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

for

N A T I O N A L A E R O N A U T I C S A N D S P A C E A D M I N I S T R A T I O N W A S H I N G T O N , D. C. JULY 1971

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. . .

TECH LIBRARY KAFB, NM

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1. Repat No. . .. ~

2. Government Accession No. 3. Rscipient'r Catalog No. NASA CR-1785

4. Title and Subtitle ~~

5. Report Date

RADIATION EFFECTS DESIGN HANDBOOK Sec t ion 1. Semiconductor Diodes

Ju ly 1971 6. Performing Orgnizatim Code

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7. Author(s) 8. Performing Organization Report No.

C. L. Hanks and D. .I. Hamman

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Q. Morming Organization Name and Addrm

I RADIATION EFFECTS INFORMATION CENTER B a t t e l l e Memorial I n s t i t u t e 11. Contract or Grant No. Columbus Labora to r i e s

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Nat iona l Aeronaut ics and Space Administration Washington, D.C. 20546

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L- ~ ~~- " . " . I 15. Supplementary Notes

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This document con ta ins summarized i n f o r m a t i o n r e l a t i n g t o s t e a d y - s t a t e r a d i a t i o n e f f e c t s on semiconductor d iodes p lus an in t roductory sec t ion on terminology. The rad ia t ion cons idered inc ludes neut rons , gamma rays , e l e c t r o n s , and pro tons . The informat ion is u s e f u l t o t h e d e s i g n e n g i n e e r f o r making e s t ima tes o f r a d i a t i o n e f f e c t s on diodes.

I 17. Key' Words (Suggested by Author(s) ) 18. Distribution Statement Radiat ion Effects , Diodes, Semiconductors S i l i c o n e o n t r o l l e d R e c t i f i e r s , R a d i a t i o n

Unc las s i f i ed - Unlimited

Damage

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PREFACE

. . . . , . .

This document is 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.. ' This Handbook will provide the general '

background and informatioh necessary to enable the designers"t0 ' ' '

.. choose suitable types'of materials 0.r classes'of 'devices. It also will include, 'where possible, predictive. techniques for forecasting behavior of materials, devices or equipment, and correlation factors for comparing different radiation environments.

Future sections of the Handbook a r e expected to discuss such subjects as t ransis tors , e lectr ical insulators , capaci tors , solar cel ls , polymeric materials, thermal-control coatings, structural metals, and interactions of radiation.

ACKNOWLEDGMENTS

The Radiation Effects Information 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 a r e indebted to the following 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

D r . A. G. Holmes-Siedle, RCA

Mr. S. Manson, NASA

Mr. D. Miller, SNPO-W

Mr. A. Reetz, NASA

D r . A. G. Stanley, MIT

Mr. W m . 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 Barrier Diodes . . . . . . . . . .

7 11 14 15 16 19 20 20 20 22

REFERENCES . . 25

BIBLIOGRAPHY . 26

INDEX . . . . . . . . . . . . . . . . . . . . 29

V

GLOSSARY

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Absorbed Dose. The radiation energy absorbed per unit mass of a material at the place or point of interest , or the time-integrated absorbed-dose rate [Unit: rad (material)], one rad being equivalent to 100 e rgs /g ram o r 0 . 0 1 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 (mater ia l ) / s ] . Dose rate is preferred.

Breakdown Voltage. age) at which the through Zener or

The value of reverse voltage (negative anode volt- current increases 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 electromagnetic radiation generated when high-energy charged particles are accelerated (or decelerated) 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 interaction 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 bremsstrahlung being the continuous portion of the X-ray spectrum.

Bulk Damage. Radiation-induced defects in the crystal lattice of a material which, in a semiconductor, act as additional recombination centers for minori ty carr iers and thus decrease the lifetime of the minor i ty car r ie rs .

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 mater ia l that results from particulate irradiation. 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 character is t ics in the "linear" operating region.

( r d A V D I O D E

A i 'IoDE AT SELECTED O P E R A T I N G P O I 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.

Electron. A small charged particle having charge equal to 4. 803 x 10-10 esu and a m a s s of 9 . 109 x 10-28 gram. In general use, it most often refers to a negative charged particle, which is more correctly termed negatron; positron refers to a particle having a positive charge.

Energy Spectrum. The distribution of radiation, 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 air , whose mass is A m , are completely stopped in air . . . Here A refers to an increment small enough s o that ' I . . . a further reduction in its size would not appreciably change the measured value . . . and, on the other hand, is st i l l large enough to contain many interactions and be t raversed by many particles. 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 rarely, more than two) fragments - the fission products. Fission is accompanied by the emission of energy; kinetic energy of neutrons and fission products and the associated gamma rays. It can be spontaneous or it can be caused by the impact of a neutron, a fast charged particle, or a photon.

viii

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Fluence. The number of particles or photons or the amount of energy that enters an imaginary sphere of unit cross-sectional area. The time-integrated f l u x .

Flux. At a given point, the number of photons or par t ic les or energy incident per unit time on a small sphere centered at that point, divided by the cross-sectional area of that sphere.

Forward Characteristic. The current-voltage characteristic of a diode when biased in the forward direction or direction of least resistance 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- erally 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.

Ionization. The separation of a normally electrically neutral atom or molecule into electrically charged components.

Ionizing Radiation. Electromagnetic radiation (gamma rays or X-rays) or particle radiation (neutrons, electrons, etc. ) capable of producing ions, i. e. , electrically charged atoms or molecules, in its passage through matter.

ix

- IR. See reverse leakage current.

IRo. The reverse leakage current measured init ially or at the begin- - ning of a tes t .

Junction Leakage Current. See reverse leakage current.

Leakage Currents. See reverse leakage current.

Majori ty Carr ier . In semiconductors, the type of carrier that constitutes more than half the total number of car r ie rs . The major i ty car r ie rs a re e lec t rons in an n-type semiconductor and holes in a p-type semiconductor.

Minority Carrier, The type of c a r r i e r that constitutes less than half the total number of c a r r i e r s in a semiconductor. The minority car r ie rs a re ho les in an n-type semiconductor and electrons in a p-type semiconductor.

Neutron. A particle with no electr ic charge, but with a mass approximately 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 centimeter) and the neutron velocity; the flux is expressed as neutrons 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-sectional area per second.

Neutrons, Fast. Neutrons with energies exceeding 10 keV, although sometimes different energy l imits are given.

Neutrons, Thermal. Neutrons in thermal equilibrium with their sur- roundings. At room temperature their mean energy is about 0.025 eV.

Nuclear Radiation. Particulate and electromagnetic radiation emitted from atomic nuclei in various nuclear processes.

Permanent Effects. Changes in material properties that persist for a time long compared with the normal response time of the system of which the material is a par t .

X

Proton. An elementary particle having a positive charge equivalent to the negative charge of an electron (4.803 x 10-10 esu) but possessing a mass approximately 1845 times as great.

Rad. A unit of dose equal to 100 e rgs per g ram. In defining a dose, - the material must be defined, e. g. , €320, C, Si.

Radioactivity. Spontaneous nuclear disintegration occurring in elements such as radium, uranium, and thorium and in some isotopes of other e lements (e . g . , Cob0) . The process is usually accompanied 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 equilibrium 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 res is t - ance to current flow through the device. The anode is biased negative in relation to the cathode.

Reverse Current. See reverse leakage current.

Reverse Leakage Current, IR. The current that flows when the diode is biased in the direction of greatest resistance. The reverse current as normally measured is a combination of reverse saturation current, carrier generation 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 f rom a steady forward current to a reverse bias in a given circuit.

Temporary Effects. Changes in material properties that persist for a t ime, but which a r e followed by complete or near ly comple te 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.

x i

VFo. The. forward voltage drop measured initially or at the beginning

of a tes t

Vz. See reference voltage - Vzo. The reference or Zener voltage measured initially or at the be-

ginning of a tes t .

Zener Voltage. See reference voltage.

xii

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 u x and/or fluence that an electronic circuit will tolerate. Therefore, radiation should be listed along with temperature and electrical bias a s 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 f ree ca r r i e r s 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 categories: majority-carrier devices and minority-carrier devices. Field-effect transistors (FET's) and Schottky barrier diodes are the primary representatives of the majority-carrier device category. Most other semiconductor devices including bipolar transistors, solar cells, diodes, rectifiers, and silicon-controlled devices are minority- carrier devices. A generalized pictorial representation of these devices is presented in the appropriate subsections.

The radiation effect of greatest in terest in minori ty-carr ier 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 carr iers . This decrease in 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 )

K T i S the lifetime damage constant [ cm2/(par t ic le . s ) ] . This expression will be developed further in the section on

transistors to show its relationship to the transistor current- amplification factor, hfe or p . The resulting expression will be useful in predicting p degradation as a result 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. Ionizing 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 carriers. These are the most apparent effects at low fluences. A s one would expect, the magnitudes of these effects vary widely, even among units of the same type made by the same manufacturer. 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 interface 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

Ionizing radiation can create free-charge carriers which will participate in the conduction process. This has the effect of generating photocurrents, that is, cur ren ts that are generated in the reverse direc'tion across any p-n junction. .The photocurrents at the base- emitter junction of transistors may be amplified by the current gain. The magnitude of this effect will depend upon the radiation f l u x and, although the magnitude of the photocurrents are generally small when compared with normal operating currents, they may be significant in certain applications.

The preceding paragraphs have emphasized radiation effects on minority-carrier devices because experience shows these to be critical components in many current applications. However, majority- carr ier devices a lso are cr i t ical in many appl icat ions. Experimental

ily

work has shown that radiation can produce surface effects in field- effect transistors (FET's) that will adversely affect the performance of these devices. It 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 conductivity can in some instances occur at exposure levels comparable to those at which bipolar transistors are st i 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 t ran- sistors over bipolar transistors, because of their independence from the minority-carrier l ifetime, has not been realized. This is primar a surface passivation problem which is slowly being improved.

It 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 semiconductor 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 value varies from one experiment to another. Therefore, in order that data could be compared on a common basis, the fluence values reported by the various experimenters were converted to n / c m 2 ( 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 in MeV. The multiplication factors used f rom this expression were

For F luenc 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. This procedure may result in e r r o r s 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 t e r m is more fully described in the section of this Handbook entitled "The Radiations in Space and Their Interactions with Matter".

For the purposes of this and future sections, the following radiation environmental descriptions are used unless specifically noted otherwise in the text.

Neutron radiation - that radiation environment resulting 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 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. )

Electron and proton radiation - particulate radiation, produced by machine sources, that is used to simulate the environment in the Van Allen belts.

Subsequent portions of this Handbook will describe the typical radiation-induced changes in important semiconductor device parameters to provide 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 a r e 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 their characterist ics and their limited application tunnel, varactor, microwave mixer, and Schottky barrier diodes are discussed in the final section of this 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 electrical characterist ics 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 fission 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 Introduction 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-JUNCTION DEVICE

Parameters that are common to most of the single-junction devices and indicative of their satisfactory operation are forward voltage drop, reverse current, and breakdown voltage. These are the parameters generally measured in determining 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 is the breakdown or reference-voltage of zener or voltage-reference diodes which is of greatest importance in 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 is 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 f irst discussed. Data presentation is graphic wherever possible and consists of shaded envelopes that enclose the data points plotted for a par t icular parameter . A data set , as referred to on the graphs, is 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 particular test .

In using the information given in the following paragraphs, the reader should remember that the intent is to provide preliminary o r 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 small margin of safety to exist.

6

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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 semiconductor'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 is i l lustrated by a comparison of Figures 2, 3 , and 4, which are composites from the available data and show changes observed in forward-voltage drop (V,) a s 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, respectively, are represented by the curves in Figures 2, 3 , and 4. Data points shown on these and other graphs in this diode section are representative and a r e not meant to be comprehensive. A ser ies 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 a s a failure cri terion, the diodes of lower current ratings are satisfactory to minimum neutron fluences of 5. o x 1014 and 2 x 1014 n / c m 2 (E > 10 keV), while those of the higher current ratings may exceed this criterion at 1 x 1014 n / c m 2 (E > 10 keV). This failure criterion has been chosen arbitrarily and may or may not be suitable for a particular application. It is, therefore, left to the designer to establish his circuit's failure criteria and determine 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 > 10 heV 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

described earlier are responsible for some of the change observed in the reverse characterist ic. The reverse-saturation current increases as the inverse of the square root of the minority-carrier lifetime, while the carrier -generation current is inversely proportional to the minority-carrier lifetime. A third component of the reverse-leakage current is surface leakage which is generally not calculable and is dependent upon surface condition, surface recombination, and the presence of surface charge. These three components of reverse current are not satisfactory for categorizing 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 ar t ic les 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 less are plot ted as a function of neutron fluence in Figure 5, while those for diodes rated in excess of 1 ampere are represented by Figure 6. Comparison of the composite results of the various investigators as presented in these two figures shows little difference in the degradation of the reverse characterist ics of the two groupings of diodes.

Comparison of Figures 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 increase in leakage currents from nanoamperes o r even a few microamperes to values 25 or 50 times greater than initial value usually will not seriously impair the diodes' performance. An increase 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 in 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 t ime, which is a measure of switching capability, is insufficient for providing graphic illustration of the effect of radiation on this parameter. However, the information which is available shows a variation of f rom l i t t le 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 this parameter as a

9

Neutron Fluence, n/cm2 (E > 10 keV) 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.

Information concerning permanent-degradation effects of electron radiation on the characteristics of switching diodes is limited to one report on silicon devices, and shows a maximum increase in 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 increased several o rders of magnitude with this fluence but remained within satisfactory l imits. 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 increase is due to the destruction of the lattice near the junction by rapid absorption at very high dose rates, i .e. , 1.77 x 10l2 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 character is t ics 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 Figures 7, 8, and 9. The graphs are composites,of the available information 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 less , and Figure 8 similarly represents rectifiers rated above 1 ampere but l e s s than or equal to 10 amperes. Figure 9 i s a composite of resul ts on those rectifiers rated above 10 amperes. These f igures show little difference in the minimum fluence at which the rectifiers experience 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 / c m 2 (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- is t ics of si l icon rectifiers are i l lustrated in Figures 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 > 10 keV ) 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 > 10 keV ) 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 -

Neutron Fluence, n/crn2(E > 10 keV) fisslon

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

Neutron Fluence, n/cmZ (E > IO keV) fission

FIGURE 11. COMPOSITE OF CHANGES IN 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

Neutron Fluence, n/crn2 ( E > 10 keV) flssion

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 rating. The data summarized in Figure 10 are f rom results o f radiation tests on rect i f iers ra ted at 1 ampere or less . Figure 11 is a similar summary of data for rect i f iers ra ted above. 1 ampere and equal to o r less than 10 amperes; data for those units having current ratings in excess of 10 amperes a re summar ized in F igure 12. These f igures i l lustrate the increase in sensitivity to radiation that occurs with increasing current or power rating that i s character is t ic of many semiconductor devices. Based upon the information presented in these graphs, rectifiers rated above 10 amperes may experience a strong increase in reverse current at approximately 1011 n / c m 2 (E > 10 keV), while those rated at 1 0 amperes o r l ess do not experience a s imilar increase until at least 10l2 n/cm2 (E > 10 keV), an order of magnitude greater neutron fluence. A similar difference in sensit ivity may also be noted between the rectifiers having current ratings of 1 ampere o r less and those rated above 1 ampere.

Limited information on the effects of electron irradiation on the electr ical character is t ics of si l icon rectifiers indicate 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 / c m 2 (E = 1.5 MeV). ( l ) The reverse current increased by approximately one order of magnitude, from a few nanoamperes to a maximum of 2 microamperes .

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 is 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 irradiation results 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 increase of as much as a factor of four has been observed with a fluence of 2.5 x 1015 n /cm2 ( E > 10 keV). It 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 electron irradiation on the characterist ics of si l icon general-purpose diodes are also very l imited but do show an increase 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- carr ier l i fe t ime 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, is important in the application of these devices. Therefore, any changes in these parameters from exposure to a radiation environment must be considered by the circuit designer: allowances must be made in his design o r 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 maximum change in reference 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 / c m 2 ( E > 10 keV).

Neutron Fluence, n/cm2 (E > IO keV) fission

FIGURE 13. COMPOSITE OF CHANGES IN REFERENCE VOLTAGE VERSUS NEUTRON FLUENCE FOR REFERENCE DIODES

34 Sets of Data

15

Another factor that must be considered but that has had l imited investigation is 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 diodes are irradiated are shown in Figures 14 through 17. (2) These graphs demonstrate that the amount of change in reference voltage from irradiation may diverge, converge, or cross with increasing temperatures (Figures 14, 15, and 16) or remain essentially 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 is operating. Therefore, depending upon the application, the amount of degradation of the reference voltage from irradiation must be determined 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 / c m 2 (E > 10 keV) but may increase by a fac tor of three at 3 x 1015 n /cm2 (E > 10 keV), as shown in Figure 18. A change in forward-voltage drop may or may not be significant, depending upon the application, and it is left to the designer to determine whether such a change would be detrimental to the performance of his circuit .

Because most investigators do not include the measurement of reverse current in testing the effects of radiation on reference diodes, data are somewhat l imited. The data that are available indicate degradation similar to that experienced by switching diodes. That is, the minimum fluence at which the reverse current increases by a factor of 10 o r more i s approximately 2 x 1014 n / c m 2 (E > 10 keV). It is 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 radiation 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 o r 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 comparable 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

Temperature, C 80 100 I20

FIGURE 14. VOLTAGE-TEMPERATURE CHARACTERISTICS FOR 1N745A(2)

21

20

19

18 - 40 - 20 0 20 40 60 80 I20

Temperature, 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 6 0 80 100 I20 Temperature, C

FIGURE 17. VOLTAGE-TEMPERATURE CHARACTERISTICS FOR IN939(2)

18

I -

Neutron Fluence, n / c d (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 switching. They are less sensit ive 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 increase in 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 satisfactorily in 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 / c m 2 (E = 800 keV). (5 ) Other studies indicated similar effects from electron irradiation 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. Information available on the effects of radiation on these devices is inadequate for reaching general conclusions as to their resistance 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 increase in current observed was 245 nanoamperes. (1) The forward- voltage drop was essentially unchanged.

Microwave Mixer Diodes

Information 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 all electronic 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 all four-layer, 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 electrical lead wires. The silicon-controlled switch has leads to all four layers 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 devices are i l lustrated pictorially in Figure 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

gate -l Anode Cathode

Cathode

Silicon-Controlled Switch

+ Anodeo 0 Cathode N P N P

-

Gate

Silicon-Controlled Rectifier

Anodeo P 0 Cathode N P N + -

Schockley Diode

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 / c m 2 (E > 10 keV). (8) Complete failure where the unit fails to fire occurs at fluences as low as 1013 n / c m 2 (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 / c m 2 (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 Bar r i e r Diodes

The Schottky barrier diode, being a majority-carrier device, 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. Ionizing 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 radiation i s bulk damage, which includes carrier removal and decrease in bulk lifetime. The series resistance of the diode increases 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 varied 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 microamperes, 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 increases required a temperature of 300 C.

2 2

Various physical configurations of aluminum-silicon Schottky barrier diodes were irradiated with low-energy electrons (15 to 20 keV) to a dose of 109 r ads (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 lo8 rad (Si02) and approached another order of magnitude increase at -5 x 108 rads (Si02) 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 in Figure 20, was constructed as platinum-silicon devices and aluminum-silicon devices. The electron dose to which these units were subjected was lo8 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 insensitive 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 / c m 2 (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 resistance from carrier removal was evident in both the platinum- silicon and aluminum-silicon devices.

23

Anode Gate 9 9

Metal

Gate-control led diode

Overlap diode

Vapor-deposited SiOe

-Thermal ly grown Si02

Anode

Anode

P Non-overlap diode

- - Anode

p-n guard ring diode k+ FIGURE 20. STRUCTURE OF SCHOTTKY DIODES(9)

24

REFERENCES

(1) Stanley, A. G., "The Effect of Electron Irradiation on Electronic Devices", Massachusetts Institute 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 Travis , C. M., Ling-Temco-Vought, Inc., Dallas, Texas, "An Analysis of Steady-State Radiation Damage of Tunnel Diodestt, Paper presented at the Conference on Nxlear Radiat ion Effects , jointly sponsored by the Institute of Electrical and Electronics Engineers, the Professional and Technical Group on Nuclear Science, and the University of Washington, Seattle, Washington, July 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 Irradiated", Electronics, 34 (4), p 28 (February 17, 1961). -

(7) "Engineering Investigation 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 Irradiation 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 Transactions on Nuclear Science, NS-16 (6) , 220-226 (December, 1969.).

(10) Wilson, D. K . , Mitchell, J. P. , Cuthbert, J. D., and Blair , R.. R., ! 'Effects of Radiation on Semiconductor Materials and Devices", Western Electric Company, Bell Telephone Laboratories, Inc. , 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.

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26

7. "Components Irradiation Test No. 8 2N918 Transis tors , 1N250 Diodes, Tantalum Capacitors", Lockheed Aircraft Gorp., Lockheed-Georgia Co. , Georgia Nuclear Labs. , Marietta, Ga. , ER-7686 (October 30, 1964), NAS8-5332, 6 2 pp.

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11. "Components and Sub-Assemblies SNAP 8 Radiation Effects Test P rogram - Volume III", Lockheed Aircraft Corp., Lockheed Georgia Co . , Georgia Nuclear Labs., Marietta, G a . , ER-7644 (January, 1965), 294 pp, Available: NASA, N65-23009.

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13. "SABRE Radiation Effects Data Book", Boeing Co., Seattle, Washington, D2-90607, Vol. 1 (November 25, 1964) (April 1 - September 15, 1964), A F 04(694)-446, 432 pp.

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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-Irradiated LiF", Journal of Physics and Chemistry of Solids, 27 ( l ) , 147- 16 1 (January, 1966).

-

27

16. Hendershott, D., "Nuclear Radiation Test Results on Electronic Parts, Report 2", General Electric 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 JPL Tes t No. 6 17, Phase I1 to Jet Propulsion Laboratory", Battelle Memorial Institute, Columbus Laboratories, Columbus, Ohio (June 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", IEEE Transactions on Nuclear Science, NS- 13 ( 6 ) , 341-349 (December, 1966).

19. Smith, E. A., "Results of Semiconductor Irradiation Test at Western New York Nuclear Research Center, January 19 and 20, 1965", Lockheed Aircraft Corp., Sunnyvale, Calif. (February 25, 1965), Interdepartmental Communication, 29 pp.

20. "Preliminary Results of Experiments 11 through 17 Conducted at the Western New York Nuclear Research Center Reactor During the Time Period December 17 through December 21, 1962", Westinghouse Electric Corp., Astronuclear Lab., Pittsburgh, Pa., WANL-TME-250 (January 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 (June, 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 Ionizing particulate radiation 1 Ionizing radiation 2, 3, 22 Isotopic sources 4 Junction 11 Junction area 7 Junction-leakage current 2 Junction 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 t ime 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.


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

%. M w m i n g Organization Name and Addrar 10. Work Unit No.

RADIATION EFFECTS INFORMATION CENTER B a t t e l l e Memorial I n s t i t u t e Columbus Labora to r i e s Columbus, Ohio . 43201

NASW-1568

12. Sponsoring Agency Name end Address

11. COntrrct or Grant No.

13. Type of Report and Period Coverd

Contractor Report National Aeronaut ics and Space Adminis t ra t ion Washington, D.C. 20546 14. Sponsoring Agency Code

I 15. Supplementary Notes

16. Abstract

This document con ta ins summar ized in format ion re la t ing to s teady-s ta te r a d i a t i o n e f f e c t s o n t h e r m a l - c o n t r o l c o a t i n g s . The r a d i a t i o n i n c l u d e s n u c l e a r , c h a r g e d p a r t i c l e s and u l t r a v i o l e t . The d a t a w i l l p rovide usefu l in format ion to , the des ign engineer respons ib le for choos ing thermal -cont ro l coa t ings in space a p p l i c a t i o n s .

17. Key' Words (Suggested by Author(r) ) 18. Distribution Statement Radiat ion Effects , Thermal-Control Coat ings, U l t r a v i o l e t E f f e c t s , T e m p e r a t u r e C o n t r o l i n Space Radis t ion Damage

Unc las s i f i ed - Unlimited

19. h u r i t y Q r r i f . (of this reportt

$3 201 Unclas s i f i ed Unc las s i f i 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 o r operation in the radiation environments to be found in space, be they natural or artificial . This Handbook provides the general background and information necessary to enable the designers to choose suitable types of mater ia ls or c lasses of devices.

Other sections of the Handbook will discuss such subjects as tran-is sistors, electrical insulators and capacitors, solar cells , structural metals, and interactions of radiation.

iii

ACKNOWLEDGMENTS

The Radiation Effects Information 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:

M r . A. Reetz, NASA, Hq

D r . J . B . Schutt, NASA, Goddard SFC

M r . E. R. Streed, Martin-Marietta, Denver

Our additional thanks are due to Academic Press, Incorporated for permission to use the copyrighted material from References 13 and 19.

V

TABLEOFCONTENTS

SECTION 2 . THERMAL-CONTROL COATINGS - P a g e

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

Primary Cosmic Radiat ion . . . . . . . . . 20

Trapped Protons . . . . . . . . . . 21 Trapped Electrons . . . . . . . . . . 21 Trapped Alpha Particles . . . . . . . . 22 Calculation of Accumulated Fluxes . . . ' . 22

Solar Particles . . . . . . . . . . . . . 22

Solar Wind . . . . . . . . . . . . 23 Auroral Radiation . . . . . . . . . . . . 24 Man- Made Radiation . . . . . . . . . . . 24 Miscellaneous Natural Sources . . . . . . . . 25

Thermal-Energy Atoms in Space . . . . . 25 Solar X.Rays . . . . . . . . . . . . 25 Neutrons . . . . . . . . . . . . . 25 Albedo Protons . . . . . . . . . . . 25 Alpha Particles . . . . . . . . . . . 25

Geomagnetically Trapped Radiation . . . . ' . . 20

Solar-Flare Radiation . . . . . . . . . . 23

ORGANIC COATINGS . . . . . . . . . . . . . . . . . 28

Zinc Oxide/RTV-602 Dimethyl Silicone Binder (S- 13) . . . Effect of UV and Proton Exposure . . . . . . . . Effect of UV and Electron Exposure . . . . . . . .

Zinc Oxide [SP-500] Coated With Potassium Silicate/ RTV-602 Silicone (S- 13G) . . . . . . . . . . . . . . .

Effect of Electron 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

Acrylic 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

Silicates . . . . . . . . . . . . . . . . . . . 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 Zirconium Sil icate Paints . . . . . . . . . . . . 49 Zinc Oxide in Potassium Sil icate (2.93) . . . . . . . 50

Stability to Proton Bombardment . . . . . . . 51 Douglas White Inorganic 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

Solar-Thermoelectr ic 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 Porce la in 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 (Grit Blasted) . . . . . . 71 Black Nickel Plate on Aluminum [ 1100(2-S)Al] . . . . 71

Westinghouse Black on Inconel. Sodium Dichromate- Blackened SS (Type 347). Sodium Dichromate- Blackened Inconel. and Sodium Dichromate- Blackened Inconel X . . . . . . . . . . . . . 71

Aluminum 1100(2-S)Al] and Pyromark Pyromark Black Ref rac tory Paint on

Black Refractory Paint on Inconel . . . . . . . . 72

PIGMENTS . . . . . . . . . . . . . . . . . . . . 73

Zinc Oxide . . . . . . . . . . . . . . . . . . . 73 Titanium Dioxide . . . . . . . . . . . . . . . . 76 Titanate s . . . . . . . . . . . . . . . . . . . 78 Zirconium Silicate . . . . . . . . . . . . . . . . 78

BINDERS . . . . . . . . . . . . . . . . . . . . . 79

Silicone Binders . . . . . . . . . . . . . . . . . 79

REFERENCES . . . . . . . . . . . . . . . . . . . 80

INDEX . . . . . . . . . . . . . . . . . . . . . 90

ix

TABLE O F CONTENTS (Continued)

Page

APPENDIX A

THERMAL CONTROL MATERIALS FOR SOLAR AND FLAT ABSORBERS AND REFLECTORS . . . . . . . . . . . A- 1

CONTOURS O F CONSTANT FLUX ELECTRONS AND PROTONS. . A - 1

APPENDIX B

TABLES AND FIGURES FOR ORGANIC THERMAL-CONTROL COATINGS . . . . . . . . . . . . . . . . . . . B- 1

APPENDIX C

TABLES AND FIGURES FOR INORGANIC THERMAL-CONTROL COATINGS . . . . . . . . . . . . . . . . . . . C- 1

X

SECTION 2. THERMAL-CONTROL COATINGS

SUMMARY AND CONCLUSIONS

Maintenance of a rather narrow range of temperatures within satell i tes is essential in both manned and unmanned vehicles. For electronic appa- ratus, the most suitable temperature range presently is 20 to 40 C . Manned spacecraft must not exceed 11 0 F (43 C ) f o r periods longer than a few minutes. (1)

Control of temperatures on an operational spacecraft is based on the exchange of radiant energy with the vehicle's environment, and therefore upon the thermal-radiation properties of the exterior surfaces. Thermal- control coatings with the desired radiative properties have been used in the aerospace industry to maintain a predetermined heat balance on space vehicles. Solar absorptance, a s , 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 solar absorptance to emittance, a s / & . These surfaces are general ly susceptible to damage by solar radiation, result ing in an increase in a s . 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.

Ideally, thermal-control surfaces can be divided into four basic c lasses , so la r absorbers , so la r re f lec tors , f l a t absorbers , and f la t re f lec- to rs . The so la r absorbers a re p r inc ipa l ly meta ls and a re re la t ive ly immune to space radiation damage. The f lat absorbers [ absorbing incident energy from ultraviolet (UV) to the far infrared (IR)] are most easily obtained in general practice, and their stability to space environments presents few problems unique to these coatings. Flat reflectors (reflecting energy incident 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 development of solar reflectors. Some of these have been adapted by suitable pigmentation to provide solar absorber systems.

”-

The principal problem in temperature control is presented by change of the as/€ ratio of a coating due to degradation by space environments such a s U V radiation; proton, alpha particle, and electron bombardment; neutron and gamma radiation; and micrometeoroid impact. These space environmental factors are shown in Table 1. Those environments of importance to coating damage are marked with an asterisk.

TABLE 1. MAJOR PORTIONS OF THE SPACE ENVIRONMENT(^)

Natural

Particle Radiation

Protons

Electrons

Galactic Van Allen* Solar F la re Solar Wind* Auroral

Van Allen96 Auroral*

Alpha Particles Solar Wind Solar Flare

Electromagnetic Solar Emissions*

Physical Impact Atmospheric Particles Micrometeoroid

Artificial

Pers i s ten t

Electrons High-Altitude Nuclear Detonations* Neutron/ Gamma Spacecraft-Borne Nuclear Reactors9; Electron/Gamma Spacecraft-Borne Isotope Power .Supplies

Transient

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 environmental 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 basic types of thermal-control surfaces, only the solar ref lectors (the, white paints primarily) are seriously damaged by space UV.

Specular surfaces and leafing aluminum are resistant to reflectance change in the IR wavelength region, but undergo substantial permanent reflectance losses in the visible and UV wavelength regions. Diffuse coatings are subject to ref lectance 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 withstand doses of approximately l o 8 rads (C) without appreciable damage. Inorganic coatings will probably withstand somewhat higher exposures.

Electron bombardment will adversely affect coatings. The damage of particle radiation to organic coatings. i s s imi la r to that caused by UV. The damage mechanism is, in effect, the same. The better coatings will withstand 1 015 t o 101 6 e / cm2 (E 145 keV). Higher doses may cause severe damage.

Specular surfaces and leafing aluminum-silicone coatings are, in general , relatively resistant to reflectance degradation due to electron exposure (E < 50 keV). Excepting leafing aluminum, the diffuse coatings or paints are, in general, subject to severe, in-air recoverable degradation in the IR wavelength region, and to substantial visible-region reflectance losses which are less recoverable or "bleachable" upon re-exposure to air. Coatings employing methyl silicone binders sustain the greatest degree of reflectance degradation 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 se r i e s of tests on various coatings, that over a wide range of fluxes and fluences (4 x l o 8 to 1 . 7 x 10 l2 e / ( cm2 . s ) , and 1013 to 8 x 1015 e/cm2, no i r - radiation rate effects from 50-keV electrons a re evident.

Electron damage at 77 K (-196 C) is general ly less severe than at 298 K (25 C). The combination of UV and electron damage is generally more severe than the sum of the damage caused by the individual factors. However, changes in reflectance of anodized aluminum (both barrier- and sulfuric 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) Galactic protons are relatively unimportant because of the relatively low f l u x , but Van Allen and solar-wind protons are damaging to coatings. The l imited data available suggest that auroral protons and low-energy solar-flare protons are unimportant with respect to coating 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) in many cases than at 298 K (25 C ) . Many times, the combination of proton and U V radiation is only slightly more damaging than U V alone. The UV tends to bleach the damage due to proton irradiation.

(5) Solar alpha particles are considered of secondary importance to coating damage when compared to the effects of solar-wind protons and solar U V irradiat ions. Their numbers are less than those of solar protons. However, their effectiveness on a a r t ic le bas i s is comparable to proton-induced damage. pz)

(6) Residual high-alt i tude earth-atmospheric particles are considered unimportant in their effects to satellite surfaces. The micrometeoroid environment of space is not important for optical damage, where damage is defined as either a change in as or E, or a change in the reflected angular

4

I -

distribution of solar energy. The latter effect , however, is important for solar concentrator and mirror appl icat ions. ( 2 )

Artificial environments such as that caused by the Starfish 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 coatings. (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 is UV radiation. Due to (a) the spectra from available UV sources not matching the solar spectrum, (b) U V damage in vacuum being more severe than UV damage in air , and (c) recovery of damage often being rapid when air is supplied to the coating, it is difficult to forecast U V damage to coatings in space on the basis of laboratory 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, laboratory data and those obtained from space satellites have not always been in agreement.

Coatings that appear to be most stable t o 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 solar exposure in OSO-I1 and Pegasus I1 experiments. This coating suffered somewhat greater damage on the interplanetary flights such as Mariner IV and Lunar Orbiter V. This damage (nu, = 0 . 0 5 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 mirrors which have shown excellent stability to both UV and particle radiation. Silvered Teflon showed no change on the OGO-VI af ter 4600 ESH. Aluminized 1-mil Teflon showed a Aa, of 0. 043 af ter 5000 hours' exposure on the Mariner V. An SiOJAluminum 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 icone 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 o 8 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 reflectance 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 ~ 1 0 1 5 p / c m 2 , Aas=O.O1

5x1016p/cm2, (E= 10 keV) , AaS=O. 42

3x1015p/cm2 (E=466 keV), AaS=O. 0 1

No evidence of cracking or spalling when cycled 4 times from 260 to -190 C

1014 e / cm2 (E=50 keV) Aas=O.Ol

lOI5 e / c m 2 , 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 in 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 C C / ~ 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 annealing effect with UV. Combined damage greater than sum of separate 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 o 8 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 o 6 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 . 2 4 0.86 485 ESH, Aas=O. 11 5x107 rads(C), b s = 0 . 0 5 Kemacryl 0.28 1000 ESH, A a ~ 0 . 1 2 2x108 rads(C), Aas=0.06,

0 .09

failure 1-3x108 rads(C), mechanical

Nonleafing Acrylic 0 . 4 4 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), Aa s= approaches saturation 0 .03 leve l

1016p/crn2, degraded coating

6 .4~10 p /c rn2 , 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, lo8 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 a c 0 . 0 6 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), Aa s=O. 10

Synthetic 0.16 0.87 485 ESH, Aas=0.O9 1 . 3 ~ 1 0 rads(C), Aas=O. 09 8

Li/A1/Si0i/Na2Si03 162 ESH, Aq=0.12

2 - 9 3 (Zinc oxide/K2Si03)

Hughes Inorganic White (H-2) (Ti02/K2Si03)

Douglas White Inorganic

Zirconium silicate/K2Si03

2 - 9 3

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, Aas increased 10 percent

0.24 0.87 485 ESH, Aas=0.04 0.14 0 .89

0 .11 0 .82 162 ESH, Aas=O. 1 3

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 ~ H O . 10

Concurrent UV and nuclear more damaging than UV followed by nuclear

36 I

38

Low energy protons 10l5e/cm2, Aa,?O1.06 cause measurable 1016e/cm2, AcCsi?O, 09 damage.

466 keV), Aa s=0.06 1015p/cm2 (E=

1 . 6 ~ 1 0 ~ ~ 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 4 9

Pegasus I1

Thermal cycling 1000 sun hrs, A%= Lunar 14, 4 times from 0.09 (Lunar Or- Orbiter 16, 533 K to 83 K , biter IV) IV 26, Aas=O. 0 3 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 enhanced stability of reflectance 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

S i 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 S i 0

0.90 0.85 No degradation

Chromate finish on aluminum

No. 1, Ag 0.05 0 .81 485 ESH, no change i n mirror Aa c

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 . 2 1 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-

t ion level

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 ~ 1 0 ~ ~ 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,

4 8

Stable up to 2 years in all charge and particle environments and combined environments of space

170 ESH, lo7 rads(C). X-ray, Ao! s=O. 01

1720 ESH, lo8 rads (C) X-ray, Ass= 0.02

Vanguard 2, 8 I1

9

49

55

37

37 100 ESH, lo7 rads (C) X-ray, Ass= 0 . 0 1

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 . 0 1 t o 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 ~ 1 0 ~ ~ p / c m ~ minor reflectance

1016e/cm2, significantly 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 ( e 1 4 5 keV), change slight reduction

in spectral re- f lectance

750 F, 30 sec in Vac - no change

7900 F , film visibly darkens

1150 ESH, 1 . 2 ~ Mariner 18,27 lo8 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 significant degradation (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

degradation after 3-1/2 years on Explorer XXIII. An RTV/ silicone coated aluminum showed a Aas = 0. 08 a f te r 1100 hours on Lunar Orbiter V.

Optical solar reflectors (OSR), mirrors consis t ing 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 re f lec tors a re ceramic mir rors and therefore are difficult to apply, particularly on i r regular surfaces. The mirrors have to be mounted by means of an adhesive or tape and the size of t he mi r ro r s is approximately 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- t ro l 2A-100 or Hughes Organic White (both Ti02/ silicone) a re representa t ive of the most stable of these coatings. Change in absorptance, Aa,, for S-13G was 0. 14 in 1200 hours on Mariner V. Absorptance of a T i O ~ / s i l i c o n e apparently increased from 0.24 to between 0.34 and 0 . 4 0 on the Apollo 9. The advantages of these coat ings are that they are easier to apply and require less prelaunch protection than the above thermal-control materials.

Unfortunately, the more, stable coatings are more difficult to apply and t o maintain during prelaunch activities. The coatings that do not require elevated-temperature cures and can be repaired easily lack environmental stability. However, some of these lat ter may be serviceable depending 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 coatings generally require organic binders and these are susceptible to radiation damage.

A summary of the effects of radiation on organic and inorganic coatings is given in Tables 2 and 3.

INTRODUCTION

In a hostile environment such as is encountered in space where vacuum, cryogenic temperatures, solar radiation, and particulate radiation are present, maintaining an operable temperature within a space vehicle is of the utmost importance. The internal temperature of the vehicle must be controlled 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 radiated to space or the vehicle will over- heat. Conversely, i f the vehicle radiates heat faster than it is 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 t hese a r e (1) the absorption of radiation by the surface, (2 ) the radiation o r reradiation of energy from the surface, and ( 3 ) the generation 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-emitted IR energy and earth-reflected solar radiation. ( 6 ) The maintenance of the proper range of temperatures in a space vehicle is one of the more important and complex design problems.

Two techniques are used to regulate the temperature of satell 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 o r thermostats control shut- t e r s o r vanes to vary the surface in terms of effective optical properties. Passive control relies on the use of surface mater ia ls with appropriate ther- mophysical characterist ics. Frequently a combination of both methods is used.

Much research has gone into the study and development of surface mate r ia l s and coatings which have absorptive and radiative properties useful for controlling temperature. It can be shown that the important parameter in determining the surface equilibrium is the ratio of the solar absorptance (as) to the hemispherical emittance (6h) of the external surface where as is the fraction of incident solar energy absorbed and ch is the fraction of energy radiated as compared to that from a black body at that temperature. (7) Four types of thermal control surfaces are used to maintain a desired temperature range within a space vehicle. These are termed solar reflector, solar absorber, flat reflector, and f lat absorber.

17

A solar reflector is a surface which reflects the incident solar energy while emitting IR energy. (8) It is characterized by a very low a s / € ratio ranging from 0.065 to 0.34. It has a low as and high E;. White organic paints with metallic- oxide pigments are representative of this class.

A solar absorber is a surface which absorbs energy while emitting a small percentage of the IR energy. It is characterized by a relatively high a s / € ratio (greater than 1) and is approximated by polished metal surfaces. It 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 efficient as solar absorbers than as emitters of IR energy (typical values, a, 0 . 2 5 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 solar absorbers are aluminum and gold surfaces . Solar absorbers are extremely sensi t ive 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 IR. ( 8 ) It has a low a s and low E . This class of surfaces has been the most difficult to develop. The most promising class of mater ia ls for this use consists of paints pigmented with metal flakes and very highly polished metal surfaces. These surfaces are generally characterized by a relatively low IR emittance with an a s / € = 1. 0. The most favored flat reflector is nonleafing aluminum silicone paint, a s = 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 fa r IR. ( 8 ) It has a high as and high E . Of the four basic surfaces, the flat absorber is the most easily obtained in general practice. Generally, any rough black matte surface will be a good approximation of a f lat absorber. Of the available finishes, Black Kemacryl Lacquer and dull-black Micobond paint (as z 0.93, E = 0.88) a r e 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 radiation characterist ics of the material, such as temperature resistance, mechanical strength, abrasion resistance, adhesive 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 is t 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 seriously is solar radiation, particularly UV. Much information is available on the effects of UV and vacuum, both f r o m 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 present 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 imits. @) 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 U V photons proceed at a higher rate because of the temperature increase 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 possess 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 U V radiation and the combination of UV radiation and vacuum on thermal-control coatings. 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 measurements had to be made while irradiated samples were still in vacuum. In ear l ier tes ts , these measurements were made in a i r af ter i r radiat ion in vacuum, 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 discussed in other sections 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 ly) are ser iously 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, trapped radiation, auroral radiation, and solar-flare radiation. ( 8 ) Those portions of the total space environment which are considered of importance in causing optical damage to spacecraft surface materials are:(9, l o )

Van Allen electrons and protons Solar-wind and solar-flare protons Auroral electrons 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.

Pr imary Cosmic Radiat ion. Cosmic pr imaries consis t pr incipal ly of protons (hydrogen nuclei) moving with relativistic or near-relativistic veloc- i t ies ( f rom 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 cosmic primary radiation f ield is essentially constant with t ime.

The effective ionization dose rate due to cosmic primaries is about 10- rad/hr, and the approximate effective dose rate due to secondaries produced in a space vehicle or in the atmosphere is about rad/hr. Hence, the cosmic-ray-induced damage is regarded as being a very minor hazard.

Geomagnetically Trapped Radiation. For orbits near the earth [up to approximately 20, 000 nautical miles (nm) or 23, 000 statute miles (sm) in altitude], 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 belt . The more stable inner belt 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 n m and consists almost entirely of sl ightly more energetic electrons than those in the inner belt . (8)

Trapped Protons. The inner zone proton flux is relatively stable in time although some changes at low altitudes occur over the solar cycle because of atmospheric changes. Farther out in the magnetosphere, the proton distributions are more easily affected by magnetic disturbances, but in general they are more s table than the e lectron f luxes. ( 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 leve ls a re shown in Figures A - 2 to A-5. ( l o , ''1 Integral flux distributions above 0 . 4 MeV a r e shown in Figure A-6 . ( l o ) It 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 radii) 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 probably are not upper limits for this zone, but are more conservative for making predictions of damage to spacecraft . Energy spectra at the magnetic equator for various 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 Figures 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 imited.

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 af ter the creat ion of the artificial electron belt by beta-decay electrons from the Starfish high-altitude nuclear explosion on July 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, ( lo) the inner zone in late 1964 was characterized by energy spectra generally similar 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 in intensit ies each year fo r L 5 1.3. Thus for the main portion of the inner zone, the fluxes of artifically injected electrons should have been about two o rde r s 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 a r e approximate mean values from data taken from 1962 to 1964, near a period of minimum solar activity. Intensities 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 fo r L = 3 . 4 and 5 in Figure A- 10 are typical 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. It can be seen that the calculation of particle fluxes accumulated by a particular spacecraft at a given time involves 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 James 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- 1 2 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 latitudes within the magnetosphere. Near the magnetic poles, and in interplanetary 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 solar f lares; and low-energy protons and electrons, which are present more continuously.

Solar-Flare Radiation. Protons from solar f lares present perhaps the most important 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 particular t ime period is treated statist ically. ( l o ) Fluxes may be as high as lo4 p/(crn2. s); average dose ra tes may range f rom 1 to 100 rads/hr ; and the total dose per f lare 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 small solar f lares during solar minimum. 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 solar f lares. In several cases where both alphas 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 is a plasma consisting of protons, elec- t rons, 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 fo r protons. The particle flux intensity varied between about 3 x lo7 and 1 x lo9 par t ic les / (cm2- s) . ( l o ) Breuch states that the solar wind is seldom less than 500 eV or greater than 3000 eV and that an average of 1250 eV for the solar wind over the past 30 years is suggested. ( 2 ) The surface dose rate will be approximately 10 r a d s / h r . (8 ) Fluxes are large, but since the energy per particle is small , the damage to materials from solar-wind particles will be confined to surfaces. (10)

6

It 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 radiation. Combined irradiation produces major synergistic effects and bleaching effects which are coating dependent. (2)

2 3

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 satell i te 's orbit been in the solar wind. (13 ) The values were then compared with da ta f rom interplanetary experiments (Lunar Orbiters IV, 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 in interplanetary orbits are at tr ibuted primarily to differences in environmental parameters between the two types of orbi ts . ( I 4 ) I t is believed 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 f rom solar uv exposure alone. (14)

Auroral Radiation. Intense 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 particle intensit ies f luctuate 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 o r storage and precipitation 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 electrons observed in the auroral regions is 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 precipitating protons in the auroral regions in 1965 showed average particle energies of 10 to 20 keV and peak fluxes greater than 106 protons/(cm2. sa steradian) for energies greater than 20 keV. A rough estimate for protons would be approximately 101o protons/(cm day), with 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 electrons

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. In intergalactic space there exists a density of about 1 atom/cm3 of thermal energies (-125 K). These atoms are predominantly protons. F o r a space vehicle traveling at lo8 cm/ sec ( 0 . 003 x velocity of light), the effective flux would be lo8 p/(cm2. s) in intergalactic 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 radiation from the sun which makes up the solar constant [ 2 cal/(cm2. min)] is not ionizing in nature, a very small portion (-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. Since this X-ray energy is absorbed strongly by materials, the interior dose rate is not important. ( 8 )

Neutrons. Except for cosmic-ray interaction with matter such as the ear th 's a tmosphere, there appears to be no major natural source of neutrons. The flux of neutrons from the cosmic-ray effects on the earth 's atmosphere is about 1 n / ( cm2 . s ) and poses no problem. ( 8 )

Albedo Protons. Impingement of cosmic particles on the earth's atmosphere also produces a scattered flux of protons which has an intensity of about 1 p / (cm2. s) . The energy range is 1 to 10 MeV, and the dose per year is probably less than 100 rads. (8)

Alpha Particles. Solar alpha particles are considered of secondary importance in coating damage when compared to the effects of solar-wind protons and solar UV i r radiat ions. Their numbers are less than those of solar

25

protons; their effectiveness on a particle-to-particle basis in producing optical damage is comparable to proton-induced damage. ( 2 )

It should be noted that the charged-particle space environment has increased importance for coatings over that normally associated with the degradation of other satellite components and systems. The charged-particle environment 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 important radiations are the Van Allen and solar-wind particles. ( 2 ) A summary of the various radiation sources is given in Table 4. ( l 5 )

2 6

TABLE 4. EXTERNAL RADIATION SOURCES(15) -

Radiation Type of Flux, Peculiar Source Radiation Energy. E particles/(cm2- s) Characteristics

Galact ic Protons 1 0 MeV - MeV 2 Least significant cosmic rays (-9Wo)

Alpha (-1 @lo 1

Solar wind

Solar cosmic Protons ray events (95%) (solar flares)

-1 keV

Spectrum is very steep above 30 MeV (-E-5); below 10 MeV, spec t rum "~ -1 .2

Solar electro- Infrared, 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 radii)

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 a t 1 A U ( ~ ) LOW energy restricts hazard to surface effects

Protons: 5 x 105 (E > 1 MeV);

Electrons: 2 x lo7 (E > 0 . 5 MeV)

Protons:

Electrons: (E > 1 0 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 cycle

Flux varies with magnetic latitude; e l e c t r o n p p u l 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 material was developed by the Illinois Institute of Technology Research Institute. It consists of a high-purity zinc oxide (New Jersey Zinc Company, S P 500) in a dimethyl silicone binder (General Electric, RTV-602), with SCR-05 ( G E ) catalyst. Earlier tests had indicated that the (S-13) coating could be expected to have good stability when exposed to U V radiation. However, space tests showed that the coating did not have the expected stability. Further investigation showed that the coating was affected by UV in vacuum, but that it quickly recovered or bleached in the near-IR region when exposed to air. Thus, the tests in which optical properties were measured in air after vacuum irradiation had been misleading. It 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 Orbiter project . ( 16) The reflectances of coatings were measured (1) in air, ( 2 ) in vacuum before UV irradiation, (3) in vacuum after various intervals of irradiation, (4) in vacuum 'at varying time periods after irradiation, (5) in an argon atmosphere after vacuum irradiation, ( 6 ) in air under reduced pressure after vacuum irradiation, and ( 7 ) in air at atmospheric pressure after vacuum irradiation. One of the coatings used in these tests was B-1056 produced by the Boeing Company and based on the S-13 formulation.

In two of the tests, argon was bled into the chamber prior to admitting a i r . ( 16) In neither experiment did the B-1056 coating bleach. The maximum exposure to argon was 30 minutes at 0 . 5 t o r r . Upon admission of air , two samples "bleached", showing no permanent change in solar absorptance. Two samples retained 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 microns) .

28

I

Figure B- 1 shows the relative reflectance of samples 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 IITRI and is shown in Figure B-2. A ref lectance 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 almost total after 2 minutes . ( l7) Major damage occurred at wavelengths greater than 1 micron and was maximum at about 2 microns ( see F igure B- 1). The damage bleached out upon exposure to air . It was noted also that no gross bleaching occurred when air pressure was less than torr . ( l6)

Pegasus reported data on the degradation of S-13 for at l eas t 1800 sun hours . As i s shown in Figure 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 continuous change with exposure to sunlight. ( 1 3 ) The results compared favor- ably with data from Pegasus I and OSO-11, both near-earth experiments. Changes in a s measured in the near-earth space environment generally were much less than those measured in interplanetary space.

Resul ts f rom the Mariner V experiment, which was continuously exposed tc the solar wind a r e shown in Figures B-4 and B-5. This flight was launched on June 14, 1967, encountered Venus on October 19, 1967, and obtained information on interplanetary space. The TCR (temperature control reference) assemblies were continuously sunlit , and normal to incident solar radiation to within less than f 1/2 degree . ( I 8 ) Data on apparent solar absorptance versus mission duration were obtained for the f irst 48 days of flight, at which time the temperature reached the upper limit of the sensor range and no further data were obtained (Figure B-5). Since it was the change in temperature which was monitored, solar absorptance was obtained by ass1.lming a constant emittance of 0 . 86 and a solar intensity of 126.4 W/ft2 a t 1 AU (this value was indicated by early results from the black TCR). Absorptance changed from about 0 . 23 ( less than 1 hour after sun acquisition) to approximately 0.41. This degradation was more rapid than was expected based on laboratory tes ts . ( 18)

The S-13 coating was also tested on the ATS-I f l ight and, again, degradation was more rapid 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 increases very rapidly as the wavelength of irradiation decreases below 300 mp . (21)

29

See Table B-1 and Figures B-7 and B-8. During UV irradiation in vacuum S-13 increases in spectral absorptance near the absorption edge of ZnO. In addition, it increases considerably in spectral absorptance in the IR region which, as stated above, bleaches out when the sample is returned to the atmosphere. As seen in Figure B-9, IR absorption is wavelength sensitive. For approximately the same degradation near the absorption edge, the short- wavelength UV ( 2 5 0 mp) is more effective in producing the near IR degradation 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. Samples receiving sequential exposure remained in si tu between exposures. All reflectance measurements were made in si tu. Table B-2 shows the spectral-reflectance changes after the four types of exposure. It may be seen that initial UV exposure preconditions the S-13 coating s o that later electron exposure leaves i t less degraded in reflectance than an electron-only exposure dose. (3) The extent of degradation also appears to depend on the ratio of exposure ra tes 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 to r r . (22) The effects of proton radiation are shown in Figures B- 10 and B- 11. The characteristic curve for zinc oxide susceptibility to proton damage 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. Increasing the dose from 1015 to 1016 p/crn2 almost doubled the peak change in absorptance with approximately 5 percent greater damage in 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 difference between the SUM of the individual environments and the combined environments except in the IR, where the effect of the sum is greater than the

30

effect of the combined environments. Figure B-15 shows that the absorptance peak around 0.4p was considerably greater for the low 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)

Illinois Institute of Technology Research Insititute (LITRI) developed a formulation using a potassium si l icate protected ZnO in RTV-602 silicone binder and designated the coating as S-13G. This is more res i s tan t to UV in a vacuum than the S- 13. The coating, catalyzed with GE's SRC-05 catalyst 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 paint possesses a shelf life in excess of 3 months. An 8-mil film of S- 13G has an as of 0. 19 0. 02 and an emittance of 0 . 88 * 0. 05. A a s is 0 . 03 for 1000 ESH employing in si tu postexposure reflective measurements and AH-6 lamp irradiation. ( 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 absorptance of 0 . 01 in 1400 ESH of i r rad ia t ion . (23) A specimen employing pigment that was first hand mulled and then wet ground for 3 hours exhibited a A a S 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 coating prepared in this way exhibited a A a s of 0 . 0 2 in the 1400 ESH tes t . (23) A grinding period of 4 to 5 hours is usually required to produce a satisfactory coating. The presence of potassium si l icate on the zinc oxide severely re- tards the formation of IR absorption bands (2. 12 microns). However, in processing this material , considerable color center s i tes are formed leading to damage under UV irradiat ion in the visible-wavelength region. ( 16) This il- lustrates the importance of the methods used for preparing the coating.

There has been a lmost a continual development of S-13G regarding its manufacture and mechanical treatment in its manufacture . The formula for this paint as reported at the 3 r d AIM Thermophysics conference, was: (24)

31

Components Weight, lbs

Sil icate-treated SP500 ZnO 25 RTV-602 silicone resin (GE) 12 S- 13G mixed thinner 14

(Comprising, percent)

Toluene 40 Xylene 20 n- butanol 15 Isopropanol 20 Butyl acetate 5

The treatment of the ZnO involved a reaction of the pigment, SP-500 ZnO (New Jersey Zinc G o . ), with PS-7 potassium silicate (Sylvania Electric G o . ) 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 pigment and (for the same reason) a minimum of grinding was used in preparing the paint. (24)

Figure 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 U V exposure to S-13G may be seen also in Figure B-18. Decreases in reflectance in the UV visible, and IR wavelength regions after UV irradiation were as follows:( 2 5’)

U V Expo sur e,

ESH

135 2 50 49 0 7 70

1130

Decrease (Increase) in Reflectance, A R = Ri-Rf (70) ~~

250 m p 425 m p ~- ~

2100 m p

10 14 19 23 25

6 8 8

Figure B-19 shows the laboratory data and those obtained from Lunar Orbi ter I1 flight. It will be noted that there was not good agreement for the S-13G coating between laboratory-test and flight data. The reported laboratory tests were conducted near 70 F. Lunar Orbiter 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. It was believed that this changing thermal input might have

3 2

caused failure of the adherence or cracking in 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 include the effects of particulate radiation. Figure B-19 also shows the in- c rease in A a s for the s- 13 coating (Boeing B- 1056) which occurred on Lunar Orbi ter I so that a comparison 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 IV and tested over B-1056 (Boeing) on both Lunar Orbiters IV 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 desired to have a test coupon of the same coating system as the EMD. ( 2 6 ) The S-13G coating 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 overcoat w a s 2 mils. Initial absportance was as = 0 . 19 1. Initial reflectance versus 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 Orbiters IV and V flights.

Figure B-24 shows the degradation of test coatings on Lunar Orbiter IV 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 comparison of these figures will show:

(1) Differences between Orbiter V test coupon and EMD's on Orbi te rs I and I1 a r e no greater than differences between the Orbiter IV and Orbiter V coupons.

( 2 ) S-13G coating over B- 1056 lessened degradation experienced by B- 1056 alone up to about 800 sun hours. After that t ime the S-13G/B-1056 curve for Orbiter I1 merged with the B-1056 curve for Orbiter I.

( 3 ) The calor imetr ic UV test predicted much less degradation on B-1056 than was experienced in flight. It is suggested that temperature of the paint during exposure may be partially responsible for this disparity. The specimen temperature in the calor imetr ic tes t was f rom 9 to 30 F, whereas Lunar Orbiter deck temperatures ranged from 40 to over 100 F.

33

Comparing the results of the S-13G coatings tested on the Mariner V with those obtained from Lunar Orbiter IV (see Figure B-26) , it will be seen that the increase in solar absorptance for each coating was approximately equal. The solar absorptance of the S-13G on the Lunar Orbiter was initially lower than that on the Mariner. ( 14)

Prel iminary resul ts of the OSO-I11 flight experiment indicated only a 0.04 increase in solar absorptance in 1000 ESH. When compared to the 0 . 12 increase for the same exposure t ime on the Lunar Orbiter, a substantial difference in the results of these two flight experiments is clearly shown. (14) The OS0 experiments were in a near-earth environment, below the earth's Van Allen belt, and therefore exposed primarily to U V 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 processing 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 degradation rates; therefore the change must be attributed to the environmental parameters . (14) There appears to be a definite difference in the degradation ra te of thermal-control coatings between the near-earth orbital environment 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 sample types. (3) Figure B-27 shows the effect of 50-keV electrons on an early formulation of S-13G coating after electron bombardment. (25) The decrease in reflectance was 11 percent at 590 mp a f t e r 6 x 1014 e/cm2, and 20 percent at 2100 m p after the same dose. Initially a rapid decrease of reflectance in the IR region occurred, which eventually tended to saturate. However, in the visible region, the buildup of damage was slow at first and then more rapid at high expo sur e. ( 5,

Coatings S-13, S-13G, and Goddard 101-7 (treated ZnO/methyl silicone) were exposed to 20-keV, 5O-keV, and 80-keV electrons separately to

3 4

doses of 1 0 l 6 e / c m . ( 2 7 ) It may be seen in Figures -B-28 to B-30 that these coatings are susceptible to electron damage, particularly at the higher energy levels. It was found that after exposure to 20-keV electrons, samples (maintained in a vacuum and not exposed to light) partially recovered in reflectance values. However, exposures to the same dose had the same re- f lectance values regardless 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 ) It was also exposed to 10-keV proton, UV, and combined (sequential) proton and UV(22) at room temperature and torr . The effect of proton radiation on this material 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 continuous 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 apparently occurred.

The S-13G coating was tested for the effects of thermal cycling. Test cycle consisted of holding 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 1 7 . 5 hours. Coatings were thermally cycled 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 catalyst . ( 26) The formulation follows:

Pigment ZnO (potassium si l icate-treated SP- 500) Resin RTV-602 (GE) Catalyst 0 . 2 percent 1, lY3,3-tetramethyl guanidine (TMG)

35

The stability of the paint to ultraviolet is indicated i n the following data:(26)

Initial absorptance 0 . 194

nas after 0 . 55 ESH UV 0 . 003

nas after 2 . 2 ESH UV 0 .005

A a S after 8. 8 ESH UV 0 . 0 0 7

Aa, af ter 125 ESH UV 0.028

A a S after l O I 4 50-keV e lec t rons /cm 0 . 0 0 7

Reflectance curves showing the wavelength at which damage occurs a r e shown in Figures B-34 and B-35.

Initial absorptance/emittance of flight coupons carried on Lunar Orbi ter I V a r e 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 degradation of B-1060 is also shown in Figure B-24. In 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 a re l i s t ed below in order of increasing degradation experienced in 1000 equivalent full sun hours of flight:( 26)

A a , After Coating 1000 Sun Hours

2-93 (McDonnell) SP-500 ZnO dispersed 0 . 049 PS- 7 potassium si l icate

Silicone Over Aluminum RTV-602 over aluminum foil, 0.081 (Boeing) 0 . 15% TMG

Hughes Inorganic H-2 T i 0 2 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 Figures 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 anticipated 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 heating.(9) In general, these coatings show good stability in the U V 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 degradation. The pigment is very susceptible to proton damage. ( 2 2 ) The coating is resistant to nuclear radiation ( l o 8 rads) and to a combined nuclear and UV environment.

Lockheed developed a coating known as Thermatrol 2A-100 which consisted 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 pigment consists of 94 percent Ti02, 1 . 8 to 2.4 percent A1203, 0 . 6 to 2. 0 percent Si02, and 0 . 5 to 1. 4 percent ZnO. ( 2 8 , 2 9 7 30) The a s / € ratio of the paint is 0 . 19. It can be applied as a paint and cured at room temperature or used as a precured tape with a pressure-sensit ive si l icone adhesive.

Several modifications have been made to improve the coating, and some of the data which follow are for earlier formulations. However, on the basis of available information, it is believed that the conclusions are applicable to the current commercial product. I t is known that the surface treatment 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.

Thermat ro l 2A-100 was exposed to a xenon source (AH-6 lamp) a t a l -sun level ( 0 . 20 to 0.40 p) for 500 hours in a vacuum at a temperature of 395 K (122 C ) . In situ values of before and after exposure were a s = 0 . 18 and 0 . 32, respectively. (z7) The total hemispherical emittance remained essentially constant at 0. 85 f 0 . 003 for the two samples tested. The change in solar absorptance appeared to reach a saturation value of 0 . 14 after 300 to 400 hours of exposure at this temperature. ( 2 8 )

In another test, only slight damage was found when a Ti02 /si l icone ( T i P u r e R-960 in RTV 602 silicone) coating was subjected to 190 sun hours UV at room temperature and torr . (22 ) See Figure B-36.

3 7

A rutile Ti02/methyl si l icone ( G E RTV 602) coating was found to offer the best stability of the white diffuse coatings to an electron environment (20 keV, 50 keV, and 80 keV), providing a dose above lo1 e/cm2 was not encountered. (27 ) However, at 10 l6 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 / c m 2 . Compare Figures B-37 and B-38. Titanium dioxide-methyl silicones were found to be less sensi t ive 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 radiation resistant of this type coating were the rutile titanium dioxide-GE RTV 602 methyl silicone and rutile Ti02-Dow Corning X R 6-3488 methyl silicone coatings. However, the TiO2GE RTV 602 appeared to craze when subjected to 1015 p/cm2 at 22 C. Figure 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 character is t ic peak of ZnO but does not return to near zero in the visible range a s does the ZnO. ( 2 2 )

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 electron exposure. All UV exposures were 18 ESH and all electron exposures were 5 x e /cm2 ( E 50 keV). Samples receiving sequential exposure remained in si tu between exposures. All reflectance measurements were made in si tu.

As may be seen in Table B-4, reflectance changes from combined exposures are less than additive,with consecutive exposure (UV followed by electron) causing significantly less damage than simultaneous exposure. In 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 a t 250 mp, 67 percent at 425 mp, and 2 percent at 2100 m p ( U V , visible, and IR wavelengths). ( 2 5 )

This coating when subjected to 20-keV protons reached threshold damage a t 1014 p/cm2, moderate damage at 1015 p/cm2, and sustained severe degradation at 1016 p /cm2. ( 3 )

Thermatrol 2A- 100 was exposed to nuclear radiation, 1.3 x l o 8 rads ( C ) , 1 . 9 x 1013 n/crn2 (E<0.48 ev), and 5 .6 x lO14n/cm2 (E>2.9 MeV).

38

N o 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 extravehicular activity period, the astronauts removed the samples along with samples of ZnO/K2Si03 and chromic acid anodized aluminum. These specimens were the f irst 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 ablative materials

Pyrotechnic discharge products

The natural space environment.

Degradation of the titanium dioxide-silicone coating resulted in a 42 to 6 7 percent in absorptance increase, and in a sl ight increase in emittance. Absorptance increased from 0 . 24 to between 0 . 34 and 0 . 40. Emittance in- c reased f rom 0 . 86 to 0 . 88. Although degradation occurred, the absolute values were well within acceptable limits for the Apollo lunar-landing missions. ( 3 2 ) It 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 Ti02 (Titanox AMO) in Dow Corning Q92-090, a methyl silicone, was tested on the ATS-I satellite. ( l 9 , 20) In this f l ight, a / € for this coating increased over 200 percent. See Figure B-41. This was more than had been anticipated from laboratory measurements.

Hughes Organic White Paint (H-10)

This coating is made with a calcined china clay (Plasm0 clay, which is primarily aluminum sil icate) dispersed in General Electric RTV-602 si l icone resin. Init ial solar absorptance as a function of wavelength is shown in Figure B-42. I t was tested on the Lunar Orbiter V and found to be equivalent

39

to the S-13G coating. Initial absorptance/emittance values are given in Table B-3. Solar absorptance, as, obtained in the laboratory was 0. 147 and, a f te r 1000 sun hours of flight on the Lunar Orbiter V . A a S = 0 . 120. ( 2 6 ) 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 in reflectance after exposure to 1017 p/cm2 (E = 20 keV). Exposure was at 22 C . The losses were confined to wavelengths shorter than 0 . 7 microns . On the other hand, reflectance as measured in situ increased at wavelengths longer than 0 . 7 microns. Thus a determination of solar absorptance 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 t o be extremely resistant to reflectance 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 / c m 2 and only small changes were observed after 8 x 1015 e / cm2 . At 2100 mp, reflectance decreased 3 percent after exposure to 6 x e / c m , 2

and 8 percent after 8 x 1015 e/cm2.

Exposure to UV resul ted in the fol lowing decreases in ref le~tance:(~)

Exposure, Decrease (Increase) in Reflectance, percent ESH 250 m p 425 m p 2100 m p

135 2 50 49 0 770

1130

10 13 17 ”

24

Silicone Over Aluminum

Lunar Orbiter V ca r r i ed a specimen of 1/4-mil 1145-0 aluminum- alloy foil over which was applied 3. 8 mi ls of RTV-602 silicone catalyzed

40

with 0. 15 percent TMG (1, 173,3-tetramethyl guanidine). Figure 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 exposure measured in si tu. The data show no measurable degradation of the silicone after 336 ESH of UV. The 1141-ESH exposure resulted in an increase in absorptance below 540 millimicrons and a decrease in absorptance above 540 millimicrons, with a net A a of 0.012. Laboratory in si tu degradation of the silicone-aluminum coating is plotted in Figure B-47. It 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 is less costly to apply than any of the other coatings tested on Lunar Orbi te rs 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 Orbiter V a r e shown in Figure B-23.

Silicone-Alkyd-Modified Paints

Fuller Gloss White

Fuller Gloss White is a Ti02-pigmented silicone-modified alkyd coating in production use that requires a 465 F cure. Its initial solar absorptance is 0 . 25 while its initial hemispherical emittance is 0 . 9 0 . 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 algebraic Sums of the two individual environments in sequential exposure ( U V followed by electron) .

Lockheed found that absorptance changed by 0 . 0 9 f 0.05 af ter 2000 sun hours. Tested for thermal-cycling resistance, the coating cracked and showed a loss of adhesion after 170 cycles of -240 to 70 F, taking 18 minutes per cycle. (33)

Ascent temperature is l imited 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. ( 3 3 ) Solar absorptance before and after irradiation was 0. 26. Hemispherical emittance, 0. 84, was unaffected. ( 3 ')

An exposure of 850 sun hours in vacuum caused a change of solar absorptance from approximately 0 . 2 5 to 0 . 3 2 . (See Figure B-48). 0 tical - property degradation was marginal in the UV-only environment. ( 3 1P

P V - 100 (Ti07 in a Silicone Alkyd Vehicle)

General Dynamics tested PV-100 coating, manufactured by Vita-Var Paint Company, and found that it was degraded by 10l6 p/cm2 (E=3 keV) in the visible and IR regions. (34) See Figure B-49. Spectral reflectance also decreased in these regions when the coating was subjected to electron 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 acrylic paint used as a thermal-control mater ia l 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. Initial total hemispherical emittance is 0 . 86. It 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 irradiation, the paint degraded more than the results of the two environments separately would predict. Small blisters were formed on the Kemacryl coating. It was believed that these were most l ikely caused by electron-induced decompositon products. It was concluded that these surface alterations had no detrimental effect on the mechanical integrity of the coating. It 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 reported as/€ as increasing f rom 0. 30 to 0. 35 after 100 hours and 0.40 after 850 sun hours, respectively. The maximum allowable ascent temperature was given a s 450 F providing alterations in surface finish, and solar absorptance due to bubbling can be tolerated. Otherwise the maximum temperature

42

I

encountered must be less 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 subjected to nuclear radiation in vacuum. ( 2 5 ) Emittance did not change. Data shown in Figure B-52 indicate an increase in as f rom 0.28 to 0 .32 after an exposure of 5 x 107 rads (C), but no further change at 2 . 5 x 108 rads (C) . (3 l ) However, degradation of optical propert ies was considered unsatisfactory after l o 8 rads .

U V exposure of 1000 sun hours increased as from approximately 0 . 26 to approximately 0.38. (31) See Figure B-48. In combined nuclear and UV radiation, this paint turned brown and bubbled. ( 3 1 ) 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 Air Force Base was subjected to 10l6 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 excellent f i lm-forming characterist ics and good UV stability. ( 3 6 ) It surpasses the acrylic polymers in adhesion and f lexi- bility, but its stability t o the heat which may be encountered during ascent conditions rules it out as a good candidate for a surface coating for outer space use. Its softening point is approximately 125 C . A further limitation is the existence of two moderately strong absorption 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. ) . It cures at

43

room temperature and has an init ial solar absorptance of 0. 25 and an init ial total hemispherical emittance of 0 . 9 1. I (37) It i s s table to e lectron bombardment, but degrades under UV irradiation. Lockheed reports init ial a s / € as 0. 24; change in absorptance ( b a s ) is reported as 0 .35 f 0. 06 after 2000 sun hours. (9) The maximum allowable ascent temperature is 450 F. (9)

Skyspar was flown aboard OSO-I and OSO-I1 Satell i tes. Agreement between laboratory tests and flight tests was extremely poor, varying several o rde r s of magnitude. However, agreement between the OSO-I and OSO-I1 data was excellent. ( 2 1 ) The main cause of coating degradation during near- earth satell i te experiments can be attr ibuted to absorbed solar-UV radiation since low-energy solar-wind protons are effectively shielded from the orbits of the satell i tes, OSO-I and -11 and Pegasus I, 11, and 111, by the ear th 's magnetosphere. It is believed that inadequate simulation of solar-UV radia- t ion is the main factor in the presently observed discrepancy between f l ight and laboratory data. Another factor is the lack of temperature control in the laboratory tes ts .

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 IR, whereas photons of greater energy produced damage primarily near the UV absorption edge. (38) Figure B-54 shows the absorptance changes due to irradiation with a band centered at 260 m p 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 absorptance extended through the visible and near-IR regions, and the sample exhibited 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 in Figures 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 o 6 rads (C) , 0 . 6 x 1013 n /cm2 ( E < 0.48 eV), 1 x 1014 n /cm2 ( E > 2.9 MeV). Changes in as a r e 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 o 7 rads (C) , as of this mater ia l changed f rom 0 . 23 to 0 . 3 0 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. Its reflectance does not vary with wavelength, thus the coating is insensit ive to spectral discrepancies between the sun and a solar simu- la tor . ( 18) It was one of the test surfaces on the Mariner IV absorptivity standard, and data indicated good coating stability in the space environment. On the Mariner V flight, this coating showed an unexpected apparent bleaching of approximately 4 percent. It 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 serious 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 properties are as follows:

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

Inorganic 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 is sodium silicate. Of these silicate coatings the most important has been lithium aluminum silicate paint.

Lithium Aluminum Silicate Paint (Lithaf rax)

This coating consists of commercial l i thium aluminum sil icate (Litha- f r a x 2123) in a silicate binder (sodium silicate D). It requires a 390 F cure and has the composition 4(Li20. Al203.8Si02)Na2Si03. Initial 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 U V resistance of the paint. In addition, the paint cannot be adequately cleaned once it i s contaminated or soiled after application. Consequently, extreme care must be taken to prevent contamination 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 resis tance 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 irradiation. I t will survive a 230 C ascent heating environment with no change in optical properties.

Although Lithafrax is 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 af ter the sequential exposure of electron and UV was less than the sum of the separate effects of electron bombardment and UV radiation.

A Lithafrax/sodium si l icate coating was subjected to nuclear radiation and to a combination of U V and nuclear radiation while in a vacuum, I r radiated to a dose of 5 x l o 7 rads , this coating changed in a, f r o m 0. 14 to 0.20. At a dose of 2 x lo8 rads , as was equal to 0.28. (31) Hemispherical emittance, 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 severely in a nuclear environment. It was found that there was no isotope dependence in optical degradation. ( 3 1 ) Figure C- 1 shows a comparison of the separate effects of UV and nuclear irradiation with the effect of concurrent irradiation for the Lithafrax/sodium silicate system. Although the exposure doses were not given, based on related data, it is probably that the nuclear exposure was 1.5 x 1013 n / c m 2 (E < 0.48 eV), 4. 3 x 1014 n / c m 2 (E > 2 . 9 MeV), and 1.4 x lo8 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 / c m 2 (E < 0.48 eV), 4.6 x 1014 n / c m 2 (E > 2 .9 MeV), and 1. 1 x lo8 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 irradiations cannot be used to predict degradation when the two radiat ions are concurrent.

Synthetic Li/Al/SiOq Coating. Lockheed reported a research coating that contained synthetic Li/Al/SiOq and cured at room temperature. (37) Initial solar absorptance was 0. 16, and initial total hemispherical emittance was 0.87. In general there was not much difference between this coating and the commercial Lithafrax coating. Its advantage l ies in i ts room- temperature cure .

The effect of nuclear radiation in vacuum on the synthetic Li/Al/SiOq/ sodium si l icate system was similar to that on Lithafrax. A dose of 1. 3 x 108 rads ( C ) gamma, 8 .2 x 10 l2 n / cm2 (E < 0.48 eV), and 5.3 x 1014 n / c m 2 (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 primaril aluminum sil icate, in Sylvania PS-7 electronic-grade potassium silicate. The pigment contains 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 is applied with an air brush; the first two coatings are each baked for 1 hour a t 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. 0 1 (Gier-Dunkle spectrometer) and emittance was 0. 89 f 0.04. (30) The coatings were thermally cycled 4 t imes f rom 533 K to 83 K. There was no evidence of cracking or spallation. How- ever , severa l a reas of a slightly brown color appeared. The increase in solar absorptance, Oa,, was between 0.04 and 0. 07. (I6) After 540 solar hours in vacuum, solar absorptance of a 6.4-mil sample increased f rom 0. 18 to 0 .22 , and exposure to the same number of hours in air gave a solar 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 IR region. (16) The spectral damage found in this test corresponds to that found in normal measurement tests in air . ( 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. In contrast, damage in the near U V 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 combined electromagnetic and particulate radiation (UV with protons alone or U V t protons t electrons). (40) Test conditions are given in Table C- 1 and da ta a re shown in Figure C-4. In this work there were no significant differences 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 electrons enhanced the stability of reflectance.

The 0.4-micron region in aluminum o ~ d e is not a t the band gap. The reflectance change has the characterist ics of a color center in that the magnitude of change is an apparent function of radiation. It could be either a I 'physics' ' color center, i. e., belonging to the general F o r V center c lass i f i - cation, or a "chemical" color center, i. e . , a function of the appearance of a new chemical impurity formed as a resul t of ionization, oxidation, or migration of an original impurity in the material . Thus in an aluminum oxide {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 color center in the near UV.

Three coatings, A1203/K2Si03 , (Ti02 t A1203)/K2Si03 , and (ZnO t T i02 t A1203)/K2Si03 were tested f o r stability to space environment on the ATS-I satellite. Absorptance increased considerably; much more than was anticipated from laboratory tests. ( l 9 , 20 ) Data a r e shown in Figures 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 is Metals and Thermit 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 approximately 12 hours. (30) The original coating has a solar absorptance of 0. 14 f 0. 02 (Gary) o r 0. 14 f 0. 01 (Gier Dunkle) and a hemispherical emittance of 0. 89 f 0.03 according to Smith and Grammer. (30)

Samples 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 electron bombardment or UV radiation. (37) It should be noted, however, that this work was not done in situ and therefore is on1 indicative of the stability of this coating, 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 Z r 0 2 - 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 simulated solar UV, solar-wind protons, and combined UV and 230-keV protons, Van de Graaff protons, and 1-MeV electrons. It has also demonstrated resistance to neutron/gamma radiation. (41)

Zinc Oxide in Potassium Silicate (2-93)

This coating is very stable in the UV and electron environment, ( 4 2 ) but is damaged by proton bombardment. ( 13) I ts use with satell i tes has been limited because of difficulties encountered in its application and to the diff i - culty of keeping it clean during preflight construction and activities. (42 ) However, it i s used where surfaces are i r regular , and on nuts and bolts and other hardware on which it i s difficult to apply coatings other than paint, A l - 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 increases in solar absorptance after 3000 ESH. Flight 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 is in 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 a r e shown in Figure C-11. The initial solar absorptance as a function of wavelength is 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 IV and V flights. Absorptance/emittance ratios, a,/Eh, as a function of sun exposure are shown in Figure C-13. Orbiter 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 contamination:

Plume impingement from the tower jettison and Saturn I1 retromotors and from the service-module and lunar-module reaction-control-system engines

Boost heating effects

Outgassing products of ablative materials

Pyrotechnic discharge products

The natural space environment.

A comparison of preflight and postflight results show that the degradation of the ZnO/KzSi03 coating ranged from 25 to 40 percent increase in absorptance. Absorptance, as increased f rom 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 ) It should be noted, however, that the retrieved samples were not returned under vacuum conditions and therefore 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 var ious regions of the U V on the solar absorptance of 2-93 coating was determined. ( 2 1 ) Table C-3 and Figure C-14 show the changes in Aas caused by the various regions of UV radiation. As is 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 barrier - layer anodized aluminum coating. (43) A plot of the change in solar absorptance versus integrated proton f l u x of 8-keV protons is shown in Figure C- 15. It 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 in solar absorptance greater than 0.01) was in the order of 3 to 7 x 1 O 1 j p / c m . 2

In another experiment, the coating was exposed in situ to particulate exposure (protons alone or protons plus electrons) and to combined electromagnetic and articulate exposure ( U V with protons or UV with protons and electrons). (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 increase in reflectance below 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 increased coloration at the band gap, but it also bleached the visible and near IR. 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. In these tests, the addition of electrons 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 IR portion of the spectrum. (22 ) .

In the proton-only environment, damage to the silicate-coated zinc oxide is 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 absorption 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 comparison of the proton-only spectral changes a t 4 2 2 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 solar radiation and an integrated exposure of 2 x 1015 p / c m 2 (E = 10 keV) at the th ree t emperah re - are shown in Figure C-21. (45) The dominating influence

52

of the ultraviolet radiation at elevated temperatures results in 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 Inorganic Paint (2-93 Type). This was coated 5 mils thick on 0~. 016-inch 6061 aluminum sheet. After 200 hours U V (compact-arc xenon source, irradiation intensity of 1 ESH) in vacuum, solar absorptance increased 10 percent. No change was observed when air was introduced. (46)

" _ .~ . Titanium Dioxide in Potassium Silicate

Hughes Inorganic White (H-2) is made with Cabot R F - 1 titanium dioxide dispersed in Sylvania PS-7 potassium silicate. Initial solar absorptance as a function of wavelength i s shown in Figure C-22. I t was tested on Lunar Orbiter IV and was found to be about equivalent to the silicone-aluminum and B-1060 coatings. ( 2 6 ) Initial absorptance and emittance values, both laboratory 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 IV and V flights. (See page 3 6 . ) Flight data for Lunar Orbiter I V a r e given in Figure B-22.

- - . -. - - Lanthanum Oxide in Potassium Silicate

This coating is susceptible to UV damage, but is less susceptible to proton damage. Increasing 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 including both proton and UV radiation roduced comparable damage to the sum of the individual environments. (f2) However, s o drast ic i s the U V - only degradation that it completely dominates the combined environments picture. (44)

53

Oxide Coatings

Rokide C

Rokide C is essentially chromic oxide (85 percent C r 2 0 3 ) flame sprayed by Norton Abrasive Company(9) at room temperature , a s = 0.90 and E = 0.85. The green coating i s extremely hard and is very inert chemically. There is no degradation of optical properties result ing from U V 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 is the use of a n i - 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 metallic 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 is an excellent reflecting material f o r 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 IR. Therefore, polished aluminum which has been anodized is expected to have a double surface effect because the polished aluminum reflects the solar radiation which is per- mitted to penetrate the aluminum oxide coating. (5) An oxide coating of sufficient thickness i s opaque in the long-wavelength IR 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 emittance. Emittance appears to be highest in the cryogenic-temperature range.

Vacuum-thermal exposure produces two major results. Water present in the oxide i s partially driven out as is evidenced by the reduction of the absorption band at 3 microns. A decrease in the reflectance in the visible spectrum was the most pronounced effect. (5) See Figures C-25 and C-26.

54

Since the distribution of energy of a 65 C surface (based on black-body radiation) peaks at approximately 8.4 microns, the reduction of the water - absorption band has very l i t t le effect on the emittance of the anodized- aluminum coating used at this temperature.

The optical properties of the bright anodized-aluminum system were only slightly,altered by UV radiation in 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 ' exposure. There appears to be a leveling-off beyond the 120 hours. This yellowing causes the ratios to double (0. 19 to 0.42) after exposures up to 120 hours. Table C - 4 and Figures C-27 and C-28 show the effect of vacuum- U V on 0.5-mil sheet.

Preliminary data indicate there is only a slight change in the optical propert ies 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 emittance for various coating thicknesses after irradiation.

Anodized aluminum was unaffected by a dose of 1016 p / c m 2 (E = 3 keV) and unaffected by electron exposure as far as spectral reflectance at a dose of 4 x 1016 e / c m 2 (E = 145 keV) . (34)

The synergistic effects of simultaneous 145-keV electron and UV radiation on the spectral reflectance of barrier-anodized aluminum and sulfuric acid-anodized aluminum along with aluminum oxide-potassium silicate thermal- control coatings were investigated at 77 K . (4) Damage to the sulfuric acid- anodized aluminum specimens was produced primarily in the wavelength region below 0. 7 microns, with only small changes evident at longer wavelengths. An increase in as of 40 percent was induced by 350 ESH of U V , while 5.8 x 1015 e/cm2 produced no change in as. Simultaneous irradiation to approximately the same doses resulted in a 35 percent increase in a s ,

Barrier-anodized aluminum was found to be very resistant to both UV and electron radiations. (4) An increase of 12 percent in as was produced by 350 sun hours of UV, while 5.8 x 1015 e /cm2 resu l ted in an 18 percent in- c r ease i n as. These changes were again exhibited primarily in the wavelength region less than 0. 7 micron.

The effects of electron and UV radiations on these materials are shown in Table C-6. Samples were prepared on 10-mil 1199 aluminum substrates.

55

Charged-particle and gamma-radiation tests were run on ba r r i e r - l aye r 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 particles/cm2 and cobalt-60 gamma-radiation 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:

Integrated AaS a t Type of Energy, Flux, Dose, Maximum

Radiation MeV par t ic les /cm2 roentgens Exposure -

Protons 1 - 9 x 1 0 -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 . 0 3 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, is produced commercially by the Aluminum Company of America. The thick, porous oxide layer is formed by an extensive dis- solution of aluminum in a fluoboric acid solution and is then sealed in an oxide hydration using deionized water. Its 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 is produced commercially in large quantities, variation in UV stabil 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 is of cri t ical importance. (47)

The coating was tested on the ATS-3 and it was found that most of the damage was caused by UV irradiation ( X > 160 mp). The loss in reflectance

56

I

was res t r ic ted to wavelengths less than 1200 mp, and laboratory testing has shown that this is caused by an increase in the absorptance of the A1203 film which begins in the near UV and progresses toward longer wavelengths with ' increased exposure. See Figures 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 results are not generally applicable, but they serve as a good indication of what may be expected of this material . (47)

Alzak coatings were subjected to 20 and 80-keV-electron radiation. It 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 irradiation on a 0 . 2 9 - m i l anodized aluminum (Alzak) i s shown in Figure C-33. Changes in the UV, visible, and IR portions of the spectrum with irradiation are as follows:(25)

Decrease (Increase) in Reflectance, 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- ium ta r t ra te . This coating showed no change in as in 1580 ESH.

Chromic acid-anodized aluminum was exposed to space radiation on Apollo 9 spacecraft. Samples were retrieved in space for postflight tests. Absorptance increased from 0. 70 to 0.73, an increase of 4 percent. Emit- tance decreased from 0.73 to 0.70. (32 ) (Note: samples exposed to air before changes in absorptance determined. )

57

Chromate Coatings (Alodine)

Alodine A-1 and A-2, two chromate finishes on aluminum, were subjected 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 . 0 1 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 IR radiation changed a maximum of 7 percent with hydrogen-ion bombardment. (48) It should be pointed out, however, that the data obtained were not in situ.

Composite Coatings -

Several composite systems show promise as thermal-control coatings. In general, these consist of a reflecting substrate coated with a semitransparent dielectric film. The reflectance of the metal substrate controls the solar absorptance, and the thickness of the transparent o r semitransparent dielectric film governs the emittance. ( 3 6 ) These films are f requent ly prepared as tapes which are bonded to the surface of the space vehicle by means of a pressure-sensitive adhesive.

Second-Surface Mirrors

Transparent or semitransparent films with a reflecting substrate are known as second-surface mirrors . Some are ceramic mirrors having dimensions about 1 x 1 x 0.008 inch and are applied to the substrate with an adhesive. Others are flexible films with a reflective metal backing which has been applied to the film by vapor deposition. Following are discussions of several types of second-surface mirrors .

Series-Emittance Thermal-Control Coatings. General Electric developed a series of such coatings. ( 3 6 ) The films suggested include Teflon, a vinyl silicone (GE 391 - 15 - 170, formerly known as PJ 113), and Butvar (polyvinyl 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 evaluated and appear to have merit . These are Dow Corning's D.C 281 silicone adhesive and Minnesota Mining's Y9050U. The la t te r i s a double-faced pressure-sensit ive tape. I t is essentially a silicone-impregnated fiber-glass cloth which is laminated to the metal surface. (36) These lat ter two adhesives failed not in shear, but by peeling as a leading edge was raised when subjected to a simulated ascent heating.

According to Linder it is theoretically possible to achieve any a s / € ratio 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. ( 3 6 )

Additional advantages of this type of system include (1) the ability to select coatings having lower emittances with the same a s / € ratio will minimize the radiant-heat loss from the vehicle and therefore will 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 Figure C -34 show the variation in total normal emittance 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 reflectance 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 extremely resistant to UV degradation. A program to develop a technique for applying this material in controlled thicknesses to a metal foil is being developed. It 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 absorptance of either of these systems were observed with exposures up to 1000 ESH and 100 megarads (C). There are indications, however, that as exposure is continued, the absorption edge of the dielectric tends to shift to longer wave lengths. A typical curve of UV reflectance 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 in 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 is better than that of TFE Teflon. In vzcuum, F E P i s only slightly better than TFE, but both are stable to approximately 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 lvered Teflon. After exposure to 1015 e / c m 2 (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 ( a s ) was detected until a f te r a dose of 3 x 1015 p / c m 2 ( 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-exit temperature from the chamber. Vacuum levels during the exposures were 1 to 2 x 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/ (c rn2-s ) .

Aluminized Teflon was used as the outer portion of a thermal shield on Mariner I1 and Mariner V. The thermal shield consisted of 18 layers 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 mirror with 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 temperature transducer was taped to the bottom side of the aluminized Teflon. The reported data were assumed to be the measured temperature of the sunlit F E P Teflon sheet. This assumption appeared to be supported by the data obtained.

60

Early mission data shown in Figure C-39 show that the FEP Teflon degradation followed a typical rate characterist ic of low U / E materials, with an init ial relatively high rate, decreasing as degradation progressed. However, 'approximately 45 days after launch, the rate began to increase again as can be seen in the shape of the curve in Figure C-39. The beginning of this increase in rate was coincident with a Class-2 solar flare, the radiation products 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 (approximately 400 to 1100-km polar orbit). Prior to launch, as measured as 0. 085. After approximately 4600 hours of solar exposure, no increase in as was detectable. ( 49)

Polyimide /Aluminum. Kapton H-film (polyimide) with an aluminum backing was also tested for use similarly to aluminized Teflon. This material has excellent high-temperature properties, good radiation resistance, but i t i s affected by UV. Although this film shows some reflectance loss in the UV, i ts moderate reflectance changes, both increases and decreases, in the visible and IR 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. ( G O )

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 in 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 / c m 2 ( 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 losses were in the vis ible and near-IR regions. Decreases in reflectance were as follows: (25)

61

Decrease in Reflectance, percent (AR = R i - R f )

Dose , e /cm 2 590 mp

1 x 1013 0 2 x 1014 4 6 x 1014 13 8 x 1015 6 0

2100 m p

"

0 0

- -

When subjected to UV radiation alone ( in si tu), decreases i n the reflectance changed as follows: (25)

Decrease ( Increase) 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 = R i - R f ) - 250 m p 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. ( 5 0 )

Polyimide film has a lso been used as a backing for a second-surface m i r r o r , S i 0 on aluminum. This composite consists of a 10,500 A Si0 ove r - coat on 1200 A aluminum vapor deposited on 1. 5-mil Kapton (polyimide), an experimental film supplied by G. T. Schjeldahl Company, Northfield, Minnesota. It was subjected to proton and electron radiation, exhibiting little change in reflectance in the U V and visible regions after receiving a dose of 1016 p / c m 2 (E = 3 keV).(34) (See Figure C-42, ) There was a slight reduction in spectral reflectance in the UV when exposed to 1.3 x 1 0 l 6 e / c m ( E = 145 keV). It i s badly degraded in UV irradiation, appearing slightly yellow-brown. (34) (See Figure C-43. )

Silicon monoxide coatings are more susceptible to 320 ESH of U V radiation than to either 1. 3 x 10 l6 e / cm2 (E = 145 keV) or 1 x 1 0 l 6 p / c m 2

6 2

(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 coatedwith surface layers 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 aluminum are silicon oxide (SiO,), silicon dioxide (SiOz), aluminum oxide (A1203)) and magnesium fluoride (MgFZ).

Silicon Oxide (SiOx). The most frequently used surface film f o r controlling the temperature of satellites has been silicon oxide (SiO,) produced by evaporation of silicon monoxide in the presence of oxygen or air. Re- commended deposit ion parameters are rates of 3 to 5 A / sec at about 8 x 10- 5 to r r of oxygen or 1 to 2 A / sec a t 1 x to r r of a i r . Films of this mater ia l show rather high absorptance in the near and far UV. However, -

this undesired absorptance is claimed to be eliminated by UV irradiation in air. ( 5 2 ) 53)

By increasing the thickness of reactively deposited silicon oxide (SiO,) on aluminum from zero to 32 quarter-wavelengths (X/4), E increases from 0. 017 to 0.53 and a / € can be varied from about 5 to 0. 2 . (53 ) Exposure to U V in air virtually eliminates the init ially high U V absorptance of this coating without changing the IR 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 U V i r radiat ion in a i r , a was found to change f rom 0. 128 to 0. 110. These coatings have been used as temperature-control surfaces on many satell i tes, and there are ample laboratory and f l ight data to show their high stability in space environment. (53)

Temperature data f rom Explorer XXIII 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 ~ ) o v e r opaque evapcjrated aluminum 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 a r e shown in Figure C-44. This coating was about equivalent with the A1203/Al coating and was one of the more stable materials.

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 is essentially transparent to solar radiation but has a strong absorption band at about lop. By controlling the film thickness of this system, one exercises control over IR 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 ) It 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 SI0 in an oxidizing atmosphere or by subsequent oxidation of an evaporated S i0 l ayer . Upon irradiation the transparent SiO, film loses oxygen and reverts to the s t raw-colored Si0 with resul t ing increase in solar absorptance.

Silicon Dioxide (Si02). Si02 films have strong absorption bands in the IR 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 large ref lectance decreases can be observed in the IR region. Figure C-45 shows the IR reflectance from 5 to 40 ,u for aluminum coated with 0.40, 0 .97, and 2.59-p films of SiO2.

Figure C-46 shows that interference effects produce a maximum 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 in a i 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 f requent ly used ( X = 550 mp). For this range of Si02 thickness, E and 6, (normal emissivi ty) of SiO2/A1 increase with increasing temperature in the temperature range measured, This is a very desirable property for a temperature-controlling coating since i t provides a certain amount of self-regulation of the satell i te temper- a tu re . Fo r a satellite coated with A1 and 6 X/4 of SiO2, an increase of the shell temperature from 10 to 20 C may be predicted to occur during 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 propert ies f rom the UV to the far IR were observed. It appears that U V irradiation is the main 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 irradiation, similarly to that observed with UV irradiation.

SiO2-coated aluminum samples were subjected to UV irradiation in 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 performed in two stages using f irst 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 samples, the reflectance decrease 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 IR reflectance and E: of the Si02-coated aluminum were found to be unaffected ,

by U V irradiation.

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 U V t ransparent films of A1203 and Si02 by evaporation with an electron gun has been developed. Because of their hardness, chemical stabil i ty, and excellent adherence, these two film mater ia ls are sui table as protect ive layers for a luminum, f ront-surface mir rors , espec ia l ly i f high reflectance in the UV is required. (52) The fact that the optical properties of vacuum-deposited A1203 and S i02 a r e less dependent on the preparation conditions than those of Si02 prepared f rom S i0 makes these film materials more suitable for many optical applications.

Aluminum Oxide (A1203). Aluminum overcoated with A1203 degrades less than that with Si02 under identical UV irradiat ions. (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 g r e a t a s 1017 e / cm2 . (3 ) Exposure was to 20-keV electrons at 22 C.

Vapor deposited A1203 (1. 1 p ) on opaque evaporated aluminum was tes ted for UV stability in the laboratory and on the ATS-I. The initial a s / € was 0. 54 as measured in the laboratory, and 0.59, measured 48 hours after launch. ( l 9 ) The changes which occurred in flight on the ATS-I a r e shown in Figure 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 is not used as a thermal-control coating, but is 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 silver from atmospheric contaminants. I t was included 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 interference maximum 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 combination.

The ATS-3 data have shown that MgF2-coated silver is 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 aluminum mirrors used in far UV, orbiting telescopes. Therefore it is important that the correlation between preparation techniques and environmental 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 r rad ia t ion as indicated by the shielded-sample data. (47) The unshielded samples, however, degraded severely, and the loss in reflectance increased with decreasing wavelength. The change showed no signs of saturating after l year

66

I

I

in orbit and may be increasing 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 environment may explain some of the disagreement.

Optical Solar Reflector. Two versions of the optical solar reflector have been developed at Lockheed Missiles and Space Go. (2) The first consists of vapor-deposited silver on Corning 7940 fused silica with an overcoating of vapor-deposited Inconel. The second is vapor-deposited aluminum on Corning 7940 fused silica with an overcoating of vapor-deposited silicon monoxide. The front surface of these mir rors cons is t s 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 Inconel 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 minimum cure of 14 days at room temperature to minimize outgassing during ascent. Reflective properties are as foll0ws:(9,5~)

Optical Solar Sample Reflector - Temperature , R a s € as / E

Silver 325-530 0 . 0 5 0 f 0 . 0 0 5 0. 81 0. 062 26 0 0.744 f 0 . 0 1 36 0 0.800 f 0 . 0 1 46 0 0.807 f 0.015 56 0 0 . 7 9 5 f 0 . 0 2 66 0 0 . 7 9 0 f 0.02

Aluminum 325-530 0. 100 f 0.005 0. 81 0. 124 26 0 0.744 f 0 . 0 1 36 0 0.800 f 0 . 0 1 46 0 0.807 f 0.015 56 0 0.795 f 0 . 0 2 66 0 0 .790 f 0 . 0 2

6 7

These optical solar reflectors (OSR) are fragile and should be protected from mechanical damage during storage and shipping. Surface contamination, including fingerprints, oil, dust, and atmospheric weathering, does not cause permanent degradation after application. However, contaminants 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 in a l l charged-particle environment and combined environments of space. These coatings have been extensively investigated and have never been damaged. ( 2 , 9 , 1 3 ) (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 Inconel overcoat) in 1580 ESH. ( 1 3 )

Solar-Thermoelectric Systems

Another composite is the solar-thermoelectric system reported by Schmidt and Park at Honeywell, Inc. (54) These multilayer coatings consist of transparent molybdenum films between nominally quarter -wavelength- thick dielectric spacers of such materials 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 primary cri teria for material selection are:

Substrate - high reflectance in the IR, high melting temperature , low vapor pressure, low electrochemical potential to provide chemical stability with the dielectric layers

Dielectric f i lms - high transmission in the IR, high melting temperature, low vapor pressures, and high electrochemical potential

Metal films - high transmission in the IR, high melting temperature , low vapor pressure, and low electrochemical 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- s t ra ted 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 high abrasion resistance; however, they can be washed in acetone or alcohol. (54) Unfortunately, there has been difficulty in reproducing these materials,

Miscellaneous Coatings

Several coatings were reported for which available information is very meager . In many cases only the solar absorptance and hemispherical emissivity were given. Composition of some of these was not available. The reported 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. It was degraded by 10l6 p /cm2 (E = 3 keV) in the visible and IR spectral regions (Figure C-53). Spectral reflectance in these regions decreased as a result of e l ec t ron i r r a - diation. Damage a proached a saturation level at doses not much greater than 4 x 1 0 l 6 e / c m 5 (E = 145 keV). (See Figure C-54.) Specimens appeared somewhat darker after electron irradiation. (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 / c m 2 (E = 3 keV) and 4 x 10 l6 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)

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Cameo Aluminum 2082 Porcelain Enamel

Type 6061 aluminum sheet, 16 mils thick, coated with 1.5 mils porcelain enamel, increased in solar absorptance only 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 absorptance values over the entire wavelength region considered. (55) (See Figures C-55 and C-56.)

Nickel Sulfide (NiS)-Dyed Anodized Aluminum [ 1100(2-S)Al]

NiS-dyed anodized aluminum was stable with relatively high absorptance values over the entire wavelength region considered. (55) (See Figures 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 solar absorptance and showed slight changes of solar absorptance when exposed to simulated space environment. They would have limited usefulness a s t he rma l - 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 simultaneous high vacuum and UV radiation of 3800 ESH plus electron radiation of 1015 e / c m 2 (E = 1 MeV), and showed no significant change of solar absorptance from the init ial high value 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 spectral region. Solar absorptance is relatively high and thermal emittance is relatively low. It was stable to simulated space environment. Thermal emittance changed 4.1 percent. (55) (See Figures C-61 and C-62 . )

Westinghouse Black on Inconel, Sodium Dichromate-Blackened SS (Tvpe 347). Sodium Dichromate-Blackened Inconel, and Sodium Dichromate -Blackened Inconel X

Various other combinations of "blackened" metals are good flat absorbers in the solar spectral region. Solar absorptance of these i s re la - t ively high, while thermal emittance is relatively low. They are s table to simulated space environment. The major disadvantage to these may be the high temperatures required during the coating process. The thermal emittance of sodium dichromate-blackened Inconel changed only 2 . 7 percent after being subjected to 4770 solar hours in vacuum and 1015 e / c m . Sodium dichromate-blackened Inconel X showed negligible change after 2560 so lar hours in vacuum plus 1015 e/cm2. (55) See Figures C-63 to C-70. Chemi- cally blackened Inconel 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

7 1

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 absorptance and emittance are relatively high. However, the paints are unaffected by prolonged exposure to simulated space environment. (55) See Figures C-71 to C-74.

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PIGMENTS

Because of the convenience of painting a surface, particularly 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 problem at the present t ime is to determine mechanisms of UV degradation in specific materials, particularly pigments. Knowing the mechanism 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. It has been found, for example, that the contribution of voids (between discrete particles and between agglomerates) is an important factor because voids increase spectral reflectance and yet tend to mitigate the absorption effect of intr insic absorbers . (56 ) Also, studies have been conducted to charac- terize degradation in terms of solid-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 regions, 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 degradation 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 zinc diffuses into the bulk of the zinc oxide. Thus, the net result of the UV irradiation is the generation of excess zinc and an increase in the concentration of f ree e lectrons.

The mechanisms by which the above actions cause the increased visible- and IR-region absorption are not clearly defined. (57) Some believe that the enhanced IR absorption is a result of additional free-carrier absorption which is caused by the increase in the free-electron concentration. Others believe that the enhanced IR absorption is a resul t of an increase in the density and population of defect levels lying near the conduction band.

The increased visible absorption is likewise not clearly understood. It has been explained by some workers that this is the result 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 se r i e s of experiments involved studies of changes in electrical properties of thin films and of crystals with UV irradiation, and studies on the effect of radiation on electron paramagnetic resonance, magnetic susceptibility, and luminescence . ( 5 7 ) These studies have shown that UV i r r a - diation of ZnO results in the production and population of defect centers with energy levels near the conduction band and that these centers are sensitive to IR radiation. UV i r radiat ion a lso increases the f ree-electron concentration to such a density that free-carrier absorption in 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 reaction. (58) Such chemical reactions change the structure of the coating, leading eventually to coloration. One approach to prevent optical degradation is to find surface additives that act as recombination centers, alter- nately capturing the holes and electrons and thus removing the photoproduced carriers with no net chemical change. In studies with ZnO,

74

single-crystal measurements have shown improvement up to a factor of 106 in rate of conductivity degradation, and powder measurements have shown photodamage protection from monolayers of additive. (58)

In these studies, it was concluded that suitable surface additives, acting as electron-hole recombination centers, could prevent degradation of thermal-control coatings by preventing irreversible chemical reactions 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- s i s , ( 2 ) it must exist in two stable oxidation states separated by one elec- t ron, ( 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 electron-capture cross sections be high, (4 ) the additive must be present in both oxidation states, and ( 5 ) it must uniformly cover the surface of each g r a i n of pigment material .

The material showing the most promise with ZnO was the redox couple, a 1: 1 ferrocyanide-ferricyanide combination. (59) Tes ts of this additive have been made using two tes t procedures . These were (1) monitoring vacuum photolysis of ZnO by measurement of the increase in dark conductance of the ZnO crystals and ( 2 ) monitoring of vacuum photolysis by electron-spin resonance (ESR) of a signal at g - 1. 96 associated indirectly 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 in vacuum (only), appears as an increasing IR absorption which increases with increasing irradiation. The other effect , induced only by mechanical and thermal treatments appears as an absorption band very near the optical absorption edge. (6 6)

It has been found that solar radiation-induced degradation of par t ic- ulate ZnO reflectance occurs in two spectral regions - the visible adjacent to the band-edge and the near IR between 0.8 and 2.8 p. Visible degradation 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 discharge which accompanies start-up of an electronic vacuum (VacIon) pump may cause significant IR degradation, but none in the visible wavelengths of sintered 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 radiation, electron irradiation, or combined environments. ( 6 2 ) Electr ical- 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) .

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The conclusions reached were: ( 6 2 )

The diffuse reflectance spectra of all irradiated specimens degraded.

UV irradiation produced significantly more degradation 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 electron-damage recovery is more rapid in the IR and small in the visible region. In both, recovery essentially ceased in about 4 to 6 hours.

Renewed irradiation with electrons following recovery produced new absorbing centers in the visible region, but the IR reflectance degradation for the second irradiation was about the same as for the f irst .

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 bombardment lead to almost complete recovery in the IR within a day, whereas little recovery in the visible was observed at this stage.

Recovery after exposure to air 53 days later was essentially complete to the preirradiation vacuum characterist ic for al l specimens.

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Titanates

Zinc orthotitanate (Zn2Ti04) is a spinel that is formed f rom 2 moles of ZnO and 1 mole of anatase TiO2. The most stable product to date is formed at 1050 C. The extraordinarily hard product requires considerable energy to grind into a suitable powder. It is believed that the grinding is largely responsible for the random instabil i ty that has been observed in 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 IR damage observed. (23) This pigment appears promising as a stable material when properly prepared. Work is continuing on developing methods for producing a stable material . ( 6 3 , 64) Other t i tanates such as iron titanate are also being investigated.

Zirconium Silicate

A se r i e s of zirconium silicates ( Z r 0 2 . 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 a S 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 development of this pigment.

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BINDERS

Silicone Binders

Polydimethyl si loxanes are the most stable polymers available in t e r m s of UV irradiation in vacuum. Both elastomeric and rigid cross- l inked si l icone polymers are stable. Since they are essentially trans- .

parent to UV, their s tabi l i ty is pr imari ly a function of their purity; thus the amount of amine catalyst used to cure the l inear polymers greatly influences the stability of the system..(6)

General Electric methyl silicone RTV-602 coated over 1199 alumi- n u m reflector sheet was tested as par t of the Lunar Orbiter V flight experiment. The increase in 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 degradation for this material . The addition 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 result , lower the degree of binder damage. Figure C-80 shows the change in solar 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 a s 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 in 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 preferentially, whereas the entire methyl si l icone molecule is comparatively transparent. The predominant mechanism is thought to be dehydrogenation, whether it be methyl or phenyl segments that are affected.

79

REFERENCES

(1) Plunkett, J. D. , "Technology Survey: NASA Contributions to the Technology of Inorganic Coatings", Denver Research Institute, Uni- vers i ty of Denver, NASA SP-5014, National Aeronautics and Space Administration, Washington, D. C., 1964.

( 2 ) Breuch, R . A . , and Greenberg, S. A., "Recent Coating Develop- ments and Exposure Parameters", Paper presented at Thermal Control Working Group Meeting, Dayton, Ohio, August 16-17, 1967.

(3) Fogdall, L. B., Cannaday, S. S. , and Brown, R. R . , "In Situ Electron, Proton, and Ultraviolet Radiation Effects on Thermal Con- trol Coatings", Final Report, Boeing Aerospace Group, Seattle, Washington, NASA-CR- 100146, D2-84118-9, Final Report, Sept. 15, 1965 - July 15, 1968. Avail: NASA; N69-23865 and CFSTI.

(4) Miles, J. K . , Cheever, P. R., and Romanko, J . , "Effects of Combined Electron-Ultraviolet Irradiation on Thermal Control Coatings in Vacuo at 77 K", General Dynamics/Ft. Worth, Paper presented at the AIAA 3rd Thermophysics Conference, Los Angeles, California, June 24-26, 1968. Avail: AIAA, Paper No. 68-781. Progress in Astronautics and Aeronautics, Volume 21, "Thermal Design Principles of Spacecraft and Entry Bodies", J. T. Bevans, editor, Academic Press, New York, 1969, pp. 725-740.

(5) Weaver, J. H . , "Bright Anodized Coatings for Temperature Control of Space Vehicles", Plating, - 51 (19) , 1165-1172 (December, 1964).

(6) Zerlaut, G. A . , Ca r ro l l , W. F . , and Gates, D. W . , "Spacecraft Temperature-Control Coatings: Selection, Utilization, and Problems Related to the Space Environment", IIT Research Institute, Tech- nology Center, Chicago, Illinois, Paper presented at 16th Interna- tional Astronautical Congress, International Astronautical Federation, Athens, Greece, September 13-18, 1965.

(7) Boebel, C. P . , and Babjak, S. J . , "Recent Developments in Exter- nal Coatings for Spacecraft", Paper presented at Aeronautics and Space Engineering and Manufacturing Meeting, Los Angeles, Calif- ornia, October 3-7, 1966, Published by the Society of Automotive Engineers , Inc. , Paper No. 660653.

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(8) Goetzel, C. G . , Rittenhouse, J. B. , and Singletary, J. B . , Editors, "Space Handbook", Lockheed Missiles and Space Co. , Sunnyvale, California, ML-TDR-64-40, March, 1964, Tech. Doc. Rpt. , AF 33 (657)-10107.

( 9 ) Breuch, R. A. , "Handbook of Optical Properties for Thermal Control Surfaces", Final Report, Vol. 111 of High-Performance Insulation Thermal Design Criteria, LMSC-A847882, Vol. 111, Lockheed Missiles and Space Co., June 25, 1967.

(10) Rittenhouse, J. B. , and Singletary, J . B. , Editors, "Space Materials Handbook. Third Edition", Lockheed Missiles and Space Company, Palo Alto, California, AFML-TR-68-205, NASA SP-3051, July, 1968. Avail: N70- 11113, AD 692353.

(1 1) Vette, James I. , "Models of the Trapped Radiation Environment. Volume I: Inner Zone Protons and Electrons", Aerospace Corpora- tion, NASA SP-3024, 1966. Avail: NASA, N66-35685. Also avail: Clearinghouse for Federal Scientific and Technical Information, Springfield, Virginia 22 15 1.

( 1 2 ) Vette, J . I. , Lucero, A. B. , and Wright, J . A. , "Models of the Trapped Radiation Environment. Volume 11: Inner and Outer Zone Electrons ' I , Aerospace Corporation, El Segundo, California, NASA SP-3024, 1966. Avail: N66-35685, AD 659723.

(13) Millard, John P. , "Results From the Thermal Control Coatings Ex- periment on OSO-III", Ames Research Center, Moffett Field, California, Paper presented at AIAA 3rd Thermophysics Conference, Los Angeles, California, June 24-26, 1968. Avail: AIAA, Paper No. 68-794. Progress in Astronautics and Aeronautics, Volume 21, "Ther- mal Design Principles of Spacecraft and Entry Bodies, J. T. Bevans, edi tor , Academic Press , New York, 1969, pp. 769-795.

(14) Slemp, W. S., and Hankinson, T. W. E . , l'Environmental Studies of Thermal Control Coatings for Lunar Orbiter", NASA Langley Research Center , Paper presented at AIAA 3rd Thermophysics Conference, Los Angeles, California, June 24-26, 1968. Avail: AIAA, Paper No. 68- 792. Progress in Astonautics and Aeronautics, Volume 21, "Thermal Design Principles of Spacecraft and Entry Bodies", J. T. Bevans, editor, Academic Press, New York, 1969, pp. 797-817.

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(15) Shulman, H. , and Ginell, W. S . , "Nuclear and Space Radiation Effects on Materials", Teledyne Isotopes and McDonnell Douglas Corporation, NASA SP-8053, NASA Space Vehicle Design Criteria (Structures), June, 1970.

(16) Blair , P. M. , Jr . , Pezdir tz , G. F . , and Jewell, R. A . , " U l t r a - violet Stability of Some W h i t e Thermal Control Coatings Characterized in Vacuum", Paper presented at AIAA Thermophysics Specialist Conference, New Orleans, Louisiana, April 17-20, 1967. Avail: AIAA, Paper No. 67-345.

(17) Zerlaut, G. A . , and Rogers, F. O . , "The Behavior of Several White Pigments as Determined by in Situ Reflectance Measurements of Irradiated Specimens", IIT Research Institute, Technology Center, Chicago, Illinois, Paper presented at Proceedings of the Joint Air Force-NASA Thermal Control Working Group, August 16- 17, 1967, Dayton, Ohio, AFML-TR-68-198, August, 1968, Tech. Rpt.

(18) Carroll , W. F . , "Mariner V Temperature Control Reference Design, Test , and Performance", Jet Propulsion Lab. , Pasadena, California, Paper presented at the AIAA 3rd Thermophysics Conference, Los Angeles, California, June 24-26, 1968.

(19) Reichard, P. J. , and Triolo, J. J. , "Preflight Testing of the ATS- 1 Thermal Coatings Experiment", NASA Goddard Space Flight' Center, Paper presented at AIAA Thermophysics Specialist Conference, New Orleans, Louisiana, April 17-20, 1967. Avail: AIAA, Paper No. 67-333, Progress in Astronautics and Aeronautics, Vol. 20 , "Thermo- physics of Spacecraft and Planetary Bodies", B. G. Heller, editor, Academic Press , New York, 1967, pp 491-513.

( 2 0 ) Data received from J. J. Triolo, NASA Goddard Space Flight Center, Greenbelt, Maryland, June, 1970.

(21 ) Arvesen, J. C., "Spectral Dependence of Ultraviolet-Induced Degrada- tion of Coatings for Spacecraft Thermal Control", Paper presented at the AIAA Thermophysics Specialist Conference, New Orleans, Louis- iana, April 17-20, 1967. Avail: AIAA, Paper No. 67-340. P rogres s in Astronautics and Aeronautics, Volume 20, "Thermophysics of Spacecraft and Planetary Bodies", G. B. Heller, editor Academic P r e s s , New York, 1967, pp. 265-280.

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(22) Holland, W. R . , "Stability of Thermal Control Coatings Exposed to Combined Space Environments ", AVCO, Electronics Division, Tulsa, Oklahoma, NASA-CR-73160, December, 1967. Avail: NASA, N68- 16904 and CFSTI.

I (23) Zerlaut, G. A . , Noble, G. , and Rogers , F. O . , "Development of Space-Stable Thermal- Control Coatings Report No. IITRI- U6002-55 (Triannual Report), March 1-July 31, 1967, IIT Research Institute, George C. Marshall Space Flight Center, NASA, Huntsville, Alabama.

(24) Zerlaut, G. A. , Rogers, F. 0. , and Noble, G. , "The Development of S - 13G-Type Thermal Control Coatings, Based on Silicate-Treated Zinc Oxide", IIT Research Institute, Paper presented at the AIAA 3rd Thermophysics Conference, Los Angeles, California, June 24-26, 1968. Avail: AIAA, Paper No. 68-790. Progress in Astronautics and Aeronautics, Volume 2 1, "Thermal Design Principle of Spacecraft and Entry Bodies, J. T. Bevans, editor, Academic Press, New York, 1969, pp. 741-766.

(25) Brown, R . R . , Fogdall, L. B . , and Cannaday, S. S . , "Electron- Ultraviolet Radiation Effects on Thermal Control Coatings", The Boeing Co., Seattle, Washington, Paper presented at the AIAA 3rd Thermophysics Conference, Los Angeles, California, June 24-26, 1968. Avail: AIAA, Paper No. 68-779. Progress in Astronautics and Aeronautics, Volume 21, "Thermal Design Principles of Space- craft and Entry Bodies", J. T. Bevans, editor, Academic Press, New York, 1969, pp. 697-724.

( 2 6 ) Caldwell, C. R . , and Nelson, P. A . , "Thermal Control Experiments on the Lunar Orbiter Spacecraft", The Boeing Company, Seattle, Washington. Paper presented at AIAA 3rd Thermophysics Conference, June 24-26, 1968, Los Angeles, California, Avail: A I M , P a p e r No. 68-793. Progress in Astronautics and Aeronautics, Volume 21, "Thermal Design Principles of Spacecraft and Entry Bodies, ' I J. T. Bevans, editor, Academic Press, New York, 1969, pp. 819-852.

( 2 7 ) Fogdall, L. B. , and Cannaday, S. S. , "Dependence of Thermal Control Coating Degradation Upon Electron Energy", The Boeing Co. Seattle, Washington, NASA-CR-103205, D2-126114-1, May, 1969, Final Report. Avail: NASA, N69-30549 and CFSTI.

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(28) Smith, F. J . , and Grammer, J. G . , "Emissivity Coatings for Low- Temperature Space Radiators", Quarterly Progress Report No. 42 for quarter ending June 30, 1966, NASA-CR 72059, Lockheed Missiles and Space Company, Sunnyvale, California. Report prepared for National Aeronautics and Space Administration, Lewis Research Center, Cleveland, Ohio.

(29) Smith, F. J. , Olson, R. L. , and Cunnington, G. R . , "Emissivity Coatings for Low-Temperature Space Radiators", Quarterly Prog- ress Report No. 1 for quarter ending September 30, 1965, NASA- CR-54807, Aerospace Sciences Laboratory, Lockheed Palo Alto Research Laboratory, Lockheed Missiles and Space Company, Sunnyvale, California. Report prepared for National Aeronautics and Space Administration, Lewis Research Center, Cleveland, Ohio, NAS-7630.

(30) Smith, F. J. , and Grammer, J . G . , "Emissivity Coatings for Low- Temperature Space Radiators", Quarterly Progress Report No . 2 for quarter ending December 31, 1965, NASA-CR 72059, Lockheed Missiles and Space Company, Sunnyvale, California. Report prepared for National Aeronautics and Space Administration, Lewis Research Center, Cleveland, Ohio.

( 3 1) Breuch, R . A. , and Pollard, H. E. , "Nuclear Environmental Effects on Spacecraft Thermal Control Coatings ' I , Lockheed Missiles and Space Company, Palo Alto, California, Paper presented at Symposium on Thermal Radiation of Solids, San Francisco, California., March 4-6, 1964, National Aeronautics and Space Administration, NASA SP-55, ML-TDR-64-159, N65-26895, 1965.

(32) Smith, J . A . , and Luedke, E. E . , "Apollo 9 Thermal Control Coat- ing Degradation", Manned Spacecraft Center, Houston, Texas, TRW Systems, Redondo Beach, California, May, 1969.

(33) Rittenhouse, J. B . , and Singletary, J. B . , "Space Materials Handbook, Supplement 1 to the Second Edition Space Materials Experience", Lockheed Palo Alto Research Laboratory, NASA SP-3025, ML-TDR-64-40, SUPP. 1, 1966.

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(34) Cheever, P. R., Miles, J. K . , and Romanko, J . , "In Situ Measure- ments of Spectral Reflectance of Thermal Control Coatings Irradiated i n Vacuo", Paper presented at AIAA Thermophysics Specialist Con- ference, New Orleans, Louisiana, April 17-20, 1967, Avail: AIAA Paper No. 67-342, Progress in Astronautics and Aeronautics, Vol. 20, ' 'Thermophysics of Spacecraft and Planetary Bodies", B. G. Heller, editor, Academic Press, New York, 1967, pp. 281-296.

(35) Gilligan, J. E. , and Caren, R. P. , "Some Fundamental Aspects of Nuclear Radiation Effects in Spacecraft Thermal Control Materials", Research Laboratories, Lockheed Missiles and Space Company, Palo Alto, California, Paper presented at Symposium on Thermal Radiation of Solids, San Francisco, California, March 4-6, 1964, National Aeronautics and Space Administration, NASA SP-55, ML- TDR-64-159, N65-26894, 1965.

(36) Linder, B . , "Series Emittance Thermal Control Coatings", Paper presented at Thermal Control Working Group Meeting, Dayton, Ohio, August 16-17, 1967.

( 3 7 ) Breuch, R . A. , Douglas, N. J . , and Vance, D. , "Effect of Electron Bombardment on the Optical Properties of Spacecraft Temperature Control Coatings", AIAA Journal, 3 (12) , 2318-2327 (December, 1965).

-

(38) Olson, R . L. , McKellar, L. A. , and Stewart, J . V . , "The Effects of Ultraviolet Radiation on Low a s / € Surfaces", NASA-SP-55, 1965.

(39) Glenn, E. E . , and Munoz-Mellowes, A., "Thermal Design and Test- ing of the Pioneer Spacecraft", TRW Systems Group, TRW Inc. , Redondo Beach, California.

(40) Farnsworth, D., "Exploratory Experimental Study on Neutral Charge Low Energy Particle Irradiation of Selected Thermal Control Coat- ings", Martin Marietta Corp., Denver, Colorado, NASA-CR-73290, January, 1969, NAS2-4962. Avail: NASA, N69-16965 and CFSTI.

(41) Bailin, L. J. , "Effects of Combined Space Radiation on Some Mate- rials of Low Solar Absorptance", Materials Sciences Laboratory, Lockheed Palo Alto Research Laboratory, Paper presented at the 11th National SAMPE Symposium and Exhibit, St. Louis, Missouri, April 19-21, 1967. Avail: DDC, AD 666364.

85

(42) Slensky, A. F. , MacMillan, H. F. , and Greenberg, S. A. , "Solar- Radiation-Induced 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) Clarke, D. R., Gillette, R. B., and Beck, T. R., "Development of a Barr ie r -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- fe rence , Palm Springs, California, March 29-31, 1967, Progress in Astronautics and Aeronautics, Volume 20, "Thermophysics of Space- craft and Planetary Bodies", G. B. Hel ler , edi tor , Academic Press , 1967, pp 315-328.

(44) McCargo, M., Greenberg, S. A. , and Breuch, R . A . , "Study of Environmental Effects Upon Particulate Radiation Induced 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, January, 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, April 17-20, 1967. Avail: AIAA, Paper No. 67-339, P rogres s i n Astronautics and Aeronautics, Volume 20, "Thermophysics of Space- craft and Planetary Bodies", G. B. Heller, editor, Academic Press, 1967, pp. 237-264,

(46) Rawuka, A. C . , "In Situ Solar Absorptance of Ultraviolet Degraded Inorganic Coatings", Materials and Process Engineering Labora- tory Report , Ser ia l No. M P 50, 749, Catalog No. R D 28700, October 5, 1967.

(47) Heaney, James B., "Results From the ATS-3 Reflectometer Experi- ment", NASA Goddard Space Flight Center, Greenbelt, Maryland, Paper presented at the A I M 4th Thermophysics Conference, San Francisco, California, June 16-18, 1969. Avail: AIAA No. 69-644.

86

(48) Jorgenson, G. V . , Wenner, G. K . , KenKnight, C. E . , E c k e r t , 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, Inc. , Report No. 2842, Summary Report, October 20, 1965.

(49) Personal Communication from A. L. Fitzkee, NASA Goddard Space Flight Center, Greenbelt, Maryland, June 3, 1970. Proton irradiation 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 - 2 1 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, June 1967-August 1967, F04695-67- C-0158, 30pp. Avail: DDC, AD 661963.

(52) Hass , G. , Ramsey, J . B. , Heaney, J. B. , and Triolo, J . J . , "Reflectance, Solar Absorptivity, and Thermal Emissivity of Si02- Coated Aluminum", Applied Optics, - 8 ( 2 ) , 275-281 (February, 1969).

(53) Bradford, A. p . , Hass , G . , Heaney, J . B., and Triolo, 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 Pa rk , 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 I11111l1111111

(56) Gilligan, J. E . , and Brzuskiewicz, J . , "A Theoretical and Experi- mental Study of Light Scattering in Thermal Control Materials", IIT Research Institute, Chicago, Illinois, Paper presented at the AIAA 5th Thermophysics Conference, Los Angeles, California, June 29-July 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 Irradiation 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, June 29-July 1, 1970. Avail: AIAA, Paper No. 70-829.

(58) Morrison, S. R . , and Sancier, K . M., "Effect of Environment on Thermal Control Coatings ' I , Stanford Research Institute, Final Report SRI Project PAD-6146, October 15, 1969.

(60) Gilligan, J. E . , "The Optical Properties Inducible in Zinc Oxide", IIT Research Institute, Chicago, Illinois. Paper presented at the AIAA 5th Aerospace Sciences Meeting, New York, New York, Janu- a r y 23-26, 1967, Avail: AIAA, Paper No. 67-214, Progress in Astronautics and Aeronautics, Volume 20, G. B. Heller, editor, "Thermophysics of Spacecraft and Planetary Bodies", Academic Press, 1967, pp. 329-347,

(61) Greenberg, S. A . , and Cuff, D. F . , "Solar-Radiation-Induced Damage to Optical Properties of ZnO-Type Pigments", Lockheed Palo Alto Research Laboratory, Lockheed Missiles and Space Corporation, Technical Summary Report for Period 27 June 1966 to 27 March 1967, NAS 8- 18114, L-92-67-1 , June 1967.

(62 ) F i r le , T. E . , and Flanagan, T. M., "Mechanisms of Degradation of Polymeric Thermal Control Coatings. Part 11. Effects of Radiation on Selected Pigments", Gulf General Atomic Incorporated, AFML- TR-68-334, Part 11, March, 1970.

88

(63) Zerlaut, G. A . , and Ashford, N . , "Development of Space-Stable Thermal-Control Coatings", IIT Research Inst., IITRI-U6002-73, January 31, 1969.

(64) Campbell, W. B. , Cochran, J. K . , Hinton, J. W. , Randall, J. W. , Versic , R. J . , and Burroughs, J. E. , "Preparation of Pigments for Space-Stable Thermal Control Coatings", The Ohio State University Research Foundation, July, 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

INDEX

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 Emit tance Rat io 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 Active 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 Aluminum 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, A l , 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 Binders 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 Porce la in

B14, B15, C14

B14, B20, B21, C14

Enamel 70 Carbon Black Pigment 45,A3 Cat-a-Lac Coating 45 Cerium Oxide 69 Cerme t 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 Cryogenic Temperature 4,11,35,

Damage Threshold 38,52 Defect Centers 74,75 Dielectric Materials 63, 65, 66,

Dimethyl Siloxane - Use Methyl

54,55, B3

68, A5

Silicones

90

Douglas Inorganic 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 Electron Irradiation 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 Isoflux Contours A14 Electron Paramagnetic Resonance

Electrostatic 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 Explorer XXIII 15,16, 63 Fasson Foi l A1 Ferrocyanide-Ferricyanide 75 Flat Absorbers 1,17,18,71,A3,A9 Flat Reflectors 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 Inorganic 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, c 4 5

Inconel 67, 68,71,72, A2-A4, C38, C40, C43

Inconel X A2, C41 Infrared Wavelengths 1,3,4,18,

1 9 , 2 7 , 2 8 , 3 0 , 3 1 , 3 4 , 3 5 , 3 7 , 3 8 , 4 0 , 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 Iron 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 Orbiter I 7,33, B5, B12, B15 Lunar Orbiter I1 7,32,33, B12, B15 Lunar Orbiter IV 7,11,24,33,34,

Lunar Orbiter 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 Mariner I1 60 Mariner IV 5,11,45,50, C13 Mariner 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 Platinum A3 Platinum Black A3 Polyimide 14, 62, C28, C29 Polyurethane 45 Polyvinyl Butyral 12,43, 58-60, B3,

Porcelain Enamel 70, A5 Potass ium Silicate 3,4, 5, 10,30-36,

C5, C26

39,48-53,55,78,B3, B29, B31,Cl- C4, C9-Cl6

Proton I r radiat ion 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 Isoflux Contour A10-Al2 PV- 100 8,42, B29, B30 Pyromark Black Ref rac tory Paint

Pyromark Ti02 Sil icone B24 QMV Beryllium A2,A3 Quilted Inconel 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 Reynolds Wrap Foil 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,

Solar 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, c 4 5

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,ClO,Cl l ,

Solar Reflectors 1-3,5,12,16-18,20,

Solar -Thermoelectric Systems 68, 69 Solar 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,Cll-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, c 5

B2, B14, C3, C13-Cl5

40,49-53,73-76, Bl-B21, B29, B31,Cl -C3,Cl l ,Cl3-C16

Zirconium. Silicate 10,49,78, B3, B29, B31

93

APPENDIX A

THERMAL CONTROL MATERIALS FOR SOLAR AND FLAT ABSORBERS AND REFLECTORS

and

CONTOURS O F CONSTANT FLUX ELECTRONS AND PROTONS

TABLE A-1. THERMAL-CONTROL MATERIALS FOR SOLAR I ABSORBERdg~ 33* 65)

Note: Unlemm 0Lherwi.c indicated, tbe8e material. show no mignificant change in absorptance o r emittance in penetrating nuclear radiation in vacuum.

Ascent Absorptance and Temperature Ultraviolet Cycling

Thermal-

Material Subatrate a,/€ Emittance, 70 F L h i t m , F Resimtance Re8istance Remark8

6061 Aluminum, chemically cleaned



2024 Aluminum, chemically cleaned (non- clad)

2024 Aluminum, sheet (clad)

Aluminum

Aluminum

Aluminum,

(I20 size grit1 sandblasted

Aluminum foil, dry-annealed

Alumlnum fot l . dull side

Aluminum foi 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 protective 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

be lo 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-rolled. 3 , 7t0.06 a. = 0. Z O t O . 05 hand sanded

Not applicable

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 . 0 5 1

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. = 0.12tO. 04 c = 0.05t0.02

Structural l imits only



Structural limits only


375

No effect

No effect

No ef fec t

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 depending on fabri- cations operations.

No effect Subject to degrrd- ation from prelaunch environment. Adhemivc im limiting factor

ment. in apace environ-

No infor- Muat not be mxtcer- mation nal during aacmnt.

Foil ahould be perforated (1132- in. d i 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 Foil , MIL-N-7786

QMV Beryllium,

polished chemically

Hanovia Gold 6518 on Rend 41

Gold, plated o n stainless steel

Gold over titanium with resin undercoat

Gold, vacuum deposited

Molybdenum, slug

Chrome-

Mylar alummized

Electroless nickel

Pure tantalum

R e d 41, vapor honed and buffed

Production Dow 1 5 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

R e 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

N o effect

No effect

No effect

No information

No effect

N o effect

No effect

No effect

If applied external- l y , the tape should have mechanical faatenmg on both ends to prevent as-

peeling the tape cent forces f rom

from substrate. Subject to handling degradation.

Very susceptible to

and by fingerprints increase in a,

prelaunch envbron- and oxidation in

ment. Primarily for engine heat shield usage.

Subject to handling degradation.

High ascent temperature has no effect on as or c i f a t p re s su re of 0 . 0 5 t o r r or less.

May be suitable for other substrates. At 1700 F. values changed to a s = 0.8t0.06 c E 0. 4010. 10.

A-2

TABLE A-2. THERMAL-CONTROL MATERIALS FOR FLAT ABSORBERS(g* 33n 65)

~___ A s c e n t

Absorp tance and Tempera tu re U l t r av io l e t Cyc l ing T h e r m a l -

M a t e r i a l S u b s t r a t e n , l t Emi t t ance , 70 F L i m i t s , F

Black Kemacry l Lacque r (She rwin Wil l iams M49BC

c u r e 12.1, r o o m - t e m p

Ful ler Black Si l icone Pa in t

517-B-2) (W. P. F u l l e r

Rokide C ( c h r o m i c ox ide , f l ame

A b r a s l v e Go., sprayed by Norton

85% Cr2031

P la t inum B lack ldepos i t of finely dlv ldrd

O M V berv l l tuml platinum o n

Dow 17 (Anodized on HM ZIA Magnesium Alloy)

Dull Black Mico- bond (Midland I n d u s t r i a l F i n i s h e s )

Dull Black Mico- bond, vinyl (pheno l i c ) Pa in t

C a r b o n - B l a c k P i g m e n t

C e r m e t ( c e r a m i c containing s i n t e r e d m e t a l )

-~ " -. _ _ _ _ ~ _ -

Any c l e a n I . 0610. 04 as = 0.9310.03 No e f f e c t a t r igid E = 0.8810. 03 450 s u b s t r a t e . p r i m e r r e q u i r e d

HMZIA-T8 1 .0110.07 a , = 0.89aO.05 No e f f e c t a t MR. FIm L = 0 , 8 8 1 0 . 0 5 1070 Z I A - 0 Mg. AI,

l e a s s t e e l s . T i , s t a i n -

s u p e r - a l l o y s , and o the r r i g id s u b s t r a t e s c a p - a b l e of wi ths tand- ing cu re cyc le

R e n i 41 I . Oba0.06 l g = 0.90+0.04 No e f f e c t a t with a 2 - 6 = 0 . 8 5 1 0 . 0 4 I660 m i l c o a t - ing of N i c h r o m e

QMV I . 11+0.08 , 5 = 0 . 9 4 a 0 . 0 3 No e i f c c t a t berylllWl7 L = 0 , 8 5 3 0 . 0 7 1200

HM2lA Mg 1. 11+0. 10 ' 5 = 0.7830.08 N o cf fec l a t Alloy L = 0 . 7 0 1 0 . 0 6 500

I . I 1 ? s = 0 . 9 3 1 0 . 0 4 t = 0.8930. 04

I . 10 as = 0.930 L = 0 . 8 4 0

R e s i s t a n c e R e s i s t a n c e R e m a r k s

A , g<O. 05 No f a i l u r e I . 5 - m i l d r y f i l m a f t e r 600 in 385 t h i ckness r equ i r ed s u n h r UV c y c l e s fo r so l a r and i n -

-150 to f ra red opackty . 70 F, 18- m i n c y c l e s

A1~<0.05 C r a c k i n g I - m i l d r y f i l m a f t e r 6 0 0 and losm of t h i c k n e s s r e q u l r e d s u n h r UV a d h e s i o n for so lar and In-

in 170 cy - f ra red opacLty , cles - 2 4 0 p e a k c u r e - c y c l c to 70 F. t e m p e r a t u r e ,

c y c l e s 18-min 465 F.

No e f fec t

N o e i i e c t

N u effect

No f a t l u r e : The bondlng betwecn 70 to Rokldu C and the I600 F s u b s t r a t c L S purc ly In 5 m t n - mechanica l and U t e s t h e r m a l s h u c k 15 a

polcn t la l p rublcm.

No I n f o r m a - P o s s e s s e s s t a b l e t l o n , p r o b - h l g h - t e m p e r a t u r c a b l y no e r n ~ t t a n c t ' . e f f c c t

N C I effect P r o p r t c t a r y p r o c e s s of Dow Chem. Co . : t h e r m a l s t a b l l l t y >500 F doubtful.

I . 16 as = 0 . 9 0 8 L = 0.780

I . 10 as = 0.650 L = 0 . 5 8 0

A- 3

TABLE A-3. THERMAL-CONTROL MATERIALS FOR SOLAR REFLECTOR^^, 33,36,49,50,65)

. "~ .. ~. ~

A s c e n t T h e r m a l - A b s o r p t a n c e a n d T e m p e r a t u r e U l t r a v i o l e t C y c l l n g

M a t e r i a l S u b s t r a t e E m i t t a n c e , 7 0 F L i m i t s , F R e s i s t a n c e R e s i s t a n c e R e m a r k s

Tinted White K e m a c r y l

w in Wi l l i ams L a c q u e r I S h e r -

M49WC17), r o o m - t e m D c u r e d

Ful l r Gloss White Si. icone Paint

a t 165 F ( 5 1 7 - W - I ) , c u r e d

White Epoxy Paint (A. Brown Sky- spa r SA 9185)

Op t i ca l So la r

vapor-depos i ted R e f l e c t o r IOSR),

s i l v e r o n C o r n i n g 7940 fu sed s i l i ca wi th an ove rcoa t ing of vapor-depos i ted Inconel

Any c lean , 0. 33+0.05 as = 0.28+0.04 r ig id to. 03 = 0.89-0 , o6 s u r f a c e ,

r e q u i r e d p r i m e r

HM2IA- 0.28f:: :; X S = 0 . 2 5 + 0 . 0 3

- 0 . 0 6 T8 Mg. H m 2 I A -

= 0. got0. O3

0 Mg, AI, Ti, SS, s u p e r - a l l o y s , a n d o t h e r r ig id sub - s t r a t e c a p - a b l e of withstanding c u r e c y c l e

Any r ig id 0. 24-t:q':: O s = 0. 91". O3

E = 0.22*0. 04 -0 . 06 s u r f a c e

0 . 0 6 2 o s = 0.50f0. 005 E = 0. 7?5+0.02 ( -135 t o t70 F )

450

6 5 0

4 5 0 200 t o

4 5 0 F:a,

by 0. 04 i n c r e a s e s

(cons tan t ] m a x i m u m allowed

500

Aa, =

a f t e r 2000 0.18+0.04

s u n h r

No f a i l u r e 5 - m i l d r y f i l m in 385 c y c l e s

t h i c k n e s s r e q u i r e d for opaci ty to

-150 to s o l a r ; I - m i l t h i c k - 70 F, 18-min opac i ty in IR.

n e s s s u f f l c i e n t for

c y c l e s R e q u i r e s 1 4 d a y s

t e m p e r a t u r e c u r e a t room-

t o m i n i m i z e b l i s - t e r i n g d u r i n g a s c e n t h e a t i n g .

m u m a s c e n t t e r n - . Used w h e r e m a x i -

p e r a t u r e L S ~ 4 5 0 . If no change in sur - f a c e c a n b e t o l e r -

p e r a t u r e <ZOO F. a t e d . m a x t e m -

A i s = 0. 0 9 C r a c k i n g 5 - m i l d r y film t h i c k - +O. 05 a f t e r 2 0 0 0 a d h e s i o n o p a c i t y t o s o l a r ;

and loss of n e s s r e q u i r e d f o r

s u n h r In 170 c y - I - m t l thdckness c l e s -240 fo r opac i ty in IR . to 70 F .

c y c l e s 1 8 - m i n

A a 2 = 0. 3 5 No f a i l u r e a, h igh ly suscep t ib l e +O. 06 a f t e r 2 0 0 0 c l e s -150 p r e l a u n c h s u n -

in 385 cy- to change f rom

s u n h r to 70 F, l igh t and f l uo res - 18-min cen t l igh ts . Not c y c l e s r e c o m m e n d e d

w h e r e a,/t i s c r i t i c a l .

4 - m i l d r y f l lm,

m i n i m i z e o u t g a s - 14 -day cu re t o

d u r i n g a s c e n t . s ing of a d h e s i v e

500 F l i m i t d u e t o a d h e s i v e .

A- 4

I

TABLE A-3. (Continued) . ~ .- ~. . . ". ~

A b s o r p t a n c e a n d T e m p e r a t u r e U l t r a v i o l e t C y c l i n g A s c e n t T h e r m a l -

M a t e r i a l S u b s t r a t e E m i t t a n c e , 7 0 F L i m i t s , F R e s i s t a n c e R e s i s t a n c e R e m a r k s

ODt ica l Solar Ref lec tor 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 . 5 1 0

1 0 . 2 5 6 L = 0 . 8 2 8

m s = 0 . 16+0.03 650 L = 0. 95+0. 03

1 4 - d a y c u r e to m i n i m i z e o u t - g a s s i n g d u r i n g a s c e n t .

Sur face i s sof t and r u b b e r y . M a t e r i a l i s e l e c t r o s t a t i c . 2 4 - h r c u r e a t r o o m t e m p e r a t u r e re- qu i r ed .

L 10.830 : 3 . 2 1 0

.- 0. n7o - 0 180

', = 0 .13+0 01 600 ,. = 0 .85fU 04

? a , = 0. 04 No e l f e c t C u r e d a t 400 F. a f t e r 2 0 0 0 s u n h r

a f t e r 2000 s u n h r

= 0 . I 4 700 A m , = 0 . 0 3 No effect L = 0 . 8 6

as = 0. 05*0 .02

CIS = 0 .14*0.02

I s = 0.20*0.02 (go ld )

( s i l v e r )

( a l u m i n u m )

L = 0. 0 3 (500 a n g s t r o m d i e l e c t r i c o v e r l a y )

i = 6 6 ( 6 0 , 0 0 0 a n g s t r o m d t e l e c t r i c o v e r l a y )

a = 0. 13 to 0. 16 = 0. 2b to 0 . 89

to

a = 0. 07-0. 0 9 c%cpondcnt on

aa = 0 . 4 4 thicknesa

c = 0.78

A- 5

TABLE A-4. THERMAL-CONTROL MATERIALS FOR t’LAT REFLECTORS(’# 33* 65)

Ascen t The rma l - Absorp tance and Tempera ture Ul t rav io le t Cycl ing

M a t e r i a l S u b s t r a t e C I S / € Emi t t ance , 70 F L i m i t s , F Res i s t ance Res i s t ance Remarks

Fu l l e r A luminum Si l icone Pa in t (172-A-1)

* I Ful l e r A luminum

S i l i cone Pa in t (171-A-152)

Fu l l e r A luminum Si l icone Paint (not identified)

Nonleafing Aluminum Acry l i c Pa in t

0 . 8 9 * 0 . 10 as = 0.25*0.07 E = 0.28*0.07

0.92*0.08 a s = 0.22*0.04 E = 0 . 2 4 + 0 . 0 4

1 . 2 a s = 0.230 € = 0.200

47.s i n c r e a s e s by 0.09*0.04 a f t e r 600 sun h r , E i s unaffected

4rrs i n c r e a s e s by 0.09*0.04 af ter 600 sun h r , E is unaffected

0 . 8 5 * 0 . 0 8 as = 0.41*0.03 650 where bub- t = 0.48*0.05 bling can be

to l e ra t ed , o the r - wise 240 F m a x i m u m

Baked at 465 F. No change ob- s e rved a t 885 F.

No change to 8 8 0 F.

Requires 14-day c u r e t o m i n i - mize b l i s t e r ing .

I

TABLE A-5. MISCELLANEOUS THERMAL-CONTROL

M a t e r i a l

LMSC Sil icone T a p e ( 1 A48)

Rok ide A , a lumi - n u m o x l d e , [ l a m e s p r a y e d by Nor ton A b r a s i v e Co , S a n J o s e , C a l i f ,

A b s o r p t a n c e a n d T e m p e r a t u r e U l t r a v i o l e t C y c l i n g A s c e n t T h e r m a l -

S u b s t r a t e a,/€ E m i t t a n c e , 7 0 F L i m i t s , F R e s i s t a n c e R e s i s t a n c e R e m a r k s . .. - ~~

Any rigid 0. I 8 as = 0. 16 700 Aa, = 0.04 No e f fec t s u b s t r a t e t = 0 . 6 6 a f t e r 2000

s u n h r

A n y 0 . 36+0. 05 a, = 0 . 2 7 t 0 . 04 m e t a l l i c L = 0 . 7 5 * 0 . 0 3 s u b s t r a t e

S t a i n l e s s S t e e l Not 0. 88 'Is = 0 . 7 5 c = 0 . 8 5 AIS1 4 1 0 ,

s a n d b l a s t e d applicable

A l u m l n u m ( 2 0 2 4 ) , AI a l loy 2 . 0 s a n d b l a s t e d

'Is = 0 . 4 2 (2024) t = 0 . 2 1

LMSC White S i l i cone A i r D r y P a i n t

No i n f o r - m a t i o n

N o i n f o r - m a t l o n

Any r igid 0. 16 a, = 0. 14 700 Aa, * 0.03 No e f fec t s u b s t r a t e E.= 0 . 8 6 a f t e r 2 0 0 0

s u n h r

T h i s m a t e r i a l w a n u s e d o n E x p l o r e r s

T i r o s 2 . T o t a l a r e a I , 3, a n d 7 and

c o v e r e d b y t h i s m a t e r i a l s m a l l : a c t u a l p e r f o r m a n c e

n o t b e e v a l u a t e d . of m a t e r i a l c a n -

m i t r e d 1 y r , E x - T i r o s 2 t r a n s -

p l o r e r 7 t r a n s - m i t t e d a b o u t 2 y r .

T h l s m a t e r l a l w l t h Rok lde A s t rLpes w a s p r l m a r y t h e r m a l - c o n t r o l s u r f a c e 01 E x p l o r - e r s I , J . and 4 .

M a t e r l a l u s e d In E x p l o r e r 7 a s

c e l l s a n d a s s t l f - s u p p o r t for s o l a r

f e n e r r i n g b e t w e e n g l a s s r e l n f o r c e d p o l y e s t e r c o n l c a l s e c t i o n s of s p a c e - c r a f t s t r u c t u r e . T h e r m a l d e s i g n w a s 0 to 60 C.

m e n t s i n s p a c e - While in orbi t in-

c r a f t w e r e n e v e r

h i g h e r t h a n 4 1 C . l o w e r t h a n 1 6 C o r

T r a n s m i t t e d f r o m

8 / 2 4 / 6 1 . 10/13/59 to

a A- 7

TABLE A-5. (Continued)

A s c e n t ~ . .~ " ~ _ .

T h e r m a l A b s o r p t a n c e a n d T e m p e r a t u r e U l t r a v i o l e t C y c l i n g

____

M a t e r i a l S u b s t r a t e as/€ E m i t t a n c e , 70 F L i m i t s , F R e s i s t a n c e R e s i s t a n c e R e m a r k s

B l a l k I l r ~ o - Any m e t a l 1 . 1 1 + 0 . 0 5 O s = 0.93*0.04 No bund I L I ~ X Q C Z I s u r f a c e Midland I n d u s t r i a l F i n i s h e s C o . , Waukegan , I l l .

No e f f e c t No i n f o r - € = 0.84*0. 03 i n f o r m a t i o n a f t e r 500 m a t i o n

s u n hf

R e y n o l d s W r a p N o t a p p l i - D u l l s i d e as = 0 . 2 0 S t r u c t u r a l No e f f e c t No e f f e c t Foi l , s m o o t h c a b l e 5 . 0 : E = 0 . 0 4

s h i n y as = 0 . I 9 l i m i t s o n l y

s i d e 6 . 3

E = 0 . 0 3

L o c k s p r a y A n o d i z e d 7 . 3 t o 4 . 8 = 0 . 2 2 to Gold Mg o r 0 . 24

AI a l l o y s € = 6 . 0 3 to c o a t e d 0 . 05 w i t h c l e a r o r w h i t e , g l o s s y o r m a t t e e p o x y

No e f f ec t No i n f o r - No e f f e c t M a t e r i a l u s e d a s to 400 F m a t i o n c o a t i n g o n v i s o r

of f a c e p l a t e o n

h e l m e t d u r i n g A s t r o n a u t W h i t e ' s

ac t iv i ty in the e x t r a - v e h i c u l a r

u s e d a s c o a t i n g o n G e m i n i 4 m i s s i o n ;

i n t e r i o r of G e m i n i 5 a d a p t e r s e c t i o n w l t h s u b s t r a t e of whi te epoxy on

a l loy HK31A-H24. Dow 17 t r ea t ed Mg

A- 8

Polished aluminum al loy I 2 10 20

Wavelength, microns

Flat 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

Flat 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/ c m 2 -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 RADII


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


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 1 1 1 , 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)

APPENDIX B

TABLES AND FIGURES FOR ORGANIC THERMAL-CONTROL COATINGS

TABLE B-1. EFFECT OF WAVELENGTH OF ULTRAVIOLET ON SPECTRAL ABSORPTANCE OF s-13 COATING(^^)

- . . "~~

P e a k E n e r g y A b s o r b e d I r r ad ia t ion by Sample , lo6 @A, 10-8

Wavelength, r n p j ou le s /m ' A a , ( a ) j o u l e s / m 2 -~ ". ..

2 5 5 (4.86 eV) 0 . 0 3 5 0 . 48 273 (4.54 eV) 14.6 0.038 0.26 293 (4. 23 e V ) 21.7 0.026 0. 12 350 ( 3 . 5 4 eV) 60. 0 0.015 0. 03

~.

7 .3

. "

- - ~- . . . ". ~- . ._ _. -

( a ) l n l l ~ a l a , 11. 200

TABLE 8-2. DECREASE IN REFLECTANCE IN S-13 (TYPE B)(3)

- . ~ ~~ - ~. . ~- - - " ~- .~ - I "_

c

Measured A f t e r 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)

Coat ing

S-13-G over B-1056 0 . 191 0 .860 0 .222 0 .200 0 .022 (L. 0. IV)

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 Inorganic (H-2) 0. 178 0 .876 0 .203 0 .216 0 .013

Hughes Organic (H-10) 0 . 147 0 .860 0. 171 0 . 162 0.009

Si l icone-over -Aluminum 0 . I97 0 . 8 0 0 0 .246 0 .239 0 .007

2 -93 (McDonnell) 0. 184 0 . 8 8 0 0 . 2 0 9 0. 183 0. 026 -~ - -.

TABLE 8-4. DECREASE IN REFLECTANCE IN T i 0 2 - METHYL PHENYL SILICONE(3)

Measured After A R = R i - Rf (70) at Selected Wavelengths

Exposure to: 425 m u 500 m u 590 m u 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)

Th ickness , So la r mils A b s o r p t a n c e E m i t t a n c e

0 . 7 5 0 . 1 8 0 . 4 5

3 . 2 0 . 2 2 0. a 5

6. 5 0 . 2 2 0 . aa

TABLE B -6. EFFECT OF SAMPLE TEMPERATURE DURING NUCLEAR IRRADIATION ON THE OPTICAL PROPERTIES OF THERMAL-CONTROL COATINGS(31)

M a t e r i a l . " - - . " ".

Skyspar epoxy-based coa t ing

"_ . ~ -. . . .

T e m p e r a t u r e During

I r rad ia t ion , F f 10

-100 0

t l O O

t 2 0 0

U S In i t i a l F ina l Dose

0. 22 0. 22 2. 2 x l o 6 r a d s ( C ) 0.22 0.22 0.6 x 1 0 1 3 n / c m 2 , E<0.48 eV 0.22 0. 23 1 x 1014n/cm2, E>2.9 MeV

0. 22 0.28 in vacuum

Z r S i 0 4 - - K ~ O / S i 0 2 7 0 0. 11 0. 13 2 . 2 x l o 6 r a d s ( C ) -320 0. 11 0. 22 2.26 x 1 0 1 4 ~ / ~ m 2 , E<O. 48 eV

4. 72 x 1014n/cm2, E>2.9 MeV in vacuum

Na20. AI203- 4,502 70 0. 17 0. 24 - NazO/SiOz -320 0. 17 0. 34 "

.. , ~- , . ~ . ~- ~

B-3

FIGURE B-1. SPECTRAL REFLECTANCE OF ~ 1 0 5 6 COATING(^^)

Wavelength, mlcrons

FIGURE B-2. EFFECT OF UV IN VACUUM ON S-13 C0ATING(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

FIGURE B -4.

IO 100 1000 Time in Sunlight, ESH

ZINC OXIDE IN SILICONE (S-13)

10,000

B-5

FIGURE B-6. ATS-1 FLIGHT DATA FOR S-13 COATING(20)

Eqvi~llenl Solar Hours. ESH

FIGURE B-7. REFLECTANCE CHANGE OF B1056 AS A FUNCTION OF uv EXPOSURE AT TWO WAVELENGTH^^^)

B -6

200 2 5 0 300 3 5 0 4 00

l r rod lat ion 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 4 0 0 800 1200 1600 2000 2400 Wavelenegth. 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 2xIOl5 p/cm2

Totol proton flux 2 ~ l O ' ~ p / c r n ~

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 / S I L I C O N E ( ~ ~ )

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 2 4

Wavelength, microns

FIGURE B-11. EFFECT OF INCREASING TOTAL PROTON FLUX FROM z x 1015 P / C M ~ TO 1 x 1 o l 6 P / C M ~ - Z~O/SILICONEW)

B -8

I

35 I,1I- 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

FIGURE B-12. EFFECT OF UV RADIATION ONLY - ZIIO/SILICONE(~~)

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/SIIJCONE(~~)

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 1015 p/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

FIGURE B-14. COMBINED 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 lo; 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/SILICONE(~~)

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. E F F E C T O F COMBINED ENVIRONMENT IMMEDIATELY AFTERACCELERATEDPROTONEXPOSUREANDAT END OF TEST - Z ~ O / S I L I C O N E ( ~ ~ )

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 IN SOLAR ABSORPTANCE OF S-13G COATING: LABORATORY DATA AND FLIGHT D A T A W )

B-12

Wavelength. microns

,- .. I:

FIGURE B-20. INITIAL REFLECTANCE S-13G USED ON LUNAR ORBITER IV(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 4 0 0 6 0 0 000 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 % 1606 I 6 0 0

I

EQUIVALENT SOLAR HOURS

0 400 000 1200 1600 2 0 0 0 2 4 0 0 - 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 T O 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(microm)

FIGURE B-26. COMPARISON OF THE CHANGE FIGURE B-27. IN SITU REFLECTANCE LOSS IN TREATED IN SOLAR ABSORPTANCE OF ZINC OXIDE-METHYL SILICONE FOL- S-13G COATINGS IN TWO LOWING EXPOSURE TO 50 KEV FLIGHT EXPERIMENTS(14) ELECTRONS(25)

B-15

1

W

z u <

WAVELENGTH, M I C R O N S

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 IN 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 - 1 3 ~ ) ( 2 2 )

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 O F INDIVIDUAL EFFECTS (S-13G)(22)

Wovelength. microns

FIGURE B-34. B-1060 (10.1 MILS), 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

. ~ ~~

After 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 M E A S U R E M E N T S ( ~ ~ )

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 SILICONE)(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 H A V E L E N G T H , M I C R O N S

FIGURE B-37. DEPENDENCE OF REFLECTANCE DEGRADATION IN RUTILE Ti02"ETHYL SILICONE UPON ELECTRON ENERGY(27)

FIGURE B-38. DEPENDENCE OF REFLECTANCE DEGRADATION IN ANATASE Ti02-METHYL SILICONE UPON ELECTRON ENERGY(27)

3 x 1 0 ' ~ 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 ( T i 0 2 SILICONE)(22)

T s 0 2 - METHYL PHENYL SILICCINE SAMPLE TYPE P Y Q O M A Q K 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 Ti02/METHYL SILICONE C O A T I N G ( ~ 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 IN LEAFING ALUMINUM-SILICONE DUE T O 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 IN 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 fail

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 8 4 7 . 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 (White Skyspar Enamel )

(Sherwin-Willioms M49WC17 White acrylic flat paint I

0 500 1000 1500 2000 2500 Exposure, sun hours

FIGURE 8-48. EFFECT OF NEAR-ULTRAVIOLET RADIATION IN 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 2 2 2 4

Wavelength, microns

FIGURE B49. SPECTRAL REFLECTANCE OF PV-100 (9-2) IN 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) IN V A C U ~ ~ ~ )

- 1 "

Note: Block area denotes maximum changes of solar absorDtance due to bubblina.

.

I- /

I I I I I

1 0 0 200 300 400 500 600 700 0

Maximum Ascent Temperature, F

0

FIGURE B-51. EFFECT OF ASCENT HEATING OR SOLAR ABSORPTANCE OF SHERWIN WILLIAMS WHITE KEMACRYL PAIN?Ig)

B-30

White ocrylic f la t paint

""_ Best f l t to dota

O L I I 0 0 5

I I 10 15 2 0 2 5

Gommo Dose, IO rods(C)/g

I O

09

0.8

07

a 0.6 -

0 W - - w 0 5 U

0.4

0 3

0 2

" 0 0 2 0 4 06 0.8 I O 12 1.4 16 1.8 2.0 2.2 2.4

Wovelength. rntcrons

FIGURE B-53. SPECTRAL REFLECTANCE OF MgO/ ACRYLIC (9 -4) IN VACUO(34)

FIGURE B - 5 4 . EFFECT OF TWO UV WAVE- LENGTHS ON THE SPECTRAL ABSORPTANCE OF SKYSPAR C O A T L N G ( ~ ~ )

B-3 1

APPENDIX C

TABLES AND FIGURES FOR INORGANIC THERMAL CONTROL COATINGS

TABLE C-1. ENVIRONMENTAL CONDITIONS(40)

Exposure Test Number: Pigment/Bindeda) 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 U N Sun Irradiance/Hour

Energy

percent

Irradiance 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 specimen appearance after completion of the test.

(a) ZnO New Jersey 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 joules /m Aa.5 (joules/rn2)-1 i @,(a),

~~~~ ~ ~~ ~

I 3 . 6 x l o 8 0.021 0 . 58 x 10-10

I1 1. 9 x l o 8 0.003 0. 16 x

III 6 . 0 x l o 8 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. OPTICAL PROPERTIES O F 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 Th ick - Neu t ron Nuc lea r n e s s , 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 . 3 5 2 . 9 3 0 . 4 0 . 091 0. 123 0 .75 0 . 75 2 . 3 5 2 . 9 3 0 . 5 0. 126 0 . 140 0. 77 0. 78 2 . 3 5 2 . 9 3

2 . 5 9 2 . 7 1 0 . 6 " 0 . 129 0 .80 0 .80

T A B L E C - 6 . E F F E C T S O F E L E C T R O N AND UV RADIATIONS ON ANODIZED-ALUMINUM COATINGS AT 77 K ( 4 )

as a f t e r as a f t e r Ini t ia l a , a f t e r 5 . 8 x 1 0 1 5 UV and Electron

Sample Type as 350 ESH e/cmZ Radiat ion

Sulfur ic acid 0. 20 0. 28 0. 20 0. 27 anodized aluminum ( 1 199 aluminum)

Bar r i e r anod ized 0. 1 7 0. 19 0. 16 0. 20 a luminum ( 1 199 All

Aluminum oxide l 0 . 1 1 0. 16 0. 19 0. 24 potass ium s i l i ca te

c-4

TABLE C-7. EMITTANCE OF TEFLON OVER VAPOR DEPOSITED ALUMINUM(36)

Thickness, mils To ta l Norma l Emi t t ance - 0. 25

__" 0. 26

n. 50 0 . 4 3 1 . 0 0 0 . 53 2 .00 n. 67 5 . 0 0 0 . 8 3

10 .00 0 .89 "" -

TABLE C-8. ULTRAVIOLET EXPOSURE OF SERIES EMITTANCE COATINGS(36)

Sample Descr ip t ion

Dosage uv, X-Ray, Solar Absorp tance

ESH(a) Before After ~

P J l 13 on a luminum 3 , 8 0 0 " 0. 15 0 . 15 PJ 1 13 on a luminum 170 10 0. 16 0 . 17 PJ 1 13 on a luminum I , 720 100 0. 16 0.18 Polyvinyl bu tyra l (Butvar ) 100 10 0. 19 0 .20 Polyvinyl bu tyra l (Butvar ) 1 , 000 IO0 0 . 18 0 . 2 0 5 - m i l Teflon on aluminum 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 Irradiation 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) Irradiation 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 Conditions Sample Change in

Envi ronment of Type of Radia t ion In t eg ra t ed P res su re , Tempera tu re , So la r In te res t Radia t ion Energy Flux t o r r K Absorptance

Art i f ic ia l Electron Electron 800 keV 1016 e / c m Z 210-6 290 0 Bel t E lec t ron 800 keV 1015 e/crnZ - <10-6 155 0

Electron plus 800 keV 6 x 1014 e /cmZ 5 1 0-6 3 00 0 s imultaneous e lectrons t plus 436 ESH ul t raviolet ( U V ) 3. 1 t o 6 . 2 eV UV

ul t raviolet e t U V Ditto - <10-7 77 0

e t U V I 3 x 1015 e / c m 2 - <10-7 300 0 plus 150 ESH

130 kcV Van Allen Protons 130 keV

Pro ton Bel t 176 keV 466 keV 987 keV 500 keV 5 0 0 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 / c m 2 -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

Solar Wind Proton and Hzt 2 keV 8 x 1015 p/cmZ < I 0-7 280 0

Proton plus 2 keV protons 5 x 1015 p/cmz <10-7 260 0 simultaneous UV t 3. 1 to 6 . 2 eV plus 255 ESH

LiV u v Pro ton I . 4 keV 1016 pIcm2 < I O - ' 3 05 0

Proton plus 2 keV protons 8 f 1015 p/cm2 < 1 0 - 7 320 0 s imultaneous UV t 3 . 1 t o 6. 2 eV t l 1 0 0 ESH UV

photons

Solar Ul t rav io le t uv 3 . 1 to 6 . 2 eV 485 ESH <10-6 290 0

uv 3 . 1 to 6 . 2 eV 436 ESH <10-6 300 0

uv 3. 1 to 6 . 2 eV 175 ESH <6 x 10-8 3 00 0

uv 3 . I t o 6 . 2 e V 2 0 0 0 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

Wavelength ,microns

FIGURE c-2. SPECTRAL REFLECTANCE OF HUGHES INORGANIC WHITE COATING(^^)

YAVELCRGIH, MICRONS

FIGURE C-3. DEPENDENCE OF REFLECTANCE DEGRADATION IN Al203-KzSi03 UPON ELECTRON ENERGu(27)

c-9

Protons, Eleclrons and Ultraviolet (I00 % Neutralizatlon)

- 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 Equivolenl Sun Hours

FIGURE C-5. ATS-1 FLIGHT DATA FOR A1203/K~Si03 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 FLIGHT DATA FOR Ti02/K2Si03 COATING(2o)

2 0 .-

I 8 -

16 -

14 -

I 2 -

10 -

0 8 -

06 -

04 -

02 -

Z n O + T ~ O 2 + A I Z O , / K P S ~ O J

a,:0170

0 -

0

FIGURE C-7. ATS-1 FLIGHT DATA FOR (ZnO + T i 0 2 + A1203)/ K2Si03 COATING(2o)

c - 1 1

FIGURE C-8. ATS-1 FLIGHT DATA FOR A1203/K~Si03 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. FLIGHT DATA FOR (Ti02 + A1203)/KZSi03 COATING(20)

c-12

FIGURE C - 10. ATS- 1 FLZGHT DATA FOR (ZnO -I- Ti02 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)(l3)

C-13

Legend

.

0.2 0 6 I .o 14 18 2 2 2.6


FIGURE C-12. INITIAL REFLECTANCE 2-93 USED ON LUNAR O R B I T E R P ~ )

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

Irradiation Wavelength, 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 OXIDE/LTV 602 (5-13) WNT Q BARRIER-LAYER ANODIZED ALUMINUM

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% Neutralizatlon)

-0.0

"0. I

0 I

1-02

FIGURE C-16. CHANGE IN SPECTRAL REFLECTANCE OF ZnO IN K2SiO3 DUE T O 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 IN K2Si03 DUE T O PROTONS, ELECTRONS, AND ULTRAVIOLET, MEASURED IN SITV(~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 Io ES

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 - b i 0 z 2 20 - 10 kev PROTONS 2 ~ 1 0 ' ~ a a

75hr UV+EUV AT IO ES AT 7.4x109pkm2-

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


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


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

Wave leng th , 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 ~ 0 3 ( ~ )

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“ 0 2 5 a o”---o 000015 in

2 0 2 0 a,

+ e 0

0 1 5 L

O 0 cn -

g 0.10 m 0

0 6 0.05

0 Actual 12 24 4 8 72 9 6 120 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

FIGURE C-29. CHANGE IN RELATIVE REFLECTANCE OF ALZAK AND A1203/Al AFTER 2000 ESH(47)

0.40 A l z a k I I 1

OUnshielded S/N 14 S/N 13, . 0'30 - +Shielded

AI

LT a 0.20 - n + +#+++ ++ 0. ++

o.l O,;r;fC + + "% ++ *

n- I I

Unshielded S/N 14

LT S/N 13, .

a 0.20 n 0. + +#+++ ++ T "% ++ *

0 500 IO00 1500 2000 ESH

FIGURE C-30. RATE OF CHANGE O F RELATIVE REFLECTANCE OF ALZAK IN THE 300-400 nm BAND AS A FUNCTION OF ESH(47)

0.40

0.30 - 0 Unshie lded S/N 14 - Alzak I I I

LT + Shielded 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 O F CHANGE OF RELATIVE REFLECTANCE OF ALZAK IN THE 300-650 IUII BAND AS A FUNCTION OF ESH(47)

C -23

FIGURE C-32. DEPENDENCE OF REFLECTANCE DEGRADATION IN 0.15-MIL ALZAK UPON ELECTRON E N E R G Y ( ~ ~ )

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 mils

0.5, I ,2 mils

Wavelength, microns

FIGURE C-35. SPECTRAL ABSORPTANCE OF SILVER-COATED TEFLON(36)

C-25

Aluminum 0.1 E

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 e f 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 - 2 6

o,30b4T 6 6-1 -2 100 IOESH ESH IO I Mrad Mrod

1 6 4 1000 ESH 100 Mrad

0 IO

0.28 0.x) 0.32 0.34 0.36 0 38 040

Wavelength, 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)

Y A V E L E N C T H , 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

SiOx/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 0 1 7 4 0 3 6 3 0 5 5 1 0 7 3 9 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 M I C R O N S I

FIGURE C-47. REFLECTANCE CHANGES IN S i02 OVER A1 DUE T O 20-keV ELECTRON EXPOSUFd27)

I- Y A V f L t N C T H I M l C R O N S t

FIGURE C -48. REFLECTANCE CHANGES IN S i02 OVER A1 DUE T O 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 IN 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

Y A V E L E N G T H 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 C L E H C T H IMICRONS I

FIGURE C-51. REFLECTANCE CHANGES IN A1203 OVER A1 DUE T O 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 0 8 I O 12 14 16 18 2.0 2 2 I

Wovelength, mlcrans

FIGURE C-53. SPECTRAL REFLECTANCE OF 3M202-A-10 (8-1) IN VACUO(34)

0.4 -. -. - After I ~ x I 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, rn~crcms

FIGURE C-54. SPECTRAL REFLECTANCE OF 3M202-A-10 (7 -1) IN 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


FIGURE C-59. SOLAR ABSORPTANCE OF BLACK NICKEL PLATE ON ALUMINUM(55)

Wavelength, rnlcrm

FIGURE C-60. EMITTANCE GF BLACK NICKEL PLATE O N ALUMINUM(55)

C - 3 6

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 total exposure 0.949

0.953

3800 ESH and 1015 e / 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 ,mlcrans

FIGURE C-65. SOLAR ABSORPTANCE OF SODIUM DICHROMATE-BLACKENED TYPE 347 STAINLESS STEEL(55)

Wavelength,microns

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

Wavelength, microns

FIGURE C-67. ABSORPTANCE OF SODIUM DICHROMATE-BLACKENED INCONEL(55)

Total Emittance 0.040

0.4 "" 4770 ESH and Id5 ekm2

exposure

0 4 8 12 Wavelength ,microns

0.5

0.6

al C

3.7 2 E

e

c .-

W - 38 p

I2 m

3.9

I O

FIGURE C-68. EMITTANCE OF SODIUM DICHROMATE-BLACKENED INCONEL(55)

C -40

Wavelength .microns

FIGURE C-69. SOLAR ABSORPTANCE OF SODIUM DICHROMATE-BLACKENED INCONEL x(55)

Wavelength, microns

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 Wavelength,rnicrons

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 total 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

Wavelength, mcrons

FIGURE C-73. SOLAR ABSORPTANCE OF PYROMARK BLACK ON INCONEL(55)

1 I To ta l 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

Wavelenglh, 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 T O 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 R T V - 6 0 2 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


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

N A T I O N A L A E R O N A U T I C S A N D S P A C E A D M I N I S T R A T I O N W A S H I N G T O N , D. C. JULY 1971


-___. - 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 B a t t e l l e M e m o r i a l I n s t i t u t e Co lumbus Labora to r i e s Columbus, Ohio 4 3 2 0 1 13. Type of Report and Period Covered

11. Contract or Grant No.

NASW-1568

12. Sponsoring Agency Name and Address C o n t r a c t o r R e p o r t

N a t i o n a l A e r o n a u t i c s a n d S p a c e A d m i n i s t r a t i o n Washington, D . C . 20546


15. Supplementary Notes

T h i s d o c u m e n t c o n t a i n s s u m m a r i z e d i n f o r m a t i o n r e l a t i n g t o s t e a d y - s t a t e r a d i a t i o n e f f e c t s on e l e c t r i c a l i n s u l a t i n g m a t e r i a l s a n d c a p a c i t o r s . T h e i n f o r - mat ion i s p r e s e n t e d i n b o t h t a b u l a r a n d g r a p h i c a l f o r m w i t h t e x t d i s c u s s i o n . The r a d i a t i o n c o n s i d e r e d i n c l u d e s n e u t r o n s , gamma r a y s , a n d c h a r g e d p a r t i c l e s . The i n fo rma t ion i s u s e f u l t o d e s i g n e n g i n e e r s r e s p o n s i b l e f o r c h o o s i n g c a n d i d a t e m a t e r i a l s o r d e v i c e s f o r u s e i n a r a d i a t i o n e n v i r o n m e n t .

.. ~ ~- .- ~

17. KeGWords (Suggested by Authoris)) 18. Distribution Statement

R a d i a t i o n E f f e c t s , E l e c t r i c a l I n s u l a t o r s , C a p a c i t o r s , R a d i a t i o n Damage

U n c l a s s i f i e d - U n l i m i t e d

19. Security Classif. (of this report) - . - - . . .

20. Security Classif. (of this page) 22. Rice' 21. NO. of Pages

U n c l a s s i f i e d $3.00 88 U n c l a s s i f i e d


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 artificial. This Handbook will provide the general background and information necessary to enable the designers to choose suitable types of mater ia l s o r c lasses of devices.

Other sections of the Handbook will discuss such subjects as transistors, solar cells , thermal-control coatings, structural metals, and interactions of radiation.

iii

ACKNOWLEDGMENTS

The Radiation Effects Information 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 review and valuable comments on this section:

Mr . F. N. Coppage, Sandia Corp.

Mr. R . H. Dickhaut, Braddock, Dum and McDonald, Inc.

D r . T . M. Flanagan, Gulf Radiation Technology

Mr . F. Frankovsky, IBM

Mr. D. H. Habing, Sandia Corp.

Mr. A. Reetz, J r . , NASA Hq.

D r . V . A. J . VanLint, Gulf Radiation Technology

V

TABLE OF CONTENTS

SECTION 3 . ELECTRICAL INSULATING MATERTALS AND CAPACITORS

ELECTRICAL INSULATING MATERIALS . . . . . . . . . . 1

INTRODUCTION . . . . . . . . . . . . . . . . . 1

RADIATION EFFECTS ON ORGANIC MATERIALS . . . . . 2

RADIATION EFFECTS ON INORGANIC MATERIALS . . . . 10

RADIATION EFFECTS ON SPECIFIC BULK. SHEET. AND FILM INSULATORS . . . . . . . . . . . 11

Polytetrafluoroethylene (PTFE) . . . . . . . . . 12 Polychlorotrifluoroethylene (Kel-F) . . . . . . . . 16 Polyethylene . . . . . . . . . . . . . . . . 18 Polystyrene . . . . . . . . . . . . . . . . 19 Polyethylene Terephthalate . . . . . . . . . . . 20 Polyamide . . . . . . . . . . . . . . . . . 20 Diallyl Phthalate . . . . . . . . . . . . . . 21 Polypropylene . . . . . . . . . . . . . . . 22 Polyurethane . . . . . . . . . . . . . . . . 22 Polyvinylidene Fluoride . . . . . . . . . . . . 23 Polyimide . . . . . . . . . . . . . . . . . 24 Polyimidazopyrrolone (Pyrrone) . . . . . . . . . 24 Epoxy Laminates . . . . . . . . . . . . . . 25

Ceramic . . . . . . . . . . . . . . . . . . 26 Mica . . . . . . . . . . . . . . . . . . 29

Miscellaneous Organics . . . . . . . . . . . . 26

RADIATION EFFECTS ON SPECIFIC WIRE AND CABLE INSULATION . . . . . . . . . . . . 29

Polytetrafluoroethylene (PTFE) . . . . . . . . . 30 Polyethylene . . . . . . . . . . . . . . . . 31 Silicone Rubber . . . . . . . . . . . . . . . 32 Polyimide'. . . . . . . . . . . . . . . . . 33 Irradiation-Modified Polyolefin . . . . . . . . . . 33 Miscellaneous Organics . . . . . . . . . . . . 34

vii

. ..

"..1111"11-I ..-. _I"." ,. -.-. ..................................... .-

TABLE O F CONTENTS (Continued)

Page

C er amic . . . . . . . . . . . . . . . . . 3 5 Miscellaneous Inorganics . . . . . . . . . . . . 36

RADIATION EFFECTS ON ENCAPSULATING COMPOUNDS . . . . . . . . . . . . . . . . . 36

RADIATION EFFECTS ON CONNECTORS AND TERMINALS . . . . . . . . . . . . . . . . 40

CAPACITORS . . . . . . . . . . . . . . . . . . . 46

INTRODUCTION . . . . . . . . . . . . . . . . . 46

Glass- and Porcelain-Dielectric Capacitors . . . . . 48 Mica-Dielectric Capacitors . . . . . . . . . . . 50 Ceramic-Dielectric Capacitors . . . . . . . . . . 51 Paper- and Paper/Plastic-Dielectric Capacitors . . . . 52 Plastic-Dielectric Capacitors . . . . . . . . . . 60 Electrolytic Capacitors . . . . . . . . . . . . 64

REFERENCES . . . . . . . . . . . . . . . . . 71

INDEX . . . . . . . . . . . . . . . . . . . 7 9

v i i i

SECTION 3 . ELECTRICAL INSULATING MATERIALS AND CAPACITORS

ELECTRICAL 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 sensitivity and what effects might occur as a r e s u l t a r e of primary importance to the circuit designer and application engineer in designing a system that includes radiation as an environmental condition. The purpose of this report is to assist in providing information regarding the radiation tolerance of various insulating materials and the degradation of their electrical properties. Deglladation of mechanical properties, however, is also a consideration to the extent that in many applications the mechanical fail- u re of an insulator or dielectric will adversely affect its electrical charac te r i s t ics . If the reader 's in terest i s such that he requires more information than is presented herein concerning changes in the basic mechanical characterist ics of organic insulating materials or the damage mechanisms involved, he is directed to the elastomeric and plastic components and materials section of this handbook.

It is impractical to attempt to compile within this document the detailed information that would be directly applicable to all circuit requirements and environmental conditions. Often the damage experienced by an insulating or dielectric material is dependent upon environmental conditions 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 might occur. For these reasons, this repor t is limited to generalized "ballpark" type information which is applicable to early design considerations. Where information on a mater ia l i s insufficient for "ballpark" generalization, however, details of specific i r radiat ions are presented.

The effects of radiation as presented in this report are often identified as damage threshold and/or 25 percent damage dose. These terms relate to changes in one or more physical propert ies , 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 in property occurs.

The scope of this report has been l imited to the effects of steady- state and space radiation and excludes information concerning transient radiation or pulse-radiation effects with the exception of the next few pages where transient effects are used for i l lustration. The information presented i s separa ted by the configuration of the test item, i. e . , bulk or sheet materials, wire and cable insulation, encapsulating compounds, connectors and terminals, and capacitors. Introductory paragraphs on organic and inorganic insulators discuss the effects of radiation in general terms on these two basic categories 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 material , keeping in mind 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 procedures to c.alculate ionization due to neutrons and protons are available in the handbook section entitled "Radiations in Space and Their Interaction with Matter".

RADIATION EFFECTS ON ORGANIC MATERIALS

Organic insulating and dielectric materials experience both temporary and permanent changes in characterist ics when subjected to a radiation environment such as that found in space or the fields of a nuclear reactor or radioisotope source. Data indicate that the temporary effects are generally rate sensit ive with a saturation of the effect at the higher radiation levels. The enhancement of the electrical conductivity is the most important of the temporary effects ; increases of s eve ra l o rde r s of magnitude are observed. The magnitude of the increase is dependent upon several factors including the material being irradiated, ambient temperature, and the radiation rate.

Absorption of energy, excitation of cha rge ca r r i e r s f ron nonconduc: ting to conducting states, and the return of these carr iers f ron conduct ing to nonconducting states are considered responsible for the induced conductivity. S . E. Harr i son , et al, ( l ) have demonstrated that, with steady- s ta te g a m m a irradiation between and l o 4 rads (HZO)/s , the excess

2

conductivity has distinct characterist ics in three t ime intervals which are denoted as A, B, and C in Figure 1. The conductivity increases exponen- t ially in response to a s tep increase in gamma dose ra te , y, during Inter- val A and is character ized by

where

uo = initial conductivity

u = conductivity at t ime t

A = empirical constant

T o = k o j - p = time constant of the response as a function of gamma dose, gamma equivalent ionizing dose, or dose ra te ko and p being empirical constants ( see F igu re 2 ) .

During Interval B, the induced conductivity is at equilibrium, and its value is determined by the rate of exposure and temperature for a specific material . This condition is characterized to a good approximation by

(u-u,) = A j' Y 7 ( 2 )

where

A,, and 6 = empirical constants (see Table 1) and

i, = gamma or gamma equivalent (ionizing) exposure rate in rads (H20) / s .

The equilibrium or saturation of the radiation induced conductivity is attributed to two conditions: (1) equal rates of f ree-carr ier generat ion and carrier annihilation through recombination, and ( 2 ) the ra te of f r e e - c a r r i e r capture in trapping states equals that of trapped-carrier decay.

The induced conductivity gradually decreases following the termination of the irradiation. The measured conductivity of Interval C has been character ized for several organic materials by

3

I

9 ""

I I I I I

00 I I

I I I I I I a b

Time, t, s

FIGURE 1. TYPICAL BEHAVIOR OF CONDUCTIVITY IN 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

FIGURE 2. LOGARITHM O F TIME CONSTANT VERSUS LOGARITHM O F 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; d a )

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 o 3 0.74 6.3 x 8.3 x 10'2 to 1.7 x lo3 0.74 1.6 x 8.3 x 10'2 to 1 .7 x lo3

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 lo3

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 o 3

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 lo3

(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 basic characterizations presented above for Intervals A, B, and C by S. E. Harr ison, e t 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 cumulative results of the temporary effects pertaining to the electr ical parameters of insulat ing mater ia ls are a reduction in breakdown and flashover voltages as well as an increase in leakage current or conductance - the latter also being identified as a decrease in the materials insulation 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 t rue i f the designer considers these changes and makes allowances to minimize their effects. Howver, where the designer 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 larger dose tolerance than organics for the same ionizing rate.

Permanent effects of radiation on organic insulating and dielectric materials are normally associated with a chemical change in the material. Most important among these chemical reactions that occur are molecular scission and crosslinkage. These chemical reactions or changes modify the physical properties of the mater ia l . A softening of the mater ia l , decreases in tensile strength and melting point, and a greater solubility could be the result of chain scission. Crosslinking leads to hardening, an increase in strength and melting point, a decrease in solubili ty, and an increase in density. Thus, the permanent effects of radiation on organic mater ia l s is predominantly a change in the physical properties. This

7

.. ... I

physical degradation, however, may also be disastrous to the electrical character is t ics of a component part such as printed circuit boards, wire insulation, and connector s. Radiation-induced embrittlement of insulating structures, such as these, where the insulation cracks or f lakes, in turn, could, cause a circuit to fail electrically through an "open" or "short" circuit. This is often the case when an insulator or dielectric material fails in a radiation environment, i. e . , physical degradation followed by failure of electrical properties. Changes in dielectric loss or dissipation factor and insulation resistance have also been recorded as permanent effects from exposure to a radiation environment. These changes, however, are often quite small, and it would be an uncommon application where they would offer any problem.

A comparison of the relative resistance of organic insulating materials to permanent effects is presented in Figure 3 . Another reaction that may occur when an organic insulator or dielectric is irradiated is gas evolution. Gas evolution from the solid organic polymers is less 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 serious concern except for organic f luids when sufficient pressure may be produced to distort or rupture a sealed enclosure. Another problem with some evolved-gas species is that they are corrosive. This is t rue of the gases produced during the irradiation of halogenated hydro- carbons such as polytetrafluoroethylene (Teflon) and Kel-F. Although failure from other .causes is likely to occur before the corrosion would become a problem, some considerat ion in this area may be advisable when selecting sealed parts - l ike miniature relays - that contain electrical contacts.

Environmental conditions other than radiation contribute to the degradation of organic insulators and dielectrics. Temperature and/or humidity may be important for some materials, and the gaseous content of the ambient atmosphere is of serious import to others. For example, the absence of oxygen is known to increase the tolerance of tetrafluoroethylene 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, glass filled Polyester, mlneral filled Diallyl Phthalate, mineral f i l led Polyester, unfilled Mylar

Sillcone, minerol filled SI Ilcone, glass fllled

Sillcone, unfilled

Urea-formaldehyde Melamine- formeldehyde

Aniline-formaldehyde Polystyrene

Polyimide Acrylonltrile/butodiene/styrene (ABS)

Polyvmyl chloride Polyethylene

Polyvlnylldene chloride Polyvinyl formal

Polycarbonate Kel-F Poly trlfluorochloroethylene Pol vlnyl butyral CelLose ocetote Polymeth I methacrylate PolyomlJe 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)

FIGURE 3. RELATIVE RADIATION RESISTANCE OF ORGANIC INSULATING MATERIALS BASED UPON CHANGES IN PHYSICAL PROPERTIES

9

RADIATION EFFECTS ON INORGANIC MATERIALS

Inorganic insulating and dielectric materials are, in general , more resis tant to radiat ion damage than are the organic insulators . Atomic displacements are responsible for nearly all of the permanent damage that occurs in inorganic insulators, but constitutes only a small par t of the damage in organic insulators. No new bond formations are produced by the irradiation of the inorganic insulating materials, and they are left unaltered chemically.

A large par t 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 carr iers in 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 inorganic materials as well as the organics. The value of 6 is a lmost 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 electrical properties. The density of crystal l ine insulators decreases from exposure to fast neutrons. Amorphous insulators, such as fused quartz and glass, experience a breakdown of their bonds Change in resistivity is the predominant effect on electrical properties; little or no change occurs in a-c characterist ics.

A comparison of the relative radiation resistance of inorganic insulators to permanent damage is presented in Figure 4.

10

Magnesium oxide Aluminum oxide Quar tz Glass (hard)(<l0I6n Glass (boron free) Sapphire Forsterite Spinel Beryllium oxide

Damage Ut i l i ty of Inorganic - Incipient to mild Nearly always usable D Z Z Z Z Z l Mild to moderate Often satisfactory - Moderate to severe Limited use

Gamma Dose, rods(Cfb) ( 0 ) Unsatisfactory at n/cm2 (b) Approximate gamma dose (4 x IOe n/cm2 = I rad (C)) IC) Varies greatly with temperature

FIGURE 4. RELATIVE RADIATION RESISTANCE(C) OF INORGANIC INSULATING MATERIALS

Based upon changes in physical properties

RADIATION ~~ EFFECTS ON SPECIFIC BULK, SHEET. -AND FILM INSULATIONS

"

Electrical insulations of the bulk, sheet, and film type have been investigated as to the effect of radiation on their physical and electrical propert ies by a number of experimenters. This section of the report summarized the resul ts of these investigations.

11

Polvtetrafluoroethvlene (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 is irradiated. The rapid degradation of these propert ies by ionizing radia- t ion is primarily attr ibuted to a prevalence of main-chain scission by liberated fluorine atoms and the production of entrapped f luorocarbon gases. Tensile sgrength and ult imate elongation decrease, and the material becomes embrittled through the main- chain scission. The embrittlement becomes severe with extended irradiation [ l o 7 rads ( C ) ] and the polytetra- f luoroethylene crumbles and/or powders. The approximate danage thres - hold and the 25 percent damage dose are 1. 7 x l o 4 rads ( C ) and 3 .4 x lo4 rads ( C ) , respectively.

There. is evidence that the damage observed when polytetrafluoroethylene is irradiated is a function of several factors . These include the various types of polytetrafluoroethylene such as TFE and the copolymer FEP, the ambient atmosphere, and the test temperature. It had been demonstrated that Tef lon-FEP is more radiat ion res is tant than TFE. In vacuum, 10-mil-thick FEP has retained 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 lustrated in Figures 5, 6 , and 7 which also give a comparison between the effects of irradiation in vacuum and air at room temperature for various sample thicknesses. The absence of air or oxygen improves the radiation resis tance of Teflon. These data also 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 properties. 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- c reased 40 and 6.0 percent after similar doses at 73 and 350 F. (4)

Polytetrafluoroethylene also experiences changes in electrical prop- e r t ies 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 dielectr ic strength. The changes observed are often insignificant in many

12

10.

FIGURE 5. COMPARISON OF ULTIMATE ELONGATION VALUES OF VARIOUS THICKNESSES OF TEFLON TFE-7 IRRADIATED IN VACUUM(3)

i

FIGURE 6. COMPARISON OF ULTIMATE ELONGATION VALUES OF VARIOUS THICKNESSES OF TEFLON TFE-7 IRRADIATED

T I FIGURE 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 mechanical integrity is maintained. Therefore, even though changes in electrical properties do occur, the degradation of physical properties is the cri teria often used in determining the acceptability of th i s mater ia l for use in a specific application.

The volume resistivity of polytetrafluoroethylene decreases two or t h ree o rde r s 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 o r d e r s of magnitude over a period of several days. Recovery may also occur with the volume resistivity approaching its preirradiation value several weeks after the irradiation.

Dielectric-constant measurements of polytetrafluoroethylene during and following exposure to a radiation environment have shown increases of less than 15 percent when irradiation in air or vacuum to respective doses of 8 x l o 6 and lo8 rads ( C ) . Recovery is essentially complete within a day o r two after the irradiation. Similar results have also been obtained under vacuum conditions at cryogenic temperatures to a dose of 7 x l o 6 rads ( C ) . ( 3 ) However, when this test was terminated at 9 . 5 x l o 7 rads ( C ) , the greatest value for the dielectric constant during exposure was approximately 22 percent higher than the init ial cryotemperature value. Recovery to within 0. 4 percent of the initial value occurred after the irradiation was terminated.

Significant increases of between two and th ree o rde r s of magnitude occur in the low-frequency dissipation factor (60-100 Hz) or loss tangent of Teflon TFE when irradiated. This is t rue for i r radiat ions at normal atmospheric conditions (air) and in vacuum at room temperature as i l lustrated by the example shown in Figure 8. Exposure to radiation in an air environment results in an increase to a maximum value which is then maintained during the irradiation. Irradiation in a vacuum environment produces a similar increase in dissipation factor; however, upon reaching a maximum value, this dissipation factor gradually decreases. The absorbed dose at which the maximum occurs appears to be a function of the exposure rate in that the beak occurs at a higher total dose with an in- c rease in the ra te of exposure.

The recovery character is t ics of the dissipation factor of Teflon i r radiated in air and vacuum are quite different. That of vacuum irradiated Teflon recovers rapidly and is essentially complete as long as it remains

14

I

I .O

0. I

0.0 I

0.001

Air

I I I I I I I-

0 I 2 3 4 5 6 7 a 9 Absorbed Dose, IO6 rads (Ag)

FIGURE 8. E F F E C T OF X-RAY IRRADIATION ON TFE-6(5)

15

in the vacuum environment, while the dissipation factor of Teflon irradiated in a normal atmosphere recovers gradually over several days or weeks. If the vacuum-irradiated Teflon is exposed to air or n i t rogen a f te r i t s re - covery under vacuum conditions the dissipation factor increases sharply. Following this increase , there i s a more gradual recovery. Examples of these recovery charac te r i s t ics a re p resented in F igure 9 after the expo sure shown in Figure 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 loss character is t ics of the copolymer Teflon FEP- 100 did not change s i nificantly when this material was irradiated to a total dose of 3 . 08 x 10 % rads (Ag). ( 6 ) It has been assumed that this dose and that in Figure 8 a re in rads s i lver s ince the ca lor imeter t a rge t used in measur ing the dose was silver and .no other material is mentioned in 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 (extrusion resin) and TFE-7 (molding resin), respectively, in this same study.

Dielectric breakdowns induced in Teflon F E P by electron irradiation to a given fluence are both flux and temperature sensitive. (7) An increase in temperature or a decrease in electron f lux 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 u x of 10 e / ( c m 2 . s ) than for a similar fluence and a flux of 10 lo e / ( c m 2 . s ) , and the number of breakdowns at liquid nitrogen temperature was seven to eight t imes greater than at room temperature .

Similar exposures of Teflon. T F E to a proton environment including a flux range of 1 x 109 to 2 x l o 1 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- tu res of -134 C o r 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 dielectric breakdown effect observed with electron irradiation.

Polychlorotrifluoroethylene (Kel-F)

Polychlorotrifluoroethylene, another fluoroethylene polymer, also experiences severe degradation of its physical properties when exposed to a radiation environment. It 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 Recovery Time, days

FIGURE 9. RECOVERY CHARACTERISTICS OF TFE-6 SPECIMENS AFTER X-RAY IRRADIATION AS SHOWN IN FIGURE 8(5)

17

1 . 3 x 106 rads (C) and a 25 percent damage dose of 2 x l o 7 r a d s (C)(4). The elongation of this mater ia l increased 47 percent and the impact strength decreased 16 percent when it was subjected to a total dose of approximately 2 . 4 x l o 7 rads (C) . (9) The ultimate tensile strength was unaffected.

Electron irradiation with a total of 3. 67 x 10 l6 e / cm2 (E = 1. 0 MeV) at 60 C so seriously degraded a specimen of polychlorotrifluorethylene that it could not be measured as to its physical and electrical properties.

The degradation of the electrical properties of polychlorotrifluoroethylene from exposure to radiation includes a reduction in volume and surface resist ivity. Decreases of between one and two orders of magnitude have been observed in both of these parameters during X-ray i r radiat ion to a total dose of 2. 1 x l o 7 rads (Ag) in a vacuum environment.(6) Essen- tially, no recovery was observed following the irradiation.

Measurements of dissipation factor during and following the irradiation of this material has actually shown decreases or improvement in this character is t ic . Low values of 0 . 001 after 1920 hours of recovery in air were observed. ( 6 )

A Russian study that included a total bremsstrahlung dose of 5 .3 x l o 7 rads ( C ) produced similar reductions in volume resistivity. (10)

Polvethvlene

In some respects, polyethylene improves with exposure to radiation in that its softening-point temperature increases for exposures of less than l o 7 rads ( C ) . In addition, the tensile strength also increases until approximately l o 8 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 o 7 rads ( C ) .

There are some differences in the results obtained from the irradiation of polyethylene; thinner films degrade at lower radiation doses than thicker films. This difference in behavior is attributed, at least in part, to the oxidation of the polyethylene when it is irradiated. 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 10 l6 e / cm2 (E = 1. 0 MeV) at 60 C i l lustrates the differences these factors make. ( l ) The hardness and st iffness in f lexure of the high-density mater ia l decreased as a resul t of the irradiation, and the low-density and carbon-fil led materials experienced increases in these properties. The high-density polyethylene also increased in tensile strength and the others decreased.

The e lectr ical propert ies of polyethylene also degrade when it is exposed to a radiation environment. Measurements of the insulating qualities such as volume resist ivity, surface resist ivity, and insulation-resistance indicate that a decrease of up to t h r e e o r d e r s of magnitude occurs in these parameters during irradiation with permanent decreases of one order of magnitude when subject to a total dose of 5. 8 x 10 l6 e / cm2 ( E = 1. 0 MeV). The dissipation factor at 1 KHz increases one to two o r d e r s of magnitude as a resul t of irradiation, and the dielectric constant changes less than *5 percent.

Electron-radiation-induced dielectric breakdown in polyethylene is sensitive to the f l u x to which the polyethylene is exposed; the number of observed breakdowns increases with an increase in electron f l u x . ( 7 ) Exposure to a flux of 1 x 10 l1 e / ( cm2 . s) resulted in 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 o l o e / (cm2.s) and none at 1 x l o l o e / ( c m 2 * s ) .

Proton irradiation 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)

Polvstvrene

Irradiation studies of polystyrene have shown it to be one of the most radiation-resistance plastics among those used for insulating purposes in electronic circuitry. It has a damage threshold of lo8 r a d s ( C ) and does not experience 25 percent damage to its physical properties below 4 x 109 r a d s ( C ) . Polystyrene is subject to postirradiation oxidation that continues for several weeks, however, oxidation plays little or no part in the radiation damage that occurs .

Electron irradiation to a fluence of 5. 8 x 10 l6 e / cm2 , (E = 1. 0 MeV) at 60 C has resul ted in decreases of approximately 50 percent in the tensile strength and ultimate elongation. (11) The hardness and the stiffness in

19

flexure also decreased 1 percent and 13 percent, respectively, during this same study. These results indicate polystyrene becomes more f lexible and softer as a resul t of the irradiation.

The insulating quality of polystyrene appears to be the only electrical property that is affected by exposure to radiation. Permanent decreases of one and two orders of magnitude have been observed in the volume resistivity and insulation resistance of this material following doses as low as 4. 5 x l o 6 rads (C) and as high as 1 x l o 8 rads (C) . Other electrical parameters, such as dielectric constant and dissipation factor, have shown li t t le 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 disagreement concerning the dose at which the trend toward improved physical properties is reversed and degradation begins. Based upon available information, the best estimate for the dose at which this reversal occurs is l o 6 to 107 rads (C) for X-ray and reactor irradiation. Radiation exposure to doses of 108 rads (C) and above causes severe embrit t lement of polyethylene terephthalate to a degree that propert ies are unmeasurable .

Degradation of the electrical properties of polyethylene terephthalate with the doses described above, 106 to l o 7 rads ( C ) , is insignificant. Changes in the insulation resistance, volume resistivity, and surface resistivity as a result of irradiation are l imited to approximately 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. 2 5 MeV and f l u x of 109 to l o l o p/(cmZ. s ) did not induce adielectric breakdown in Mylar 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 experiences threshold damage at a dose of 8 .6 x lo5 rads (C) and 25 percent damage at 4 . 7 x l o 6 rads (C) . These doses are based upon losses in ultimate elongation and impact strength. Another property of polyamide that deteriorates from radiation exposure is 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 / c m 2 ( E = 1 . 0 MeV) at 60 C( l l ) . This same exposure improved the tensile strength by 49 to 107 percent. These results agree with other radiation studies which have shown increases in tensile strength of 25 percent for doses over 109 rads ( C ) .

Information 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 approximately one order of magnitude in the insulation resistance and a decrease of less 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 r a d s ( C ) . Insignificant changes a re observed in the hardness and flexibility of this material when irradiated to these total doses. The ultimate elongation and tensile strength of Orlon-filled diallyl phthalate actually increased or improved with exposure to an electron dose of 5 . 8 x 10 l6 e / cm2 (E = 1.0 MeV) at 60 C .

The electrical properties of diallyl phthalate such as dielectric constant, dissipation factor, and insulation resistance are affected by exposure to a radiation environment such as described above. The amount of degradation or change in these parameters because of this exposure is of little practical significance. Permanent changes in dielectric constant were less than 6 percent while the dissipation factor recovered to below the initial value. Increases in insulation resistance during exposure are followed by complete recovery within approximately 1 hour after the irradiation is terminated.

21

Polypropylene

Polyprolylene is subject to a seve re l o s s in physical properties when exposed to a radiation environment. Above a total dose of 1 x l o 7 rads (C) this material becomes embrit t led and exTeriences decreases in tensile and impact strengths that approach 60 and 75 percent, respectively, at a dose of 5 x l o 7 rads (C) . An electron fluence of 5. 8 x 10 l6 e / cm2 (E = 1 . 0 MeV) at 60 C resulted in decreases of 87 to 96 percent in utlimate elongation and tensile strength. (11) This electron fluence also produced a decrease in hardness of 25 percent which is in agreement with resul ts f rom other studies where polypropylene became increasingly softer and more flexible with doses of between 2.6 x lo8 and 8 . 7 x lo8 rads ( C ) when lower doses caused embrit t lement of the mater ia l . ( 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 plasticized 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 t t le o r no practical significance. The dielectric constant decreases slightly and the insulation resistance decreases less than an order of magnitude. Measurements of a -c loss such as power factor and dissipation factor at 1 KHz to 1 MHz have varied from no observable change to an increase from between 0 . 0005 and 0.0008 to between 0 . 002 and 0 . 0 0 3 . N o information 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 u x to which it is exposed for a specific fluence. (7 ) The maximum number of breakdowns observed at room temperature with a f l u x of 1 x 10 l1 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 electrical properties when exposed to a radiation environment. Irradiation to doses up to 7 x 108 r a d s (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 o 8 rads ( C ) indicates the possibility of approaching a damage threshold. N o information is available above this dose, with exception of the results from an electron f luence of 5. 8 x' 1016 e /cm2 (E = 1. 0 MeV) at 60 C.( ') Serious deterioration of physical propert ies occurred from this radiation exposure and included a 67 and 176 percent increase in hardness and st iffness in f lexure, respectively. A 59 percent decrease in tensi le s t rength and a 99 percent decrease in ult imate elongation were also noted following irradiation to this electron fluence.

Information concerning the effect of radiation on the electrical prop- e r t ies of polyurethane is l imited to results from two radiation studies: the electron irradiation mentioned above and a reactor exposure to a neutron fluence of 1. 2 x 1014 n / c m 2 (E > 0. 5 MeV) and gamma dose of 1 . 4 x lo6 r ads (C) at 16 C to 29 C. (14) Insignificant permanent changes in the insulating properties, volume resistivity, or insulation resistance of less 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 only disagreement in the results of the two studies was the dielectric constant which decreased 6-1/4 percent at 1 KHz from the e lectron i r radiation and increased approximately 16 percent from the reactor exposure.

Polyvinylidene Fluoride

Polyvinylidene fluoride (Kynar 400) has shown higher radiation tolerance than other fluorocarbons such as Teflon and Kel-F. It has demonstrated an ability to withstand irradiation to a dose of l o 7 rads (C) in air or vacuum with no indication of degradation in physical properties except color change. An order-of-magnitude increase in the radiation dose to 108 rads (C) and above causes embrit t lement and loss of flexibility and tensile strength. Low temperature, however, increases the radiation tolerance of polyvinylidene fluoride in that doses of this magnitude, l o8 r ads (C) , at cryogenic temperatures do not reach damage threshold.

Changes in the electrical properties of polyvinylidene fluoride include decreases of between two and three orders of magnitude in volume resistivity during and after irradiation to doses up to 2. 1 x l o 7 and 6. 6 x 10 7 rads (C) in an air and a vacuum-cryotemperature environment, respectively. ( 3 ) A decrease of approximately f ive orders of magnitude occurred with a dose of 2. 1 x 108 rads (C) in the air atmosphere. Dissipa- t ion factor increased less than one decade, and the dielectr ic constant was essentially unaffected by the irradiation.

23

Polvimide

Polyimide (Kapton) has shown little or no change in either its physical or e lectr ical propert ies to gamma doses (Co 60) of up to 109 rads (C) . (15) Tensile strength remained essentially 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 e lectr ical res is t ivi ty remained at 1 x 1019 ohm-cm or above and only decreased to 3 x 10l8 ohm-cm at a total dose of 1 x 101o r a d s ( C ) , This same dose left the dielectric constant essentially unchanged and decreased the breakdown voltage to approximately 75 percent of its initial value.

Dielectric breakdown induced in polyimide (Kapton) by electron irradiation has been shown to be sensitive to both flux and temperature. (7) A total of eight breakdowns on two samples were observed at room temperature for a f l u x of 1011 e / ( c m 2 . 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 / ( c m 2 . s ) . The effect of temperature on the number of dielectric breakdowns is illustrated by the results 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 while 75 and 120 breakdowns occurred with the specimens irradiated 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 10l1 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)

Polyimidazopyrrolone polymers (Pyrrone) have been subjected to various radiation environments including electron, proton, and gamma (Co 60) . Exposure to high doses of electron radiation, 1 x l o l 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 nonirradiated 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 / c m 2 (E = 2 MeV). However, this fluence caused an increase in dark current by a factor of 5 in 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 electron irradiation to a given fluence is sensitive to both flux and temperature; the number of breakdowns that occur tends to increase with flux and decrease with temperature . ( 7 ) An order of magnitude increase in electron f lux, from 109 e / ( c m 2 . s ) to 101o e / (cm2. s) , resulted in twice as many breakdowns for similar fluences of e/crn2 (Ek = 30 keV) at room temperature. Also, the number of breakdowns recorded at liquid nitrogen temperature was more than twice that observed at room temperature for a flux of either 1010 o r 1011 e/(cm2. s ) .

N o 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 ra tes were 109 and 1O1O p/ (cm2. s) with specimens subjzcted to each rate for the total fluence.

The exposure of Pyr rone , both PMDA-DAB and BTDA-DAB, to a g a m a dose rate of 10 to 1000 rads /min ( C o 60) produced current densit ies 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 radiation-induced charge carriers migrating in the electric f ield.

EDOXV Laminates

Epoxy-glass laminates have shown little or no degradation in mechanical and/or electrical properties from reactor irradiation to 2 x 1013 n/crn2 ( E > 0 . 1 MeV) and 1 x lo8 rads ( C ) or cobalt-60 gamma irradiation to 1 x 107 r a d s ( C ) . ( 3 7 15) Variations in breakdown voltage have been observed at gamma doses below this level, however, with decreases of 15 to 30 percent f rom preirradiat ion values at 1 x 107 r a d s ( C ) and 50 to 70 percent at 1 x 109 r a d s ( C ) . Other electrical properties such as resist ivity, dielectric constant, and dissipation factor are not degraded significantly at this total dose.

25

The tensile strength of epoxy-glass laminates remains unchanged to a gamma dose of 1 x l o 7 rads (C) bu t 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) will cause an epoxy- glass laminate to become brit t le and weak or to lose most of the res in binder.

Miscellaneous Organics

Radiation-effects information is available on organic bulk, sheet, and/or film materials other than those discussed on the preceding pages. The information, however, is limited to results from only one radiation- effects test of each mater ia l . Therefore , these resul ts are l imited to the tabular presentations of Tables 2 and 3 . Table 2 is a listing of mater ia ls that were s o seriously 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 radiation environments; it indicates only that they did not survive the indicated electron fluence. The listing in Table 3 consists of those mater ia ls that survived exposure to the radiation environment and includes some of the particulars concerning changes observed in their physical and electrical propert ies .

Ceramics

Ceramic insulat ing mater ia ls , such as s i l ica , Steat i te , Als imag, 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 o 7 r ads (C) . Similar results have also been observed with reactor irradiation to doses as high as 1017 n/cm2 ( E > 0 . 1 MeV) and lo9 rads (C) . Permanent de- c r e a s e s of between one and tow orders of magnitude will occur in the volume and surface resistivity of ceramic insulating materials 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. ( 2 0 ) 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 INDICATEDW)

~ .. ~~~ " . - .~ " - " _ - - .. . ~ ~~ - - - .~ -

Total Electron Fluence at 60 C Material Identification (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 o 9 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 lo9 rads)

Cellulose butyrate 4.10 x 10l6 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 o 8 rads)

5.80 x 1016 e/cm2 (1.8 x l o 9 rads)

Polyfluoroethylenepropylene, Teflon FEP (copolymer) 3.67 x 1OI6 e/cm2 (1.1 x l o 9 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 Identification Total Integrated 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

9 1 -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 increased 5 percent. Dielectric constant increased 4 to 6 percent. DF increased to 0 .01 at 1 KHz and 0.40 at 1 MHz. IRde- 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 increased 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 o 6 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 darkening in color is the only observable change in the ceramics ' physical properties 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 which there are radiation effects data for sheet or other basic physical 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 lo8 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, l9) 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 in f lexure 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 lo7 rads (C). The resist ivity was unchanged and the dielectric constant increased less than 10 percent for the same total dose of 1 x 1010 rads ( C ) (Co 6 0 ) . 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 SPECIFIC WIRE AND CABLE INSULATION

Both organic and inorganic wire insulations have been tested and evaluated as to their radiation resistance. A serious deterioration of physical properties as a resu l t of irradiation has occurred with some organics, and others, demonstrating a high level of radiation tolerance, have survived doses of up to 1 x l o 8 rads (C) . Special cables and wires insulated with inorganic materials have shown similar radiation resistance

29

I . .

to doses of 8 .8 x 109 and 8 . 8 x l o l l rads (C). Changes in the electrical properties of wire having e i ther organic or inorganic insulat ion are generally of little practical significance and include both temporary and permanent 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 exposure is terminated. Permanent decreases in dielectr ic s t rength have also been observed following exposure to radiation as have increases in dissipation factor and the attenuation of coaxial cables. Details concerning these and other effects of radiation are discussed in the following paragraphs as they pertain to specific wire and cable insulation.

Polytetrafluoroethylene (PTFE)

Polytetrafluorethylene (Teflon) wire insulation has shown severe degradation in physical properties as a resul t of exposure to a radiation environment. The extent of the damage that occurs is sensitive to total dose and varies from a noticeable decrease in wire flexibility to the complete disintegration of the material .

The lowest total dose at which information on changes in physical charscter is t ics is available is 10 rads ( C ) with a 5 psia oxygen atmosphere and ambient temperature of 9 0 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 MIL-W-1687D. Similar results also occurred for a dose of 6 x 10 rads ( C ) with a vacuum of loe6 t o r r and a temperature of 150 C . These results indicate two possibil i t ies: the TFE Teflon (polytetrafluoroethylene) insulated wire with the ML coating has a lower radiation tolerance and/or the l o 3 to 6 x l o 4 rads ( C ) total dose is the threshold 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 deterioration has been reported after total exposures of l o 7 and l o 8 r a d s ( C ) . The damage is such that the inner core of a Teflon-insulated coaxial cable wil 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- t ion or other mechanical s t resses as a par t of the intended environment.

The irradiation of polytetrafluoroethylene-insulated wire a lso resul ts in the degradation of electrical properties. Insulation resistance measurements performed before and after irradiation have shown l i t t le or no significant change in this parameter. Breakdown voltage has decreased as much as 50 percent .between twisted pairs of wire having initial breakdown at voltages as high as 15.8 to 28. 2 kV.(22, 23) The posttest range was 9 . 1 to 14. 2 Kv. Several electrical characterist ics of coaxial cables have shown the effects of degradation. The attenuation of a 10-foot length of RG-225/U at 400 MHz increased 0 . 20 db while the change for a similar sample of RG 142/U was so great it could not be measured after a total exposure of 3 x 1 0 l 6 n / c m 2 ( E > 0 . 1 MeV) and 2 . 3 x lo8 rads ( C ) . (24) The RG 142/U cable also experienced larger increases in other measured para- m e t e r s 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 physical and electrical properties of wire and cable that incorporate polyethylene as the insulating media have shown little or no degradation for total doses up to 107 and l o 8 rads ( C ) a t temperatures of f rom 15 C to 100 C. This is 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 o 7 rads ( C ) with the darkening of the polyethylene, but it still remains resil ient with no indication of st iffness. I t is estimated that threshold damage occurs at approximately 4 .4 x l o 8 rads ( C ) . Loss of flexibility has been observed, however, after cable insulated with polyethylene and having outer jackets of either Estane or Alathon received a total dose of 8. 8 x lo8 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 coaxial or shielded type, in that some materials 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 e lec t r ica l p roper t ies of polyethylene-insulated wire and cable have shown some degradation during and following exposure to a radiation environment. Insulation resistance is both rate and dose sensit ive with changes of one to three orders of magnitude observed during exposure. Re- covery is essentially complete following the termination of the irradiation. The characterist ic impedance of coaxial cables has shown some variation as a result of radiation exposure but the extent of these variations is of little significance ( 0 . 5 to -10 percent). Limited data on other coaxial- cable parameters indicate that l i t t le or no change occurs in attenuation, VSWR, or apparent electrical length when these cables are irradiated.

An induced current is also an electrical characterist ic that has been observed in e lectr ical cable 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 during the cable 's exposure to the radiation which included 1. 2 x 1 0 l 2 n / ( c m 2 . s ) ( E > 2 . 9 MeV) and 6 . 6 x l o 7 rads ( C ) r / h r g a m a 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 o 5 rads ( C ) . A slight change or lightening in color with a barely perceptible loss in resil ience or f lexibil i ty has been observed in f lat-ribbon multiconductor wire insulated with this material after an exposure of 8. 8 x 10 6 rads ( C ) . ( 2 7 ) Serious deterioration of the wire 's mechanical quali t ies occurs with a total dose of 8 . 8 x l o 7 rads ( C ) and above. There is a definite loss in flexibility, and the silicone rubber insulation will crack and/or crumble when the wire is stressed mechanically.

The insulation resistance of wire insulated with silicon rubber decreases one or two o r d e r s of magnitude during irradiation with recovery to within one order of magnitude when the exposure is terminated. If the environmental conditions also include moisture and/or elevated temperature the combined effect can decrease the insulation resistance even further. The breakdown voltage of silicon wire insulation has shown some variation between - and postirradiation measurements after doses of 1 x lo3 and 4 x 10 r a d s ( C ) . ( 2 2 , 23) These changes in breakdown voltage, however, include both increases and decreases and are of little significance.

r e

3 2

Polyimide

Polyimide res in film, ML, wire insulation has shown no indication of deterioration in physical or electrical properties up to a dose of 1 . 5 x lo8 r a d s (C) and 4 . 4 x 1017 n / c m 2 (E > 0. 1 MeV). Flexibility and stripping characterist ics are unaffected with no visible difference between wire that has been irradiated and that which has not. Measurements of electrical parameters such as insulation resistance, capacitance, and dissipation factor have shown no significant difference between pre- and postirradiation values. Wires with a combination of glass braid and polyimide resin film insulation exhibited a breakdown voltage of approximately 1000 wires before and after receiving the total exposure indicated above. (27)

The absence of degradation at doses up to 1. 5 x l o 8 rads ( C ) demon- s t r a t e s a high level of radiation resistance for this wire insulation with a possibility of satisfactory performance at even higher doses.

Irradiation-Modified Polvolefin

Irradiation-modified polyolefin+-insulated wire has experienced no serious degradation in physical or electrical properties when irradiated to a total dose of 5 x l o 8 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 standard 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 mirrors was also included in this same study. N o corrosive effect was observed.

Information 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 magnitude 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 in this study were (1) an X-ray dose of 6 x l o 4 rads (C) with a vacuum of to r r and tempera ture of 150 C and ( 2 ) an X-ray dose of 1 x 10 rads (C) with a 5-psi oxygen atmosphere and a tempera ture of 9 0 C. The stability of the insulating qualities of this mater ia l when i r radiated was a lso demonstrated in another study when wire insulated with this material com- pleted a wet dielectric-strength test of 2 . 5 kV after a radiation dose of 5 x lo8 r a d s ( C ) . ( 2 8 )

3

Coaxial cable insulated with irradiation-modified polyolefin (polyethylene) 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 o 8 rads ( C ) and 3 . 0 x 10l6 n /cm-2 (E > 0. 1 MeV).(24) At the same t ime there was little change in VSWR and the apparent change in electrical length was 0 . 08 and 0 . 106 wavelength.

Irradiation-modified polyolefin-insulated wire and cable has demon- s t ra ted 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 results of a study of electron irradiation 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 o l o e / ( c m 2 . s ) ( E > 60 keV) at room temperature varied inversely with the total capacitance in the system. The average pulse height decreased from 5. 1 volts at 1. 1 x

resis tance f rom 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), electron-discharge patterns (Lichtenberg f igures) were found in the insulation. Rough calculations indicated that

farad to less than 0 . 01 volt at 1. 0 x farad. Increasing 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 discharges were possibly as high as 11,000 volts, and power densities of 3 x 101o watts/ cm2 were indicated if a discharge t ime of 0 .01 microsecond 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 irradiation, and at some point in time it is released and transported to the conductor and is observed as a voltage pulse. A surface i r regular i ty or pin prick init iates the release mechanism. Such pulses could be damaging to sensitive electronic circuits.

TABLE 4. RADIATION EFFECTS ON MISCELLANEOUS ORGAMC WIRE INSULATIONS ~ ___ - - ~~ - - ~

- "

Total Integrated Material Identification Exposure(a) ". ~ _, - ~~ ~ - _

Alkanex 4.6 x l o 7 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.

Ceramic

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 temperature . A tendency to powder during stripping tests is the only indication of deterioration of physical properties. The stability of electrical properties has also been satisfactory with some loss in dielectric strength and insulation resistance being observed. A decrease of approximately 16 percent occurred in breakdown voltage or dielectric strength between pre- and postirradiation measurements in one study.(27) Results of other studies

3 5

have shown a definite difference between the dielectric strength of i r rad ia- ted and-control specimens. These differences could be termed insignificant 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 specimens. ( l 9 ) Considerable difficulty due to the hygroscopic property of the ceramic insulation was encountered with these measurements and may have contributed to some of the difference. Changes in the insulation resistance as a resul t of exposure to a radiation environment have been insignificant.

Miscellaneous Inorganics

Radiation-effects information on seven inorganic wire insulations other than the ceramic discussed above is l imited to single evaluations of the radiation resistance of each wire or cable. Of the seven wires and cables tested, four are standard products and three are special or non- production i tems. Because of the limited information available, information concerning the radiation resistance of these wires and cab le s a r e presented in the tabular format of Table 5.

RADIATION EFFECTS ON ENCAPSULATING COMPOUNDS

Encapsulating compounds that have been evaluated as to their radiation 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 materials tested and the radiation environment to which they were exposed.

19 of

Sil icone resin encapsulating materials, such as RTV-501 and Sylgard 2 and 183, have not been seriously degraded at radiation exposure doses 2 x 1013 to 1. 5 x 1015 n / c m 2 ( E > 0. 1 MeV) and 1 . 8 x l o 6 to 8 . 8 x 108

rads (C). Degradation of the physical properties has been limited to a slight but insignificant weight loss of less than 1 per cent. Insulation resistance dat.a show permanent decreases of 40 to 50 percent with the minimum resis tance of approximately 1 x 10l2 ohms after a total exposure

36

I

TABLE 5. RADIATION EFFECTS ON MISCELLANEOUS INORGANIC WIRE INSULATION

Material Identification ~. ~~~

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 Integrated 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 o 7 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. N o electrical tests.(27)

Room temperature. No visible signs of degradation. No electrical tests. (27)

200 C. No breaking, cracking, or spalling was evident when subjected to a bend test. Weight loss <0.2 percent. No electrical tests. Slightly darker in color.(lg)

200 C. No breaking, cracking, or spalling was evident when subjected to a bend test. Weight loss ~ 0 . 1 5 percent. 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 o 6 rads ( C ) gamma. In the only study where measurements were performed during irradiation, the insulation resistance decreased by something in excess of one order of magnitude (> 2 x 10l2 ohms to 1 x 10l1 ohms) when the reactor was at its maximurn power level of 30 kW. (37) An est imate of the neutron and gamma r a t e at this level is 1. 5 x 10l1 n/cm2. s) ( E > 0. 1 MeV) and 6 x lo4 rads (C)/hour, respectively.

Limited information on a polyurethane foam encapsulant indicates that th is mater ia l may be more sensi t ive to radiat ion exposure than other encapsulating materials. Decreases in insulation resistance have approached three orders of magnitude during exposure to approximately 1. 5 x 1 0 l 1 n / c m 2 . s ) ( E > 0 . 1 MeV) and 6 x 104 rads (C) hour . Ful l recovery occurred, however, within 3 days after the irradiation was terminated with a total dose of 1. 5 x 1015 n/cm2 (E > 0 . 1 MeV) and 1.8 x l o 6 rads (C) gamma. (38)

Several , but not necessarily all epoxy resin encapsulants have shown a radiation resistance that is above average for plastics. Polyfunctional epoxy resin and polyfunctional epoxy novolac resin with,anhydride or aromatic amine hardeners appear to be the most res is tant . Epoxies have withstood neutron and gamma doses up to 1. 1 x 10 l6 n / cm2 ( E > 0. 5 MeV) and 1 x l o 9 r ads (C) f rom a reactor source without serious deterioration. Similarly, electron irradiation to a total exposure of 5. 8 x 10l6 e /cm2 ( E = 1.0 MeV) at 60 C and cobalt-60 irradiation to 1 x 108 rads (C) p roduced only limited degradation of an epoxy's physical and electrical properties. Epoxies that have shown a satisfactory radiation tolerance within the limits to which they were tested are listed in Table 6 .

Information concerning the degradation of an epoxy encapsulant's physical properties indicate that a noticeable darkening in color and a slight loss in weight occurs when these materials are irradiated. 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 tensile strength (8 percent), and decreases in ult imate 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 in excess of 10 rads (C) may result in failure in some applications where the epoxy is under stress. The ult imate tensile strength of epoxies has decreased to between 43 and 24 percent of the initial value at 109 rads (C).(15) Compressive strength was essentially 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 o 7 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 lo7 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 lo9 rads (C) gamma 1.1 x 1016 n/cm2 (E > 0.5 MeV)

8.8 x l o 7 rads (C) gamma 4.0 x 1013 n/cm2 (E > 0.1 MeV)

1 x l o 9 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 lo8 rads (C) gamma 2 x 1013 nlcm2 (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 o 9 rads (C) gamma 1.1 x 1016 n/cm2 (E > 0.5 MeV)

1 x lo9 rads (C) gamma 1.1 x 1016 n/cm2 (E > 0.5 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 e lectr ical propert ies of epoxy encapsulants show some variation in radiation tolerance but are generally of adequate stability for use in most electronic circuits. The insulation resistance has decreased by as much as two o r d e r s of magnitude during irradiation with a minimum 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 lat ter shows the greatest sensit ivity to radiation by increasing approximately one order of magnitude. Polyfunctional epoxy resin and polyfunctional epoxy novolac resin with anhydride or aromatic amine hardeners have retained 90 percent of their initial dielectric strength at 1 x lo9 rads ( C).(37) Diglycidylethers of bisphenol A araldite epoxy with an aliphatic amine hardener retained 84 percent of its init ial dielectric strength at 6 . 8 x 108 rads (C), but was severly damaged physically at 109 r ads (C) so that the dielectric strength could not be measured.

The above information is representative of the radiation resistance 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 evaluated as par t of one study where it was subjected to a total integrated exposure of 1 x l o 8 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 measurements of capacitance, dissipation factor, and insulation resistance. Di- electric strength of control and irradiated specimens was comparable following 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 properties. These changes are associated with the insulating material ra ther than the metals used in these devices . The la t ter requires some consideration, however, since metals used in connector and terminal construction become radioactive when irradiated and, thus, offer a biological hazard to maintenance personnel.

40

I

The degradation of the insulating materials physical properties, which may ult imately lead to electrical failure, is a permanent effect and a major concern in selecting a connector or terminal for use in a radiation environment. This degradation of physical properties is manifested in the crumbling or disintegration of some organics that are employed as the insulating media. Thus, a connector or terminal that includes a mater ia l of this type will fail through structural collapse in a radiation environment of sufficient total exposure. Tetrafluoroethylene (Teflon) and similar fluorocarbon mater ia ls are wel l known for their lack of radiation resistance and this mode of failure.

Inorganic insulated connectors and terminals of the hermetic 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 p ins used as conductors (an area of high stress under normal conditions). If this type of damage is more extensive than s imple surface f rac tures , a loss in the sealing properties of the connector will result.

The changes in the electrical properties of connectors and terminals are generally temporary, with complete or what can essentially be termed complete recovery soon after the irradiation has been terminated. Changes in insulation resistance breakdown voltage and corona voltages have been reported by experimenters. The consensus is 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 environmental conditions other than radiation, such as humidity and/or minor differences in the same insulating material, m a y 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 electrical performance. Decreases in insulation resistance of between one and two o r d e r s of magnitude have occurred during the irradiation of these connectors with recovery to within one order of magnitude of the preirradiation values within minutes after the irradiation was terminated. Neoprene- insulated connectors have shown a minimum insulation resistance of approximately 1 x 109 o h m s during exposure to 1.5 x 10 l1 n / cm2- s) (E > 0. 1 MeV) and 6 . 1 x l o 4 rads (C)/hr. Buna-N-insulated connectors have exhibited minimums of less than 10 megohms for neutron fluxes and

41

g a m a dose ra tes of 8 . 4 x 1O1O n/cmz. s) ( E > 0 . 9 MeV) and 6 . 1 x l o4 rads (C) /hr . Resul t s f rom insu la t ion- res i s tance measurements on the neoprene-insulated connectors are presented in Figure 10. Breakdown- voltage measurements on these connectors indicate values in excess of 500 volts during irradiation and greater than 1000 volts 3 weeks later.

100 I I

E 40 watt 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 O F NEOPRENE- INSULATED CONNECTORS VERSUS TOTAL EXPOSURE(38, 39)

Physical degradation has resulted in the recommendation that Buna-N-insulated connectors be replaced after a gamma exposure of 2 x 106 r ads ( C ) a t room tempera ture .

Plastic-insulated connectors that have been investigated as to their radiation resistance include units with phenol formaldehyde, melamine formaldehyde, and glass-fiber filled diallyl phthalate insulation. Con- nectors having a glass-insulated hermetic seal or glass-fiber f i l led diallyl 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 / c m 2 (E > 2 . 9 MeV) and -7 x lo8 rads (C). Feedthrough terminals incorporating the latter for insulating purposes have also been tested in a radiation environment. Degradation in the insulation resistance of the connectors consisted of a decrease of between one and two o r d e r s of magnitude during irradiation. Combined effects of temperature (55 to 65 C) and radiation have resulted in decreases of four and five orders of magnitude.(l8, 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 resistance recovered to within one order of magnitude of the preirradiation 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 plastic insulators tested as connector insulation the diallyl phthalate was least subject to mechanical degradation.

Feedthrough terminals insulated with glass-fiber filled diallyl phthalate that survived a total exposure of 3 . 1 x 10 l 6 n / c m 2 ( E > 0. 5 MeV) and 9 . 8 x l o 8 r a d s ( C ) gamma at room temperature experienced decreases of f r o m 2000 to 3000 volts in corona ignition and extinction voltages during exposure at altitude equivalents of sea level to 70,000 feet. The insulation resistance remained fairly constant at 6-7 x l o 7 ohms during irradiation at a neutron fluence of 2 . 3 x 101o n / (cm2. s ) ( E > 0. 5 MeV) and a gamma r a t e of 2 . 6 x lo5 rads (C)/hr . wi th a pretest res is tance of : 1 x 10l2 ohms. Capacitance and dissipation factor were fairly independent of the altitude and radiation conditions to which the terminals were subjected. Several of the terminals failed because of low corona voltages and insulation resistance: included were all of the smaller size and 50 percent of those classified as medium and large sizes.

Radiation-effects information on inorganic insulated connectors include the glass hermetic-seal type and a ceramic (alumina)-insulated AN type connector. Similar information is also available on ceramic-insulated feedthrough terminals. Insulation resistance data indicate that both types of connectors have a decrease of approximately two orders of magnitude during irradiation with recovery approaching preirradiation values after total exposures of 2-10 x 1015 n / c m 2 ( E > 0. 1 MeV) and 8 . 8 x lo6 rads (C) gamma at 55 C. Results of insulation resistance measurements on the ceramic-insulated connectors are presented in Figure 11. Combined effects of radiation and temperature (156 F) have produced decreases of up to f ive orders of magnitude in insulation resistance during irradiation at a neutron fluence of 1 . 2 x 10l2 n /cm2. s) ( E > 2 . 9 MeV) and a gamma rage of

43

IO''

IO'

cn

r 0

E

.- cn

Q) cn LT

1o9

I oa 0

I

A l 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

FIGURE 11. INSULATION RESISTANCE OF CERAMC- INSULATED CONNECTORS(32)

44

6 . 6 x l o 7 rads (C)/hr. (26) Recovery following irradiation was within one o r two o r d e r s of magnitude of the init ial values. The glass hermetic-seal ,~ type connectors exhibited breakdown voltage characteristics in excess of 500 volts during irradiation 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 connectors. One connector exhibited a distinct failure when the corona ignition voltage or a voltage breakdown of one pin was observed to occur at approximately 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 r o m a total exposure of 4. 2 x 1013 n /cm2 (E > 0 . 1 MeV) and 9 . 3 x l o 7 rads gamma a t 200 C. The insulation resistance was 1014-1015 o h m s before and after the irradiation.

It is recommended that the reader consult the section on sheet and bulk insulating materials for additional information on the connector insulations discussed above and others that may be of interest. In addition, the activation of metal par ts provides a continuing source of radiation to the connector and surrounding electronic parts even after irradiation from the pr imary source has terminated. In glass to metal seals , wi th mater ia ls like Kovar or similar alloys, the interface between the metal and glass, a most sensi t ive area, is in an a rea of high radiation concentration and high physical stress and, thus, is more subject 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 organics , a re used in one o r more par t s 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 capacitor dielectrics is l imited as little o r no change i s shown in this property. Therefore, the effect on the dielectr ic constant is second-order effect , especially for inorganic dielectrics. 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.

Ionization of the air surrounding or within the capacitor structure, degradation of the dielectric and filler material, and radiation-induced temperature increases may cause decreases in the insulat ion res is tance. The ionization effect is the main insulation effect observed during irradiation tests. Insulation resistance measurements of paper-dielectric capacitors exposed to intense radiation illustrate the effects of both ionization and insulation breakdowns within the capacitor. Upon irradiation, the insulation resistance immediately 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 materials. Decreases in insulation resistance will occur with increasing temper- a tures; therefore , any r ise in temperature associated with radiat ion wil 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 capacitors according to dielectric material is shown in Figure 12.

46

Ceramic

Glass

M i c a

Paper and Paper/Plastic

Plastic

Electrolytic

FIGURE 12.

Mild - to - moderate permanent damage

Moderate- to -severe permanent damage (behavior spread)

Severe permanent damage

IO l3 loi4 1015 IOi6 1017 Fast Neutron Fluence, n/cm2

I I I 1 I ~~~~ ~ ~~

lo5 IO6 lo7 IO8 lo9 Estimated Ioniz ing Dose, R

RELATIVE RADIATION SENSITIVITY O F CAPACITORS

If the capacitors 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 interest . In 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 resistance 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 u x ra te , and the permanent effects are mainly the result of total exposure. More specific information concerning the various types of capacitors, as classified by dielectric material, is presented in the following sections.

I

47

Glass - and Porcelain-Dielectr ic " Capacitors ~- ~~~ ~

The basic construction of glass -dielectric capacitors includes alternate l aye r s of glass r ibbon and electrode or plate (aluminum) material with an outer covering of glass . These layers are sealed together into a monolithic block by high temperature and pressure. Vitreous-enamel (porcelain- dielectr ic) capaci tors are of similar construction, with alternate layers of ceramic glaze and s i lver that are fused into a monolithic block with an ex- t e r i o r 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 oscil lators. They are well suited for cri t ical high R - F applications, within the limitations of their self-resonance frequency, and where a minimum of noise is required.

Capaci tors having glass- or porcelain- (vi t reous enamel) dielectr ics compared to capacitors of other dielectric materials, have shown a relatively high resistance to damage from exposure to a neutron environment. The damage or effect of the radiation on the electrical properties of these capac- i tors includes both permanent damage and temporary effects. The temporary effects are at tr ibuted to ionization in the capacitor and in t h e i m e d i a t e area surrounding the capacitor and i ts leads. Experimenters 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 encapsulation, however, sometimes presents more of an ionization problem in temporary effects because of charge equilibration.

Glass - and porcelain-dielectric capacitors have exhibited both temporary and permanent changes in capacitance as a resul t of irradiation. Changes in dissipation factor and insulation resistance are generally temporary effects with recovery to near preirradiation values within a few hours after the termination 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).

Capacitance measurements on glass -dielectric capacitors during irradiation have shown maximum temporary changes or variations between +4.0 percent and -2,'5 percent. Permanent changes between t3. 1 and -2. 5 p e r - 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 maximum

48

change of only +O. 1 percent, with an average increase of 0.05 percent has been observed, however, with a neutron flux and fluence of -4 x 10 l2 n / (cm2- s ) , E > 10 keV, and 8 x 1014 n/cm2, respectively. (40) The gamma environment included a ra te of 5.4 x l o 6 rads (C) /hr and a total dose of 3 x lo6 r ads (C). Several factors may be responsible for the differences in the results reported by various experiments, such as lack of close simi- lari ty in test specimens due to production changes and/or differences between production lots, instrumentation difficulties, and lead effects.

Maximum changes or variations in the capacitance of porcelain- dielectric capacitors during irradiation include a decrease of 3. 5 percent and an increase of 2.1 percent. Permanent changes between - 4 . 0 and +3.5 percent have also occurred. In many cases, however, the capacitance remains much more stable with temporary and permanent changes of l e s s than 1. 0 percent.

In general, the capacitance of glass- and porcelain-dielectric capacitors remains stable enough in a radiation environment that they are suitable for many of their intended applications, with the exception of circuits involving critical tuning where precision capacitors are a necessity. Applications i n circuits of this type require shielding to protect the capacitors against the radiation environment.

The dissipation factor of glass- and porcelain-dielectric capacitors experiences temporary effects from exposure to a nuclear-radiation environment. Glass-dielectric capacitors have shown increases from init ial dissipation 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 10l8 n /cm2 (E = unknown) and 7 .7 x l o 8 rads (C), respectively. The dissipation factor of porcelain-dielectric capacitors has approached 0. 05 during and after exposure to a nuclear-radiation environment. These devices have shown both complete recovery to preirradiation values and additional in- c r eases when the irradiation was terminated. The maximum, with the postirradiation increase, has never exceeded 0. 05, and in several tes ts the dissipation factor did not exceed 0. 0 1 o r 1. 0 percent at the following neutron and g a m m a 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 10l1 rads (C).

The insulation resistance of glass- and porcelain-dielectric capacitors decreases between two and three orders of magnitude when they are subjected

49

I

to a nuclear-radiat ion environment . This effect i s temporary and the insula- t ion resistance recovers when the irradiation is terminated.

Mica-Dielectric Capacitors

The internal construction of mica-dielectric capacitors includes alternate layers of mica-dielectric and metall ic electrodes. The electrodes or capaci tor plates may be of metal foil or deposited si lver. The deposited silver units, because of the intimate contact between the electrode and di- e lectr ic , are used where high-stabi l i ty capaci tors are required, such as in timing and frequency-determining circuits and other applications where s tabi l i ty is of primary importance. They are not, however, recommended for applications that may include high-humidity, high-temperature, and constant 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 s i lver (s i lver micas) , and larger dr i f ts are to be expected with these units, particularly at elevated temperature.

The capacitance and dissipation factor of mica capac i tors a re suscept - ible to permanent damage from irradiation, while changes in insulation resis tance are general ly temporary. The permanent changes in capaci tance and dissipation factor are possibly due to changes in the physical structure of the capacitors, such as separation of the metal electrode and dielectric layers. Visual examination following exposure has shown severe damage in the form of casing f ractures as a result 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 o 8 rads (C ).

Changes in the dissipation factor of mica-dielectr ic 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 similar diss ipa- tion factor (0. 1 0 ) was the result of a temporary increase during a dose-rate tes t , and decreased to 0. 04 during a fluence or integrated exposure tes t that was a pa r t of the same study. (42) No predominant or significant changes

50

were reported in tes ts 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 o 7 and 1 x 108 r ads (C). (32343)

The insulation resistance of mica-dielectr ic capaci tors decreases to values in the range of 108 and 109 ohms during their exposure to a nuclear- radiation environment, 109 n/(cm2* s ) (E 1 0 .5 MeV) and 3 x l o 5 rads (C)/ hr . Recovery to near preirradiat ion values , 1010 and 1011 ohms, occurs immediately following or soon after the irradiation is terminated. The decrease in insulation resistance is generally attributed to the ionization within the capacitor structure and in the near vicinity of the capacitor, as a resul t of the radiation environment.

Ceramic-Dielectric CaDacitors

Basically, a ceramic-dielectr ic capaci tor consis ts of a ceramic di- e lectr ic with a thin metallic film, such as si lver, applied to ei ther side and fired at high temperature. The f ired metall ic film serves as the e lectrodes or capaci tor plates of the device. Ceramic capacitors are available as two basic types (general purpose and temperature compensating), with several body designs: disk, tabular, standoff, and feedthrough. The general- purpose units are used in applications where large capacitance changes and higher losses are not cr i t ical . Typical uses are for bypass , f i l ter , and noncritical coupling circuits. The temperature-compensating units are used in more cri t ical applications that make use of their temperature character is t ics to compensate for parameter changes of other elements or components in the circuit, These applications include critical coupling and tuning circuits.

Ceramic capacitors have shown various degrees of sensitivity to steady-state nuclear -radiation environments. The capacitance and dissipation factor appear to be susceptible to both temporary and permanent effects, while the insulation resistance suffers from temporary effects due to ionization. The changes in capacitance for general-purpose ceramic capacitors are negligible when the extremely wide tolerances and temperature coefficients that are associated with these devices are considered. The capacitance changes that occur may be attr ibuted, at least in part , to temperature effects and aging. The latter results in a gradual decrease in capacitance with time.

51

The capacitances of general-purpose ceramic capaci tors have decreased during irradiation with but few exceptions, when increases were observed. These changes in capacitance vary from a minimum of 1 o r 2 percent to a maximum of 20 percent. Typically, however, the maximum change is in the range of 10 to 15 percent. The permanent effect, i. e . , change in capacitance, is normally less than the temporary effect that is observed during the actual exposure to the radiation environment. The difference between the temporary and permanent effect on capacitance 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 in dielectric constant, i s a consideration.

Information on the effect of radiation on the dissipation factor of ceramic-dielectr ic capaci tors is l imited, and there are no clear t rends indicated. The dissipation factor of these devices has increased during and after irradiation, remained rather stable, or even decreased. (42) The increases observed usually did not exceed 0.02.

The insulation resistance of ceramic-dielectr ic capaci tors decreases as much as two to f ive 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 o 8 rads (C), respectively. Recovery generally approaches the preirradiation 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 flux 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 o 5 rads (C)/hr and a total dose of 4 . 6 7 x 108 rads (C).

PaDer- and PaDer/Plastic-Dielectric Canacitors

The basic physical s t ructure of paper-dielectr ic capaci tors consis ts of two metal-foil str ips or deposited metal f i lms' separated by two or more l aye r s of paper dielectric. The paper is generally impregnated with wax, oil, or synthetic compounds to increase its voltage breakdown and to provide the desired characterist ics. The paper/plastic-dielectric capacitors are similar in Construction, with the addition of l aye r s of plastic film in the paper layers. Paper and paper/plastic capacitors are used in 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 bypass 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 t h r e e o r d e r s of magnitude. Plain paper or paper/plastic is a more suitable dielectric for applications that include nuclear radiation as an environmental condition than the same or similar dielectric that has been oil impregnated. This is because the oi l or o ther hydrocarbon used to impregnate the dielectr ic releases hydrogen or hydrocarbon gases when the device is placed in a radiation environment. The pressure buildup from the evolved gases subsequently causes the distortion of the capacitor element and a change in capacitance and dissipation factor. Hermetically sealed units have actually ruptured their enclosures and/or leaked at the terminal seals as a result of this pressure. The ionization within the capacitor structure and the immediate surrounding area that occurs during irradiation also contributes to changes in the e lectr ical character is t ics of paper and paper/plastic capacitors. These changes, 'however, are temporary and manifest themselves 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 this construction are an increase of approximate ly 18 percent and a decrease of 50 percent. The 18 percent increase has been observed with a capacitor type that is molded in mineral-fi l led high-temperature plastic. If the results of two radiation studies in which these ex t remes occur red for a sample size of two is deleted from consideration, the range of capacitance degradation would be much less , +8. 5 and -20 percent. It is readily understandable that the evolving of gas, with the associated distortion of the capacitor structure, could result in a decrease in capacitance by increasing the spacing between the capacitor plates or electrodes. The increase in capacitance is not as easy to explain unless the distortion may also in some instances increase the effective area of the capacitor plates.

The dissipation factor of paper- and paper/plastic-dielectric capaci- t o r s i nc reases when the capacitors are subjected to a nuclear-radiation environment. These increases typically have been less 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 flux of 3 . 0 x

5 3

1011n/(cm2- s)(epicadmium)for a fluence of 4 x 10l7 n/cm2 and a g a m a rate and total dose of 8. 7 x l o 5 rads (C) /hr and 3 x l o 8 rads (C), respectively.

The insulation resistance of paper- and paper/plastic-dielectric capac- to rs decreases as a resul t of i r radiat ion. The temporary decrease that occurs is generally attr ibuted to the ionization that is produced by the radiation environment. A permanent decrease in the insulation resistance may be the result of (1) a decrease in the volume resist ivity of the substance used to impregnate the device and (2) the process that results in the embrit- t lement of the kraft-paper dielectric. Increases due to interelectrode distort ion from pressure buildup is also a strong possibility.

Several programs have included sufficient quantit ies of paper- and/or paper/plastic-dielectric capacitors to provide statistical confidence in the results. The following discussions of individual test programs are presented for this reason.

One hundred CP08AlKE 105M paper-dielectr ic capaci tors were subjected to combined environments of high temperature and nuclear radiation. (45) The ambient temperature was controlled at 85 C with the reactor power level limited to 1 megawatt during the f irst 24 hours. The reactor power level was then raised to 10 megawatts for the duration of the experiment while the temperature was st i l l controlled at 85 C. The radiation environmental conditions for this study included a neutron fluence of 1.4 x 10l6 n/cm2 (E > 2. 9 MeV) and a total g a m a exposure of 9. 0 x 108 rads (C).

Observations of capacitance during the combined environmental conditions 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 increased further, there was a general 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 tolerance level for several measurements when the capacitors failed catastrophically. Figure 13 i s a graphic presentation 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-circuit- type failures, 9, although not shorted, could not be charged, and only 10 capacitors were chargeable. The threshold 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 loi4 1015 IOi6 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 SIZE O F 100 UNITS CAPACITANCE AND CATASTROPHIC FAILURE)(4 E!

and catastrophically failed units, as shown in Figure 13, was 1.04 x 1014 n / c m 2 (E > 2.9 MeV) and 3.92 x lo6 rads (c) .

In ano the r i n~es t iga t ion (~6) w i th a large sample size, 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/Mylar 0 .1 pf, 600-~0lt , CPM08 capacitors. The cobalt-60 source used provided a maximum gamma exposure of 8.77 x 104 rads (C) /hr .

I

Results of this investigation which included a constant-temperature environment and a temperature-cycled environment are given in Figure 14. The temperature-cycled group was subjected to room temperature and 135 C

55

2000 vdc

160 hr 2000 vdc Irradiated

100 hr

decrease In capacitance Prior ;to -failure

0. 5%

6.0 to lO.O%

Pulsed 2000 vdc I r radiated

Pulsed 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 . Constant 135 C

*Because of equipment malfunction, the units failed at 636 h r . If there had been no tronble, 7 5 percent of the units should have failed by 1086 hr.

Prior-to-failure decrease in capacitance

2 O/O 2000 vdc 15 failed”

2000 vdc

I

I 1 566 hr

Irradiated - 9 O/O

312 hr Pulsed 2000 vdc Irradiated 0 6 O/o

131 hr I ~~~

Pulsed 2000 vdc -1 I 2 O/O

I

I I 9 failed 650 hr

b. Temperature -Cycled Units

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. E F F E C T S O F GAMMA RADIATION ON PAPER/MYLAR CAPACITORS FOR 100 PERCENT SAMPLE-SIZE FAILURE(46)

56

with 30 minutes to stabil ize at each temperature . A total of 90 minutes was required a t each temperature to make all necessary measurements . Mea- surements of dissipation factor and insulation resistance for both the constant- temperature group and the temperature-cycled group revealed no trend toward degradation before failure. All the failures that are indicated resulted from voltage breakdown. As a comparison, four units were passively irradiated in the gamma source for 1000 hours. These units showed the following results:

(1) No case ruptures

( 2 ) 6 percent decreases in 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 t h i r d ~ t u d y ( ~ 9 ) included both paper- and paper/plastic-dielectric capacitors with deposited metal (metallized) plates or electrodes manufactured about 1965. Both types were subjected to five environmental conditions with d-c voltage applied. The paper-dielectric capacitors were also subjected 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 / plastic capacitors and 120 paper capacitors. Each group of 20 specimens was subjected to one of the environmental conditions indicated in Table 7.

The sixth group of paper-dielectric capacitors (Test Group VI) was subjected to the same environmental conditions as Test Group I11 with no voltage applied.

Failure-rate computations at the 50 ,60 , and 90 percent confidence levels, as shown in Table 8 for the metall ized-paper capacitors, indicate that temperature was the greatest contributor to their failure, since the capacitors in Test Group V (50 C) exhibited a much lower failure rate than that for any of the other test groups. The units subjected to normal atmospheric pressure, Test Group I, also experienced a failure rate approximately one-half that observed for units in the vacuum environments, with the exception of those in Test Group V. The no-load condition of Test Group V I resulted in a lower failure rate than that for Test Group 111, which was subjected to identical environmental conditions, but included the application of a d-c voltage.

57

TABLE 7. TEST DESIGN, RATED VOLTAGE APPLIED

Test Temperature , Pressure, Neutron Group C t o r r Fluence

Gamma Dose

I 100 76 0 None None

I1 100 10-5 None None

I11 (a ) 100 10-5 -1013 n / c m 2 - l o 7 rads (C)

IV (b) 100 10-5 -1013 n / c m 2 - l o 7 rads (C)

V ( 4 50 -1013 n /cm2 - lo7 rads (C)

(E > 0. 1 MeV)

(E > 0.1 MeV)

(E > 0. 1 MeV) -

(a) 10,000 hours a t 3 x l o 5 n/(cm2- s) and 1 x l o 3 rads (C)/hr. (b) 100 hours a t 3 x 107 n/(cm2. s) and 1 x 105 rads (C)/hr followed by 10,000 hours a t 100 C and l o m 5 torr

without radiation.

TABLE 8. FAILURE RATE FOR P323ZN105K CAPACITOR, AT 50, 60, AND 90 PERCENT CONFIDENCE LEVELS(39)

Failure Rate at Indicated 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 IV 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 e lectr ical character is t ics of these capacitors experienced a grea te r degree of degradation from a 100 C ambient with a load voltage applied than from the radiation environment. Any radiation damage that occurred, however, may have been annealed by the elevated 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 catastrophic failures and degradation that resulted from the 100 C ambients. Therefore, the application o r design engineer would need to be more concerned 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 metall ized/Mylar (plastic) capacitors, also manufactured about 1965, that were subjected to the various test conditions in Table 7.

TABLE 9. FAILURE RATE FOR 118P1059252 CAPACITOR AT 50, 60, AND 90 PERCENT CONFIDENCE LEVELS(39)

~

~- - -.

Failure Rate at Indicated Confidence Level, Dercent/lOOO h r

Percent Recorded Test Group 50 P e r c e n t 6 0 P e r c e n t 90 Percent as Fa i led

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

All 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. N o significant amount of degradation was noted in the dissipation factor. The results from the insulation-leakage-current measurements indicated the greatest degradation in this parameter occurred in the 100 C vacuum environments of T e s t Groups 11, 111, and IV. The maximum leakage current approached 1.0 mil- l iamperes in al l three of these tes t groups,

It was concluded from the results obtained that a radiation environment of the level used in this study is not a significant factor in the application of these capacitors. The application engineer needs to be more concerned with the degradation associated with elevated temperature.

Plast ic-Dielectr ic Capaci tors

Most plastic-dielectric materials harden and eventually become brit t le when irradiated. This results in flaking and crumbling especially under s t ress . The e lec t r ica l p roper t ies of Mylar are s table 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 specimen to approach a quiescent state after irradiation. Dielectric constant and dielectric loss show no p e r - manent dose-rate effect. Some properties of Mylar do exhibit a dose- ra te effect that is generally less at higher dose rates. For example, dielectric strength is considerably reduced at lower dose rates, but at higher dose rates the change is not near ly as great .

Plast ic-dielectr ic capaci tors are s imilar in construct ion to the paper and paper/plastic capacitors, with the exception that the dielectric is a thin plastic film rather than paper or paper and plastic. Materials commonly used as the dielectric 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 higher voltages, a liquid f i l l is required to reduce corona and increase voltage- flashover limits. Applications for plastic-dielectric capacitors are the same as those for the paper and paper/plastic capacitors.

Radiation-effects testing of plastic-dielectric capacitors has essentially been limited to devices employing Mylar as the dielectric film. There - fore, the following discussion of radiation effects on plastic-dielectric capac- i tors is concerned with or l imited to Mylar capacitors.

60

Experiments to determine 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 magnitude less than the inorganics, i. e. , glass, ceramic, and mica. As in the case for paper- and paper/plastic-dielectric capacitors, plain plastic is a more suitable dielectric for nuclear-radiation environments than the same or similar dielectric impregnated with oil or wax. Impregnated hermetically sealed units may even experience a rupture of the exter ior case or enclosure. This rupture may be the pushing out of the glass-to-metal end seals so that the mater ia l used to impregnate the capaci tor leaks out , or , i f there i s a sufficient buildup of pressure, the end seal may even be blown completely f ree of the capacitor, with the capacitor element extending beyond the limits of i ts enclosure. Such a violent rupture occurring in an actual application, offers, in addition to electrical failure, a physical hazard to other component parts in the vicinity of the capacitor.

The capacitance of plastic-dielectric (Mylar) capacitors subjected to a radiation environment has both increased and decreased when pre- and post- i r radiat ion measurements are compared. In general , these changes are within *4 percent of the preirradiation value at neutron fluences of lO15n/cm (E 2 .9 MeV) and 10l6 n/cm2 (E > 0.3 MeV). However, decreases of as much as 10 percent and as small as <1 percent have also been recorded for similar capacitors and fluences. The differences in the sensitivity to a radiation environment may possibly be the result of differences in the Mylar and i ts t reatment before or during the manufacture of the capacitors, or differences in the material used to impregnate them. The evolving of gas by the breakdown of the oil o r 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 dissipation factor of the long leads required between the test capacitors in the radiation environment and the instrumentation used to measure their electrical characterist ics. The maximum observed increase in dissipation factor is 6 0 percent of the init ial value measured before the capacitors were inserted in the reactor . This increase occurred a t a neutron fluence of 6 x 1017 n / cm2 (epicadmium) and a total gamma dose of 4.4 x 108 rads (C).

The insulation resistance of plastic-dielectric capacitors decreases when they are exposed to nuclear radiation. Permanent changes in the insulation resistance may be due to the chemical breakdown process that occurs

6 1

in the oil or wax substances used to impregnate the capacitor or a change in the plastic-dielectric-materials characterist ics. The insulation resistance of capacitors having a Mylar dielectr ic decreases as much as three and four o rde r s of magnitude, with minimum values as low as 10 megohms. Recovery af ter the i r radiat ion is terminated normally re turns the insulat ion res is tance to near preirradiation values, i. e., within an order of magnitude.

Two programs have included quantit ies or sample sizes of Mylar- dielectric capacitors to provide a higher than usual statistical confidence in the results. The following discussions of individual tes t programs are presented 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 during the f irst 24 hours. The reactor power was then increased 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 CONFIDENCE LEVEL, BASED O N A SAMPLE SIZE O F 98 UNITS (CAPACITANCE AND CATASTROPHIC FAILURE)(45)

62

fluence and total gamma exposures to which these Mylar capacitors were subjected were 1.32 x 10l6 n /cm2 (E 7 2.9 MeV.) and 8.5 x lo8 rads (C), respectively. The capacitance values of the Mylar capacitors exhibited very little change for an extended period of radiation; a general increase was observed toward the end of the test . At the end of the test several units exceeded the 10 percent tolerance level specified for the capacitor. Prior 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 capacitors revealed that 94 units had failed catastrophically and 81 had ruptured a s a resul t of the test conditions. One capacitor that exhibited a nonshorted condition could not be charged, and 18 units of the entire test group were chargeable,

The second study that included a large sample size 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 VII). (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 sample size 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 111 and IV, resulted

TABLE 10. FAILURE RATE FOR 683G10592W2 CAPACITOR AT 50, 60 , AND 90 PERCENT CONFIDENCE LEVELS(39)

Failure Rate at Indicated Confidence Level, percent / 1000 h r

"" ______ ~. - .

' Percent Recorded Test Group 50 Pe rcen t 6 0 Pe rcen t 90 Percent as Fai led - . - . ~ ~- . . . .

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 in these failures, while results 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 environments indicates that these capaci tors are qui te suscept ible to radiat ion damage, even at the low levels used in this study, when in combination with a 100 C ambient 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 electrolytic capacitors, and they are generally used in applications where this is of prime concern. A major disadvantage of e lectrolyt ic capaci tors is that they are polar, and applications of nonpolar capacitors require 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 e lectro- lytic capacitor, which as stated above is i ts major advantage.

The construction of an electrolytic capacitor includes an electrode or capacitor plate of some form that has been anodized on one side to form a dielectric film or insulating layer. A wet or dry e lectrolyte is provided between this anodized surface and the other terminal of the capacitor. Tantalum and aluminum are the commonly used metals for the anodized electrodes in electrolytic capacitors, and the capacitors are identified by which material is used. The tantalum electrolytics are generally considered 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 increasing leakage currents and decreasing 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 rapid ra te than that for the tantalum. Applications for electrolytic capacitors include filter- ing and bypass circuits.

Information on the results of radiation-effects experiments with tantalum- and aluminum-electrolytic capacitors indicates that both types m a y 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 equipment may be required. This is due to the activation of the tantalum when subjected to thermal neutrons and the long half-l ife, 112 days, associated with the resulting 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 e lectr ical character is t ics of electrolytic capacitors have experienced both temporary and permanent changes when exposed to nuclear radiation. The capacitance and dissipation factor suffer from both temporary and permanent effects. The leakage current, however, generally experiences a temporary increase with complete or near ly complete recovery to preirradiation values when the irradiation is terminated. Some of the electrolytic capacitors also experience physical damage because of their construc- t ion. These are the types that employ Teflon in the construction of the end seals of the capacitor case. Teflon is very sensit ive to the nuclear- radiation environment, especially if oxygen is present in the atmosphere during the irradiation. It also suffers damage if exposed to oxygen after being irradiated in 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 tantalum types and between the maximums of -2 and $65 pe r - cent for aluminum. The changes are not necessarily permanent, and the capacitance in some studies has recovered to near the preirradiation value. Others, however, have shown additional degradation after the irradiation was terminated. Temporary increases in capaci tance during i r radiat ion may be due to temperature effects from gamma heating. The permanent changes or those that show recovery over an extended period of t ime would be indicative

65

The dissipation factor of tantalum and aluminum electrolytic capacitors has shown both temporary and permanent effects from exposure to a nuclear- radiation environment. The dissipation factor of high-capacity aluminum- electrolytic capacitors has increased by as much as 0.50, from preirradiation 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 o 5 rads (C), respectively. (47) Much smaller increases have occurred with some small-capacity units 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 difference in these results is very likely due to the large volumetric difference in the capacitors, and should be a consideration in what to expect in the application of similar devices.

The dissipation factor of tantalum-electrolytic capacitors may increase to where it exceeds 0. 50 during irradiation. These high values or large increases occur when the Teflon end seals fail and there is a loss of e lectrolyte. Maximum increases in dissipation factor remain below 0. 10 i f there is no loss of electrolyte and may not exceed 0.05 with neutron and gamma flux and total exposure levels as high as 3 x 10l1 n / (cm2* s ) and 6 x 1017 n/cm2 (epicadmiurn), and 8.7 x l o 5 rads (C)/hr and 4.4 x 108 rads (C), respectively.

The leakage current of aluminum- and tantalum-electrolytic capacitors increases during irradiation by one o r two o rde r s 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 increased to values as high as 1000 mic ro - amperes for large capaci tors such as 47 mfd and 100 Vde. Smaller capacitors experience lower leakage currents since there is a direct proportionali ty between the product of capacitance, applied voltage and dose rate, and the leakage current . This increase is normally a temporary effect and the leakage current returns to near preirradiation values after the radiation exposure has been terminated. This recovery may not occur immediately but can require a period of several days.

Two programs on tantalum capacitors have included sufficient quanti- t ies 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 this reason.

66

One hundred Type TES-1M-25-20 solid-electrolytic-tantalum capacitors, nominal capacitance 1 .0 pf, were subjected to a combined environment of high temperature and nuclear radiation in one program. (45) The ambient temperature was controlled at 85 C with the reactor power limited to 1 megawatt during the first 24 hours. The reactor power was then increased to 10 megawatts for the duration of the experiment while the temperature continued to be controlled at 85 C. The neutron fluence and total gamma exposure to which these capacitors were subjected included 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 tantalum capacitors increased very early in 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 loi5 I Ol6 I 017 Average Integrated Neutron Fiuence,n/cm2

I (E> 2.9 MeV)- I I 105 I06 lo7 108 to9

-~

Average Gamma Dose,rads (C)-----

FIGURE 16. RELIABILITY INDEX FOR TANTALUM CAPACITORS FOR A 95 PERCENT CONFIDENCE LEVEL, BASED O N A SAMPLE SIZE O F 98 UNITS (CAPACITANCE AND DISSIPATION FACTOR)(45)

67

a r e plotted on the basis of both capacitance and dissipation factor. No ca tas - trophic failures occurred during the exposure, which, with the capacitance increases observed, would indicate that tantalum capacitors may be used in noncritical circuits to an integrated exposure of at least 1.6 x 1016 n /cm2 (E > 2. 9 MeV) and 5. 1 x l o 8 rads (C). Postirradiation examination of the tantalum capacitors revealed 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 u d y ( ~ 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 tantalum capacitors were also subjected to one of the environments with no voltage applied. These additional capacitors, Test Group (VI) , were subjected to the same environmental conditions as Test Group 111, Table 7. The basic sample size 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.

N o fa i lures were observed for 120 wet-foil tantalum capacitors, and no leakage or physical damage was detected during the f inal visual inspection.

Fai lure-rate computat ions are presented in Table 11 for these capacitors. The minor difference between the failure rates for Test Group IV and

TABLE 11. FAILURE RATE FOR 5K106AA6 CAPACITOR AT 50, 60 , AND 90 PERCENT CONFIDENCE LEVELS(39)


Percent Recorded Test Group 50 Pe rcen t 6 0 Pe rcen t 90 Percent as Fai led

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

V I 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 associated with the 100 hours of high-flux radiation that these components received prior to the beginning of the 10, 000-hour life test.

The range of capacitance remained well within the specified lirnit. A general increase was observed in the dissipation factor for all test groups, with the exception of Test Group V (50 C, vacuum, low-flux radiation environment). This would indicate that the 100 C ambient of the other test groups was responsible for the increase. N o dissipation-factor degradation was apparent in the results from the radiation environments.

The results indicate that the various environmental conditions and combinations thereof that were included in this study offer no particular problem in the application of these capacitors.

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 measurements. Two of the remaining 22 indicated a high leakage-current condition (approaching short circuit), and 20 were open circuits during final measurements. The visual examination when the test was terminated revealed that the plastic covering on the capacitors in Test Group I (100 C, atmospheric p r e s s u r e , 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 melted on four capacitors.

Failure-rate computations for these units, Table 12, indicated a much higher failure rate for the capacitors in Test Groups I and I1 (nonradiation environments). The higher values for Test Group I were attributed, at leas t 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 failure rate for the capacitors in Test Group I1 (compared to that of T e s t Groups III and IV), which had their plastic covers removed.

A beneficial effect from the radiation was considered an unlikely possibility, but was given as one possible explanation of the catastrophic-failure distribution for these capacitors , i. e. , high failure rates for the nonirradiated groups.

6 9

TABLE 12. FAILURE RATE FOR HP56C50D1 CAPACITOR AT 50, 60, AND 90 PERCENT CONFIDENCE LEVELS(39)

- -~ ~ .~ ~ - ~~


Percent Recorded "~ - . __

Test Group 50 Percent 60 Percent 90 Percent as Fa i led ~~ __ ~~~ ~ ~~ -

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 capacitors show that they can survive 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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74

(31) Hansen, J. F., and Shatzen, M. L., "Radiation Effects on Electrical Insulation", Paper presented at the 3rd Semi-Annual Radiation Effects Symposium, Lockheed Aircraft Corp., October 28-30, 1958, Volume 5, Avail: DDC, AD 296310. BRC 8718

(32) "M&TC System Study", Bendix Corp., Systems Division, Ann Arbor, Michigan, BSR-371, December, 1960, Final Report, Volume 1, Part 11, A F 33(600)-35026, 458 pp. BRC 15101

(33) Long, W. G . , and Keating, W. E . , North American Aviation, Inc., Atomics International, Canoga Park, California, "Design and Evalua- tion of a High Temperature, Radiation Resistant Cable Harness. Part 1 - Design Requirements: Physical , Electrical , Materials, and Terminations", Insulation, 12 (2), 37-40 (February, -1966). BRC 31154

-

(34) Long, W. G. , and Keating, W. E . , North American Aviation, Inc., Atomics International, Canoga Park, California, "Design and Evaluation of a High Temperature Radiation Resistant Cable Harness. Part 2 - Electrical Properties: Thermal-Vacuum and Radiation Test- ing", Insulation, 12 ( 3 ) , 52-56 (March, 1966). BRC 31303 -

(35) Fuschillo, N. , and Mink, F. V. , "Investigation for 2000 F Power Wire", Melpar, Inc. , Falls Church, Virginia, AFAPL-TR-66-97, November, 1966, A F 33(615)-2721, 102 pp. BRC 34400

(36) Zwilsky, K. M. , Fuschillo, N . , Hahn, H . , L a r e , P. J . , Pentecost, J. L . , and Slawecki, G. D. , "2000 F Power Wire for Aerospace Environ- ment", Westinghouse Air Brake Go., Melpar, Inc. , Falls Church, Virginia, AFAPL-TR-64- 127, November, 1964, Final Report, April 1, 1963 - September 30, 1964, AF 33(657)-11046, 71 pp. BRC 25803

(37) Van de Voorde, Marcel, "The Effect of Nuclear Radiation on the Electr ical Propert ies of Epoxy Resins", CERN, European Organization for Nuclear Research, Geneva, Switzerland, CERN-68-13, April 17, 1968, 45 pp, Avail: NASA, N68-28193. BRC 39016

(38) Armstrong, E. L., "Results of I r radiat ion Tests on Electronics Par ts and Modules Conducted at the Vallecitos Atomic Laboratory", Lockheed Aircraft Corporation, Missiles and Space Division, Sunnyvale, Calif- ornia, SS-840-T62-6, LMSC-A054870, August 27, 1962, A F 04(695)- 136, 163 pp, Avail: DDC, AD 459127. BRC 19607

75

(39) Hanks, C. L. , and Hamman, D, J . , "A Study of the Reliability of Electronic Components in a Nuclear-Radiation Environment, Volume I - Results Obtained on JPL T e s t No. 617, Phase I1 to Jet Propuls ion Laboratory", Battelle Memorial Institute, Columbus Laboratories, Columbus, Ohio, June 1, 1966, Final Report, 217 pp. BRC 33142

(40) Hendershott , D., "Nuclear Radiation Test Results on Electronic Parts, Report I", General Electric Company, Re-Entry Systems Department, Philadelphia, Pennsylvania, GE- 65SD202 1 (August, 1965) , 48 pp.

(41) Sherwin, R. , and Montner, J. , "Performance of Radiation-Resistant Magnetic Amplifier Controls Under Fast Neutron and Gamma Irradia- tion", Marquardt Corporation, Van Nuys, California, S-222 (August 30, 1961), Preliminary Report , June - August, 1961, A F 33(616)-7857, 42 pp. , Avail: DDC, AD 435095.

(42) Crabtree, R. D. , and Wheeler, G. A. , "Investigation of Radiation Effects Problems in Nuclear Heat Exchanger Rockets", General Dynamics/Fort Worth, Fort Worth, Texas, FZK- 160 (January 21, 1963), Final Summary Report, NAS8- 1609, 587 pp., Avail: NASA, N67- 26294.

(43) "NARF Final Progress Report", General Dynamics Corporation, Fort Worth Division, Nuclear Aerospace Research Facil i ty, Fort Worth, Texas, NARF-62-18P, FZK-9-184, Final Progress Report , October 1, 1961 - September 30, 1962, A F 33(657)-7201, 375 pp. , Avail: DDC, AD 412780.

(44) Robinson, M. N. , Kimble, S. G. , Davies, N. F. , and Walker, D. M., "Low Flux Nuclear Radiation Effects on Electronic Components", North American Aviation, Incorporated, Atomics International Division, Canoga Park, California, NAA-SR- 10284 (April 20, 1965), AT(11- 1)- Gen-8, 146 pp. , Avail: CFSTI and NASA, N65-22999.

(45) Pryor , S. G. , 111, "Reliability Testing of Capacitors in Combined Environments", Lockheed Aircraft Corporation, Nuclear Products, Georgia Division, Marietta, Georgia, NR- 116 (December, 1960), Apri l 1 - September 30, 1960, A F 33(600)-38947, Avail: DDC, AD 249049.

(46) "Evaluation-Development of MIL-C- 14157B Capacitors for Nuclear Radiation Environments", Admiral Corporation, Chicago, Illinois (August 21, 1961), Final Report, NObsr-77612, 122 pp. , Avail: DDC, AD 265046.

76

(47) Burnett, J. R. , Azary, Z . , and Sandifer, C. W. , "Flashing Light Satell i te System for SNAP Radiation Environments", Edgerton, Germeshausen & Grier, Incorporated, Santa Barbara, California, EGG-S-227-R, (January, 1963), A F 19(628)-495, 41 pp.

77

INDEX

91-LD Resin 28 Acetal Resin 27 A-C LOSS 16, 22 Acrylic Resins 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 Allyl Carbonate Plastic 27 Alox 26 Alsimag 26 Aluminum 33, 48, 64, 65 Aluminum Capacitor 64-66 Aluminum Isotope 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 Electrolyte 46 Breakdown Voltage 7, 24, 25, 29,

Buna-N - Use Acrylonitrile Buta-

Calcium Aluminate 36, 40 Capacitance 33, 34, 40, 43, 46,

Capacitor Plate 46, 50, 51, 53,

Ca r r i e r Cha rac t e r i s t i c s 2, 3, 10, 25

79

31-33, 35, 36, 41-43, 45, 52, 64

diene Rubber

48-54, 57, 60, 61, 63-69

64

Casing Fracture 50 Cellulos Acetate 9, 27 Cellulose Bytyrate 27 Cellulose Propionate 27 Cements/Bonding/ 26 Ceramic Capaci tor 46, 47, 51, 52 Ceramic Glaze 48 Ceramici te 3 5 Ceramitemp 35 Chain Scission 7, 12, 22 Charge Equilibration 48 Chemical Breakdown 6 1 Chemical Change 66 Chlorinated Polyethers 27 Chrome-Plating 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 Potential 50 Copper 26, 28 Corona Voltages 41, 45, 60 Corrosion 8, 33 Cracking 8, 31, 32, 41 Crosslinking 7 Cryogenic Temperatures 14, 16,

Damage Thresholds 1, 2, 9, 11, 12,

Dark Curren t 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

Dielectric Film 64 Dielectr ic Loss - - See also Dissipa-

Dielectric 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 Fiberglass 37 F i l led Polymers 9 , 18, 21, 39, 42

Flaking - See Also Disintegration 60 Flashover Voltage 7, 60 Flexure Properties 19-23, 28-33, 38 F o r s t e r i t e 11 Fused Quartz 10 Gamma Heating 46, 65 Gas Evolution 8, 33, 46, 53, 6 1, 69 Gl.ass Capacitor 46-48 Glasses 10, 11, 29, 33, 37, 42,

Glass Laminates 9 , 25, 26, 28 Glass-to-Metal Seals 41, 45 Hardness 7, 19, 21-23, 28, 38,

Heat Dissipation 69 Hermetic Seal 41-43, 45 H-Fi lm - U s e Polyimides

28, 38

31, 35, 54, 60

36, 38-40

43) 53

43, 48

60, 69

80

Impact Strength 18, 21, 22 Induced Conductivity - Use Photo-

Insulation Resistance 7, 8, 19-23, conductivity

26, 28, 30-33, 35-38, 40-46, 48- 54, 57, 60-62

54 Ionization Effect 46, 48, 51, 53,

Kaowool 37 Kapton - Use Polyimides Kel-F - U s e Polytrifluorochloro-

ethylene Kovar 45 Leakage Current 7, 60, 64-66, 68,

Leakage Resistance 47 Liquid Fil ler 60 Low Frequency Current 52 Lucalox 26 Magnesium Oxide 11, 37 Melamine Formaldehyde 9 , 42 Melting 69 Melting Point 7 Mica 29, 37 Mica Capacitor 46, 47, 50, 51 Mi r ro r s 33 Mylar 9 , 20, 34, 60, 62 Mylar Capacitor 60-64 Natural Rubber 9 Neoprene Rubber 9 , 41, 42 Network 53 Nylon 6 , 9 , 20 Oil Impregnated 52, 53, 61, 62 Open Circuit Failure 69 Orlon 21 Oscillators 48 Oxidation 18, 19 Paper Capacitor 46, 52-60 Paper/Mylar Capacitor 55-60 Paper/Plastic Capacitor 47, 52-60 Phenol Formaldehyde 42 Phenolic Resins 9 Phosphate-Bonded Cements 26

69

Phosroc I11 ,37 Photoconductivity 2-6, 10, 25, 32 Plastic Capacitors 47, 52.-64 Polycarbonates 9 , 27, 60 Polyester Resins 9 , 28 Polyethylene 5, 6 , 9 , 18, 19, 31,

Polyethylene Terephthalate - Use

Polyimidazopyrrolone - Use Pyr rone Polyimides 6, 9 , 24, 30, 33 Polymethyl Methacrylate 9 , 27 Polyolefins, Radiation-Modified 33, 34 Polypropylene 6 , 9 , 22, 35 Polystyrene 5, 6 , 9 , 19, 20, 60 Polytetrafluoroethylene - Use

Polytr i f luorochloroethylene 8, 9 ,

Polyurethanes 9 , 22, 23, 36, 38 Polyvinyl Butyral 9 Polyvinyl Chloride 9, 27 Polyvinylfluoride 28 Polyvinyl Formal 9 Polyvinylidene Chloride 9 Polyvinylidene Fluoride 9 , 23 Porcelain Dielectric Capacitor 48, 49 Potting - Use Encapsulation Pressure Buildup 46, 53, 54, 6 1 P y r o c e r a m 26 Pyr rone 24, 25 Quartz 10, 11, 37 Recovery Characterist ics 14, 16- 18,

30, 32, 38, 40, 41, 43, 45, 48, 49, 51, 52

32, 34, 60

Mylar

Teflon

16, 18

Refras i l 3 7 Reliability Indices 54, 55, 58, 62,

Resistivity - U s e Conductivity R-F Application 48 Rupture 54, - 6 1, 63

63, 67

Sapphire 1 1 Seal ing Propert ies 41 Seals 41-43, 45, 53, 65, 66, 69 Shielding 49 Short Circui t Fai lure 54 Silica 26, 37 Silicone-Alkyd 3 5 Silicone Resins 9 , 28, 36 Silicone Rubbers 9 , 32, 35, 36, 38,

Silver 48, 50, 51 Silver -Ion Migration 50 Sodium Isotope 65 Softening Point Temperature 18 Solder 69 Solubility 7 Spinel 11 Steatite 26 S t r e s s 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 Isotope 65 Teflon 6 , 8, 9, 12-17, 27 , 30, 31,

Temperature Cycling 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 Formaldehyde 9 Vacuum 12-17, 23, 30, 34 Vinyl Chloride-Acetate 9 , 28 Vitreous Enamel Capacitor 48 Volume Resistivity 12, 14, 18-20,

21-24, 26, 28, 29, 38

23, 26, 28, 40

E

81

Volumetric Efficiency 64 W a x Impregnated 48, 52, 61, 62

82

Weight Loss 22, 28, 36-38 Yield 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


for

N A T I O N A L A E R O N A U T I C S A N D S P A C E A D M I N I S T R A T I O N WASHINGTON, D . C. A U G U S T 1971

I

. .


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

A u g u s t 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 B a t t e l l e Memorial I n s t i t u t e

Columbus, Ohio 43201 NASW-1568 Columbus Laboratories


~

13. Type of Report and Period Covered 2. Sponsoring Agency Name and Address Contractor Report

National Aeronautics and Space Administration Washington, D. C. 20.546



T h i s document con ta ins summarized informat ion re la t ing to s teady-s ta te r a d i a t i o n e f f e c t s on t r a n s i s t o r s . The radiat ions considered include neutrons, p ro tons , e lec t rons , and electromagnetic. The information i s usefu l to the des ign engineer for es t imat ing the e f fec ts o f rad ia t ion on t r a n s i s t o r s .

7. KeiWords (Suggested by Authoris)) I 18. Distribution Statement

Radiat ion effects , Transis tors , Semiconductors , Bipolar Trans is tor , Uni junc t ion Trans is tors , JFETS, MOSFET

Unclassified-Unlimited

9. Security aas i f . (of this report) 20. Security Classif. (of this page) I 21. Noi;' Pages I 22. Rice'

Unclass i f ied Unclass i f ied $3 .oo

. For sale by the National Technical Information Service, Springfield, Virginia 22151

ACKNOWLEDGMENTS

L

The R a d i a t i o n E f f e c t s I n f o r m a t i o n C e n t e r owes t h a n k s t o s e v e r a l i n d i v i d u a l s for t h e i r comments and sugges t ions dur ing t h e p r e p a r a t i o n of t h i s d o c u m e n t . The e f f o r t w a s moni tored and funded b y the Space V e h i c l e s D i v i s i o n a n d t h e Power and Electr ic P r o p u l s i o n D i v i s i o n o f t h e O f f i c e of Advanced Research and Technology, NASA Headquar te rs , Washington , D. C . , a n d t h e AEC- NASA Space Nuclear Propuls ion Off ice , Germantown, Maryland . A l so , we are i n d e b t e d t o t h e f o l l o w i n g f o r their t e c h n i c a l r ev iew and va luab le comments on t h i s s e c t i o n :

M r . R. A. B reckenr idge , NASA-Langley Resea rch Cen te r

D r . A. G. Holmes-Siedle , RCA

M r . S . Manson, NASA Hq.

M r . D. Miller, NASA-Space Nuclear Systems O f f i c e

M r . A. Ree tz , Jr. , NASA Hq.

D r . A . G . S t a n l e y , M a s s a c h u s e t t s I n s t i t u t e of Technology

M r . W . T. White , NASA-Marshall Space F l i g h t C e n t e r

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 art if icial . This Handbook will provide the general background and information necessary to enable designers to choose suitable types of mater ia l s o r c lasses of devices .

Other sections of the Handbook discuss such subjects as solar cells, thermal-control coatings, structural metals, interactions of radiation, electrical insulating materiais, and capacitors.

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, consisting 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 following paragraphs is to give a broad picture of radiation effects on general classes of t ransis tors . If the intended application requires a radiation fluence greater than that for which information is presented, further information for the specific device of interest should be sought.

BIPOLAR TRANSISTORS

The two structures of bipolar t ransis tors are shown schematically Figure 1. Both silicon and germanium bipolar transistors are available

. both of these s t ructures .

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 large disordered c lusters 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 o 5 r ads ) is absorbed by the material.

Lattice damage degrades the electrical characteristics of bipolar transistors by increasing the number of trapping, scattering, and recombination 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 conduction 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 germanium increases o r 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 carriers. Since the mobili ty is directly proportional to the mean-free path, radiation exposure reduces the mobility of charge carr iers .

( 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 degradation of the forward current gain (hFE, p ) resulting from the radiation- induced decrease of minority-carrier l ifetime, 7, p is defined by:

2D p z - 7 ,

W 2

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 expression 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 /particle) 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 measurable 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 variations 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 a r e 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 o r 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 experimental values of A (1/P) and @ in the relation:

This approximation is larger than the theoretical 7 Ialue of KF. b ~y the amount [ A ( l / p ) J s a t / 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 according 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: neutron, proton, electron, and electromagnetic. Points for selected sets of bipolar transistor data are included on these plots. Table 1 l ists the maximum, 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 environment of interest l ies: ( 1 ) outside the envelope i n the low-fluence region, (2 ) . within the envelope, o r ( 3 ) outside the envelope in the high-fluence region. The interpretation of these three alternatives is 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

FIGURE 2 , NEUTRON ENVIRONMENT AUDIO AND GENERAL PURPOSE APPLICATIONS, BIPOLAR TRANSISTOR BETA RATIO VERSUS F L U E N C E

21 sets of data

Fluence, n/cm2

FIGURE 3. NEUTRON ENVIRONMENT HIGH-FREQUENCY APPLICATIONS, BIPOLAR TRANSISTOR BETA RATIO VERSUS FLUENCE . .

131 s e t s of data

I .o

0.8

1 0.6

0.4

0.2

0.0

FIGURE 4. NEUTRON ENVIRONMENT LOW-LEVEL-SWITCHING APPLICATIONS, BIPOLAR TRANSISTOR BETA RATIO VERSUS FLUENCE

6 2 s e t s of data

Fluence, n/cm2

FIGURE 5. NEUTRON ENVIRONMENT HIGH-LEVEL-SWITCHING APPLICATIONS, BIPOLAR TRANSISTOR BETA RATIO VERSUS FLUENCE

73 s e t s of data

FI uence, n/cm2

FIGURE 6. NEUTRON ENVIRONMENT POWER APPLICATIONS, BIPOLAR TRANSISTOR BETA RATIO VERSUS F L U E N C E

7 2 s e t s of d a t a

I .o

0.8

0.6 \

0.4

0.2

0.0

FIGURE 7. PROTON ENVIRONMENT AUDIO AND GENERAL PURPOSE APPLICATIONS, BIPOLAR TRANSISTOR BETA RATIO V E R S U S F L U E N C E

3 s e t s of d a t a

9

I .o

0.8

$ o.6 a" 0.4

0.2

0.0

. FIGURE 8. PROTON ENVIRONMENT HIGH-FREQUENCY APPLICATIONS, BIPOLAR TRANSISTOR BETA RATIO VERSUS FLUENCE

2 9 sets of data

I .o

0.8

0.2

0.0 109 IOIO IOII IO'* 1013 loi4 loi5

Fluence, p/cm2

FIGURE 9. PROTON ENVIRONMENT LOW-LEVEL-SWITCHING APPLICATIONS, BIPOLAR TRANSLSTOR BETA RATIO VERSUS FLUENCE

11 sets of data

10

I .o

0.8

6 0.6 & 0.4

0.2

\

0.0

FIGURE 10. PROTON ENVIRONMENT HIGH-LEVEL-SWITCHING APPLICATIONS, BIPOLAR TRANSISTOR BETA RATIO VERSUS FLUENCE

26 sets of data

Fluence, p/cm2

FIGURE 1 1 . PROTON ENVIRONMENT POWER APPLICATIONS, BIPOLAR TRANSISTOR BETA RATIO VERSUS F L U E N C E

26 sets of data

11

Fluence, e/cm2

FIGURE 12. ELECTRON ENVIRONMENT AUDIO AND GENERAL PURPOSE APPLICATIONS, BIPOLAR TRANSISTOR BETA RATIO VERSUS FLUENCE

78 s e t s of data

Fluence, e/cm2

FIGURE 13. ELECTRON ENVIRONMENT HIGH-FREQUENCY APPLICATIONS, BIPOLAR c TRANSISTOR BETA RATIO VERSUS FLUENCE

288 s e t s 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

FIGURE 16. ELECTRON ENVIRONMENT POWER APPLICATIONS, BIPOLAR TRANSISTOR BETA RATIO VERSUS F L U E N C E

167 s e t s 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)

FIGURE 17. ELECTROMAGNETIC ENVIRONMENT AUDIO AND GENERAL PURPOSE APPLICATIONS, BIPOLAR TRANSISTOR BETA RATIO VERSUS FLUENCE

33 s e t s 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

FIGURE 18. ELECTROMAGNETIC ENVIRONMENT HIGH-FREQUENCY APPLICATIONS, BIPOLAR TRANSISTOR BETA RATIO VERSUS FLUENCE

164 sets of data

1.0

0.8

QO 0.6

Q 0.4

\ LL

0.2

0.0

FIGURE 19. ELECTROMAGNETIC ENVIRONMENT LOW-LEVEL-SWITCHING APPLICATIONS, BIPOLAR TRANSISTOR BETA RATIO V E R S U S F L U E N C E

59 sets of data

FIGURE 20. ELECTROMAGNETIC ENVIRONMENT HIGH-LEVEL-SWITCHING APPLICATIONS, BIPOLAR TRANSISTOR BETA RATIO VERSUS F L U E N C E

106 sets of data

FIGURE 2 1. ELECTROMAGNETIC ENVIRONMENT POWER APPLICATIONS, BIPOLAR TRANSISTOR BETA RATIO VERSUS F L U E N C E

120 s e t s of data

16

T A B L E 1. RANGE AND MEDIAN VALUES OF' BULK DAMAGE CONSTANT, Kb, F O R VARIOUS APPLICATION-ENVIRONMENT COMBINATIONS

I S i z e of Data

Env i ronmen t Min imum Kb Median Kb Maximum Kb Base (a )

Audio and Genera l Purpose Appl ica t ions

Neu t ron 3.96 X c m 2 / n 3 .38 x c m 2 / n 2.62 x c m 2 / n 2 1 P r o t o n 5 .08 X c m 2 / p 7.00 x c m 2 / p 1 .11 x 1 0 - 1 4 c m 2 / p 3 E l e c t r o n 7 .38 x c m 2 / e 1.72 x c m 2 / e 5 . 6 3 x c m 2 / e 7 8 E l e c t r o m a g n e t i c 2 .43 x r a d - l 1.43 x r a d - ' 1.92 x r a d - l 3 3

High-Frequency App l i ca t ions

Neut ron 3 .57 x 1 0 - l ~ c m 2 / n 4.52 x 10-16 cm /n 1 .10 x 1 0 - 1 4 c m 2 / n 1 3 1 P r o t o n 6 . 2 4 x c m 2 / p 1 . 2 6 x 10-14 c m / P 2 . 3 8 . ~ c m /p 29 E l e c t r o n ' 7.38 x c m 2 / e 3 . 7 1 x 1 0 - 1 7 c m / e 6 . 7 0 X c m 2 / e 2 8 8 E l e c t r o m a g n e t i c 5 . 8 5 x 1 0 - l ' r a d - l 8 . 1 0 x 10-9 r ad - l 1 .92 X rad-1 164

2 2 2 2

Low-Level -Swi tch ing Appl ica t ions

Neutron 1 .52 X c m 2 / n 3 . 9 9 x 10-16 cm /n 2 .56 x c m 2 / n 6 2 Pro ton 1 .66 X c m 2 / p 5 . 7 2 x 1 0 - 1 5 c m /P 5 .50 x c m 2 / p 11 E lec t ron 7 .38 X c m /e 1.28 x c m 2 / e 6 4 2 . 7 3 x 1 0 - 1 7 c m /e E l e c t r o m a g n e t i c 2 . 1 0 x r ad - ' 1 .37 X r a d - l 2.44 x r a d - l 59

2 2 2 2

High-Level-Switching Applicat ions

Neu t ron 1. 15 x c m 2 / n 5 . 4 6 X c m 2 / n 4 . 6 0 x 10-14 cm2/n 73 P ro ton 1 .77 x 1 0 - l ~ c m 2 / p 1 . 2 9 X c m 2 / p 7 . 0 0 x 1 0 - l 4 c m /P 26 E lec t ron 2 .22 x 1 0 - 1 8 c m 2 / e 3 . 9 4 x 10-17 c m / e 146 E lec t romagne t i c 5 .85 x r ad - l 5 .95 X 10 -9 r ad - l 2 .39 x r a d - ' 106

2 2 2 5 .00 x 1 0 - 1 5 c m /e

Power ADDlications

Neu t ron 5 .25 X c m / n 1 . 3 0 x c m 2 / n 1 . 2 1 x 10-13 c m /n 72 P ro ton 1 .77 X c m / p 1 . 2 9 X c m 2 / p 7 . 0 0 x 1 0 - 1 4 c m 2 / p 26 E l e c t r o n 4 . 2 7 X c rn2 /e 5 .87 x c m 2 / e 6 . 70 X c m / e 167 Elec t romagnet ic 5 .85 x r a d - ' 4 . 2 7 x 10-9 rad-1 2 .39 x rad- ' 120

2 2

2

2

(a) T h e s i z e of t he da t a base g ives t he number of computed va lues of Kb u sed t o de t e rmine t he l i s t ed r ange and med ian va lues .

UNIJUNCTION TRANSISTORS

The .unijunction transistor structure is shown schematically in Figure 22. Sometimes called a "double-base diode", this device displays a negative resistance characteristic which results from conductivity modulation of a moderately high resist ivity si l icon bar by means of injected minority carriers from the rectifying emitter 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 UNIJUNCTION 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- tac t s i s of the order of 5 x cm. This corresponds to a bipolar tran- s is tor with an exceptionally wide base and results in the formation of an enormous number of trapping centers because of irradiation. The electrical 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 properties 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 Irradiation 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 environment should be approached with caution, If their 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- ar ies for power t ransis tors in Figures 6, 11, 16, and 21.

FIELD-EFFECT TRANSISTORS

Field-effect transistors are unipolar devices which operate by electric-field control of major i ty-carr ier conduction. The two basic types of field-effect transistors are the junction-field-effect transistor (JFET) and the insulated-gate-field-effect transistor (IGFET), discussed in the following paragraphs ~

Junction-Field-Effect Transistors

A P N junction is the interface between channel and gate in a JFET. The structure is diagrammed and the schematic symbol shown in Figure 23 for both N-channel and P-channel JFET's. All JFET's operate in the depletion mode where a reverse bias, applied between gate and source, con- t rols the current flow. Under these conditions a depletion region surrounds the channel of the JFET. 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 With a zero gate-to- source bias voltage the current flow is a maximum.

For the N-channel JFET's, a negative gate voltage turns the device off, whereas for the P-channel JFET'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 voltage gain measured in terms of transconductance, Gm, similar to vacuurn pentode tubes. A third important parameter is the total gate leakage current, Igss, which is the current flowing from gate to channel for a zero drain-to-source potential. These three JFET pa rame te r s a r e the most sensitive to radiation damage.

Source Drain

P

N

a. N- Channel JFET Structural Diagram

"0

Gate

0

Source Drain

c. P-Channel JFET Structural Diagram

Gate

+ D

P

- s

b. N-Channel JFET Schematic Symbol

- D

b + s d. P-Channel JFET Schematic Symbol

FIGURE 23. STRUCTURAL DIAGRAMS AND SCHEMATIC SYMBOLS FOR N - AND P-CHANNEL JUNCTION-FIELD-EFFECT TRANSISTORS

x)

. ~ "" -

The general effects of radiation on JFET's can be summarized as follows :

(1) The transconductance, Gm, and the "pinch-off" voltage, will decrease because of a radiation-induced change

vP, in effective impurity concentration that increases channel

, resistivity and changes carrier mobility.

(2) Increases in leakage current, Igss, will be observed as a result 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 ratio of postirradiation to preirradiation transconductance, Gm(F)/Gm(O), are plotted versus fluence for P-channel JFET's in Figures 24 and 25 in the neutron and the electromagnetic environment, respectively. Available information is too limited to permit similar plots for other radiation environments or for N-channel JFET's. However, based on observations for a very few part types it appears that significant radiation-induced decreases in JFET 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 JFET 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 fo r JFET ' s a r e too l imited to permit the presentation of trend plots. However, it appears that the fluences producing significant reductions in the value of this parameter are at leas t as l a rge as those producing significant reductions in Gm.

The significance of radiation-induced increases in I depends upon the circuit usage. Where signal levels are high; increased values 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 JFET's a l so is very l imited. Figure 26 shows available values for the ratio of postirradiation to preirradiation P-channel JFET leakage current, Igss(F)/Igss(0), plotted versus neutron fluence. These data are for a single

T h e 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 1.2 1 0

W c5 X \

X

X

0 .o I IO 1013 loi4 1015 10'6

Fluence, n/crn2

FIGURE 24. NEUTRON ENVIRONMENT, P -CHANNEL JUNCTION-FELD- EFFECT TRANSISTOR, RADIATION EFFECT ON TRANSCONDUCTANCE

28 s e t s of data

2.0

X

IO 104 lo5 IO6 lo7 IO* Fluence, rads (material)

FIGURE 25. ELECTROMAGNETIC ENVIRONMENT, P-CHANNEL JUNCTION- FIELD-EFFECT TRANSISTOR, RADIATION EFFECT ON TRANSCONDUCTANCE

143 s e t s of data

22

0 -8 U \

cz,

h

LL Y

u) u) cz,

J-l

X

X

FIGURE 26. NEUTRON ENVLRONMENT, P-CHANNEL JUNCTION-FIELD- E F F E C T T R A N S I S T O R , R A D I A T I O N E F F E C T ON L E A K A G E C U R R E N T

6 se ts of data

FIGURE 2 7.

6.8 847 X

52

36

20

4 IO 6 lo7

Fluence, rads(material1 IO8

ELECTROMAGNETIC ENVIRONMENT, N-CHANNEL JUNCTION- F IELD-EFFECT TRANSISTOR, RADIATION EFFECT ON LEAKAGE CURRENT

3 s e t s of data

. part type, the TIX693. The Igss(F)/Igss(0) data available for a 2N3089A N-channel JFET at three electromagnetic f luences are plotted in Figure 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.

Insulated-Gate-Field-Effect Transistors

The IGFET has a dielectric layer that insulates the channel from the gate. There are several dielectric materials used for this layer, but the most common is silicon dioxide (SiO2). An IGFET using Si02 as dielectric is normally called a metal-oxide-semiconductor field-effect transistor (MOSFET).

Thin-film field-effect transistors (TFT's) constitute another important category of IGFET's. The TFT's employ geometrically controlled surface 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, ceramic, or sapphire.

Metal-Oxide-Semiconductor Field- Effect Transistors

MOSFET's are constructed to operate in one or both of the depletion or enhancement modes. In the depletion mode a reverse bias applied between gate and source produces a depletion region surrounding the channel thereby reducing the current flow. As for the JFET's the bias 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 schematic syrrrbols fo r depletion mode MOSFET's a r e shown in Figure 28.

In the enhancement-mode MOSFET, the application of reverse bias between gate and source induces a channel, increasing or "enhancing" the current flow. With 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 a r e shown in Figure 29. Some MOSFET types are constructed for operation in either the depletion mode o r in the enhancement mode.

Transconductance, Gm, gate leakage current, Igss; and "pinch-off" voltage, Vp , are important parameters for depletion 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 FIELD-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 FIELD-EFFECT TRANSISTORS

they are for J .FET's. For the enhancement mode MOSFET's, the important voltage parameter is the threshold voltage, Vgth, which is the voltage from gate to source required to enhance the Lhannel and thus increase current 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 summarized 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 ) Increases in the leakage currents, I,,, o r Idss , a re observed as the result of carrier generation- recombination in the depletion region and surface contaminants near the junction edge.

(3) Changes in channel resistivity and carrier mobility result f rom 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, o r the "pinch-off" voltage, Vp, fo r depletion-mode devices. In general, degradation of Vgth o r 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 t o 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 approximately 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 because 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 independent 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 is l imited 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) selected f rom 22 measurements for the two types of P-channel enhancement MOSFET's are plotted versus I . 5 MeV electron fluence in Figure 30. N o leakage current data are available at this time.

Other Insulated-Gate-Field- Effect Transistors

Metal-insulator-semiconductor field-effect transistors (MISFET's) are IGFET 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 a r e of particular interest where a high radiation flux exists in the use environment since laboratory prototype devices indicate an improved radiation tolerance to flux dependent effects. No specific information is available fo r commercial MISFET devices at high radiation fluences but it i s reasonable to expect a performance comparable to that of MOSFET devices.

Witche l l , I. P. , "Radiation-Induced 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, January, 1967.

28

FIGURE 30. ELECTRON ENVIRONMENT, P-CHANNEL MOS FIELD-EFFECT TRANSISTOR, RADIATION- EFFECT ON GATE THRESHOLD VOLTAGE

Twenty-two sets of data.

Thin-Fi lm Transis tors

As previously stated TFT's consist essentially of an FET structure deposited on a polycrystalline substrate. Various combinations of semiconductor films, gate insulating materials and substrate materials may be used. Most of the small amount of available radiation-effects informa- t ion for TFT's is for developmental devices and its applicability to production 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

T A B L E 2 . RADIATION EFFECTS O N MOSFET PARAMETERS

TA 2330 TA 2330 TA 2330 F N 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

Enhancemen t Enhancemen t Enhancemen t Enhancemen t Enhancemen t Enhancemen t Enhancemen t Enhancemen t Enhancemen t Enhancemen t Enhancemen t

Enhancemen t Enhancemen t

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 1 0 1 4 n / c m 2 ( E > 10 keV) 0. 15 5 x 10 l4 n / c m 2 (E > 10 keV) " 5 x 1014 n /cm2 (E> 10 keV) " 5 x l o 5 rads (Si) (Co60)

1 .01 2 x 10" p / c m 2 (E= 100MeV)

" 5 x 1 0 l 2 e / c m 2 ( E = 1 . 5 M e V ) 1 .34 8 x 1 0 l 1 p / c m 2 (E = 140MeV)

1 . 0 - 2.48 1 x 10'0 - 5 x 1 0 1 ~ e/cm 2

( E = l . 5 M e V " 5 x lo1' e/cm J ( E = 1 . 5 M e V )

(E = 1.5 MeV) 0.95 - 5.25 1 x l o l o - 5 x 1 0 l 2 e /cm 2

(a) See Figure 30.

BIBLIOGRAPHY

Anspaugh, B. E. , "High Energy Proton Testing of Mariner rV Components", California Institute of Technology, Jet Propulsion Laboratories, Pasadena, California, JPL-TM-33-314, Tach. Memo, NAS7-100, January 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 Jersey, "High-Energy Radiation Damage in Silicon Transistors", paper presented at the IEEE Annual Conference on Nuclear and Space Radiation Effects, Ann Arbor, Michigan, July 12-15, 1965.

Garret t , C. G. B. , and Brattain, W. H. , "Some Experiments on, and a Theory of, Surface Breakdown", Journal of Applied Physics, 27,1956, p 299. - Gordon, F. , Jr . , and Wannemacher, H. E. , Jr . , "The Effects of Space Radiation on MOSFET Devices and Some Application Implications 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 Insulated-Gate Field- Effect Transistor", Procceedings of the IRE, - 51, 1963, p 1190.

Holmes-Siedle, A. G. , Radio Corporation of America, Princeton, New Je r sey , "Space Radiation: Its Influence on Satellite Design", RCA Engineering, - 11, June-July, 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, Inc., Woodland Hills, California, FDL-TDR-64-30, Feburary, 1964, Tech. Doc. Rpt. , January, 1963 - March, 1964, A F 33(657)-10584.

Lockheed Aircraft Corporation, "Components Irradiation Test No. 19 Gamma Irradiation of 2N914, 2N198, S2N930, 2N2192, and 2N2369 Transis tors" , 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- sistors", paper presented at the IEEE Conference on Nuclear and Space Radiation Effects, Missoula, Montana, July 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, January, 1967, Final Repo'rt, NAS 8-20 135.

Pelet ier , D. P., "The Effects of Ionizing Radiation on Transistors", The Johns 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 America, "TOS Radiation Program Report. Analysis and Evaluation of Test Results", Astro-Electronics Division, Princeton, New Jersey, September, 1965.

Radio Corporation of America, "TOS Radiation Test. Series No. 2 (February, 1965)", Astro-Electronics Division, Princeton, New Jersey, 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", IEEE Transactions of Nuclear Science, NS-12 ( l ) , February, 1965, 11th Nuclear Science Symposium Instrurnenta- tion in Space and Laboratory, Philadelphia, Pennsylvania, October 28-30, 1964, pp 457-463.

Rind, E., and Bryant, F. R . , NASA, Langley Research Center, Instrument Research Division, Hampton, Virginia, "Experimental Investigation of Simulated Space Particulate Radiation Effects on Microelectronics ' I , paper presented at the Conference on Nuclear Radiation Effects, jointly sponsored by the Institute of Electrical and Electronics Engineers, the Professional and Technical Group on Nuclear Science, and the University of Washington, Seattle, Washington, July 20-23, 1964.

Roberts, C. S . , and Hoerni, J. A. , "Comparative Effects of 1 MeV Electron Irradiation on Field Effect and Injection 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, Inc., Atomics International 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 IRE, - 51, 1963, p 119.

Wannemacher, H. E. , "Gamma, Electron, and Proton Radiation Exposures of P-Channel, Enhancement, Metal Oxide Semiconductor, Field Effect Transis tors 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 Transis tors 6 ,7 ,9 , 12, 14,

Beta Ratio 5- 16 Bipolar Transistors 1 - 19 Cadmium Selenide 24 Cadmium Sulfide 24 Carrier Mobility 21,27 Charge Buildup 28 Charge Carr iers 3 ,27 Clusters 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 Irradiation 12- 14, 17,2 1,

FI 100 29,30 Field-Effect Transistors 19-38 F N 1002 30 Forward Current Gain .3 Frenkel Defects 1 Gamma Irradiation 30 Germanium 3 High-Frequency Transistors 6,7,

10, 12, 15, 17 Impedance 19 Impurity Concentration 2 1,27 Insulated-Gate-Field-Effect

17

27

14-17,2124

28-30

Transis tors 24-30

Junction-Field-Effect Transistors

Leakage Current 19,21,23,24,27 Low Frequency Common Emitter

Low-Frequency Gain 3-5 Metal-Insulator-Semiconductor

Field-Effect Transistors 28

Effect Transis tors 28

Effect Transis tors 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 Irradiation 7-9, 17,21-23,

Pinch-Off Voltage 19,2 1,24 Power Trans is tors 6 , 9 , 11, 14, 16,

Prediction Equations 3-5 Proton Irradiation 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? Transistors 24,29 Threshold 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

-


.... -.- ..

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. ______ ~ovemment 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 ~Iemorial Institute 11. Contract or Grant No.

Columbus Laboratories NASW-1568 Columbus, Ohio ~32')1

--- 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


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

20.

Security Classif. (of this page) 121.

No. of Pages 122. Price" Unclassified Unclassified 67 $3.00

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• For sale by the National Technical Information Service, Springfield, Virginia 22151

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 radiation 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 subjects 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 deocription 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 environment 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 t~apped 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 08 / (cm2 . s) ~2 x 106/(c:rr2 . s) ~3 x 104 / (cm2 . 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)

~107/(cm2. s) ~ 104 / (cm2 . s) ~108/(cm2. s) ~107/(cm2·s) ~O. 1/(cm2 . 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/ cm2 of energy greater than 30 MeV per flare. Proton energies ranging from 107 eV to 1 09 ~V or higher have been observed in conjunction with solar -flare activities. (3, 5,39) The radiations 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 systern. This radiation is about 85 percent protons, 14 percent helium ions, and the rest heavier nuclei. Energies range from 107 to 10 19 eV with an average of about 10 12 eV. The free-space proton flux near Earth is about 2.5 protons/ (cm2 . s) when solar activity is at a maximum and about 5. 0 protons/ (cm2 . 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/(cm2 . s) Particles (1 A. U. from Sun) Energy, eV

Protons 5x 109 (normal) 2 x 103

2x 1013 (high activity) 2 x 104

Electrons 5x 109 (normal) 2 2x 1013 (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 reactors and shielding necessary must be made on a point-to-point basis determined 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 electromagnetic radiation. Because these radiations have different characteristics, they interact with material in different ways. Following is a brief description 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 Coulombforce 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 ~nergy 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 collision with nuclei in which subatOInic particle s (neutrons and protons) are knocked out of the target nucleus. At higher energies, a significant proportion 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 "evaporationll 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

(0NO)-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/cm2 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/cm3) times the thickness of material (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/cm2 . (9) To determine 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 penetrating than the original electron and is an additional source of radiation damage.

The range of monoenergetic electrons is given approximately by the followin~ 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 ~20 MeV ,

Ro (mgl cm2) = 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 U2 35 or Pu23 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

4Be9 6C12 n + a -+ + 0

Nearly monoenergetic neutrons called photoneutrons also may be obtained 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 threshold energies (1. 67 and 2.23 MeV) for this reaction. Using this reaction, electrons can be used to produce neutrons through the bremsstrahlung generated when high-energy electrons are slowed down in a high-density target. A reaction which produces nearly monoenergetic neutrons is the fusion reaction 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, epithermal, 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 nuclearreactor-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 sufficient 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 absorbing 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 cm2 ). 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, Ino 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 reaction 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 increases 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 disappearing; 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 energ~T-absorption coefficients (energyabsorption cross sections) for each mechanism and the total energyabsorption 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 interaction 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 reactions 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 materials are ionization and atomic displacement. All of the radiations discussed 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 ... ." u~ 0.01 ~ \ \ "~,,,

~ - \-Photoelectric ~ '\ / / ...... ::l... \ effect \ // > .. /

\ ' , / """...." \ \ " II .. '" , \ ." LTotal J-"'"

\ ,.... __ .. --1 \ - I \ \ I .. \--r-----~ .. ~_ I

Hydrogen Aluminum Lead

... -----

-'---, --..,. , , , , , "L,.. \ "-

.. Compton effect ""'... / Pair production , , , , r~

0.001~----~------~--~--~~------~------~'~~~~~----~----------~--~~ 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 electron 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 characteristic X-rays.

The ejected electron and the resultant positively charged atom constitute 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 al~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 v02

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 coefficients 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 deterITIined 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 between 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 EZm 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 EZm 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(E2 > E) = -2- [Reference (28)]

Ef3

Note: Since Eo = 1/2 ml v o2 = 1/2 mlc2 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 EZm { [(Ezm)l/Z ] Ezm}] - {3 In ~ + TIa{3 Z ~ - 1 - In ~

Z. 495 x 10-25 (cm2 ) 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

Elm

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 logarithm(~) 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 »Ed ) 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 defects 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 experimentally to reduce substantially the amount of experimental data required 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. Correlation 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 interactions, al._ neutrons and electromagnetic radiations cause ionization indirectly through the interaction of charged secondary particles and recoiling 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 Cm3 of Carbon(a), Relative Particle MeV cm particles/ cm2 Effectiveness

Fission Neutron 1-2 »1 102 x 10 10 o. 17-0.08

Ga:rnma Photon 1. 25 »1 1.7x 109 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 106 850

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 requires more than 1. 0 cm to deposit the same quantity of energy, the net result 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 highenergy 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 displaced 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 104 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 relatively 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 (EZ) 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 confirmed 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 displacements 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 surface (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 thickness or sensitive region is comparable to or less than the range of the electrons, 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 electrons 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 containing ~ 103 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 103 defects in a volume of the crystal containing 105 to 106 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 uniform but quite intense damage distribution.

From the preceding, it is obvious that different radiations produce different 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 correlation 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 interstitials recoInbine or forIn secondary, therInally stable defects. This annealing proce ss can either enhance or detract froIn a Inaterial's properties, depending upon the property in question. The attainInent of this therInally stable condition is both a function of tiIne and teInperature. The annealing behavior of irradiated substances is a cOInplicated and not wellunderstood 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 description 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 proportional 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 reading, 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 bulkionization effects in silicon is a function only of the ionization energy deposition. 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 detailed 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 experiment 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 determining 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 misused 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 ionization 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 experimenters utilizing the facility. These spectra are, in general, determined from data obtained from high-resolution spectrometers (recoil proton, Li6 ,

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 decision must be made to determine the accuracies required. For high resolution measurements, fairly expensive, time-consuming spectrometer measurement should be made. In most cases, however, lower resolution measurements 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 recommended procedures will be given in this document. General recommendation 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 section) is almost a constant, 0eff' Therefore, the foil response is approximately proportional to <I> (E> Et) 0eff'

A method based on irradiating a number of foils with different thresholds has proved to be very useful. The limitations to the foregoing approximate 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

100

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 spectrum has not changed unknowingly. Obviously, the accuracy of the neutronfluence 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 measurements 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 material 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 ionization 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:malldia: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 deposited dose fro:m incident protons is co:mplicated by the generation of secondary 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 contribute 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

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 mediumatomic-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 ~onuniformit}'" 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/ cm2 , 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 Inaterial. 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 literature. 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 cobaltglass-chip system. At doses greater than 106 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 (~l06 rads) and corrections may be required at very high dose rates. Before using a particular dosimetry system, one should consult the literature to determine 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 unused materials. The TLD materials can be annealed and reused only at high doses.

TLD materials can be obtained in several forms and chemical compositions. 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 material); 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. TLDsystem 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 radiation and the incident beam is in electron equilibrium for the calorimeter material, 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 conductor 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 provides 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 determine 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 electronbeam measurements, if the calorimeter material is the same as the experimental 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, corrections 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 producing 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 [-109 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 measures 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 ~ I~

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. il

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 e1ectronbeam 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 characteristics 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 container 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/cm2(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/ cm2 aluminum or 9 g/ cm2 copper).

If too soft a spectrum is indicated, experimental design should be changed, since environment correlation may be difficult, that is, the radiation 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 indicates 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 :macroscopic dose deposition pattern is the entity of interest, that is, the depth-dose distribution and so:metimes the LET, (2) the absorption coefficients for semiconductors 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 cm2 .

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 occurring. 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 cm2 .

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 twoparticle 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 twoparticle 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 molecule 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 (cm2 /g).

The term "interactions" refers to processes whereby the energy or direction 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)' = (Ee - + 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 degraded in energy and whose energy spectra have been broadened by interaction 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- 19 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.

REFERENCES

(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 Calculations of High-Energy Nuclear Interactions, 1. Systematics of Nuclear Evaporation", Physical Review, III, (6), 1659 (September 15, 1958).

54

Ii II ~ "' ii i~ ~ '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 Calculations 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 Intranuclear 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 Irradi~tion With Light, II. Attenuated Total Reflectance Spectra of Coatings Exposed to Ultraviolet Light", Technical Note N -694, U. S. Naval Civil Engineering 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 Laboratory, LA-3753, UC-34, Physics TID-4500 (1967).

(25) Bussolati, C., Fiorentini, A., and Fabri, G., "Energy for ElectronHole 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 Semiconductors", 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 Irradiation", 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 Measurement 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


Section 6. Solid-state Photodevices

by J. E. Drennm


f o r

N A T I O N A L A E R O N A U T I C S A N D S P A C E A D M I N I S T R A T I O N W A S H I N G T O N , D. C. A U G U S T 1971


1. Report No. -

2. Government Accession No. 3. Recipient's Catalog No. NASA CR-1872

4. Title and Subtitle 5. Report 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

R a d i a t i o n E f f e c t s I n f o r n l a t i o n C e n t e r

Columbus L a b o r a t o r i e s B a t t e l l e Kernorial I n s t i t u t e

Columbus, Ohio 4 3 n l 2. Sponsoring Agency Name and Address

N a t i o n a l A e r o n a u t i c s a n d S p a c e A d m i n i s t r a t i o n Washington, D. C . x)546


NASW-1568

13. Type of Report and Period Covered

Handbook - S e v e r a l Y e a r s


5. Supplementary Notes ~ ~

6. Abstract

T h i s d o c u m e n t s u m m a r i z e s i n f o r m a t i o n c o n c e r n i n g t h e e f f e c t s o f r a d i a t i o n o n l l y s o l a r c e l l s . T h e f o r m s o f r a d i a t i o n i n c l u d e

e l e c t r o m a g n e t i c . S e v e r a l c u r v e s a r e p r e s e n t e d . s o l i d - s t a t e p h o t o d e v i c e s , e s p e c i a n e u t r o n s , p r o t o n s , e l e c t r o n s , a n d

. .

7. Key Words (Suggested by Author(s)) .~

R a d i a t i o n E f f e c t s o n S o l a r Ce l l s , N e u t r o n s , P r o t o n s , E l e c t r o n s , Gamma-Rays

18. Distribution Statement

U n c l a s s i f i e d - U n l i m i t e d

9. Security Classif. (of this report) 22. Rice' 21. No. of Pages 20. Security Classif. (of this page)

U n c l a s s i f i e d $3 .oo 34 U n c l a s s i f i e d ~


I

ACKNOWLEDGMENTS

The Radiation Effects Information 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:

Dr. B . Anspaugh, Jet 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 art i- ficial. This Handbook will provide the general background and information necessary to enable the designers to choose suitable types of mater ia l s o r c lasses of devices.

Other sections of the Handbook will discuss such subjects as t rans is - tors, thermal-control coatings, structural metals, and interactions of radiation, electrical insulating materials, and capacitors.

V

TABLE O F CONTENTS

Page

INTRODUCTION . . . . . . . . . . . . . RADIATION EFFECTS O N 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 2 0

2 3

vi i

" . . .

SECTION 6. SOLID-STATE PHOTODEVICES

INTRODUCTION

A photodevice, as the name implies, is intended to provide an electrical response to incident photons of radiation. This section will consider t w o basic types of photocells in use: photovoltaic and photoconductive "bulk effect".

The photovoltaic cell generates a voltage across a P / N o r N / P junction as a function of the photons impinging on it. Silicon, gallium arsenide, cadmium sulfide, and selenium are normally used to make cells of this class. This class of cel ls i s the only self-generating type requiring no external power supply. Solar cells are photovoltaic cells employed to generate electric 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 entire layer of material changes in resistance under illumination. This response is analogous to a thermistor except that heat is replaced by l ight. The photoconductive cell decreases in resistance as tha light level increases. The absolute value of resistance of a par t icular cel l a t 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 in solar cells intended to convert solar energy to usefu l 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 r o m infrared through visible and ultraviolet and the use of these radiation wavelengths for control or other electronic purposes. Both classes of cells may be used for detection and/or measurement of nuclear radiation.

1

RADIATION EFFECTS ON PHOTOVOLTAIC DEVICES

Solar Cells

The solar cell is one of the most critical components in some satell i te systems where i t consti tutes the primary source of electric power to operate the electronic systems. In 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, optically transparent covers. The optical properties of cover mater ia ls employed to protect the basic solar cell from the space environment are degraded by exposure to radiation, and the cell itself is degraded by radiation penetrating the protective cover.

The basic kinds of solar cells available f o r 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 sil icon solar cells indicates in general the following:

(1) In the range from 15 to 65 percent electron-induced degra- dat ion ( increase) in short-circui t current , Isc (and, fo r practical purposes, that f o r maximum available power, .

P(max)) degradationin si l icon solar cells is independent 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 respective rates fo r radiation-induced Isc and P(max) degradation in silicon cells of all types under solar 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 degradation rate for ISC in gall ium-arsenide cells 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 icon solar cells is found to be approximately inversely proportional to proton energy over the range of proton energies f r o m 6 . 7 MeV to about 100 MeV. At energies above 100 MeV, the damage dependence upon fur ther increases in proton energy appears to become gradually less, theoretically approaching a plateau independent of proton energy.

(5) For s i l icon cel ls , the short-circui t current is l i t t le affected by low-energy protons (E < 1 MeV), but the open-circuit voltage decreases more rapidly under low-energy-proton bombardment than fo r higher energy irradiations.

(6 ) The sensitivity to radiation-induced degradation of silicon solar cells is significantly greater f o r 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.

In the normal space application for solar cells, the cells are either exposed directly to the space radiation or else a thin, transparent protective 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. G C 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 major factors causing solar-cell degradation 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 REIC files has been employed as the basis fo r preparation of the performance envelopes in Figures 1 through i 6 . * In these figures the ratio of maximum available power to the initial value of maximum available power, P (max)/P (max)o, is p lot ted as a function of radiation fluence. *+ The envelopes presented encompass the data available in the REIC files. Representative data points are plotted within 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 solar cells; however, f o r an application environment falling within the envelope, radiation-induced degradation of solar-cell performance ranging f rom 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.

Figures 17 and 18 show the dependence of critical fluence, Oc, upon electron energy for five resistivities of N / P and P / N sil icon solar cells , respectively. The semiempirical model is a s 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. The envelopes 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

V E R S U S E L E C T R O N F L U E N C E

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 cells

FIGURE 3 . P(MAx)/P(MAx)~ V E R S U S E L E C T R O N F L U E N C E

4 s e t s of data.

1.000 I ud N/P silicon solar cells

Fluence, e/cm2

FIGURE 4. P(MAx)/P(MAx)~ V E R S U S E L E C T R O N F L U E N C E

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

FIGURE 5. P(MAx)/P(MAx)~ VERSUS ELECTRON FLUENCE

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)

FIGURE 6. P(MAx)/P(MAx), V E R S U S E L E C T R O N F L U E N C E

2 1 sets of data.

7

l.Oo01" P/N silicon solar cells . Resistivity = 3. ohm-centimeters

FIGURE 7. P(MAx)/P(MAx)~ V E R S U S E L E C T R O N F L U E N C E

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

FIGURE 9 . P(MAX)/P(MAX)~ V E R S U S E L E C T R O N F L U E N C E

3 se ts of data.

I.000 1" P/N silicon 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 se ts 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

1 0 ' ~ Fluence, p/cm2

13 se ts 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 1 0 ' ~ d 4 td5 Id6

Fluence, p/cm2 c

FIGURE 12. P ( M A x ) / P ( ~ x ) ~ VERSUS PROTON FLUENCE

(0 .5 M E V <E <20 MEV)

0 se ts of data.

1 0

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

FIGURE 13. P(MAx)/P(MAx)~ VERSUS PROTON FLUENCE

(0 .5 M E V < E <20 MEV)

0 se ts 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

FIGURE 14. P ( ~ X ) / P ( " & X ) ~ VERSUS PROTON FLUENCE

(0.5 M E V <E <20 MEV)

13 sets of data.

1 1

0.200

N/P silicon solar cells Resistivity= 20. ohm-centimters.

Fluence, p/cm2

FIGURE 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 FLUENCE

(0.5 M E V <E <20 MEV)

0 se ts of data.

P/N silicon solar cells

F I G U R E 16. P(MAx)/P(MAx)~ VERSUS PROTON FLUENCE

(0.5 M E V < E <20 MEV)

16 se ts of data.

12

was used to generate these curves. The data available in the REIC were fitted to this model by the method of least squares to determine the coefficients given in Table 1.

Figures 19 and 20 show the dependence of QC upon proton energy for five resistivities of N / P silicon solar cells and 1 ohm-centimeter- resist ivity 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. In the case of the P / N cells, the available data were not sufficient to permit determining a value for D other than zero. The coefficient values determined from the data are l is ted in Table 1.

TABLE 1. MODEL COEFFICIENTS

Electron Irradiation

N / P Silicon 0 . 09839 - 1. 520 9.325 0 . 09496

P / N Silicon 0. 09 545 - 1.407 8.425 0 . 1208

Proton Irradiation

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 imited amount of data available for neutron-irradiated solar cells confirm that their behavior under this form of radiation is similar to that produced by electrons and protons although the damage produced is not identical . For N / P silicon solar cells of nominally 5 to 10 ohm-centimeter base resist ivity, an average value (subject to considerable variance of critical fluence, QC 7 x 10l1 n/cm2 ( E > 10 keV), has been observed. The effect of changes in neutron energy spectrum has not been documented.

Figure 21 shows the maximum available power ratio, P(max)/P(max)o,

versus incremental f luence, 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 se ts of data.

10ZF r R= I ohm-cm \ f R = 3 ohm-cm

R = 5 ohm-cm R= 10 ohm-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

FIGURE 19. CRITICAL FLUENCE VERSUS PROTON ENERGY, R=1-20 OHM-CM, N / P

26 sets of data.

Fluence, p/cm2

FIGURE 20. CRITICAL 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:

IJse the critical fluence value for neutron irradiation or determine the appropriate cri t ical f luence value 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 Figure 21 with the value of A@ determined in Step ( 2 ) and read the corresponding 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 O F 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 outside 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 energies outside the range from 4 keV to 40 MeV or for proton energies outside 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 variables. The variabil i ty of these data is too great to permit the development of simple predictive relationships for radiation effects.

In addition to the N / P o r P / N silicon solar cells with fixed base resis- t ivit ies, drift-field or graded-base solar cells have been produced that exhibit improved radiation tolerance. The radiation-induced degradation pattern for these cells is about the same as for conventional N / P solar cells (P(max)/P(max)o degrades about 20 percent per decade increase in f luence above the threshold fluence). However, the threshold fluence and critical f luence are a factor of three or more greater than those for conventional N./P cells . This is i l lustrated 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 result is similar to the result of annealing radiation damage but occurs with reasonable rates at much lower temperatures than the usual annealing temperatures. Thus, though high f l u x radiation will degrade the lithium- doped solar cells , the properties will recover in hours or days to nearly 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 redegradation. 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 solar cells ( 2 to 3 .percent) averages 20 pe rcen t o r l e s s of the typical silicon solar- cell efficiency. However, available data show that QC for these cells exc&eds 1017 e/crn2 for electron energies ranging 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 solar cel ls at a proton fluence of 4 x 10l2 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 similar comparison is possible for 1-ohm-centimeter-resistivity P / N S i cells and CdS ce l l s a t a 1- MeV electron fluence of 5 x 10 l 5 e / c m z . 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 comparable area. The CdS cells would have an output advantage 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 1 0 ' ~ I x IOi6 I x 1 0 "

Electron Fluence, @ , 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

Figure 23 shows P(max) /P(max)o. for gall ium arsenide solar cells as a function of electron fluence for energles ranging from 1 to 50 MeV. Figure 24 shows P(max)/P(max)o as a function of proton fluence for energies ranging from 0. 1 to 95. 5 MeV. The available GaAs solar-cell data are not sufficient to permit a more complete analysis.

Solar-Cell Cover Glasses and Adhesives

The preceding discussion has treated the solar cell as a device without considering whether or not the semiconductor element is protected by a transparent shield. Experimental data have shown that the degradation of the semiconductor element of the solar cells result ing from space radiation can be substantially reduced if the solar cells are protected with a transparent shield. However, the use of such a shield may present other problems, 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 G f

glasses, fused quartz and si l icas, sapphire, and plastic materials, as well as various adhesives have been studied for a range of electron and proton energies and exposure. The reader is referred to the "Handbook of Space- Radiation Effects on Solar-Cell Power Systems":: for a more detailed discussion 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 OPTICAL CHARACTERISTICS O F SOLAR-CELL COVER MATERIALS

Material Description

Percent Change in Transmit tance 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 microsheet + A-R coating + "blue" filter 3. 7 2. 1

( 5 ) Fused si l ica (66 mil) Corning 7940 1. 7 2 . 2 1 . 1 ( 6 ) Fused si l ica-Corning 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 10l1 p

(1) Microsheet (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 ADHESIVES(~~ 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 U V 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 Je r sey , AED-R-3389, NASA- CR-98717, November 15, 1968, Qtly Rpt. No. 2, July 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 Jersey, AED-R-3440, NASA-CR-103871, April 21, 1969, Final Rpt. , April 23, 1968 - April 21, 1969, NAS7-100, 119 pp. Avail: NASA, N69-33590 and NTIS.

Car te r , 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 Janda, R. J . , '!Handbook of Space-Radiation Effects on Solar-Cell Power Systems", Exotech, Inc. , 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, IV: High Energy Proton Radiation Damage in Solar Cells", Space Tech- nology Labs. , Inc. , Redondo Beach, California, MR-27, STL-8653-6017- KU-000, January 20, 1963, NAS5-1851, 57 pp.

Denny, J M. , Downing, R. G. , Hoffnung, W . I. , and Van Atta, W . K. , '!Charged Particle Radiation Damage in Semiconductors, V: Effect of 1 MeV Electron Bombardment on Solar Cells", Space Technology Labs. , Inc . , Redondo Beach, California, MR-28, STL-8653-6018-KU-000, February 11, 1963, NAS5-1851, 75 pp.

Denny, J. M. , Downing, R . G . , Simon, G. W . , and Van Atta, W . K . , "Charged Particle Radiation Damage in Semiconductors, VI: The Electron Energy Dependence of Radiation Damage in Silicon Solar Cells", Space

23

Technology Laboratories, Inc., Redondo Beach, California, STL-8653- 6019-KU-000, February 13, 1963, NAS5-1851, 24 pp.

Denny, J. M. , and Downing, R. G. , "Charged Particle Radiation Damage in Semiconductors, VIII: The Electron Energy Dependence of Radiation Damage in Photovoltaic Devices'!, Space Technology Laboratories, Inc. , Redondo Beach, California, STL-8653-6025-KU-000, July 15, 1963, NAS5-1851, 20 pp.

Denny, J . M. , and Downing, R. G. , "Charged Particle Radiation Damage in Semiconductors, IX: Proton Radiation Damage in Silicon Solar Cells", Space Technology Laboratories, Inc. , Redcndo Beach, California, STL- 8653-6026-KU-000, August 31, 1963, NAS5-1851, 34 pp. Avail: NASA, N65- 18050.

De Pangher, J. , and Crowther, D. L. , "Study of Drift-Field Solar Cells Damaged by Low-Energy Protons", Lockheed Missiles and Space Company, Palo Alto, California, October 15 - November 19, 1965, NAS5-9627, 26 pp, Avail: NASA, N66- 14279.

Downing, R. G. , TRW Systems, Redondo Beach, California, "Low Energy Proton Degradation in Silicon Solar Cells", Paper presented at Fifth Photovoltaic Specialists Conference, Proceedings held at NASA, Goddard Space Flight Center, Greenbelt, Maryland, October 19, ' 1965, PIC-SOL- 209/6. 1, NASA-CR-70169, January, 1966, pp D-7-1 - D-7-11, Avail: NASA, N66-17339.

Downing, R. G . , Car ter , J . R. , Scott, R. E. , and Van Atta, W . K . , "Charged Particle Radiation Damage in Semiconductors - XIV: Study of Radiation Effects in Lithium Doped Silicon Solar Cells", TRW Systems, Redondo Beach, California, TRW-10971-6014-RO-00, NASA-CR-103788, May 27, 1969, Final Rpt. , NAS7-100, 153 pp, Avail: NASA, N69-33422 and NTIS.

Drennan, J; E. and Hamman, D. J. , "Space Radiation Damage to Electronic Components and Materials", Battelle Memorial Institute, Columbus Labora- tories, Columbus, Ohio, REIC Report No. 39, January 31, 1966, AF 33(616)-1124, 65 pp, Avail: DDC, AD 480010.

Haynes, G. A . . , and Ellis, W . E. , "Effects of 22 MeV Proton .and 2 .4 MeV Electron Radiation on Boron- and Aluminum- Doped Silicon Solar Cells",

24

"

NASA, Langley Research Center, Langley Station, Hampton, Virginia, NASA-TN-D-4407, April, 1968, 66 pp, Avail.: NASA, N68-19924.

"Radiation Effects on Lithium P on N Solar Cells", Lockheed-Georgia Co. , Marietta, Georgia, LAC-ER-9357, NAS5- 10415, 33 pp.

Patterson, J. L . , and Miller, W. E . , NASA, Langley Research Center, "Protecting Explorer XVI Solar Cells", Astronautics & Aerospace Engineering - 1, (9) , NASA-RP-115, October, 1963, pp 48-51.

Stat ler , R. L. , U. S . Naval Research Lab., Washington, D. C . , . "Status of Silicon Solar Cell Radiation Damage", Paper presented at Fifth Photo- voltaic Specialists Conference, Proceedings held at NASA, Goddard Space Flight Center, Greenbelt, Maryland, October 19, 1965, PIC-SOL-209/6. 1, NASA-CR-70169, January 1966, pp D-2-1 - D-2-20, Avail: NASA, N66-17344.

Statler, . R. L. , "Radiation Damage in Silicon Solar Cells from 4. 6-MeV Proton Bombardment", U. S. Naval Research Laboratory, Washington, D. C . , NRL-R-6333, November 15, 1965, Final Rpt., 44 pp.

Weller, J. F . , and Stat ler , R. L. , U. S . Naval Research Lab., Washington, D. C. , "Low Energy Proton Damage to Solar Cells", Paper presented at the N E E Summer General Meeting, Toronto, Canada, June 19, 1963, 14 pp, Avail: AIEE as CP-63-1184.

25

I

Index

Adhesive 17, 20-22 A-R Coating 21 Blue Filter 2 1 Blue -Red Filter 2 1 Cadmium Selenide Solar Cell 1, 2 Cadmium Sulfide Solar Cell 1 , 2,

Corning 0211 21 Corning 7940 2 1, 22 Cover Material 17, 20-22 Crit ical 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 Electron 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 11 22 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

Microsheet 02 11 21 Neutron Critical Fluence 16 Neutron Fluelrce 4 Neutron Irradiation 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 Glas s 22 P/N Sil icon Solar Cell 1-4, 8, 9,

Proton Energy Level 13, 15, 17, 18,

Proton Fluence 10-12, 18-20 Proton Irradiation 13 Proton Radiation Energy Dependence

Proton Radiation 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 Circuit Current 2, 3 Silica 20 Silicon 1 Soda Lime Plateglass 22 Solar Illumination 2 Solex 22

17, 18

12-15, 17, 18

20, 21

3, 4

27

Spectral Transmittance 22 Spectrasil A 22 Suprasil I1 22 Thin Film Cadmium Sulfide Solar

Threshold Fluence 17 Transparent Adhesive 21, 22 Ultrasil 22 Ultraviolet Radiation 2 2 Vycor 22

Cell 18

28 NASA-Langley, 1971 - 9 CR-1872

NASA CR-1785, Radiation Effects Design Hdbk

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