the earth near the equator. There are two
belts, the inner belt extends to about 45
0
north and south
geomagnetic latitudes and from about 800 kilometers to
about 8000 kilometers in altitude. The outer belt fluctuates
in size and intensity with solar activity but is symmetrical
about the equator and extends to about 70° geomagnetic
latitude north and south and to altitudes as high as 130,000
kilometers. Similar magnetically concentrations
of charged particles are thought to exist on the planets
Jupiter and Saturn. The proton and electron fluxes that
have been measured in the hearts of the Van Allen belts
are given in Table 1. For more detailed information,
contact the National Space Science Date.. Center at Goddard
Space Flight Center, Greenbelt, Maryland. (4S)
TABLE 1. VAN ALLEN RADIATION BELT INTENSITIES(S)
Particle
Electrons
Electrons
Protons
Electrons
Electrons
Protons
Protons
Protons
Energy Flux
Heart of Inner Zone (Alt = 3600 km)
(E > 40 keV)
(E > 600 keV)
(E> 30 MeV)
1 0
8
/ (cm
2
. s)
x 106/(c:rr
2
. s)
x 10
4
/ (cm
2
. s)
Heart of Outer Zone (Alt = 2S, 000 km)
(E> 40 keV)
(1. 5 < E < 5 Me V)
(0. 1 < E < S Me V)
(E> 1 MeV)
(E > 75 MeV)
  s)
10
4
/ (cm
2
. s)
  s)
 
1/(cm
2
. s)
(2) Solar flares are bursts of high-energy particles originating
in the sun. Although protons are the predominant particles
in the solar flares, alpha particles and other nuclei are also
present. The average percentage of alpha particles in the
total integrated flux is unknown. But, over a short period
of time, the number of alpha particles may be nearly equal
to or greater than the number of protons. For example, in
the event of November IS, 1960, N(p) :: 1 at an energy greater
N(a)
2
than 30 MeV, whereas the November 12, 1960, event was
much richer in alphas. It would be more accurate to
assume that
[
N(P) ] integrated -< O. 05 at all values of rigidity.
N(a)
The frequency of occurrence of all flares - including both
the big and the small - range s from about two to fourteen
per year. Solar flares severe enough to produce significant
fluxes (Class 3 or 3+) occur about one or two times per year
during periods of solar activity, last from 10 to 100 hours,
and create proton fluences of ~ p to 109 protons/ cm
2
of
energy greater than 30 MeV per flare. Proton energies
ranging from 10
7
eV to 1 09 ~   or higher have been observed
in conjunction with solar -flare activities. (3, 5,39) The radia-
tions given are for a distance of one astronomical unit (A. U. )
from the sun (1 A. U. = 92,950,000 miles, the mean distance
from Sun to Earth).
(3) Galactic cosmic radiation originate s outside the solar sys-
tern. This radiation is about 85 percent protons, 14 percent
helium ions, and the rest heavier nuclei. Energies range
from 107 to 10
1
9 eV with an average of about 10
12
eV. The
free-space proton flux near Earth is about 2.5 protons/
(cm
2
. s) when solar activity is at a maximum and about
5. 0 protons/ (cm
2
. s) at solar minimum. (3)
(4) Solar wind is an ionized plasma continuously emitted by the
sun. The solar wind varies with the relative activity of the
sun and distance from the sun. Typical fluxes and energies
for the solar wind at 1 A. U(2) are given in Table 2.
TABLE 2. SOLAR WIND RADIA TION INTENSITIES
Flux, particles/(cm
2
. s)
Particles (1 A. U. from Sun) Energy, eV
Protons 5x 10
9
(normal) 2 x 10
3
2x 10
13
(high activity) 2 x 10
4
Electrons 5x 109 (normal) 2
2x 10
13
(high activity) 11
3
An additional source of radiation is associated with vehicles powered
by nuclear reactors. These reactors can produce extremely high neutron
and gamma fluxes. Determination of radiation received from these re-
actors and shielding necessary must be made on a point-to-point basis de-
termined by distance from the reactor, operating history of the reactor,
operating power of the reactor, and intervening materials.
TYPES OF RADIA TION AND THEIR INTERACTION WITH MATTER
Introduction
The different types of radiation that may be encountered in space are
protons and heavy charged particles, electrons, neutrons, and electro-
magnetic radiation. Because these radiations have different characteristics,
they interact with material in different ways. Following is a brief descrip-
tion of these radiations and a general description of the ways in which they
interact with matter. A more detailed description of their interactions with
descriptive equations is presented in the subsections on ionization and
atomic displacements.
Protons and Heavy Charged Particles
A proton is a positively charged hydrogen ion. Most of the solar and
galactic cosmic radiation and a large portion of the Van Allen-belt radiation
that a spacecraft would encounter will be high-energy protons. Energies of
protons will range from a few thousand electron volts for protons in the solar
wind to 10
19
eV for protons from galactic sources; however, most proton
fluences of significance will be in the energy range 10
5
to 109 eV.
The primary process for energy loss by protons and heavy charged
particles (i. e., particles of mass» electron mass) is through Coulomb-
force interactions with atomic electrons, leaving atoms along the path of the
incident particle ionized or in an excited state (ionization is treated more
thoroughly elsewhere in this section). A portion of the particle ~ n   r g y is
expended in elastic collisions with atoms, which can result in displaced
atoms.
4
Protons with energies in the tens of MeV can undergo inelastic colli-
sion with nuclei in which subatOInic particle s (neutrons and protons) are
knocked out of the target nucleus. At higher energies, a significant pro-
portion of the incident protons interact in this manner (15 percent for 150
MeV protons). (6) In this interaction the incident proton knocks out several
particles (neutrons and/or protons) by direct interaction with individual
nucleons in the target nucleus, thus producing a multiplication of particles
or cascade effect. These emitted particles, called cascade particles, have
motions strongly concentrated in the forward direction relative to the
incident-proton direction.
The target nucleus, after passage of the incident proton and emission
of the cascade particles, is left in an excited state. The nucleus loses this
excitation energy by an "evaporation
ll
process whereby neutrons, protons,
and light nuclei are emitted isotropically from the excited nucleus. These
secondarily emitted cascade and "evaporation
ll
particles have a much
greater potential for radiation damage than does the incident proton, because
of their greater number and slower velocities. The average number of
incident neutrons and protons emitted per incident proton per inelastic
collision for these two processes is a function of incident proton energy
and atomic mass of the target nucleus. (15)
The nuclear, inelastic-scattering cross section for this interaction is
approximately equal to the geometric cross section of the nucleus for
incident particles whose energy is much greater than that of the Coulomb
barrier, which is about 8 MeV. Thus, the cross section is given by
0=7T(1.3
where A is the atomic mass of the target nucleus. The mean free path of a
particle with respect to inelastic-scattering processes is then
(
0N
O)-1
A. = --
In A
where No is Avogadro
l
s number.
The fraction of the incident protons that will on the average undergo
this type of interaction will be
"The units g/cm
2
are frequently used to indicate the thickness of material required to attenuate radiation by a
specified amount. The units are derived from the density of the material (g/cm
3
) times the thickness of mate-
rial (cm) required to attenuate the radiation by the specified amount.
5
F - 1 - e-x/'A.in
- ,
where x is the thickness of material traversed in units of g/cm
2
. (9) To de-
termine the importance of nuclear secondaries for specific cases, elaborate
Monte Carlo or probabilistic calculations are required to follow the cascade
process. Results are summarized in Reference (40).
An empirical formula for the range of protons in the energy range from
10 to 1000 MeV is given by(46)
R(E) = :b In (1 + 2bEr) .
In general, for materials of atomic number, Z < 20, a value of r = 1. 78
should be used, and for Z >20, r <1. 75. The coefficients a and b for several
materials are given in Table 3.
TABLE 3. COEFFICIENTS FOR THE RANGE EQUATION
r =
1. 75 r
Material a b
a
Carbon 2.58 x 10-
3
1. 2:l\ 10-
6
2.33 x 10-
3
2.0xlO-
6
Aluminum 3.10 x 10-
3
1. 9 x 10-
6
2.77 x 10-
3
2.5 x 10-
6
Iron 3.70 x 10
-3
2.6 x 10-
6
3.26 x 10-
3
3.0 x 10-
6
Copper 3.85xlO-
3
2.7 x 10-
6
3.40 x 10-
3
3. 25 x 10-
6
Silver
4.55 x 10-
3
3.7 x 10-
6
Tungsten 5.50 x 10-
3
4.2 x 10-
6
Polyethylene
2. 15 x 10-
3
1. 1 x 10-
6
1. 95 x 10-
3
1.7 x 10-
6
Tissue 2.32 x 10-
3
1. 2 x 10-
6
2. 11 x 10-
3
2.0 x 10-
6
Water
2.32 x 10-
3
1. 2 x 10-
6
2. 10 x 10-
3
2.0 x 10-
6
Air 2.68 x 10-
3
1. 4 x 10-
6
2.41xl0-
3
2. I x 10-
6
Si0
2
2.87 x 10-
3
1.7x
10-
6
2.58 x 10-
3
2. 5 x 10-
6
Glass 3.17xlO-
3
2. 1 x 10-
6
2.83 x 10-
3
2.8 x 10-
6
6
I
Electrons (Beta Particle)
An electron is a particle whose mass is about 1/1800 the mass of a
proton and which carries a unit negative charge. * Electrons in the space
environment are found primarily in the Van Allen belts and as secondary
particles emitted as a result of the interaction of other radiations with
matter. Electrons interact with matter primarily through ionization of the
atoms in the absorbing material. Another mechanism for energy loss that is
significant for high-energy electrons is the generation of X-rays,
bremsstrahlung. The ratio of the energy loss per unit path length from
ionization to that from bremsstrahlung generation is approximately
(DE/ dx)bremsstrahlung E Z
(dE/dx)ionization = 800
where E is the electron's energy in MeV and Z is the atomic number of the
absorber. The bremsstrahlung radiation thus created is much more pene-
trating than the original electron and is an additional source of radiation
damage.
The range of monoenergetic electrons is given approximately by the
empirical relationships:(38)
For energies from 0.01 MeV to -3 MeV,
where n = 1. 265-0.0954 In E.
For energies from -2.5 MeV to   MeV ,
Ro (mgl cm
2
) = 530E-I06 ,
where E is in MeV.
Electrons traveling at velocities near the speed of light (energies
>0. 51 MeV) may produce atomic displacements through Coulomb scattering.
*A particle of equal mass but with positive charge is called a positron.
7
Neutrons
Neutrons are uncharged particles whose mass is nearly equal to that
of a proton. Nuclear reactions are the only sources of neutrons. Neutrons
created as the result of the fission of U
2
35 or Pu
23
9 (i. e., fission neutrons)
have energies from O. 075 to 17 MeV and fit the energy distribution N(E) =
0.484 sinh (2E)1/2 e-
E
where N(E) is the number of neutrons of energy
E(MeV) per unit energy (MeV) interval for each neutron emitted. (21)
Neutrons also are produced by the interaction of a particles with the
light elements beryllium, boron, and lithium by reactions such as
4Be
9 6C12 n
+ a -+ + 0
Nearly monoenergetic neutrons called photoneutrons also may be ob-
tained from the interaction of gamma rays (or bremsstrahlung) with matter
when the energy of the gamma ray is greater than the binding energy of the
last neutron in the target nucleus. Beryllium and deuterium have low thresh-
old energies (1. 67 and 2.23 MeV) for this reaction. Using this reaction,
electrons can be used to produce neutrons through the bremsstrahlung gen-
erated when high-energy electrons are slowed down in a high-density target.
A reaction which produces nearly monoenergetic neutrons is the fusion reac-
tion which occurs when deuterium (H2) or tritium (H3) is bombarded by
deuterium ions with energies of about 50 to 200 keY.
Neutrons may be divided by energy into three groups: tnermal, epi-
thermal, and fast. Thermal neutrons have kinetic energies similar to that
of atoms in the medium (E - 0.025 eV at 20 C) and are produced by slowing
down fast and epithermal neutrons through elastic and inelastic scattering
processes. Epithermal neutrons have energies between those of fast and
thermal neutrons. Neutrons whose kinetic energy is greater than -10 keY
may be considered fast neutrons. Reactions of thermal and epithermal
neutrons will not be a major concern in space applications, except in nuclear-
reactor-powered rockets, but fast neutrons can create atomic displacements
and, indirectly, ionization. Mechanisms through which fast neutrons can
produce ionization are:
(1) Elastic scattering, in which the recoil nucleus has suf-
ficient energy to produce ionization
8
(2) Inelastic scattering, in which a gamma photon is emitted
that can produce secondary ionization in addition to the
ionization that may be created by the recoiling nucleus
(3) Nuclear reactions induced by neutrons in which an ionizing
particle is emitted, such as (n, p) or (n, a) reactions.
In addition, boron and lithium have high capture cross sections for
thermal neutrons with the resultant emission of an alpha particle.
High-Energy Electromagnetic Radiation
Electromagnetic radiation may be thought of as a discrete quantity of
energy (one photon) which when emitted travels in a straight line at the
speed of light. The wavelike nature of electromagnetic radiation is revealed
by the photon's frequency given by E = hu where h is Planck's constant and
u is the frequency associated with the photon. In the energy range of interest,
there are three types of electromagnetic radiation (gamma rays, X-rays, and
ultraviolet light), which are distinguished primarily by the sources from
which they originate and to a lesser extent by their energies.
The electromagnetic radiations of highest energy are usually gamma
rays. They originate within the nucleus of an atom and generally have
energies greater than 0.1 MeV. X-rays usually are thought of as being of
lower energy than gamma rays and originate in interactions involving orbital
electrons, by blackbody radiation from a heated mass or by the inelastic
scattering of charged particles by a nucleus (bremsstrahlung). The terms
X-ray and gamma ray frequently are used interchangeably. Ultraviolet rays
are part of the spectral radiation from the sun (-7 to 9 percent), are lower
in energy than X-rays, and are only weakly ionizing. They have the ability
to produce light-absorbing color centers in glass, to change the emissivity
of some thermal-control surfaces, and to change the physical and optical
properties of some organic materials.
Electromagnetic radiation has a characteristic exponential attenuation
in Inatter which is dependent upon the energy of the photon and on the ab-
sorbing material. When describing the interaction of photons with matter,
units that frequently are used are the cross section per electron, 0e, or the
cross section per atom, ° = ZOe, where Z is the atomic number of the
absorbing material and 0" and 0e are expressed in square centimeters or
9
barns (1 barn = 10-
24
cm
2
). A more useful term is the linear attenuation
coefficient
".
where p is the material's density, No is Avogadro's number, and A is the
atomic mass of the material. The attenuation of a beam of photons passing
through a medium is then
I = 10 e -/1x
where I is the intensity of a beam of photons of initial intensity 10 after
traversing a thicknes s (x) of material whose linear attenuation coefficient
for that beam of photons is /1. The term mass -attenuation coefficient, /11 p,
is sometimes used in place of linear-attenuation coefficient. This is just the
linear-attenuation coefficient divided by the density of the material. The
above equation is then expressed as
I = 10 e - (/1 I p) px
Electromagnetic radiation interacts with matter through three primary
mechanisms: pair production, the Compton effect, and the photoelectric
effect. For lower energies, the predominant mechanism for energy transfer
from incident photons to the absorbing material is the photoelectric effect.
In this interaction, a tightly bound orbital electron (K or L shell) absorbs the
entire energy of the photon and is ejected from the atom with an energy
E = Eo - EB, where Eo is the initial energy of the photon and EB is the
binding energy of the electron. The atom then loses the energy imparted
to it by emission of X-rays or Auger electrons. Exact expressions for the
cros s section for photoelectric absorption are quite complex and will not be
given here. This cross section(22) varies approximately as
a = const. Z
4
/E3
o
For photon energies from about 0.2 to 2 MeV, the Compton effect
predominates in energy-transfer processes. In the Compton effect, the
photon interacts with an orbital electron, the photon losing part of its
energy to the electron. The energetic electron and lower energy photon
then move off, the photon traveling at some angle </J with respect to its former
direction. The energy of the scattered photon is given by
10
(1 - cos 7jJ)
where Ino is the rest Inass of an electron, c. is the velocity of light, and Eo
is the energy of the incident photon. For electrons, In
o
C
2
= 0.511 MeV. The
The kinetic energy of the electron is then given by
is
The InaxiInuIn energy that Inay be transferred to the COInpton electron
2
2 Eo
E ( ) - [Reference (35)]
e Inax - 2 + 2 E
InOC 0
In the energy range 0.2 to 2 MeV, which covers Inost fission gaInIna rays,
the COInpton effect predoIninates for low and Inoderate Z Inaterials, and the
energy iInparted to the electron and thus readily available for ionization of
the absorbing InediuIn is nearly independent of energy and atoInic nUInber
for low atoInic nUInbers. This fact Inakes dosiInetry in this energy range
Inuch siInpler.
At photon energies above a few MeV, pair production begins to dOIninate
energy-transfer processes. In this process the photon is cOInpletely
absorbed, and in its place an electron-positron pair is forIned. This reac-
tion can take place only in the field of a charged particle, usually a nucleus.
The energetics of this reaction can be described by
= (E + In c
2
) + (E + + In c
2
) = E + E + + 1. 02 MeV
e- 0 e 0 e- e
where Ee+ and Ee- are the kinetic energies of the positron and electron.
The cross section for pair production is proportional to Z2 and thus in-
creases rapidly with increasing atom.ic nUInber of the absorbing InediuIn.
The positron eInitted usually loses energy by ionization until it is nearly at
rest, at which tiIne it interacts with an electron, both particles disappear-
ing; two 0.51 MeV gaInIna rays then appear, Inoving off in opposite
directions.
11
The total attenuation cross section for a particular gamma-ray energy
is the sum of all contributing attenuation mechanisms. The crOSE; section
for each mechanism can be further broken down into cross sections for the
energy of the scattered photon and cross sections for the energy imparted
to the interacting electron or energy absorbed.
Figure 1 shows the separate   coefficients (energy-
absorption cross sections) for each mechanism and the total energy-
absorption coefficients for several elements as a function of energy. These
coefficients allow for the escape of all secondary photons, including
bremsstrahlung from the absorbing medium. If all secondary and scattered
photons are assumed to escape from the absorber without further interac-
tion and all secondary electrons created are stopped in the absorber, then
the energy transferred to the absorber will be given by the total gamma-ray
absorption coefficient, which is the sum of the absorption coefficients for
each type of interaction. The energetic electrons resulting from these reac-
tions usually deposit energy in the absorber through ionization processes.
Reference (24) contains a very complete listing of cross sections for
photon interactions.
EFFECTS OF THE INTERACTION OF RADIATION WITH MATTER
The two basic mechanisms by which radiation creates damage in ma-
terials are ionization and atomic displacement. All of the radiations dis-
cussed previously may directly or indirectly create damage in the absorbing
material by ionization and by displace-ment of atoms in the material.
Ionization
Ionization is caused by the passage of charged particles through matter.
A charged particle in passing through a medium may lose its kinetic energy
by any of four principal interactions:
(1) Inelastic collision with a nucleus. An interaction in which
the incident particle is deflected by the nucleus. In such
collisions a portion of the particle energy goes into creating
an emitted photon (bremsstrahlung) or into excitation of the
nucleus.
12
.....
w
0.1,-----,-----------------------------------------------------------------
\'
,\
,
\\
, ,

-- ..........
,
, \'
, \ ........... :--
\ '\'\ " ...... ,
"'E : \ \ , Compton effect ... ."
0.01 \ \  
- \-Photoelectric '\ / / ......
::l... \ effect \ // > .. /
\ ' , / """...."
\ \ " II .. '" ,
\ ." LTotal J-"'"
\
,.... __ .. --1
\ - I
\ \ I
.. .. I
Hydrogen
Aluminum
Lead
... -----
-'---- , --..,.
,
,
,
,
,
"L,.. \ "-
.. Compton effect ""'... /
Pair production
,
,
,
,

0.1 1.0 10 100
Eo I MeV
FIGURE 1. MASS ABSORPTION COEFFICIENTS FOR VARIOUS ELEMENTS(24)
(2) Elastic collision with a nucleus. An interaction in which
the incident particle is deflected and part of its kinetic
energy is given up in imparting a kinetic energy to the
struck nucleus as required by conservation of momentum.
(3) Elastic collision with an atom. An interaction in which the
incident particle is deflected elastically by the atom as a
whole. The energy transfer in this interaction is usually
less than the lowest quantity of energy required to remove
any atomic electron from the atom.
(4) Inelastic collisions with atomic electrons. In this interaction,
enough energy is imparted to one or more atomic electrons to
experience a transition to a higher energy state (excitation)
or is removed completely from the atom (ionization).
Inelastic collision with atomic electronR is the primary mechanism
through which energetic charged particles and, indirectly, electromagnetic
radiations affect or act upon materials. For a better understanding of the
mechanisms of electron excitation and ionization, a simplistic description
is given here for those not familiar with the processes. For a more
rigorous treatment, the interested reader is referred to Reference (22)
or any good basic atomic physics text.
Ionization is the removal of an orbital electron(s) from a neutral
atom or molecule. Atoms consist of a nucleus of protons and neutrons
surrounded by what may be considered a series of concentric shells of
orbital electrons. The number of electrons surrounding the nucleus
normally is equal to the number of protons inside the nucleus. The number
of protons in the nucleus, i. e., the atomic number, determines the identity
of the nucleus. The electron shells have been named from work in X-ray
·spectroscopy. The innermost shell is the K shell, the next innermost, the
L shell, the next, the M shell, and so on. Each shell may contain only a
specified maximum number of electrons and the innermost shells must be
filled before an electron can remain in an outer shell. The closer an elec-
tron is to the nucleus, the more tightly it is bound to the nucleus, i. e., the
greater is the quantity of energy required to remove it from the nucleus.
The minimum quantity of energy necessary to move an electron from a
particular shell to a position where it is essentially free of the nucleus is
called the ionization potential, Ei. In practice, the average energy, E
p
,
that must be expended to remove an electron is two to four times greater
than the ionization potential, because of energy losses in other nonionizing
mechanisms such as excitation and kinetic energy of the ejected electron.
14
The ejected electron can have sufficient energy to cause further ionization
itself.
If an electron is removed from an inner shell, the vacancy (hole)
created by its absence must be filled by an electron from a she 11 further
removed from the nucleus. The electron that fills the vacancy has reduced
its total energy in doing so. This energy is given up as a discrete quantity
of energy called an X-ray photon whose energy just equals the difference in
the energy of the electron before and after the transition to the shell closer
to the nucleus. The energies of the photons emitted in this process are fixed
for all pos sible transitions for any particular element and are called char-
acteristic X-rays.
The ejected electron and the resultant positively charged atom con-
stitute what is called an ion pair. The average energy, E
p
' required to
create an ion pair varies with the temperature, the incident particle, and
the incident particle's energy, Ep tending to be higher in gases .!..or heavier
incident particles. The possibility of theoretically calculating Ep is limited
because of a lack of good ;:ros s -section data; thus, experimentally obtained
values of Ep are more accurate. The ionization potential   l ~ d the average
energy expended per ion pair for several common materials are given in
Table 4.
Measurement of ionization potentials in liquids, conducting solids,
and insulators is very difficult, hence most studies of ionization have been
limited to gases and semiconductors. The counterpart of the ion pair (ip)
formed in gases is the electron-hole pair (ehp) formed in semiconductors.
A charged particle loses energy in a semiconductor by moving an electron
from the valence band of the semiconductor to the conduction band. The
vacancy left behind by the electron has many of the properties of a positively
charged particle. The energy-balance equation according to Shockley(26) is
where Eg is the energy band gap in the semiconductor, 1'" is the number of
phonons generated per ionization, Er is the phonon energy, and EF is the
residual electron or hole energy after an ion pair has been formed.
The value of Ep in gases and semiconductors is a relatively constant
function of energy for incident particle energies above about 1/2 m v0
2
where m is the mass of the incident particle and Vo = 2 TI e
2
/h is the velocity
15
TABLE 4. AVERAGE ENERGY REQUIRED TO CREATE AN
ION PAIR OR ELECTRON-HOLE PAIR
Ep
Material 'Y and X-rays
Gases eV lip
Air 33.73±0.lS
Helium 41. S ± 0.4
Hydrogen 36.6 ± 0.3
Oxygen 31.8 ± 0.3
Carbon 32.9 ± 0.3
dioxicle
Water 30. 1 ± 0.3
Solids eV lehp
Silicon 3.8 - 4.2
Germanium 2.8 - 4. S
Gallium
arsenide
Cadmium
s111 fide
(a) For].l mesons.
(b) For 2.7 -MeY tritium particles.
(c) Unspecified.
Ep
a Particles
eV lip
34.98 ± o. OS
46.0 ± o. S
36.2 ±0.2
32.3 ±O.l
34. 1 ± O. 1
37.6
eV lehp
3. S7 ± O. OS
2.89 ±0.06
16
Ep
Protons
eV lip
36.0±0.4
29. <1 + IS
- 0
31.S±2
34.9 ± o. S
Miscellaneous
eV lip
31. 0 ± O. 8(a)
eV lehp
3. 62 ± o. 04( b)
S-10(c)
of an electron in the first Bohr orbit of hydrogen where e is the charge on an
electron and!:. is Planck's constant. Below this energy, Ep tends to increase.
The value of Ep is slightly temperature dependent, having temperature coef-
ficients of -0.001 eV / (ehp-K) for electrons and -0.0015 eV / (ehp-K) for
a particles in silicon. (2 5)
Atomic Displacement
Atomic-displacement damage is the result of atoms being displaced
from their usual sites in crystal lattices. This effect is usually significant
only in materials which have a highly ordered crystal structure and whose
macroscopic material properties are changed by changes i:r.. this structure.
The simplest form of this defect, a Frenkel defect, is a vacant lattice site
(vacancy) and an extra atom inserted between lattice position (interstitial).
A step-wise de scription of the production of displacement damage is as
follows:
(1) An incident energetic particle or a high-energy secondary
particle collide s with a lattice atom and imparts to it a
recoil energy E2.
(2) The target atom leaves its lattice position, thus creating
a vacancy.
(3) The recoiling atom then dissipates its energy in ionization,
in thermal excitation, and if its energy is great enough, by
displacing other lattice atoms.
(4) Eventually, all the recoil atoms corne to thermal equilibrium
in interstitial positions with the exception of the few that fall
into vacancies. Some of the interstitials may be isolated
(i. e., not in the strain field of other interstitials, vacancies,
or impurity atoms), 'but for values of the recoil energy much
greater than the displacement threshold energy, most will be
associated with other defects.
(S) The defects thus created tend to anneal, the simple defects
and clusters moving through the crystal via thermal energy.
Thus, the rate of annealing is temperature dependent.
17
• ••• 111 ••• 111
(6 )
(7 )
Eventually the ITIobile defects are either annihilated by
the recoITIbination of vacancy-interstitial pairs or are
iITIITIobilized by the forITIation of stable defect cOITIplexes,
or escape to a free surface.
Meanwhile, the ITIacroscopic properties of the ITIaterial are
generally changed by the presence of the defects.
Heavy Charged Particles
The priITIary ITIechanisITI for atoITIic displaceITIent by charged particles
is through Rutherford scattering. In this interaction an incident charged
particle is deflected in the electrostatic field of another charged particle.
The incident particle thus loses part of its energy to the target particle.
Both particles then ITIove away froITI the interaction site in directions deter-
ITIined by conservation of ITIOITIentUITI. This is an elastic collision, and hence
the total kinetic energy of the particles before and after the interaction is
unchanged. In interactions of interest, the incident particle is assuITIed to be
an energetic proton and the target particle, an atOITI.
Basic paraITIeters in this interaction are:
v 0 = velocity of incident particle before interaction
Eo = energy of incident particle before interaction
ITII = ITIas s of incident particle
ITI2 = ITIass of struck (target) particle
Z 1 = charge nUITIber of incident particle
Z2 = charge nUITIber of struck particle (equals atoITIic nUITIber for
atoITIs)
e = unit electronic charge
El and v 1 are the kinetic energy and velocity oj recoiling incident
particle
E2 and v2 are the kinetic energy and velocity of recoiling target
particle
e = the recoil angle in the center of ITIass coordinate systeITI
(C systeITI)
18
{3 = ratio of particle velocity to velocity of light = vol c
a=Z2
/137
•
The nonrelativistic cross section then for transferring an energy be-
tween EZ and EZ + dE2 to a particle can be shown to be
21l' (Z 1 ZZeZ)Z dEZ
do = ----2=---- --2
m2
V
o E2
For relativistic interactions this becomes
2 E2 tGz ) liZ E
Z
tJ dEZ
{3 --+1l'a{3 --  
EZm EZ
m
EZt:. EZZ
where E
Zm
is the maximum energy that can be transferred to the recoiling
particle:
The spectrum of recoil energies, EZ, produced by monoenergetic
incident particles varies as (1/E2)Z; thus, most recoiling atoms will have
energies much less than EZ
m
. (33)
In the energy range 0.01 to 50 MeV, this expression for EZ
m
holds
for nonrelativistic particles and is valid for neutrons, protons, and other
heavy particles. (35)
Integration of this to obtain the number of recoil atoms of energy
greater than some energy E yields
19
E2m
a(E2 > E) = S da
E
= P 2   ~ __ 1 _ _ f32 + TI af3
f32 E E2m E2m
where
P2 =
if E2m » E, then
E2m
In--
E
_ P2
a(E
2
> E) = -2- [Reference (28)]
Ef3
Note: Since Eo = 1/2 ml v
o
2
= 1/2 mlc
2
f32,
a varies as I/Eo.
Electrons
Electrons, because of their small mass, must travel at relativistic
velocities to produce atomic pisplacements. The calculations relating to the
determination of these cross sections are rather complicated but the net
result is that in the vicinity of the displacement threshold, the cross section
rises steeply with increasing energy and then levels off and becomes nearly
constant. This behavior is to be contrasted with the approximate l/Eo
dependence of heavier particle cross sections.
The maximum energy that can be transferred to a target particle of
mass m2 » ml by an electron of mass ml is, for Eo « m2
c2
,
20
The mean energy transferred to the displaced particle is approximately
where Ed is the displacement threshold or the minimum energy that can be
imparted to an atom and still displace it. (Z9)
The displacement cross section for relativistic electrons is :(30)
where
  (b")2 = 7T
4
Z EZ
m
{ [(Ezm)l/Z ] Ezm}]
- {3 In + TIa{3 Z   - 1 - In  
Z. 495 x 10-
25
(cm
2
) Z22
[34 (1 - (32)
As the cross section becomes constant it approaches the value
TI 2 E2m
0- -; - (b') --
d 4 Ed
In all practical cases the energy transferred to the displaced atom is
only slightly larger than the threshold energy. The net result of electron
radiation, then, is a pattern of isolated single displacements since the
recoiling atom usually has insufficient energy to cause secondary
displacements. (36)
Neutrons
The primary mechanism for energy loss for lower energy neutrons
(E less than about 1 MeV for low Z materials) is elastic scattering with
atoms in which the kinetic energy of the incident neutron is just equal to
the total kinetic energy of the recoiling atom and recoiling neutron. For
most elements, the elastic-scattering cross sections range from 2 to
10 barns for neutrons of low energy. The notable exception is hydrogen,
for which the value is as high as 20 barns in the chemically unbound state
21
and can be even higher at very low energies when the hydrogen is in the
chemically bound state. (21) Exceptions to this general rule are resonance
peaks in the cross section versus energy curves. Treatment of these peaks
is not within the scope of this section·. For exact values of neutron cross
sections the interested reader is referred to Reference (31).
If
m
1
= mass of the neutron in atomic mass units = 1
m2 = mass of the atom in atomic mass units = atomic mass
Eo = initial energy of the neutron
E 1 = recoil energy of the neutron
El
m
in = minimum energy of recoil neutron
EZ = kinetic energy imparted to the target atom,
the maximum fractional energy that a neutron can transfer to the target
atom in a single collision, assuming isotropic scattering*, is
1 _ (m2 - 1)2
m2 + 1
Thus the -maximum pos sible fractional energy los s per collision is higher
for loW'er-atomic-number scatterers.
E2
= 0 14 b t f 1 d max 0 02
. , u or ea E =. .
o
E2max
For example, for aluminum E
o
A more useful expression for energy loss would be the average energy
lost per collision. A convenient way of describing this is as the average
decrease in the   of the neutron's energy. This can be. written
as:
*This equation should be mUltiplied by an anisotropy correction factor of between 1/2 and 2/3 for fission
spectrum neutrons. At higher energies the anisotropy becomes greater.
22
For values of m2 greater than 10, the approximation
2
  - m2 + 2/3
can be used. For lower values of m2, the error increases but is still only
about 3 percent for m2 = 2.
The average number of collisions a neutron of energy Eo undergoes in
being slowed to an energy Ef is then
In (Eo/Ef)
average number collisions =  
Anothe.,E. useful expression is the average energy of a neutron after
a collision, El:
= Eo [1 + (m2 - 1) 2 ]
2 m2 + 1
thus a neutron on the average will lose one-half of its kinetic energy in each
collision, with a hydrogen atom. This is why hydrogenous materials are so
effective in slowing down fast neutrons.
The minimum energy that can be imparted to the recoiling nucleus is
zero. Therefore, since the energy spectrum of recoiling nuclei is nearly
uniform between E2 . and E2 ,the average energy of the recoiling
min max
nucleus is
or just one -half of the maximum value.
At high neutron energies (> 1 MeV), the cross section for elastic
scattering and the cross section for absorption plus inelastic scattering
both approach the geometrical cross section of the nucleus. Therefore,
the total cross section approaches the limit of 2 7T R2, where R is the
radius of the nucleus and may be approximated by
23
Typical values for the scattering cross section for fast neutrons are in the
range of 2 to 4 barns for most nuclei.
The following expression relates the displacement cross section, ad'
to the scattering cross section:
(
m2 Ed)
ad = a 1 - ;; a (for E »E
d
)
s 4 E s 0
o
where Ed is the threshold energy for displacement.
CORRELA TION OF EFFECTS CREATED BY
DIFFERENT RADIATIONS
Theory can predict the effects of radiation on materials only to a
limited extent. It is therefore desirable that samples of all of the materials
or components proposed for use in the space environment be tested in the
actual environment of space. Because of costs, time involved, and other
practical considerations, all samples cannot be te sted in this environment;
therefore, the effects of this environment must be simulated in earth-bound
laboratories.
The most obvious method of simulating the space environment is to
reproduce this environment exactly in the laboratory. For several practical
reasons, this cannot be done on the large scale required. The alternative
method of testing materials is to expose them to other terrestrial radiations,
and from their re sponse to the se radiations, determine what their re sponse
to space radiations will be. This method has the advantage that data from
other radiation-effects studie s can then be used to provide information on the
response of materials to space radiations.
Attempting to correlate the effect of one radiation environment with the
effect that another will have on matter must be done with extreme care. An
understanding of the mechanisms of the radiation damage is essential. The
microscopic changes in the material and how the radiation induces these
microscopic changes must be understood. How these changes can be induced
by other means, that is, by a different type of radiation, by radiation of a
different energy spectra and flux, or by nonradiative mechanisms must be
determined.
24
When attempting to utilize the laboratory irradiation of materials to
simulate the effects that would result from space irradiation, the exact
conditions of both irradiations must be known and given due consideration.
The degree to which radiation affects a device or material is a complex
function, dependent upon the environment (temperature, surrounding
atmosphere, etc.), rate of irradiation, the spatial distribution of the de-
fects created, the orientation of the sample with respect to the incident
radiation, and the past history of the sample, in addition to the more
obvious variables such as the type of radiation and energy spectra. Attempts
to correlate the effects of one type of radiation in an environment to the
effects that another radiation will produce in another environment should
not be attempted unless the mechanisms for creating the damage are
thoroughly understood. With this knowledge, the approximate equivalence
of various environments can be deduced theoretically and then proven ex-
perimentally to reduce substantially the amount of experimental data re-
quired and to facilitate the application of existing radiation-effects data.
There are two basic mechanisms by which radiation can induce
damage in materials - energy deposition and atomic displacement. Correla-
tion of radiation effects is discussed separately for each of these two
mechanisms.
Energy Deposition
Permanent radiation damage in many materials, particularly organic
materials, depends primarily upon the amount of energy deposited in the
material. The primary mechanism for energy transfer from the incident
radiation to the absorbing material is through ionization of atoms or
molecules of the material.
All radiations, providing their energy is high enough, can produce
ionization. Charged particles are able to cause ionization by direct inter-
actions, al._ neutrons and electromagnetic radiations cause ionization
indirectly through the interaction of charged secondary particles and re-
coiling nuclei from scattering interactions. Since the probability of a
charged particle ionizing an acorn or molecule is a function of the time the
charged particle spends in the vicinity of the atom, slower particles (i. e. ,
greater mas s or lower energy) are more effective in causing ionization.
Table 5 shows the relative particle effectiveness for energy deposition in
carbon for several particles. This table is given only to indicate relative
25
effectiveness. Actual values will vary for other samples because of different
physical environments, material composition, physical size, and other
factors.
TABLE 5. PARTICLE EFFECTIVENESS FOR ENERGY
DEPOSITION IN CARBON(34)(b)
Integrated Flux
Range in for l-Rad Dose in
Energy, Carbon, 1 Cm
3
of Carbon(a), Relative
Particle MeV cm particles/ cm
2
Effectiveness
Fission Neutron 1-2 »1 102 x 10
10
o. 17-0.08
Ga:rnma Photon 1. 25 »1 1.7x 10
9
1
Electron 0.3 0.08 3.2 x 10
7
53
Electron 1.7 0.8 3.3 x 10
7
51
Electron 5 1. 1 3.0 x 10
7
57
Proton 18 0.2 2x 10
6
850
Proton 110 >1 1 x 10
7
170
Proton 740 >1 3 x 10
7
57
Alpha 40 0.06 2x 10
5
8500
(a) Particles whose range is < 1 cm deposit the I-rad dose within a thickness equal to the particle range.
(b) This table is given as an example 0f relative effectiveness. Actual values may vary.
Although different radiations may deposit the same quantity of energy,
they may deposit it differently. For example, 740 MeV protons and 0.3 MeV
electrons ha'·e similar values of relative effectiveness, but the electron
deposits its energy in the firsi O. 08 cm of material, while the proton re-
quires more than 1. 0 cm to deposit the same quantity of energy, the net re-
sult being different distributions of deposited energy. This mayor may not
affect the magnitude of the radiat.ion-induced damage, depending upon the
parameter of interest.
26
This exa:mple serves to point up the hazards of trying to correlate the
relative effectiveness of the various radiations for depositing energy in a
:material. It can be done, but the exact conditions of the two irradiations and
the :manner in which they interactiwith the :material :must be known and be
:maintained throughout the experi:ments.
Displace:ment Effects
The pri:mary :mechanis:m for radiation-da:mage effects in :materials
with a, crystalline structure is the displace:ment of ato:ms fro:m their lattice
sites with the subsequent creation of lattice vacancies and interstitial ato:ms.
Displace:ments can be caused directly by fast neutrons, protons, and high-
energy electrons and can result indirectly fro:m incident ga:m:ma-ray photons,
via the secondary electron.
To produce a displace:ment, the incident particle :must transfer a :mlnl-
:mu:m quantity of energy, that is, the threshold energy (Ed), to the struck
ato:m. This energy is usually several ti:mes greater than the energy required
to create a Frenkel pair by a ther:modyna:mically reversible process. For
:monato:mic solids, the threshold displace:ment energy typically ranges fro:m
lO to 30 eV, but varies with te:mperature and crystallographic direction.
The energy i:mparted to the displaced ato:m in excess of that required
to displace it goes into kinetic energy. Frequently, the displaced ato:m will
have sufficient energy to create further displace:ments, which results in a
cascade effect.
Expressions for the average energy transferred to the pri:mary dis-
placed ato:m by fission neutrons and by protons are given below. For the
sake of co:mparison, values obtained by calculating the results of bo:mbarding
copper (Ed = Z5 eV) with 1. 5-MeV particles are given. >:<
By fission neutrons: EZ = l/Z EZ:m = Eo/Z (l - rZ) = 5 x 10
4
eV
By heavy charged particles: EZ =
*See elsewhere in this section for definitions of the terms in these equations.
Z7
It can be seen that the average energy transferred to a displaced atom
by a fission neutron is much greater than that transferred by a· charged
particle. The neutron-displaced atoms will then be able to cause a rela-
tively greater number of secondary and even tertiary displacements than are
caused by atoms displaced by a charged particle. In the case of electrons,
EZ is only slightly greater than Ed, and hence very few if any secondary
displacements occur.
The energetic displaced atoms not only lose energy by displacing other
atoms, but if the displaced atom has sufficient energy, it will be ionized and
may dissipate energy by exdtation of bound electrons and ionization of atoms
in the crystal.
The average numbe::.... of displaced atoms Ns (E
Z
) resulting when a
primary recoil of energy EZ finally comes to rest is a function of the recoil
atom only. Within the accuracy required for most displacement-effects work,
it ha s the form:
fEZ
Ns (EZ) =
ZEd
where (1 - f) is the fraction of the recoil atom's energy which is consumed by
ionization and Ed is an average over all crystal directions of the displacement
threshold energy, Ed' The quantity f approaches unity for lower values of EZ
and is usually assumed to have the form calculated by Lindhard(41) and con-
firmed experimentally by Sattle;:-T4Z) These data are summarized in Figure Z
for silicon. Ed is somewhat higher (probably of the order of a factor of two)
than the threshold, Ed, for the most favorable direction. (43)
For photon radiations, the values presented in Table 6 are the displace-
ments due to the Compton electrons that are assumed to be in equilibrium
with the photons.
Z8
t\I
W
l.L.
I
-
c.:
.2
-
0
N
'c
..9
c.:
-
III
0
....J
>-
0'
'-
C1>
c.:
w
"0
c.:
0
+=
0
e
l.L.
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
13.3
a
0
t:J.
,
(
l-
I
Sattler's Data
Il,
Coincidence experiment
Iq it'"
Ordinary surface - barrier det ector
V J
Total depleted surface- barrier
~ ~
detector, high bias .
~
~ ~
/..:0
V t : J   ~
/00
r
s
t:J. '
~
0
v;: ~
~ Lindhard's calculated value
/ r;.
'7
(
I
I I I I I , I I I I I I I I I I
133 1333
Energy of Recoil Silicon Atom, keY
FIGURE 2. FRACTIONAL ENERGY LOST IN IONIZATION VERSUS
ENERGY OF RECOIL SILICON ATOM
29
TABLE 6. THEORETICAL DISPLACEMENT
PRODUCTION
Ns
Si(b) Ge(b)
I-MeV neutrons{ a)
500 300
14-MeV neutrons(a)
1500 700
I-MeV electrons 1.3 1.0
40-MeV electrons 5.0 4.4
1- Me V photons 1 1
10-MeV protons 6 5. 6
IOO-MeV protons 7 7
(a) The neutron data take into account anisotropic scattering
events and a correction factor for the energy loss of the recoil
atoms in nondisplacing (inelastic) collisions.
(b) The values used for the displacement -energy threshold are
Ed (Ge) 30 eV and Ed (8i) 25 eV.
Distribution of Defects
As mentioned previously, electrons tend to create individual defects
consisting of one displaced atom. Since gamma rays produce displacements
via secondary electrons, the same can be said for them. Because of the low
penetrating power of electrons, the defects tend to be located near the sur-
face (within the range of the electron), while gamma-ray-induced defects are
more uniformly distributed throughout the irradiated material. This neat,
orderly description is somewhat clouded by the possibility of the generation
of bremsstrahlung by the incident electrons. Bremsstrahlung produces
defects just like those produced by gamma, rays. For samples whose thick-
ness or sensitive region is comparable to or less than the range of the elec-
trons, the correlation between electron- and photon-induced damage may be
good. For example, correlation between I-MeV gamma rays and electrons
whose energies are equal to or slightly Ie S8 than 1 MeV would be expected to
be good since the gamma ray produces displacements via the secondary elec-
trons and the secondary electrons would have energies comparable to the
incident electrons.
30
Since the energy imparted to the displaced atom by an electron is
slight, it may not travel more than a few atomic distances before it stops.
The relatively close positions of the vacancy and interstitial could have a
significant effect on the macroscopic property changes and annealing kinetics
of the material.
Incident heavy charged particles lose a small portion of their energy
in each primary interaction. Each primary displaced atom displaces on the
order of 10 more atoms, forming a small cluster of defects in a region con-
taining   10
3
atoms. Since the incident particle loses only a small fraction
of its energy in each primary interaction, it dissipates its energy by creating
small clusters of defects, and an occasional larger one, distributed along
its path. The defect clusters due to heavy charged particles are relatively
uniformly distributed, with the cluster density being more dense toward the
end of the incident particle's range.
Fast neutrons can transfer a much larger fraction of their energy in a
primary displacement. The displaced atom then has sufficient energy to
create a large number of defects through secondary and tertiary processes.
The net result of a 1. 5-MeV neutron displacing an atom could be a clustering
of 102 to 10
3
defects in a volume of the crystal containing 105 to 10
6
atoms.
Since most neutron fluxes are not monoenergetic but repre sent a range of
energies, neutrons produce a variety of cluster sizes. For low exposures
« 1017· n / cm2) where clusters are still well separated, the damage tends to
be very much more nonhomogeneous than for heavy charged particles. At
fluences above this level, clusters tend to overlap and produce a more uni-
form but quite intense damage distribution.
From the preceding, it is obvious that different radiations produce dif-
ferent types of damage, both with regard to distribution\and severity. The
degree to which these difference s are significant depends upon the material
parameter that is being changed by the radiation. In a given material, two
radiations that produce the same or not too dissimilar spectrum and density
of primary recoil atoms will produce the same effect. If this is the case for
two radiations and other conditions are not significantly different, a correla-
tion can possibly be made.
Annealing
The treatment of defect creation predicts the number of defects created,
but does not consider the annealing of defects. The defects created are usually
31
not therInally stable but will diffuse therInally until vacancies and inter-
stitials recoInbine or forIn secondary, therInally stable defects. This
annealing proce ss can either enhance or detract froIn a Inaterial's proper-
ties, depending upon the property in question. The attainInent of this ther-
Inally stable condition is both a function of tiIne and teInperature. The
annealing behavior of irradiated substances is a cOInplicated and not well-
understood process. A treatInent of the subject is beyond the scope of this
section and it is Inentioned only to Inake the reader aware of the existence of
the phenoInenon.
DOSIMETR y,!<
Introduction
DosiInetry is the task of Ineasuring and providing a quantitative descrip-
tion of a radiation dose, preferably in terInS relevant to the radiation effect
being studied. In its Inost general forIn, the environInent can be described
by stating the (possibly tiIne dependent) nUInber of nuclear or atoInic particles
of various types and energies (the spectruIn) which cross a given surface.
Unfortunately, such a cOInplete de scription is rarely available or econoInically
Ineasurable, but, fortunately, it is not required for Inost radiation-effects
experiInents. In InatheInatical terIns, for a radiation spectruIn ct>(E)dE and
a radiation effect with energy dependence R(E), the total effect produced by
the spectruIn is
R = S R(E) ct> (E)dE
For exaInple, if a particular radiation effect of interest has a response,
R(E), which is fairly insensitive to energy, that is if R(E) = constant, then
the total effect is just
R ;; constant S ct>(E)dE ;; constant x 1>
The integral in the above equation, denoted by 1>, is just the total neutron
fluence, and the particular effect, used as the exaInple, is one proportional
'"An excellent source of more detailed information on radiation dosimetry is contained in Volumes J, II,
and III of Reference (1).
32
only to the total fluence. Since this effect is independent of spectral shape,
the total radiation fluence is the relevant quantity and is all that :must be
deter:mined when describing the environ:ment. On the other hand, if an effect
such as neutron-displace:ment da:mage in silicon, which is quite dependent
on neutron energy, is being studied, the total effect is described by the first
equation, in which case both the total fluence and its energy spectru:m are
relevant and should be deter:mined.
The :measure:ment of a radiation environ:ment also entails the deter-
:mination of a radiation effect. In this case a dosi:meter with a known response
function D(E) which has been calibrated with respect to the radiation field is
used and a :measure:ment
D = S D(E} D(E)dE
is obtained. If the dosi:meter response function, D(E), is approxi:mately pro-
portional to R(E) for the energy range of i:mportance to these integrals, it is
a fortuitously appropriate dosi:meter. If it is not, other infor:mation, such as
an esti:mate of the shape of ¢(E), will be needed to relate the dosi:meter read-
ing, D, to the expected effect, R. The appropriateness of the detector is
:measured, therefore, by how closely its response function is related to the
response function for the radiation effect being studied for the type of radiation
considered. This sa:me conclusion applies to the appropriatenes s of a
dosi:metry unit.
For exa:mple, it has been established that the :magnitude of bulk-
ionization effects in silicon is a function only of the ionization energy deposi-
tion. Therefore, the appropriate unit for describing ionizing radiation when
interested in ionization-induced currents in a silicon device is a unit of
energy deposition in silicon, e. g., rad (Si). Any dosi:meters whose reading
can easily be converted to rad (Si) in a way which is not sensitive to the de-
tailed spectru:m of the incident radiation is then useful. By way of contrast,
displace:ment effects in silicon represent a totally different response to the
radiation spectru:m, and the rad (Si) is an inappropriate unit. In this case
the total fluence and spectru:m of neutrons :measured or the equivalent fluence
of so:me energy or spectru:m of energies of neutrons which would produce the
sa:me concentration of displaced ato:ms in silicon [neutrons/ (c:m2)-1 MeV
equivalentJ as the :measured fluence and spectru:m is frequently used.
33
Perhaps the most common error made in a radiation-effects experi-
ment is to neglect the effect of the perturbation of the radiation spectrum
created by the presence of the experiment. It is this perturbed spectrum and
not the free-field spectrum which must be used. in the correlation or in de-
termining the total radiation fluence from a monitor dosimeter (or foil) used
with the experiment.
Before proceeding with a definition of units and descriptions of
dosimeters, it is appropriate to comment on two commonly used and mis-
used terms: correlation and simulation. As applied to radiation effects,
they a-re defined as follows:
Simulation is the production of a particular radiation effect by
any means.
Correlation is the establishment of the relative intensities of
different spectra or types of radiation required
to produce the same effect.
Note that simulation does not necessarily imply any need to reproduce
a radiation environment, only its effect. If the same effect can be produced
by electrical or optical stimulation means rather than nuclear radiation,
these are valid simulation techniques for that effect. Note also that the
correlation between radiations must be established separately for each class
of effect. For example, the correlation between different energy neutrons
is much different for displacement effects than for ionization effects.
Neutron Measurements
General Principles
In order to perform the weighting of different neutron energies, it is
necessary to have a reasonably good picture of the neutron-energy spectrum
for energies above lO keV. The contribution to displacement effects or ioni-
zation from neutrons below 10 keY in 'reactor environments is usually
negligible. Many neutron-producing facilities will be able to provide fairly
detailed spectral information on the free-field neutron environment to experi-
menters utilizing the facility. These spectra are, in general, determined
from data obtained from high-resolution spectrometers (recoil proton, Li
6
,
34
He
3
, etc.), from low-resolution measurements utilizing activation techniques,
or from reactor physics calculations. In general, if a radiation-effects
experiment is small, there is a good chance that the free-field spectrum will
not be significantly perturbed and thus will be relevant to the experiment being
conducted. If additional spectroscopy measurements are necessary, a deci-
sion must be made to determine the accuracies required. For high resolu-
tion measurements, fairly expensive, time-consuming spectrometer mea-
surement should be made. In most cases, however, lower resolution mea-
surements will be acceptable and activation spectroscopy measurements will
suffice. Inasmuch as the techniques followed in a spectrometer measurement
are highly dependent upon the instrumentation involved, and the calculation
of the approximate spectrum is beyond the scope of this manual, no recom-
mended procedures will be given in this document. General recommenda-
tion will, however, be given concerning foil activation techniques.
Foil Activation Measurements
Foil activation techniques utilize neutron-induced reactions, leading to
radioactive isotopes, for which there is a threshold energy, or for which an
artificial threshold can be produced by shielding. The process is illustrated
schematically in Figure 3. The top graph shows a typical neutron spectrum.
The middle graph shows an idealistic response function for a threshold foil.
The product of these two functions is shown in the bottom graph. The area
under this curve is the total foil response (which is proportional to the foil
activity). It can be seen that, roughly, the neutrons with energy above Et
contribute to the response, and the effective response coefficient (cross sec-
tion) is almost a constant, 0eff' Therefore, the foil response is approxi-
mately proportional to <I> (E> Et) 0eff'
A method based on irradiating a number of foils with different thres-
holds has proved to be very useful. The limitations to the foregoing approxi-
mate analysis are obvious: o(E) is not constant above Eb and E
t
itself is a
function of the spectral shape. The steeper spectra tend. to push E
t
downward.
In an actual situation, where the cros s section is not constant but the spectral
shape, <I>(E), is known, one can obtain a spectral averaged cross section from
the expression
1
00
o(E) <I>(E) dE
o
0=------------------
35
With this average cross section and the :measured foil activity, the neutron
fluence above the threshold energy, E
t
, can be obtained. Since the spectru:m
is known, the total neutron fluence can thus be deter:mined. This process is
the :most co:m:mon :measure:ment :made in neutron-effects testing. The :most
co:m:monly used :monitor foil :material is S-32, which has a threshold energy
of approxi:mately 3 MeV. The Ni
58
(n, p)Co
58
reaction is also useful and is
now seeing widespread use. If this :method is used, one :must be careful to
insure that the experi:ment has not perturbed the spectru:m, since large
errors can unknowingly be introduced when utilizing this technique.
w
b
CTeff
w
b
Activitya! CT(E) cl>(E) dE
FIG URE 3. THRESHOLD FOIL METHOD
36
E
E
E
In situations where the spectral shape is not as well known, a series of
threshold foils can be used. By assu:ming a spectral shape (e. g., a fission
spectru:m of "best esti:mate" for the particular reactor), an average cross
section can be co:mputed, and the fluence above the various thresholds, based
upon the assu:med cross section, deter:mined. A curve of the integral fluence
as a function of energy can be deter:mined by this :method. Fro:m this curve
the ratio of total fluence to that above a :monitor foil's threshold (e. g., S-32)
can be deter:mined so that further exposures can be :made with the use of only
the one :monitor foil. Co:m:monly used threshold reactions are listed in
Table 7 together with their effective thresholds and cross sections for a
fis sion spectru:m. If the integral curve obtained in the previous :manner
differs considerably fro:m an integral curve of the as su:med spectru:m,
further data evaluation :must be done.
TABLE 7. THRESHOLD REACTIONS
Foil
Au-l97 (n, -y) Au-l98
Pu-239 (n, f) f. p.
Np-237 (n, f) f. p.
U-238 (n, £) f. p.
Ni:-58 (n, p) Co-58
S-32 (n, p) P-32
Mg-24 (n, p) Na-24
Al-27 (n, a) Na-24
(a) Surrounded by I-em boron-IO.
Effective
Threshold, E
i
,
MeV
ther:mal
O.Olo(a)
0.600(a)
1. 50( a)
3.0
3.00
6.30
7.5
Effective C ros s Section
for Watt Fis sion Spectru:m,
barns
98.9
1.7
1. 65
0.55
0.55
0.30
0.067
0.079
a,
Co:mputer codes have been developed, such as SAND II, RDMM, and
SPECTRA, which can be used to extract further spectral infor:mation fro:m
the set of activation data. The SAND II and SPECTRA codes co:mpute both
differential and integral spectra, based upon iterative techniques, and
utilize both the response-function differences of the various reactions over
37
the entire sensitive energy regions and other physical information available
about the source to obtain these solutions. RDMM computes differential
flux as a continuous analytical function. If the spectral shape is calculated
by one of these codes for the particular experimental setup, and if no changes
in the setup are made, a single m')nitor foil may be used for subsequent
irradiations. It is wise, however, to check routinely to insure that the spec-
trum has not changed unknowingly. Obviously, the accuracy of the neutron-
fluence measurements with foil activation techniques will be limited by the
accuracy of the cross-section knowledge, the calibration of the counting
equipment, and the degree of sophistication exercised in reducing the foil
activitie s to fluence information.
The three codes may be obtained from the Atomic Energy Commission
Radiation Shielding Information Center at Oak Ridge National Laboratory.
Evaluated energy-dependent cross sections for neutron-detector reactions
are also available from the center. being tabulated on magnetic tape
(SAND II cross-section library format).
Photon, Proton, and Electron Measurements
General Principles
Photon, proton, and electron measurements are primarily measure-
ments of ionization effects. Therefore, the dose (or ionization density) in
the material of interest is most closely related to the effect. The response
function relating this effect to the photon energy is known as the mass
absorption coefficient. Shown in Figure 4 (see also Figure 1) are mass
absorption coefficients for silicon (used as an example of a typical low Z
material). As can be seen for these materials, the absorption coefficients
are essentially independent of energy over the energy range, 150 keV < E <
1 MeV, and are very slowly varying functions up to an energy as high as
10 MeV. On the basis of these characteristics, the absorbed dose per unit
energy fluence for bremsstrahlung distributions over this energy range is
fairly insensitive to the spectral shape, and dose measured in a low-Z
dosimeter can be converted quite easily to dose in a low-to-medium-Z mate-
rial of interest. For high-energy electrons and for the Compton effect of
high-energy photons and low- or medium-Z material, an approximate rule
of thumb (±5 percent) is that the dose is proportional to Z/ A of the target
material, where A is the mass number. For higher accuracies, even a
38
L
crude spectral shape used with the equations given for D and R can convert
dose measured in any dosimeter, D, to the dose in the. material of interest,
R, viz.,
R=
S
R(E) <p(E) dE
D ~  
S
D(E) <P(E) dE
For electron-beam exposures in a known spectrum, dose may be converted
from one material to another by using the above equation and dEl dX values
given in the literature. (44)
1.0
~
(IJ
E
u
c
0
. ~
en
c
-
c
Q)
:§
0.'
-
-
Q)
0
u
c
.2
-
n
L-
0
II)
.0
«
II)
II)
~
0.01
0.01
10
Photo Energy, MeV
FIGURE 4. MASS ABSORPTION COEFFICIENT IN SILICON
The use of high-energy electrons, 0.5 < E ~ 15 MeV, to produce ioni-
zation effects is straightforward. Their rate of energy deposition is almost
39
independent of energy and :material, Z < 40. The only cautions are that the
electron energy needs to be high enough to penetrate the target and radiative
losses :must be considered. In addition, thin plates can scatter a s:mall-
dia:meter electron bea:m into a cone-shaped bea:m. Therefore, objects in the
bea:m ahead of the target, such as a chassis, :must be in place during dosi:metry
calibration.
High-energy protons deposit energy pri:marily through ionization, but
can create ato:mic displace:ment. The :measure:ment and prediction of de-
posited dose fro:m incident protons is co:mplicated by the generation of sec-
ondary particles and photons in inelastic scattering processes. In general,
for absorbers of thickness less than the .range of the incident protons, the
dose fro:m the pri:mary protons predo:minates. For a thickness greater than
the pri:mary proton's range, secondary particles and ga:m:ma rays can contri-
bute significantly to the absorbed dose. (32)
Since photons (ga:m:ma or X-rays) are indirectly ionizing radiation and
lose energy through the creation of high-energy electrons which subsequently
lose energy through further ionization, extra care :must be taken in accounting
for lack of electron equilibriu:m. If a pure photon bea:m were incident on a
slab of :material, the energy deposition as a function of depth in the slab would
be as shown sche:matically in Figure 5. Although the a:mount of energy initially
i:mparted to the :material by photons decreases with depth, the actual dose
builds up to a :maxi:mu:m at a depth corresponding to the :maxi:mu:m electron
Q.>
IJ)
o
o
Re
Distance Into Slab
FIGURE 5. ENERGY DEPOSITION BY PHOTONS
40
Ii
11
l\
I!
il
il
~  
I:
I
I
range, then decreases very slowly at the rate of attenuation of the photon
beam. This loss of dose to the material near the surface corresponds to
that energy lost by the electrons which are scattered out of the material
before all of their energy is deposited. At a point corresponding to the
maximum electron range and beyond, the beam is in electron equilibrium,
meaning that for every secondary electron leaving a small region of interest,
another enters the region or, equivalently, the ratio of electrons to photons
remains constant. For high photon energies (> 200 keV) in low- and medium-
atomic-number materials (Z < 40), the ratio of electrons to photons is almost
independent of material. At lower energy and higher Z, the ratio changes
when the beam goes froTI) one material to another, in a fashion similar to
that shown in Figure 5. Therefore, in order to avoid complications from
  of dose and to provide accurate dosimetry, exposures should
be performed under conditions of electron equilibrium. Unless electron
equil:i.brium is established correctly in the radiation source, a foil of
approximately the correct Z and an electron-range thickness should be
interposed in front of the target. The same rule applies to the cases of
dosimeters. The electron range is approximately
Re = 412 E(l. 265 - 0.0954 loge E) for 0.01 MeV < E < 3 MeV
Re = 530 E-I06 for 2.5 MeV < E < 20 MeV
where Re is in mg/ cm
2
, and E is in MeV.
When reporting absorbed-dose measurements, the unit rad, radiation
absorbed dose, is used. One rad corresponds to the deposition of 100 ergs/g
of radiation energy in a small volume of the material of interest at a point
of interest. It is important to note that the material in which the energy is
deposited must be specified when reporting with this unit of measure, i. e. ,
rads (Si), rads (H20), etc. Dosimeters for use in experiments should be
calibrated in known spectra to read rads (dosimetry material).
If nonconducting dosimetry materials or experiments are exposed to
intense electron beams characteristic of flash X-ray machines, care must
be taken to account for the effect of the potential buildup in the sample (from
trapped electrons) on the dose to the sample.
The various dosimeters useful for ionization-effects studies with photons,
protons, and electrons are described below.
41
DosiInetry Devices
Radio-Photo LUIninescent Devices (RPL)
In RPL devices, irradiation produces stable fluorescence centers
which Inay be stiInulated by subsequent ultraviolet (UV) illuInination to eInit
visible light. The total light eInis sion is a Ineasure of the absorbed dose
in the RPL Inaterial (if in electron equilibriUIn) which was previously
exposed.
An exaInple of a RPL dosiIneter is a silver Inetaphosphate glass rod
or plate systeIn. These dosiIneters can also be used with special energy
shields (e. g., -1. 2 g/ cIn2 Pb, 0.6 g/ cIn2 Sn, 0.2 g/ cIn2 AI, and 0.11 g/ cIn2
low-Z plastic) which suppress the low-energy response of the high-Z silver
by absorption sufficiently that the total response is essentially independent of
energy, yielding a reading proportional only to exposure (photon fluence)
for photon spectra of energy 100 keV < E < 5 MeV. By knowing the total
fluence and the spectral shape, one can evaluate the dose for any other Inate-
rial. With a thinner shield Inatching the average Z of the glass, it would
Ineasure dose in the glass.
Glass rods should be cleaned and read before irradiation for an expected
dose of < 100 rads (glass). They should not be routinely reused. If absolutely
necessary, annealing is possible using procedures docuInented in the litera-
ture. ExtreIne care should be taken to avoid glass-rod chipping.
For high-energy electron-beaIn dosiInetry, the rods should be used
directly on or in the experiInent without shields; then one is Ineasuring local
absorbed dose, rads (glass).
Optical-Density Devices
In optical-density devices, radiation produces stable color centers which:
absorb light. MeasureInents of the optical transInission, usually at a fixed t
wavelength, can be related to the dose in the active Inaterial. !
;1
~
~
~
q
An exaInple of an optical-transInissivity-change dosiIneter is a cobalt-
glass-chip system. At doses greater than 10
6
rads, saturation is approached
and the readings can become very inaccurate. Other Inaterials which are ~  
3
used as calorimetric dosimeters include dyed plastics such as blue cellophane, . ~
:i
!:
il
42
I
cinemoid films-, etc. Again these should be used within their accurate range
  ~ l 0 6 rads) and corrections may be required at very high dose rates. Before
using a particular dosimetry system, one should consult the literature to de-
termine rate and environment effects which may be characteristic of the
particular system.
Thermoluminescent Devices (TLD)
TLD irradiation produces metastable centers which can be induced to
emit light by heating. The amount of light is related to the dose in the TLD
material.
An example of a TLD dosimetry system uses lithium fluoride with a
readout unit that heats the exposed material and registers the area under
the luminescent peak. The heating rate should be checked for linearity or at
least reproducibility, and for doses below 1 rad (LiF), the readout should be
performed with the material in an inert or dry nitrogen atmosphere. Because
of the radiation damage, low dose readings should always be taken with un-
used materials. The TLD materials can be annealed and reused only at
high doses.
TLD materials can be obtained in several forms and chemical com-
positions. Examples include powders, extrusions, encapsulations in Teflon,
etc. Chemically differing dosimeters including calcium fluoride, lithium
chlorate, etc., are also available.
Because of their sensitivity to preirradiation heating history, TLD's
should be used as delivered from the manufacturer or system vendor and no
preirradiation annealing should be attempted in routine dosimetry.
Manganese-activated calcium fluoride is, for some applications, a more
useful TLD material than LiF since: (1) it does not saturate at as low a dose;
that is, it is not as easily damaged; and (2) its Z is closer to silicon, so that
with an aluminum or silicon case one can get a good approximation of rad (Si).
The wall material surrounding the TLD material should match the TLD
atomic number and should be thick enough to establish electron equilibrium.
Then (if the calibration is correct) the dose measured will be rad (TLD ma-
terial); otherwise the dose will be intermediate between rad (TLD material)
and rad (wall material).
43
The TLD reader should be checked regularly for proper operation of
the phototubes and heating units; a regular (daily or weekly) calibration made
with cobalt-60 or other standard source, and a log kept to show trends. TLD-
system manufacturers' recommendations for care of the reader should be
followed. To check heating rates, and to allow for examination of the entire
glow curve, the readout units should be provided with outputs for strip-chart
recording of temperature and light output. Ii dosimeters are reused, they
should be periodically checked in a standard source to insure that radiation
damage has not changed their sensitivities.
Thin Calorimeters
A thin calorimeter determines the dose by measuring the temperature
rise in a small sample of known material. Since the temperature rise can be
converted to energy deposition (dose) by the material's specific heat, the
measurement is a direct determination of the average dose in the sample. If
the sample is thin, i. e., it absorbs a negligible fraction of the incident radia-
tion and the incident beam is in electron equilibrium for the calorimeter ma-
terial, the temperature rise is independent of thickness.
The three important elements of a thin calorimeter are the absorber,
the temperature sensor, and the thermal isolation. The absorber can be any
material, preferably having approximately the correct atomic number as
judged by the effect being studied, and also preferably a good thermal con-
ductor to assure rapid thermal equilibrium. Metal foils (Be, AI, Fe, Cu,
Ag, Pt, Au) as well as thin semiconductor chips (Si, Ge) have been used
successfully.
The temperature sensor should represent a small perturbation on the
absorber. A thermocouple satisfies this criterion well, particularly if it
almost matches the atomic number of the absorber. A small copper-
constantan thermocouple on a copper foil is a good example. A more sensi-
tive calorimeter results from using a small thermistor as both absorber and
temperature sensor. A chemical analysis of the thermistor can establish its
effective atomic number, and a calibration against a known material is re - .
quired to establish the combination of specific heat and temperature coefficient. Ii
Care must be taken in as sembly to minimize the amount of solder used in i!
attaching leads, because this may enhance the amount of higher Z material. I
Re sistance welding can be used to eliminate this problem. If the thermistor
is not thin to the radiation, the temperature measurement must be performed
44
for a sufficiently long duration in order to insure that thermal equilibrium
is established within the thermistor (0. 1 to 1 second).
In order to measure accurately a small, sudden temperature rise,
some degree of thermal isolation is required. Obviously the leads to the
temperature sensor should be small wire   ~ 3 mils). For single-pulse
measurements, a block of Styrofoam provides good isolation, but the heat
lost to the inside layer of Styrofoam is a small correction, particularly
for very thin calorimeters. Use of the calorimeter in vacuum also pro-
vides excellent isolation. For accurate measurements, expecially on a
short string of LINAC pulses, the absorber can be suspended in a small,
evacuated can with water-cooled constant-temperature walls and a thin
window for beam entrance. The detailed design depends on the radiation
beam being measured and the accuracy requirements, and may have to take
into account scattering from the walls of the chamber.
For single pulses typical of flash X-ray machines, a cooling curve
should be established and exponentially extrapolated to zero time to deter-
mine the temperature at the time of the burst.
The response of the calorimeter is calibrated by the specific heat
of the absorber and the temperature calibration of the sensor. In electron-
beam measurements, if the calorimeter material is the same as the experi-
mental material being tested, rads (experimental material) can be measured
directly. If, however, the dose to the calorimeter must be converted to
dose in another material of significantly different atomic number, correc-
tions must be made for differences in dE/dX, backscattering, and
brems strahlung los se s.
PIN Detectors
Reverse-biased PIN diodes (usually silicon, but a cooled germanium
device can also be used) collect charges produced by ionization in the intrinsic
semiconductor region. Calibration is based on the known efficiency for pro-
ducing electron-hole pairs (3.7 eV /pair in silicon) and the active volume of
the junction region. The charge collection time is short (-ns) and therefore
a PIN diode can be used to measure not only the dose in the semiconductor
but also the shape of the radiation pulse [dose rate (Si) versus time]. Care
must be taken to use the detector only at low dose rates where the linearity is
established. At high dose rates [-10
9
rads (Si)/s] the internal electric field
is modified by the high currents and the output becomes nonlinear. It is
45
important to note that a PIN detector will not read rads (Si) unless electron
equilibrium in the silicon active volume has been established. Many standard
commercial detectors can derive measurable portions of their signal from
the high-Z case or from their tantalum-plate contacts. One can, however,
obtain from manufacturers, on special order, degenerate silicon contacts
to which the leads are attached or with very thin contacts so that the detector
may be placed in electron equilibrium through the introduction of additional
silicon (or aluminum foils). One should be careful to determine whether the
addition of inactive material to create electron equilibrium for the most
energetic portion of a distributed spectrum has attenuated the low-energy
portion of the spectrum and make a suitable correction to determine the dose
of a thin silicon sample.
Compton Diode and SEMIRAD
The operation of compton diodes and SEMIRADS is based on the charge
transfer of electrons between materials under irradiation. The calibration
depends on the spectrum and is not uniquely related to dose in any material,
except for a limited range of spectra. The time resolution is potentially
excellent and such devices are very useful as pUlse-shape monitors at high
dose rates. For very high dose rates, Compton diodes are recommended
since SEMIRADS will undergo saturation.
Scintillator - Photodiode Detectors
Various organic scintillators having both fast response and a large
linear range are available for measurements of ionizing dose rate versus
time. Examples are plastics such as Pilot Band NEI02; organic liquids,
such as NE211, and NE226, which have 2 - to 3 -ns re solution. At high dose
rates the light emitted is intense, so that the photodiode needs to be designed
so as to avoid space charge limitation. An FW 114 photodiode is frequently
used with adequate bias voltage to avoid saturation. This combination mea-
sures energy deposition in the scintillator., i. e., rad (scintillator). Organic
scintillators have been shown to have nonlinear characteristics at high rates
(_lOll rads/s) and should not be used at rates above this value.
Faraday Cup ~
  ~
A Faraday cup can be used for electron-fluence measurements, which il
are convertible to rad (Z) entrance -dose units in a material to be inserted in t
II
If
46
,.
1\
I.
i
l
I
il
'\
:1
II
.1,
the beam if the incident electron energy is known. Values of electron-energy
loss rate, dE/dX, are given in Reference· (44). When using a Faraday cup
to monitor an electron beam, a guard voltage should be applied and a
reentrant cup used with a 10w-Z stopping material, backed up with a higher
Z shield material. The incident beam must be collimated and accompanying
secondary electrons must be swept out by a magnetic analyzer. For accurate
work, .the whole cup should be placed in a vacuum; for fast-pulsed e1ectron-
beam work, if the pulse shape is to be determined, a coaxial cup design
matched to the cable impedance may be desirable.
The accuracy achievable with the proper Faraday cup techniques is
good enough to warrant their use as calibration tools. The much greater
convenience in LINAC use of a simple, but less accurate, 10w-Z stopping
block current collector renders this a useful tool also.
Summary of Typical Dosimeter Sensitivity
Tables 8 and 9 list typical gamma-ray and neutron sensitivities (much
of it experimental, but some vendor's data) for a variety of dosimeters used.
Some of these sensitivities may be varied by geometrical design, voltages
applied, and other methods, so the data are to be taken as representative
only. It should be noted that the thermal-neutron response of the dosimeters
must be considered, as they are not necessarily negligible.
Spe ctrum Monitoring
In nuclear physics studies, elaborate tools have been developed for
detailed photon spectrum measurements. However, for space requirements,
the spectral-information accuracy requirements rarely justify such methods.
Simpler techniques based on a knowledge of the general source character-
istics and some absorption measurements, along with any spectral information
provided by the facility operations group, are usually adequate.
A combination of dosimeters having different atomic numbers and
shielding is recommended for spectral monitoring, for example: high- and
10w-Z bare glass rods, or LiF and CaFz (Mn) in plastic and aluminum con-
tainer pairs, respectively, to read rads (low Z) and rads (high Z). The dose
ratio is a measure only of the spectral quality, not of the spectral details;
if the ratio is appreciably different from 1. 0, the spectrum may be either
47
TABLE 8. GAMMA-RAY AND NEUTRON SENSITIVITY OF ACTIVE DOSIMETERS
Gamma-Ray Sensitivity, Neutron Sensitivity,
coulomb coulomb
Dosimeter Type Model No., etc. R(Co-60) n/cm
2
(E)
Silicon p -i-n 004-PIN -2501E 6 x
10-
9
5 x 10-
17
(14 MeV)
2 x 10 -18 (fission)
Photodiode- Pilot B 2 x
10-
8
1 x 10 -18 (fission)
scintillator NE 211 (xylene) 1 x
10-9
1.5
x 10 -19 (fission)
(FW114) NE 226 (C6F6)
~ 1 x 10-9
1 x 10 -21 (fission)
Semirad
Ti wall Econ 7318 1.2x
10-11
3.5 x 10-
20
(14 MeV)
1.5
x 10 -21 (fission)
Stainless steel Reuter Stokes - 1. 7 -6 x 10-
11
Negligible (fission)
gamma sensitive Not negligible (fusion)
Stainless steel Reuter Stokes - 3.5 x
10-
11
3 x 10 -22 (fission)
U-238 neutron sensitive 1 x 10-
21
(14 MeV)
Compton diode (Representati ve 1.4 x
10-
11
5.3
x 10-
21
model, EG&G)
Cerenkov (Representati ve 2.5
x 10-
10
8 x
10-
9
detector model, EG&G)
Note: This table was developed from private communications to D. J. Hamman of Battelle Memorial
Institute from Nancy Gibson of the U. S. Army Nuclear Defense Laboratory.
TABLE 9. NEUTRON SENSITIVITY OF PASSIVE GAMMA-RAY DOSIMETERS
Neutron Absorbed
Dose(a) • 10-
10
R/(n· cm-
2
). at Indicated
Neutron Energies, MeV
Dosimeter Type Material Thermal 1 2 3 5.3 8 14.5
TLD CaFi
Mn
a. Vacuum tube type 1.41 0.67 0.81 0.65 6.2 0.14 2.1
b. Micro TLD 1. 00 1.9 2.0 8.2 6.7 4.4
LiF
TLD-100 200 2.3 5.2 6.4 14.0 15.0 23.0
TLD-600 625 8.9 11.0 11.0 22.0 18.0 48.0
TLD-700 None 4.2 8.1 8.3 20.0 16.0 37.0
RPLD AgP04 glass
High Z 3.6 ~ 1   6 1.5 ~ 1   7 2.8 6.4
Low Z 28 .s2.3 .s3.4 .s8.2 2.5 5.1
UV transmission Cobalt glass 36.3 58 ± 500/0 for fast neutrons
Note: This table was developed from private communications to D. J. Hamman of Battelle Memorial
Institute from Nancy Gibson of the U. S. Army Nuclear Defense Laboratory.
(a) Underlined values were obtained with dosimeters irradiated in an energy discrimination shield.
All others were bare.
48
,
II
very soft (containing low-energy components < 200 keV) or of very high
energy (> 5 MeV). This point should be checked, if there is some doubt
considering the source, by measuring the broad-beam absorption curve or
first and second half-value layers in aluminum or copper and comparing
it with that for ::obalt-60 (first HVL = 17 g/ cm
2
aluminum or 9 g/ cm
2
copper).
If too soft a spectrum is indicated, experimental design should be
changed, since environment correlation may be difficult, that is, the radia-
tion may be attenuated severely by transistor cans, which poses the problem
of determining rad (S1) in the device from an exposure or dose measurement
outside the can. A ratio of rad (Z = 29) to rad (Z = 13) higher than 1. 5 indi-
cates an appreciable amount of radiation below 200 keV. Extreme care should
be taken in experimental design with such low energies to as sure that the
dosimetry measures the doses desired at interior points of the experilnent.
Since (1) in ga:m:ma-ray effect si:mulation the :microscopic and :macro-
scopic dose deposition pattern is the entity of interest, that is, the depth-dose
distribution and so:metimes the LET, (2) the absorption coefficients for semi-
conductors and :most insulator materials do not vary :much for photon energies
in the range of 200 keV to 10 MeV, and (3) most useful sources have energies
within this range, it is not felt that detailed spectral infor:mation is needed for
routine work. However, ga:m:ma-ray si:mulation facilities should have enough
spectral information to be able to convert dose :measurements in the dosimetry
:materials used to absorbed dose in all materials.
GLOSSARY
absorbed dose. See dose.
alpha particle (alpha radiation). An energetic doubly ionized heliUln atom
consisting of two protons and two neutrons.
astrono:mical unit. An interplanetary unit of measure equal to the mean
distance between the Earth and the Sun. lAU = 92,950,000 miles.
ato:mic displace:ment. The displacement of an ato:m from its usual site in a
crystal lattice.
barn. A unit used for specifying nuclear cross sections, equal to 10-
24
cm
2
.
49
beta radiation (beta particle). A form of radiation consisting of energetic
electrons.
bremsstrahlung. Electromagnetic radiation resulting from the inelastic
collision of electrons or other charged particles with a nucleus, the
interaction being between the charged particle and the coulomb field of
the nucleus. The bremsstrahlung energy spectrum is continuous from
zero to the maximum energy of the incident particles. Bremsstrahlung
is synonomous with X-ray continuous spectra.
Compton effect. The collision of a photon with a free electron in which the
photon gives up part of its energy to the electron, thus resulting in a
recoiling electron (Compton electron) and a photon of lower energy. For
this interaction, orbital electrons are essentially free electrons.
cross section. A measure of the probability of a particular process occur-
ring. The cross section of an atom or nucleus for a particular reaction
has the units of an area and is actually the effective target area presented
to an incident particle or photon for a particular reaction. A commonly
used unit for cross sections is the barn, equal to 10-
24
cm
2
.
dose. The absorbed dose (D) is the quotient of l::.ED by l::.m, where l::.ED
is'"the energy imparted by ionizing radiation to the matter in a volume
element and l::.m is the mass of matter in that volume element
l::.ED
D::: l::.m = (ergs/g, rads).
elastic scattering. Scattering in which the total kinetic energy of a two-
particle system is l:..nchanged after scattering.
electron (beta particle ). A charged particle carrying a unit electronic
- charge either positive (positron) or negative (negatron). The term electron
is commonly used instead of negatron when discussing the negatively
charged particle. The mass of an electron is about 1/1800 of the mass
of a proton.
exposure. The exposure is the quotient of l::.Q by l::.m, where l::.Q is the sum ~
of the electrical charges on all the ions of one sign produced in air when ,t
all the electrons (negatrons and positrons) liberated by photons in a volume li,'
element of air whose mass is l::.m are completely stopped in air. ~  
'I
m
i
Ir
!I
I'
i!
~
50 !
fission neutron. Neutrons produced in a fission process which have not yet
been involved in interactions with other materials.
fission. The splitting of a nucleus into two (or vary rarely more) fragments -
the fission products. Fission is accompanied by the emission of neutrons
and the release of energy. It can be spontaneous or it can be brought about
by the interaction of the nucleus with a fast charged particle, a photon, or
more commonly, a neutron.
fission neutron spectrum. The energy spectrum of neutrons emerging from
a fission reaction.
galactic cosmic radiation. High-energy particulate radiations originating
outside the solar system.
gamma ray. Highly penetrating electromagnetic radiation from the nuclei of
radioactive substances. They are of the same nature as X-rays differing
-:mly in their origin. Gamma rays are emitted with discrete energies.
E = hv.
heavy charged particle. A charged particle whose mass is much greater than
the mass of an electron.
inelastic scattering. Scattering in which the total kinetic energy of a two-
particle system is decreased, and one or both of the particles is left in an
excited state.
ionization. The separation of a normally electrically neutral atom or mole-
cule into electrically charged components.
ionization potential. The minimum quantity of energy necessary to move an
electron from a particular shell to a position where it is essentially free
of the nucle us.
ionizing radiation. Any radiation consisting of directly or indirectly ionizing
particles or a mixture of both.
51
mass attenuation coefficient. The quotient of dN by the product of p, N, and
dl, where N is the number of particles (photons) incident normally upon a
layer of thickness dl and density p, and dN is the number of particles
1 dN
(photons) that experience interactions in this layer. }J./p = pN dl (cm
2
/g).
The term "interactions" refers to processes whereby the energy or direc-
tion of the incident particle (photon) is altered.
mass energy transfer coefficient. The quotient of dEK, by the product of E,
p, and dl, where E is the sum of the energies (excluding rest energies) of
the indirectly ionizing particles incident normally upon a layer of thickness
dl and density p, and dEK is the sum of the kinetic energies of all the
1 dEK 2
charged particles liberated in this layer. }J.K/P = Ep   (cm /g).
mass energy absorption coefficient. The product of the mass energy transfer
coefficient and (I-G), where G is the fraction of the energy of secondary
charged particles that is lost to bremsstrahlung in the material.
neutron. A particle with no electrical charge, but with a mass approximately
equal to that of a proton.
pair production. An interaction where a photon of energy E)" greater than
1. 02 MeV, is absorbed in the field of a charged particle and in its place
an electron-positron pair is created whose total energy, kinetic plus rest
mass energy, is exactly equal to the energy of the incident photon.
E)' = (E
e
- + m
o
c
2
) + (Ee+ + m
o
c
2
) = Ee- + Ee+ + 1. 02 MeV.
photoelectric effect. An interaction in which a tightly bound orbital electron
absorbs the entire energy of an incident photon and is ejected from the atom
with an energy equal to the difference between the energy of the incident
gamma-ray or X-ray photon and the binding energy of the electron.
Ee = E)' - E
B
.
Planck's constant. A universal constant relating the frequency of a radia-
tion to its energy such that E = hv, where E is the energy, v is the frequency,
and h is Planck's constant. h = 6.625 x 10-
27
erg-so
positron. A particle whose mas s is the same as an electron's but which
carries a unit positive charge.
52
proton. A positively charged high-energy hydrogen ion with a mass of
1. 66 x 10-
24
g.
rad (radiation absorbed dose). A unit of absorbed dose equal to 100 ergs/g.
In defining a dose, the absorbing material must be given, e. g., rads
absorbed in carbon = rads (C).
reactor neutron (spectrum). Neutrons and the energy spectra thereof, as
found in nuclear reactors. That is, fis sion neutrons which have been de-
graded in energy and whose energy spectra have been broadened by inter-
action with materials in the reactor.
roentgen. The unit of exposure that produces charge in the amount of
2. 58 x 10-
14
coulomb/kg of air and is equivalent to a dose of 87.7 ergs/ g
in air [ O. 877 rads (air)].
solar flare. A localized region of exceptional brightness on the sun, that
develops very suddenly, generally not too far from a sunspot group. Flares
are graded as to their importance (brightness, duration, and dimensions)
from 1- for a minor flare to a 3+ for the largest flares, with obvious
graduations in between. Radiations of several different types may be
emitted from a flare.
solar wind. An ionized plasma emitted continuously by the sun.
threshold displacement energy. The minimum quantity of energy required to
-displace an atom from its lattice side in an atomic collision.
threshold energy. The energy below which a particular reaction will not take
place.
ultraviolet radiation. Spectral radiation with a wavelength (energy) between
that of visible light and X-rays.
unit charge. The electronic charge carried by one electron, equal to
1. 6 x 10-
1
9 coulomb.
Van Allen belt(s}. Toroidal belts of charged particles which surround the
earth near the equator.
53
. ,
X-ray. High-frequency electromagnetic radiation produced by any of these
processes: (1) radiation from a heated mass in accordance with Planck's
radiation law, (2) bremsstrahlung, and (3) electron transition between
atomic energy levels, usually excited by incident beams of high-energy
particles, resulting in characteristic, 'discrete energy spectra.
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(1) Sondhaus, C. A. ,and Evans, R. D., "Dosimetry of Radiation in Space
Flight", Radiation Dosimetry, Vol III, Attic, F. H., and Tochilin, E.,
Academic Press, New York (1969).
(2) Chapman, M. C., "Design Criteria for Radiation Resistant Flight
Control Systems for Aerospace Vehicles", Northrop Space Laboratories,
Contract No, AF 33(657) -7851 (April, 1963).
(3) Burrell, M. 0., Wright, J, J., and Watts, J. W., "An Analysis of
Energetic Space Radiation and Dose Rates", George C. Marshall Space
Flight Center, NASA TN D-4404 (February, 1968).
(4) Glasstone, Samuel, Sourcebook on the Space Sciences, D. Van Nostrand
Co., Inc., Princeton, New Jersey (1965) .
(5) Roberts, W. T., "Space Radiations: A Compilation and Discussion",
George C. Marshall Space Flight Center, MTP-AERO-64-4
(January, 1964).
(6) Strauch, K., "Measurements of Secondary Spectra From High-Energy
Nuclear Reactions", Proc. Symp. Protection Against Radiation Hazards
in Space, Gatlinburg, Tennessee, USAEC-TID-7652, Vol 2, 409
(1962),
(7) Leach, E. R., Fairand, B, p" and Bettenhausen, L. H., "The Space
Environment and Its Interactions With Matter", REIC Report No. 37,
Battelle Memorial Institute, Columbus, Ohio (January 15, 1965),
(8 ) Dostrovsky, 1., Rabinowitz, P., and Bivins, R., "Monte Carlo Calcu-
lations of High-Energy Nuclear Interactions, 1. Systematics of Nuclear
Evaporation", Physical Review, III, (6), 1659 (September 15, 1958).
54
Ii
II
~
"'
ii
  ~
~
'I
!
U
(9) Babkov, V. G., Demin, V. P., Keirim-Marcus, 1. B., Kovalev, Yeo
Ye., Larichev, A. V., Sakovich, W. A., Smirennyy, L. N., and
Sychkov, M. A., "Radiation Safety During Space Flights ", NASA,
Tech. Transl. F356 (1964).
(lO) Aukerman, L. W., "Proton and Electron Damage to Solar Cells",
REIC Report No. 23, Battelle Memorial Institute, Columbus, Ohio
(April 1, 1962).
(11) Drennan, J. E., and Hamman, D. J., "Space-Radiation Damage to
Electronic Components and Materials", REIC Report No. 39, Battelle
Memorial Institute, Columbus, Ohio (January 31, 1966).
(12) Sternheimer, R. M., "Range-Energy Relations for Protons in Be, C,
AI, Cu, Pb, and Air", Physical Review, 115 (l), 137 (July 1, 1959).
(13) Goloskie, R., and Strauch, K., "Measurement of Proton Inelastic Cross
Sections Between 77 MeV and 133 MeV", Nuc. Phy., 29, 474-485 (1962).
(14) Bussard, R. W., and DeLauer, R. D., Fundamentals of Nuclear Flight,
McGraw-Hill Book Company, New York (1965).
(IS) Wallace, R., and Sondhaus, C., "Techniques Used in Shielding Calcula-
tions for High-Energy Accelerators: Applications to Space Shielding",
Proc. Svmp. Protection Against Radiation Hazards in Space,
Gatlinburg, Tennessee, USAEC-T ID-7652, Vol 2, 829 (1962).
(16) Metropolis, N., Bivins, R., Storm, M., Turkevich, A., Miller,
J. M., and Friedlander, G., "Monte Carlo Calculations on Intra-
nuclear Cascades, 1. Low-Energy Studies, II. High-Energy Studies
and P-ion Process", Physical Review, 110, 185, 204 (1958).
(17) Campbell, F. J., "States of Solar Cell Cover Material Radiation
Damage'!, Proc. Fifth Photovoltaic Specialists Conference, Vol II
(October 18, 1965).
(l8) Weaver, J. H., "Effects of Vacuum-Ultraviolet Environment on the
Optical Properties of B right Anodized Aluminum", Technical Report
No. AFML-TR-64-355 (January, 1965).
55
(19) Hearst, P. J., "Degradation of Organic Coatings by   With
Light, II. Attenuated Total Reflectance Spectra of Coatings Exposed
to Ultraviolet Light", Technical Note N -694, U. S. Naval Civil Engi-
neering Laboratory, Port Hueneme, California (February, 1965).
(20) Kaplan,!., Nuclear Physics, Addison-Wesley Publishing Company,
Inc., Reading, Massachusetts (1963).
(21) Glasstone, S., and Sesonske, A., Nuclear Reactor Engineering, D. Van
Nostrand Company, Inc., Princeton, New Jersey (1963).
(22) Evans, R. D., The Atomic Nucleus, McGraw-Hill Book Company,
New York (1955).
(23) Kalinowski, J. J., and Thatcher, R. K., Transient-Radiation Effects
on Electronics Handbook, Edition 2, Revision 2, Battelle Memorial
Institute, DASA NWER Subtask TE 017 (September, 1969).
(24) Storm, E., and Israel, H.!., "Photon Cros s Sections From O. 001 to
100 Me V for Elements 1 through 100", Los Alamos Scientific Labora-
tory, LA-3753, UC-34, Physics TID-4500 (1967).
(25) Bussolati, C., Fiorentini, A., and Fabri, G., "Energy for Electron-
Hole Pair Generation in Silicon by Electrons and Alpha Particles",
Physical Review, 136, A1756-A1758 (1964).
(26) Shockley, W., "Problems Related to p-n Junctions· in Silicon", Czech.
J. Phys., B 11,81-121 (1961).
(27) Myers, 1. T., "Ionization", Radiation Dosimetry, Vol I, Attix, F. H.,
and Roesch, W. C., Academic Press, New York (1968).
(28) Bilinski, J. R., Brooks, E. H., Cocca, U., Maier, R. J., and
Siegworth, D. W., "Proton-Neutron Damage Correlation in Semi-
conductors", Final Report Contract No. NAS 1-1595, General
Electric Company, Syracuse, New York (1962).
(29) Aukerman, L. W., "Proton and Electron Damage to Solar Cells",
REIC Report No. 23, Battelle Memorial Institute (April, 1962).
56
(30) Seitz, F., and Koehler, J. S., "Displacement of Atoms During Irradi-
ation", Solid State Physics, Vol 2, F. Seitz and D. Turnbull, Academic
Press, Inc., New York (1956).
(31) Hughes, D. J., and Schwartz, R. B., "Neutron Cross Sections",
Brookhaven National Laboratory Report BNL-325, 2nd Edition, U. S.
Government Printing Office, Washington, D. C. (July 1, 1958).
(32) Maienschein, F. C., et al., "Experimental Techniques for the Meas-
urement of Nuclear Secondaries From the Interaction of Protons of a
Few Hundred MeVII, Proc. Symp. Protection Against Radiation Hazards
in Space, Gatlinburg, Tennessee, Vol 2 (November, 1962)
(33) van Lint, V. A. J., and Wikner, E. G., IICorrelation of Radiation Types
With Radiation Effects", IEEE Transactions on Nuclear Sciences,
NS-I0, No.1, pp 80-87 (January, 1963).
(34) Keister, G. L., "Permanent Radiation Effects to Electronic Parts
and Materials", Boeing Aircraft Company, Report Number D2-6595
(1961).
(35) Billington, D. S., and Crawford, J. H., Jr., Radiation Damage in
Solids, Princeton University Press, Princeton, New Jersey (1961).
(36) Chadderton, L. T., Radiation Damage in Crystals, John Wiley and
Sons, Inc., New York (1965).
(37) Dienes, G. J., and Vineyard, G. H., Radiation Effects in Solids,
Interscience Publishers, Inc., New York (1957).
(38) Katz, L., and Penfold, A. S., "Range-Energy Relations for Electrc..ns
and the Determination of Beta-Ray End-Point Energies by Absorptionll,
Revs. Mod. Phys., 24, 28(1952).
(39) Jag, J. Singh, personal communication.
(40) A1smiller, NSE, 27, 158 (1967).
(41) Lindhard, J., Scharff, M., and Schiott, H. E., Kg!. Danske
Videnskab. Selskab Mat. -Fys. Medd., 33 (14), (1963).
57
(42) Sattler, A. R., Phys. Rev., 138, A1815 (1965).
(43) Loferski, J., and Rappaport, P., Phys. Rev., 98, 1861 (1955).
'.
(44) Berger, M. J., and Seltzer, S. M., "Tables of Energy Losses and
Ranges of Electrons and Positions", N. B. S., Washington, D. C.
(1964), NASA, SP-30 12.
(45) Vette, J. 1., et aI., "Models of the Trapped Radiation Environment",
NASA, SP-3024.
(46) Burrell, Martin 0., "The Calculation of Proton Penetration and Dose
Rates", George C. Marshall Space Flight Center, Huntsville, Alabama,
NASA TM X-53063 (August 17, 1964).
58
Air 6, 16, 50, 53
Alpha Radiation 2,3,9,26,49
Aluminum 6, 13, 22, 37, 43, 44,
46, 49
Anneal 17, 31, 32, 43
Astronomical Unit 49
Atomic Displacements 8, 12, 15,
17, 18, 20, 21, 24, 25, 27, 28,
30-34, 40, 49, 53
Attenuation 10, 12, 41, 49
Auger Electrons 10
Barn 49, 50
Beryllium 8, 44
Boron 8, 9, 37
Bremsstrahlung 7, 8, 12, 30, 38,
45, 50
Cadmium Sulfide 16
Calcium Fluoride 43, 47, 48
Calorimetry 42 -45
Carbon 6, 25, 26, 53
Carbon Dioxide 16
Cascade Particles 5, 6
Cellophane 42
Cerenkov Detector 48
Cinemoid Films 43
Cobalt 42, 48
Color Centers 9
Compton Effect 10, 11, 13, 28,
46, 48, 50
Computer Codes 37, 38
Conductor 15
Contacts 46
Copper 6, 27, 44, 49
Cosmic Radiation 3, 4, 51
Coulomb-Force 4, 5, 7
Cross Section 5, 9, 10, 12, 15,
20-24, 35-38, 49, 50
Deuterium 8
Diodes 45, 46, 48
Dose 50
Dosimetry 32 -49
Index
Electromagnetic Radiation 9-11, 14,
25, 50, 51, 54
Electron Equilibrium 40, 41, 43, 46
Electron Radiation 2, 3, 7, 11, 20, 21,
26-28, 30, 38-42, 46, 50
Emissivity 9
Energy Absorption Coefficients 12, 52
Energy Band Gap 15
Energy Deposition 25-27, 29, 33, 39-
41, 44, 46, 49
Energy Spectrum 32-38, 50, 53, 54
Energy Transfer 10, 11, 14, 19, 20-
22, 25, 27-29, 31, 52
Exposure 50
Faraday Cup 46, 47
Fission 51
Fluence Measurement 33, 36-38, 42,
46
Fluorescence Centers 42
Flux 38
Frenkel Defect 17, 27
Gallium Arsenide 16
Gamma Radiation 9, 11, 12, 26, 30,
38, 40-42, 44, 47-49, 51
Gas 15, 16
Germanium 16, 30, 44, 45
Glass 6, 9, 42, 47, 48
Glow Curve 44
Gold 37, 44
Heating Rate 43, 44
Heavy Charged Particles 18-20, 31,
51
Helium 16
Hydrogen 13, 16, 17, 21, 23
Incident Protons 5
Induced Current 33
Ionization 8, 9, 11, 12, 14, 15, 17,
25, 28, 29, 33, 34, 38, 39, 41, 51
Iron 6, 44.
Lead 13, 22
Lithium 8, 9
59
------_ ........ •...... _.. . __ ._---------
Lithium Chlorate 43
Lithium Floride 43, 47, 48
Luminescence 43
Magnesium 37
Manganese 43, 47, 48
Mass Absorption Coefficients 13,
38, 39, 52
Monte Carlo Method 6
NEI02 46
NE211 Xylene 46, 48
NE226 Hexafluorobenzene 46, 48
Neptunium 37
Neutrons 5,8, 19,21-28,30,
31, 33-35, 47, 48, 51-53
Nickel 36, 37
Optical-Density Device 42, 43
Optical Transmission 42, 43, 48
Oxygen 16
Pair Production 10, 13, 16, 52
Photodiode 46, 48
Photoelectric Effect 10, 13, 52
Photoneutrons 8
Phototubes 44
Pilot B 46, 48
PIN Detectors 45, 46, 48
Planck's Constant 9, 52
Platinum 44
Plutonium 37
Polyethylene 6
Positron 11, 52
Proton Radiation 2 -6, 19, 26, 27,
38, 40, 41, 53
Pulsed Radiation 45
Rad 53
Radiation Correlation 34
Radio-Photo Luminescent Device 42,
48
RDMM 37, 38
Resonance Peaks 22
Roentgen 53
SAND II 37, 38
Saturation 46
Scattering 5,8-10, 18,21-25,30,40,
41, 50, 51
Scintillators 46, 48
Secondary Electrons 12, 15, 30, 40,
41
Semiconductor 15-17, 28-30, 33, 38,
43-46, 48
SEMIRAD 46, 48
Silicon 16, 17, 28-30, 33, 38, 39,
43-46, 48
Silicon Dioxide 6
Silver 6, 44
Silver Metaphosphate 42, 48
Simulated Space Environment 24, 25
Simulation 34, 49
Solar Flares 2, 3, 53
Solar Wind 3, 53
SPECTRA 37
Spectrometers 34, 35
Stainless Steels 48
Styrofoam 45
Sulfur 36, 37
Sulface-Barrier Detectors 29
Tantalum 46
Teflon 43
Temperature Dependence 17
Thermal Control Coatings 9
Thermal Insulation 45
Thermistor 44, 45
Thermocouple 44
Thermoluminescent Devices 43, 44,
48
Threshold Energy 17, 21, 24, 27,
28, 3 0, 35 - 37, 53
Thre shold Foil 34 -41
Tissue 6
Titanium 48
Transistors 49
Tungsten 6
Ultraviolet 9, 48, 53
Unit Charge 18, 53
Uranium 37
60
I
J
Van Allen Radiation Belts 1, 2, 4,
7, 53
Water 6, 16
X-Ray Radiation 7, 9, 10, 15, 38,
40-42, 50, 51, 54
NASA-LangleY,1971 - 29 CR-l87l
61
NASA
i
N A S A C O N T R A C T O R
R E P O R T
RADIATION EFFECTS
DESIGN HANDBOOK
Section 6. Solid-state Photodevices
by J. E. Drennm
Prepared by
RADIATION EFFECTS INFORMATION CENTER
BATTELLE MEMORIAL INSTITUTE
Columbus, Ohi o 43201
f or
NA TI ONA L A ERONA UTI CS A ND SPA CE A DMI NI STRA TI ON WA SHI NGTON, D. C. A UGUST 1971
TECH LIBRARY KAFB, NM
1. Report No.
-
2. Government Accession No. 3. Recipient's Catalog No.
NASA CR-1872
4. Title and Subtitle 5. Repor t Date
RADIATION EFFECTS DESIGN HANDBOOK
SECTION 6 . SOLID-STATE PHOTODEVICES
I August 1971
6. Performing Organization Code
"" . ~~ - ~ ~ ~ I ~~ ~
7. Author(s) 8. Performing Organization Report No.
J. E. Drennan
10. Work Unit No.
9. Performing Organization Name and Address
Radi ati on Ef f ects I nf ornl ati on Center
Columbus L aboratori es
Battel l e Kernorial I nsti tute
Columbus, Ohio 43nl
2. Sponsoring Agency Name and Address
Nati onal Aeronauti cs and Space Admi ni strati on
Washington, D. C. x)546
11. Contract or Grant No.
NASW-1568
13. Type of Report and Period Covered
Handbook - Several Y ears
14. Sponsoring Agency Code
5. Supplementary Notes
~ ~
6. Abstract
Thi s document summari zes i nf ormati on concerni ng t he ef f ects of radi ati on on
l l y sol ar cel l s. The f orms of radi ati on i ncl ude
el ectromagneti c.
Several curves are presented.
sol i d- state photodevi ces, especi a
neutrons, protons, el ectrons, and
. .
7. Key Words (Suggested by Author(s))
.~
Radi ati on Ef f ects on Sol ar Cel l s, Neutrons,
Protons, El ectrons, Gamma-Rays
18. Distribution Statement
Uncl assi f i ed - Unl i mi ted
9. Security Classif. (of this report) 22. Rice' 21. No. of Pages 20. Security Classif. (of this page)
Uncl assi f i ed $3 .oo 34
Uncl assi f i ed
~
For sale by the National Technical Information Service, Springfield, Virginia 22151
I
ACKNOWLEDGMENTS
The Radiation Effects I nformation Center owes thanks to several in-
dividuals for their comments and suggestions during the preparation of this
document. The effort was monitored and funded by the Space Vehicles
Division and the Power and Electric Propulsion Division of the Office of
Advanced Research and Technology, NASA Headquarters, Washington,
D. C., and the AEC-NASA Space Nuclear Propulsion Office, Germantown,
Maryland. Also, we are i ndebted to the following for their technical re-
view and valuable comments on this section:
Dr. B. Anspaugh, J et Propulsion Laboratory
Mr. S. Manson, NASA Headquarters
Mr. D. J . Miller, Space Nuclear Systems Office
Mr. A. Reetz, J r., NASA Headquarters
Dr. J . J . Singh, NASA-Langley Research Center
iii
PREFACE
This document is the sixth section of a Radiation Effects Design
Handbook designed to aid engineers in the design of equipment for operation
in the radiation environments to be found in space, be they natural or arti -
ficial. This Handbook will provide the general background and information
necessary to enable the designers to choose suitable types of materi al s or
cl asses of devices.
Other sections of the Handbook will discuss such subjects as transi s-
tors, thermal-control coatings, structural metals, and interactions of
radiation, electrical insulating materials, and capacitors.
V
TABLE OF CONTENTS
Page
INTRODUCTION . . . . . . . . . . . . .
RADIATION EFFECTS ON PHOTOVOLTAIC DEVICES
Solar Cells . . . . . . . . . . . . .
Silicon Solar Cells . . . . . . . . . .
Thin-Film Cadmium Sulfide Solar Cells .
Gallium Arsenide Solar Cells . . . . .
Solar-Cell Cover Glasses and Adhesives .
BIBLIOGRAPHY . . . . . . ; . . . . . .
. . . . .
. . . . .
. . . . .
. . . . .
. . . . .
. . . . .
. . . . .
. . . . .
1
2
2
2
18
20
20
2 3
vi i
" . . .
SECTION 6. SOLID-STATE PHOTODEVICES
INTRODUCTION
A photodevice, as the name implies, is intended to provide an elec-
trical response to incident photons of radiation. This section will consider
t wo basic types of photocells in use: photovoltaic and photoconductive
"bulk effect".
The photovoltaic cell generates a voltage across a P / N or N / P junc-
tion as a function of the photons impinging on it. Silicon, gallium arsenide,
cadmium sulfide, and selenium are normally used to make cells of this
cl ass. Thi s cl ass of cel l s i s the only self-generating type requiring no
external power supply. Solar cells are photovoltaic cells employed to gen-
erate el ectri c power from incident solar photon radiation.
Photoconductive cells employing the bulk effect are normally made of
cadmium sulfide (CdS) or cadmium selenide (CdSe) and have no juncti.on.
The enti re l ayer of material changes in resistance under illumination. This
response is analogous to a thermi stor except that heat i s repl aced by l i ght.
The photoconductive cell decreases in resistance as tha light level increases.
The absolute value of resi stance of a parti cul ar cel l at a specific light level
depends on the photosensitive material employed, cell size, electrode geom-
etry, and the spectral composition of the incident light.
Although some overlap is possible, generally the prime usage of
photovoltaic cells i s i n sol ar cel l s i ntended to convert sol ar energy to use-
ful electric power. The photoconductive cells primarily are used in
applications that are now combined in the field of optoelectronics. The
field of optoelectronics generally involves a combination of solid-state
technology and light measurement. Hence, the field of optoelectronics
would include the detection and/or measurement of radiation energy f rom
infrared through visible and ultraviolet and the use of these radiation wave-
lengths for control or other electronic purposes. Both classes of cel l s may
be used for detecti on and/or measurement of nuclear radiation.
1
RADIATION EFFECTS ON PHOTOVOLTAIC DEVICES
Sol ar Cel l s
The solar cell is one of the most critical components in some sat-
el l i te systems where i t consti tutes the pri mary source of electric power to
operate the electronic systems. I n this application, the solar cells are
normally located outside the space-vehicle skin where they are exposed to
the direct space-radiation environment modified only by relatively thin,
opti cal l y transparent covers. The opti cal properti es of cover materi al s
employed to protect the basic solar cell from the space environment are
degraded by exposure to radiation, and the cell itself is degraded by radia-
tion penetrating the protective cover.
The basic kinds of sol ar cel l s avai l abl e f or engineering use include
various kinds of silicon P / N and N / P cells, gallium-arsenide cells, and
cadmium-sulfide cells. The state-of-the-art in efficiencies of gallium-
arsenide and cadmium-sulfide cells (8 to 9 percent and 2 to 3 percent,
respectively) restrict the choice for practical systems to the more efficient
silicon cells at present, even though both of the compound semiconductor
cell types appear to be more resistant to radiation damage than are the
silicon cells.
Silicon Solar Cells
The information available about radiation effects on si l i con sol ar cel l s
indicates in general the following:
(1) In the range from 15 to 65 percent electron-induced degra-
dati on (i ncrease) i n short-ci rcui t current, I sc (and, for
practi cal purposes, that f or maximum available power, .
P(max)) degradati oni n si l i con sol ar cel l s i s i ndependent
of the energy of the bombarding electron, depending only
on the optical absorption characteristics of light in
silicon and, thus, on the illumination source. The
respecti ve rates for radiation-induced Isc and P(max)
degradation in silicon cells of all types under sol ar
illumination are approximately 15 and 20 percent per
decade of radiation fluence above the threshold fluence.
2
. . "
(2) A similar statement can be made for gallium-arsenide
cells, except that the degradation rate also appears to
be independent of illumination source. The typical
degradati on rate for ISC i n gal l i um-arseni de cel l s is
45 to 50 percent per decade of radiation fluence.
( 3) The fluence threshold for silicon solar-cell damage
and the critical fluence, QC*, depend upon cell type
(N/P, P/ N), base resistivity, and the type and
energy of the bombarding particle.
( 4 ) The energy dependence of proton-radiation damage in
si l i con sol ar cel l s is found to be approximately in-
versel y proporti onal to proton energy over the range
of proton energies f rom 6.7 MeV to about 100 MeV.
At energies above 100 MeV, the damage dependence
upon further i ncreases i n proton energy appears to
become gradually less, theoretically approaching a
plateau independent of proton energy.
(5) For si l i con cel l s, the short-ci rcui t current i s l i ttl e
affected by low-energy protons (E < 1 MeV), but
the open-circuit voltage decreases more rapidly
under low-energy-proton bombardment than for
higher energy irradiations.
(6) The sensitivity to radiation-induced degradation of
silicon solar cells is significantly greater f or P/ N
than for N / P cells.
(7) Silicon solar cells containing an additional lithium
dopant generally can perform satisfactorily at
higher radiation fluences than comparable cells
that do not contain the lithium dopant.
I n the normal space application for solar cells, the cells are either
exposed directly to the space radiation or else a thin, transparent protec-
tive cover is employed. Such a cover is usually of such a thickness to
protect against proton energies up to 20 MeV. In either case, electron and
*@ is defined as the value of radiation fluence producing 20 percent degradation in maximum available power
P(max); that is, at',@, the ratio P(max)/P(max)o =0.8 or in other words critical fluence aC, can be defined as
the value of fluence for which P(max) is 80 percent of its preirradiation value. GC is about one decade
greater than the threshold fluence where the first significant bulk radiation effects should be observed and has
the advantage of being experimentally measurable whereas the threshold fluence is normally masked by
surface effects.
3
proton bombardment are the maj or factors causi ng sol ar-cel l degradati on
and most of the available radiation-effects data pertain to these radiation
particles. However, i f the environment contains an appreciable neutron
component, than the neutron fluence also will contribute to the solar-cell
degradation.
To assist the electronic-design engineer during early design phases,
the information in the REI C files has been employed as the basis for prepara-
tion of the performance envelopes in Figures 1 through i 6. * I n these
figures the ratio of maximum available power to the initial value of max-
imum available power, P (max)/P (max)o, i s pl otted as a function of radi a-
tion fluence. *+ The envelopes presented encompass the data available in
the REIC fi l es. Representati ve data poi nts are pl otted wi thi n these
envelopes .
The intended use of these envelopes is as follows: i f the electronic
designer finds the radiation fluence of his expected application environment
to be outside the appropriate envelope in the low-fluence direction, he
should not expect significant radiation-induced degradation of sol ar cel l s;
however, f or an application environment falling within the envelope, radia-
tion-induced degradation of solar-cell performance ranging from mild to
severe should be anticipated; jfinally, i f the application environment falls
outside the envelope in the high-fluence direction, very severe radiation-
induced solar-cell degradation can be expected.
Fi gures 17 and 18 show the dependence of critical fluence, Oc, upon
electron energy for five resistivities of N / P and P / N si l i con sol ar cel l s,
respectively. The semiempirical model is as follows:
where
P(max)o =preirradiation value of maximum power
E =electron energy
p = solar-cell resistivity
=electron fluence
* Extrapolation of these envelopes outside the range plotted should not be attempted.
The range of proton energies for which data are plotted i s from 0.5 to 20 MeV. Theenvelopes were
generated assuming the degradation rate to be independent of energy over this range. Some of the
data spread undoubtedly results because this assumption is not strictly true. However, the available
data are not sufficient to provide more accurate envelopes.
4
N/P silicon solar cells
Resistivity= I . ohm-centimeters
I I1111I
c
5 0.400
ti-
E
m
\ \
\ \
I I l l I I 1 I I I I I I I I I I l l I I I I I I I I LJ
I Ol2 I 013 loi4 I 015 I Ol6 I 017 I ole 1019
Fluence ,e /cm2
VERSUS EL ECTRON FL UENCE
9
E
a-
x
0
"
a-
E
0
x
N/P silicon solar cells
Resistivity=3. ohm-centimeters
o . m r n 1 I I I I I I
10" I 014 I 015 I Ol6 ld7 l0l8 I 019 1020
Fluence, e /cm2
8 s e t s of data.
5
1 . o o o I C N/P silicon solar cel l s
FI GURE 3 . P(MAx)/P(MAx)~ VERSUS EL ECTRON FL UENCE
4 s e t s of data.
1.000 I ud N/P silicon solar cells
Fluence, e/cm2
FI GURE 4. P(MAx)/P(MAx)~ VERSUS EL ECTRON FL UENCE
32 s e t s of data.
6
l.m
1" N/P silicon solar cells
0
0.800
a
0
0.600
0
0.400
0
0.200
a
l.m
a
N/P silicon solar cells
0 Resistivity =20. ohm-centimeten
0.800
a
0
0.600
0
0.400
0
0.200
a
o.m"-""l 111 1 1 1 1 1 I I 1 1 1 1 I 1 1 1 I I 1 I I I I 1 I I I I I I1
loi3 I 014 I 0Is I Ol6 loi7 toi8 td9 102O
Fluence, e/cm2
o.ml"l."l 111 1 1 1 1 1 I I 1 1 1 1 I 1 1 1 I I 1 I I I I 1 I I I I I I1
loi3 I 014 I 0Is I Ol6 loi7 toi8 td9 1O2O
Fluence, e/cm2
FI GURE 5. P(MAx)/P(MAx)~ VERSUS EL ECTRON FL UENCE
1 set of data.
I.oooI" N/P silicon solar cells
a
0.800
c.
0
g 0.600
a-
E
"
e
a
0.400 Q
ci-
a
0.200 a
d)
FI GURE 6. P(MAx)/P(MAx), VERSUS EL ECTRON FL UENCE
21 sets of data.
7
l.Oo01" P/N silicon solar cells
. Resistivity =3. ohm-centimeters
FI GURE 7. P(MAx)/P(MAx)~ VERSUS EL ECTRON FL UENCE
0 sets of data.
1.000 I m P/N silicon solar cells
0.800
B 0.600
E
0.200
8
I .ooo
0.800
0
g 0.600
E
a-
"
E 0.400
x
a-
0.200
0.000
m
P/N silicon solar cells
m Resistivity =IO. ohm-centimeters
m
m'
n
n
n
n
m
n
,
,
I I l l 1 I I I l l I 1 1 1 1 . I I l l 1 I I l l 1 I I l l 1
1015
Fluence, e/cm2
FI GURE 9. P(MAX)/P(MAX)~ VERSUS EL ECTRON FL UENCE
3 sets of data.
I.000 1" P/ Nsilicon solar cells
m
0.800 m
0
B 0.600 m
a-
E
"
m
h
m
E 0.400 m
x
a-
m
0.200 m
m
I
0 sets of data.
9
r NIP silicon solar cells
m
0.800
0
m
-
6 0.600
a-
E
\
m
-
5 0.400 01
E
a-
m
0.200
01
0.000 1 I I
10' ~
Fluence, p/cm2
13 sets of data.
1.000
NIP silicon solar cells
Resistivity=3. ohm-centimeters
0.800
0)
m
-
0
0.600
m
a-
E
"
n"
m
0.400
m
0.200
1.
o,oooI I I I I 1 . I I I l l I I I l l I. I I l l I 1 I l l I I I l l
Id0 lo" ION2 10'~ d 4 td5 Id6
Fluence, p/cm2
c
FI GURE 12. P ( M A x) / P ( ~x) ~ VERSUS PROTON FL UENCE
(0.5 MEV <E <20 MEV)
0 sets of data.
10
I
-0
E
0
e-
c
X
0
E
n-
1.000
N/P silicon solar cells
0 Resistivity =5. ohm-centimeters
0.800
-
m
0.600
m
0.400
m
0.200
m
~ . ~ O O - -
I 1 1 , I 1 1 1 1 1 I I l l I I I 1 1 1 1 I 1 1 1 1
I O'O IO' I IOb2 loi3 1 0 " loi5 Id6
Fluence, p/cm2
1.000
N/P silicon solar cells
0
0.800
-
m
0.600
m
0.400
m
0.200
m
~ . ~ O O - -
I 1 1 , I 1 1 1 1 1 I I l l I I I 1 1 1 1 I 1 1 1 1
I O'O IO' I IOb2 loi3 1 0 " loi5 Id6
Fluence, p/cm2
FI GURE 13. P(MAx)/P(MAx)~ VERSUS PROTON FL UENCE
(0.5 MEV <E <20 MEV)
0 sets of data.
-
0
X
F
e-
-
B
a-
E
1.000 m
N/P silicon solar cells
Resistivity=IO. ohm-centimeters
m
0.800
m
m
0.600
01
m
0.400
*
(D
0.200
m
0.000
I 1 1 1 J"I I I I I l l 1 I l l . I I I 1
IO" IOi2 ld3 I 014 loi5 IOb6
Fluence, p/cm2
FI GURE 14. P( ~X ) / P( " &X ) ~ VERSUS PROTON FL UENCE
(0.5 MEV <E <20 MEV)
13 s et s of data.
1 1
0.200
N/P silicon solar cells
Resistivity=20. ohm-centimters.
Fluence, p/cm2
FI GURE 15.
1.000
m
0.800 Q)
m
-
0
6 0.600 m
E
n-
"
n-
m
2 0.400
0
P(MAx)/P(MAx)~ VERSUS PROTON FL UENCE
(0.5 MEV <E <20 MEV)
0 sets of data.
P/N silicon solar cells
FI GURE 16. P(MAx)/P(MAx)~ VERSUS PROTON FLUENCE
(0.5 MEV <E <20 MEV)
16 sets of data.
12
was used to generate these curves. The data available in the REI C were
fitted to this model by the method of least squares to determine the coeffi-
cients given in Table 1.
Fi gures 19 and 20 show the dependence of QC upon proton energy for
five resistivities of N / P silicon solar cells and 1 ohm-centimeter-
resi sti vi ty P / N silicon solar cells, respectively. The available data for
energies above 5 MeV were fitted to the model described earlier except that
the value for the coefficient, A, was predetermined to be zero. I n the case
of the P / N cells, the available data were not sufficient to permit deter-
mining a value for D other than zero. The coefficient values determined
from the data are l i sted in Table 1.
TABLE 1. MODEL COEFFI CI ENTS
Electron I rradiation
N/ P Silicon 0. 09839 - 1. 520 9.325 0. 09496
P / N Silicon 0. 09 545 - 1.407 8.425 0. 1208
Proton I rradi ati on
N/ P Silicon 0. 0 0 . 1232 2. 102 0. 1926
P/ N Silicon 0. 0 0. 1485 1. 822 0. 0
~- ~ ~.
~-
_ _ _ ~
-
The very l i mi ted amount of data available for neutron-irradiated solar
cells confirm that their behavior under this form of radiation is si mi l ar to
that produced by electrons and protons although the damage produced is not
i denti cal . For N / P silicon solar cells of nominally 5 to 10 ohm-centimeter
base resi sti vi ty, an average value (subject to considerable variance of
critical fluence, QC 7 x 10l 1 n/cm2 (E > 10 keV), has been observed. The
effect of changes in neutron energy spectrum has not been documented.
Fi gure 21 shows the maximum available power ratio, P(max)/P(max)o,
versus i ncremental fl uence, A@. The incremental fluence is defined as
the amount of fluence exceeding the critical fluence value. Thus, Figure 21
13
R=3 ohm-cm
R= 5 ahm-cm
Fluence, e/cm2
FIGURE 17. CRITICAL FLUENCE VERSUS ELECTRON ENERGY,
R=1-20 OHM-CM, N / P
67 sets of data.
10ZF
r R= I ohm-cm
\ f R =3 ohm-cm
R =5 ohm-cm
R=10ohm-cm
R= 20 ohm-cm
P
Q,
L
lo-ll I 1 I I I I I I l l I I I I
Id2 d 3 1d4 d 5
Fluence, e/cm2
FIGURE 18. CRITICAL FLUENCE VERSUS ELECTRON ENERGY,
R=1-20 OHM-CM, P / N
30 sets of data.
14
IO2
-
-
2
F
ZG l o "
5
-
Q)
w
c
-
-
-
-
IO0
I I I l l I I I I I I I I I
Id0 Id ' 1Ol2 1 0 "
Fluence, p/cm2
FI GURE 19. CRI TI CAL FLUENCE VERSUS PROTON ENERGY ,
R=1-20 OHM-CM, N / P
26 sets of data.
Fluence, p/cm2
FI GURE 20. CRI TI CAL FLUENCE VERSUS PROTON ENERGY ,
R=l OHM-CM, P / N
16 sets of data.
15
may be used in conjunction with the neutron critical fluence or with
Figure 17, 18, 19, or 20 to predict the typical P(max)/P(m&,value for
a specified solar-cell type, radiation-particle type and energy, and a
specified fluence by the following procedure:
I J se the critical fluence value for neutron irradiation
or determi ne the appropri ate cri ti cal fl uence val ue
from Figures 17, 18, 19, or 20.
Determine A@by subtracting QC from the specified
application fluence. If A@is negative, P(max)/P(max)o
>0.8.
For positive values of A@, enter Fi gure 21 with the
value of A@determined in Step (2) and read the cor-
responding value of typical P /P
(max) (max) *
0
c
0
x
E
ci-
"
E
n-
x
0
0.55 -
0.50
0.45
-
0.40 -
0.35
-
0.30 -
0.25
-
-
0.20
0. I5
I I I I I I I I I 1
-
I 10 lXIOL 1X1O3
Incremental Fluence, A@
FIGURE 21. DEGRADATION OF P(MAx)/P(MAx) AS A
FUNCTION OF FLUENCE ABOVE
THE CRITICAL FLUENCE OC
0
The user is cautioned not to attempt extrapolation of these curves outsi de
the plotted range.
16
The model also can be used to predict a value for'P(max)/P(max)
for given conditions. However, the model is not valid for electron
energi es outsi de the range from 4 keV to 40 MeV or for proton energies out-
side the range from 5 to 100 MeV. The data available for proton energies
less than 5 MeV show a high dependence upon cell structure, the type and
thickness of cover materials and adhesives, and other manufacturing
vari abl es. The vari abi l i ty of these data i s too great to permit the develop-
ment of simple predictive relationships for radiation effects.
In addition to the N/ P or P / N silicon solar cells with fixed base resis-
ti vi ti es, dri ft-fi el d or graded-base sol ar cel l s have been produced that ex-
hibit improved radiation tolerance. The radiation-induced degradation
pattern for these cel l s is about the same as for conventional N/ P sol ar cel l s
(P(max)/P(max)o degrades about 20 percent per decade i ncrease i n fl uence
above the threshold fluence). However, the threshold fluence and critical
fl uence are a factor of three or more greater than those for conventi onal
N./P cel l s. Thi s is i l l ustrated by the comparison of radiation-induced
change of P( max) /P( max) for N/ P graded-base cells and conventional cells
of various resitivities shown in Figure 22.
Another approach to increasing the radiation tolerance of silicon solar
cells is the addition of lithium as a dopant in the semiconductor. The lithium
diffuses to damage centers produced when high-energy particles bombard the
silicon. The action of the lithium diffusion is to effect a recovery of the
radiation-degraded electrical properties of the semiconductor. The end re-
sul t i s si mi l ar to the resul t of annealing radiation damage but occurs with
reasonable rates at much lower temperatures than the usual annealing
temperatures. Thus, though high f l ux radiation will degrade the lithium-
doped sol ar cel l s, the properti es wi l l recover i n hours or days to nearl y
their original condition even at room temperature.
Much effort has been expended since about 1967 to establish the
optimum design for lithium-doped silicon solar cells. A number of trade-
offs are required to obtain acceptable electrical properties and avoid re-
degradation. The information available in the REIC indicates that the
lithium-doped devices are still mainly experimental. No information is
available about the performance of "production" devices. However, this
technology seems to hold considerable promise for the immediate future.
17
I
Thin-Film Cadmium Sulfide ~~~ "_ Solar ~ -~Cells ~~
The initial efficiency of CdS sol ar cel l s (2 to 3 .percent) averages
20 percent or l ess of the typical silicon solar- cell efficiency. However,
available data show that QC for these cells exc&eds 1017 e/crn2 for electron
energi es rangi ng from 60 keV to 2. 5 MeV and exceeds 3 x 1014 p/cm2 for
proton energies ranging from 2 to 10 MeV. Thus, the actual power output
of the CdS sol ar cel l s at a proton fluence of 4 x 10l 2 p/cm2 (E = 1.8 -
3 . 0 MeV) may be almost the same as that of 1-ohm-centimeter-resistivity
N / P silicon solar cells after this exposure. The CdS cells will not have
degraded significantly, while the Si cells will be severely degraded. A
si mi l ar compari son is possible for 1-ohm-centimeter-resistivity P / N Si
cells and CdS cel l s at a 1- MeV electron fluence of 5 x 10 l 5 e/cmz. It i s
seen that, even though the CdS cell output for radiation fluences less than
these values is relatively constant, this output will be less than that for a
silicon cell of comparabl e area. The CdS cel l s would have an output ad-
vantage only at fluences higher than these.
x
0
E
nu
FIGURE 22. N / P SILICON SOLAR-CELL MAXIMUM AVAILABLE
POWER RATIO VERSUS 1.0-MEV ELECTRON
FLUENCE FOR VARIOUS CELL RESISTIVITIES
18
-
0
0.8
0.7
0.6
0.5
0.4
0.3
I I I I I I l l I I l l
I x loi4 I X 10'~ I x IOi6 I x 1 0 "
Electron Fl uence, @ , e/cm2
FIGURE 23. P(MAx)/P(MAx)~ VERSUS ELECTRON FLUENCE FOR
GaAs SOLAR CELLS
-
0
x
E
a-
\
0.9
0.8
0.7
0.6
0.5
0.4
I x IOi0 I x IO" I x IOi2 I X lob3 I X loi4
Proton Fluence, @, p/cm2
FIGURE 24. P(MAx)/P(MAx)~ VERSUS PROTON FLUENCE FOR
GaAs SOLAR CELLS
19
Gallium Arsenide Solar Cells
Fi gure 23 shows P(max) /P(max)o. for gal l i um arseni de sol ar cel l s as
a function of electron fluence for energles ranging from 1 to 50 MeV.
Fi gure 24 shows P(max)/P(max)o as a function of proton fluence for ener-
gies ranging from 0. 1 to 95. 5 MeV. The available GaAs solar-cell data are
not sufficient to permit a more compl ete anal ysi s.
Solar-Cell Cover Glasses and Adhesives
The preceding discussion has treated the sol ar cel l as a device with-
out considering whether or not the semiconductor element is protected
by a transparent shi el d. Experi mental data have shown that the degradati on
of the semiconductor element of the sol ar cel l s resul ti ng from space radi a-
tion can be substantially reduced i f the solar cells are protected with a
transparent shield. However, the use of such a shi el d may present other
probl ems, such as the effects of radiation on the light transmissivity of
the shield material and adhesive. Also, the protected-solar-cell efficiency
may initially be less than that for an unprotected cell because some light
energy may be lost in the shield material and adhesive. A variety Gf
gl asses, fused quartz and si l i cas, sapphi re, and plastic materials, as well
as various adhesives have been studied for a range of electron and proton
energi es and exposure. The reader i s referred to the "Handbook of Space-
Radiation Effects on Solar-Cell Power Systems":: for a more detai l ed di s-
cussion of these subjects.
Some generalized information on space radiation effects on transparent
materials and adhesives is presented in Tables 2, 3 , and 4.
:: See, in Bibliography, Cook, W. C., "Handbook of Space-Radiation Effects on Solar-Cell Power
Systems", 1963.
20
TABLE 2. EFFECTS OF ELECTRONS AND PROTONS ON OPTI CAL
CHARACTERISTICS OF SOLAR-CELL
COVER MATERIALS
Materi al Descri pti on
Percent Change in
Transmi ttance
Wavelength, p
0. 5 0.6 0.7
(A) 1-MeV Electrons (Total Dose: e cm-2)
(1) Microsheet (6-mil) Corning 0211
5. 6 3. 3 2. 2
(2) Same as (1) t A-R coating t "blue" filter 7.3 5. 1 4. 2
( 3 ) Same as (1) +A-R coating t "blue-red" filter 9.9 8. 6 6.9
(4) 3 mil mi crosheet +A-R coating +"blue" filter 3. 7 2. 1
(5) Fused si l i ca (66 mil) Corning 7940 1. 7 2. 2 1. 1
(6) Fused si l i ca-Corni ng 7940 (20 mil) +A-R 1. 1 2. 2 1.1
coating t "blue" filter
(7) Adhesive ES- 10 (Spectrolab)
(8) Adhesive 15-E (Furane)
(9) Adhesive DER-332 (LC) (Dow)
1. 7 1. 7 1. 1
8. 6 9. 1 4. 5
24 13 12
(B) 4.6-MeV Protons (Total Dose: 4 x 10l 1 p
(1) Mi crosheet (6 mil) Corning 0211 3. 4 1. 1 1. 1
(2) Same as ( 1) t A-R coating t "blue" filter 5. 2 2. 1 1. 1
( 3 ) Fused silica (30 mil) Corning 7940 no change
(4) Fused silica (20 mil) t A-R coating t "blue no change
filter"
21
TABLE 3. EFFECTS OF 1.2-MeV ELECTRON RADIATION ON TRANSPARENT MATERIALS
~~ "
~- ~" .- .- - ~ -~ - ~ - ~ -~ _ _ _ ~ ~ .~.~
Decrease in Light
Type Number or Sample Total Fluence, Transmission,
Manufacturers Trade Name Thickness, in, e cm-2 percent
Fused Silica
Corning Glass Works
Corning Glass Works
Engelhard Industries, Inc.
Amersil Quartz Div.
Amersil Quartz Div.
Amersil Quartz Div.
Amersil Quartz Div.
Amersil Quartz Div.
Thermal American
Fused Quartz Co.
General Electric Co.
Willoughby Quartz Plant
Willoughby Quartz Plant
Willoughby Quartz Plant
Dynasil Corporation
No. 7940 (UV grade)
No. 7340 (Optical
grad e)
Suprasil I1
Optic a1
Homosil
Ultrasil
Infrasil I1
Spectrasil A
GE 104
GE 105
GE 106
Dynasil Optical Glass
1/16, 1/8
1/8
1/16, 3/32
1/16
1/16
1/16
1/16
1/8
3/32
3/32
3/32
1/8
2.7 X 1015
2.7 x
2.7 X 1015
2.7 X 1015
2. 7 X 1015
2.7 X 1015
2.. 7 x 1015
0.0
0.0
1.8
2.1
6.4
23. 0
0.0
0.8
30.0
26.6
0.0
Other Materials
Linde Company
Sapphire
0.020 2.1 X 1 0 ~5 0.0
Pittsburgh Plate Glass Solex
1/4
2.7 x 2.7
Corning Glass Works
Vycor
1/4
1.7 X 1015 58.9
Company
-- Soda lime plate glass 1/4 1.7 x 1015 26.0
-
-
TABLE 4. EFFECTS OF ULTRAVIOLET RADIATION ON SPECTRAL
TRANSMITTANCE OF TRANSPARENT ADHESI VES(~~ b)
Percent Change in Transmittance
at Indicated Wavelength
~-
Material Designation 0. 5 , ! J 0.61-1 0;71-1
0.8l.l
ES -10 (Spectrolab)
23 13 8.6 6.4
15-E (Epocast)
43 31 27 25
(a) Specimens are 1 to 2-mil-thick films cast between sheets of fused
silica, 30-mil base, and 6-mil cover sheet with no cutoff filter
to limit the UV reaching the specimen.
(b) Exposure equivalent to 630 hr of space UV.
22
BIBLIOGRAPHY
Brown, D. M. , "Low Energy Proton Damage Effects in Silicon and Galliurn
Arsenide Solar Cells", NASA, Goddard Space Flight Center, Greenbelt,
Maryland, NASA-TM-X-54990, 20 pp, Avail: NASA, N65-16347.
Brucker, G. J . , "Action of Lithium in Radiation-Hardened Silicon Solar
Cells", Astro Electronics, Princeton, New J ersey, AED-R-3389, NASA-
CR-98717, November 15, 1968, Qtly Rpt. No. 2, J uly 16 - October 15,
1968, NAS5-10239, 81 pp, Avail: NASA, N69-14919 and NTIS.
Brucker, G. J . , Faith, T. J . , and Holmes-Siedle, A. G. , "Action of
Lithium in Radiation-Hardened Silicon Solar Cells", RCA, Princeton,
New J ersey, AED-R-3440, NASA-CR-103871, April 21, 1969, Final
Rpt., Apri l 23, 1968 - April 21, 1969, NAS7-100, 119 pp. Avail: NASA,
N69-33590 and NTIS.
Carter, J . R. , and Downing, R. G. , "Effects of Low Energy Protons and
High Energy Electrons on Silicon", TRW Space Technology Laboratories,
Redondo Beach, California, NASA-CR-404, March, 1966, NAS5-3805,
50 pp. Avail: NASA, N66 - 18429.
Cooley, W C. , and J anda, R. J . , '!Handbook of Space-Radiation Effects on
Solar-Cell Power Systems", Exotech, I nc. , Alexandria, Virginia, NASA-
SP-3003, 1963, 107 pp.
Denny, J . M. , Downing, R. G. , Kirkpatrick, M. E. , Simon, G. W . , and
Van Atta, W. K . , "Charged Particle Radiation Damage in Semiconductors,
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nology Labs., I nc. , Redondo Beach, California, MR-27, STL-8653-6017-
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23
Technology Laboratories, I nc., Redondo Beach, California, STL-8653-
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24
"
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25
I
Index
Adhesive 17, 20-22
A-R Coating 21
Blue Filter 2 1
Blue -Red Filter 2 1
Cadmium Selenide Sol ar Cel l 1, 2
Cadmium Sulfide Solar Cell 1 , 2,
Corning 0211 21
Corning 7940 2 1, 22
Cover Materi al 17, 20-22
Cri ti cal Fluence 13 - 19
Damage Center 17
Degradation Pattern 17
Degradation Rate 2-12, 18-22
DER-332 (LC) (Dow) 2 1
Dynasil Optical Glass 22
Efficiency Level 20, 2 1
El ectron Energy Level 2, 4, 14,
Electron Fluence 4-9, 18-20, 22
Electron Total Dose Effect 21, 22
ES-10 (Spectrolab) 21, 22
Furane 15E 2 1,22
Fused Quartz 20, 22
Fused Silica 7940 21, 22
Gallium Arsenide Solar Cell 1-3,
GE 104 22
GE 105 22
GE 106 22
Glass 20-22
Homosil 22
Infrasil 1122
Initial Efficiency 18
Light Effect 1
Light Transmittance 20-22
Lithium Diffusion 17
Lithium Dopant 3, 17
Maximum Available Power 2 - 13 ,
18
17, 18, 20-22
19, 20
16-20
Mi crosheet 02 11 21
Neutron Critical Fluence 16
Neutron Fluelrce 4
Neutron I rradiation 13, 16
N/P Silicon Solar Cell 1-7, 10-15,
Nuclear Radiation Detection 1
Nuclear Radiation Measurement 1
Open Circuit Voltage 3
Optical 22
Optical Absorption 2
Optoelectronics 1
Photoconductive Photocell 1
Photovoltaic Photocell 1
Plastic 20
Plate Gl as s 22
P/N Si l i con Sol ar Cel l 1-4, 8, 9,
Proton Energy Level 13, 15, 17, 18,
Proton Fluence 10-12, 18-20
Proton I rradiation 13
Proton Radiation Energy Dependence
Proton Radi ati on Energy Level 3, 4
Proton Total Dose Effect 21
Radiation Resistance 2
Radiation Tolerance 17
Redegradation 17
Resistivity 1, 4-15, 18
Sapphire 20, 22
Selenium 1
Semiempirical Model 4, 13, 17
Short Ci rcui t Current 2, 3
Silica 20
Silicon 1
Soda Lime Pl ategl ass 22
Solar I llumination 2
Solex 22
17, 18
12-15, 17, 18
20, 21
3, 4
27
Spectral Transmi ttance 22
Spectrasi l A 22
Suprasil I1 22
Thin Film Cadmium Sulfide Solar
Threshold Fluence 17
Transparent Adhesive 21, 22
Ultrasil 22
Ultraviolet Radiation 22
Vycor 22
Cell 18
28
NASA-Langley, 1971 - 9 CR-1872