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NASACONTRACTOR
REPORT
RADIATION EFFECTS DESIGN HANDBOOK
Section 3. ElectricalInsulatingMaterials
and Capacitors
by C. L. Hunks and D. J. Hunzmun
Prepared by
RADIATION EFFECTS INFORMATION CENTER
BATTELLE MEMORIAL INSTITUTE
Columbus, Ohio 4 3 2 0 1
for
NATIONAL
AERONAUTICS
AND
SPACE
ADMINISTRATION
WASHINGTON,
D. C.
JULY 1971
TECH LIBRARY KAFB, NM
-
-___.
1. Report No.
-
2. Government AccessionNo.
3. Recipient'sCatalogNo.
NASA CR-1787
I 5. Report Date
~~
4. Title and Subtitle
RADIATIONEFFECTSDESIGN
HANDBOOK
SECTION 3 . ELECTRICAL
INSULATING
MATERIALS
CAPACITORS
~~
"
~
~
~~~~
July 1971
AND
6. Performing Organization Code
~
7. Author(s)
8. Performing Organkation Report No.
C. L. Hanksand
D. J . Hamman
10. Work Unit No.
9. Performing Organization Name and Address
RADIATION
EFFECTS
INFORMATION
CENTER
BattelleMemorialInstitute
C o l u m b u sL a b o r a t o r i e s
43201
Columbus,
Ohio
11. Contract or Grant No.
NASW-1568
13. Type of Report andPeriodCovered
12. SponsoringAgencyNameandAddress
ContractorReport
14. SponsoringAgencyCode
N a t i o n a lA e r o n a u t i c sa n dS p a c eA d m i n i s t r a t i o n
20546
Washington, D.C.
15. Supplementary Notes
T h i s d o c u m e n tc o n t a i n ss u m m a r i z e di n f o r m a t i o nr e l a t i n g
to steady-state
r a d i a t i o ne f f e c t s on e l e c t r i c a li n s u l a t i n gm a t e r i a l sa n dc a p a c i t o r s .
T h ei n f o r m a t i o n i s p r e s e n t e di nb o t ht a b u l a ra n dg r a p h i c a lf o r mw i t ht e x td i s c u s s i o n .
The r a d i a t i o nc o n s i d e r e di n c l u d e sn e u t r o n s ,
gamma r a y s ,a n dc h a r g e dp a r t i c l e s .
i s u s e f u lt od e s i g ne n g i n e e r sr e s p o n s i b l ef o rc h o o s i n gc a n d i d a t e
T h ei n f o r m a t i o n
a r a d i a t i o ne n v i r o n m e n t .
m a t e r i a l s o r d e v i c e sf o ru s ei n
..
~
~- .-
~
17. KeGWords (Suggested by Authoris))
18. Distribution Statement
R a d i a t i o nE f f e c t s ,E l e c t r i c a lI 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
-.- - ..
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Unclassified
Unclassified-Unlimited
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20. Security Classif. (of this page)
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21. NO. of Pages
88
For sale by the National Technical Information
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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
n e c e s s a r y to enable the designers to choose suitable types of m a t e r i a l s o r
c l a s s e s of devices.
Other sections of the Handbook w i l l d i s c u s s s u c h s u b j e c t s a s t r a n s i s tors, 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:
M r . F . N . Coppage,SandiaCorp.
M r . R . H. Dickhaut,Braddock,DumandMcDonald,Inc.
D r . T . M . Flanagan, Gulf RadiationTechnology
M r . F. Frankovsky, IBM
Mr.D.
H. Habing,SandiaCorp.
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
. . . . . . . . . .
1
. . . . . . . . . . . . . . . .
1
. . . . .
2
RADIATION E F F E C T S ON INORGANIC MATERIALS
. . . .
10
RADIATION E F F E C T S ON SPECIFIC BULK. SHEET.
AND F I L M INSULATORS . . . . . . . . .
. .
11
ELECTRICAL INSULATING
MATERIALS
INTRODUCTION .
RADIATION E F F E C T S ON ORGANIC MATERIALS
P o l y t e t r a f l u o r o e t h y l e( P
n eT F E )
. . . . .
Polychlorotrifluoroethylene ( K e l - F ) . . . .
Polyethylene . . . . . . . . . . . .
Polystyrene . . . . . . . . . . . .
Polyethylene
Terephthalate
. . . . . . .
Polyamide . . . . . . . . . . . . .
Diallyl
Phthalate
. . . . . . . . . .
Polypropylene
. . . . . . . . . . .
Polyurethane . . . . . . . . . . . .
Polyvinylidene
Fluoride
. . . . . . . .
Polyimide . . . . . . . . . . . . .
P o l y i m i d a z o p y r r o l o(nPey r r o n e )
. . . . .
Epoxy
Laminates
. . . . . . . . . .
. . . . . . . .
M i s c e l l a n e oO
u sr g a n i c s
Ceramic . . . . . . . . . . . . . .
Mica
. . . . . . . . . . . . . .
RADIATION E F F E C T S ON SPECIFIC WIRE
AND CABLE INSULATION . . . . . .
P o l y t e t r a f l u o r o e t h y l e( n
PeT F E )
Polyethylene . . . . . .
Silicone
Rubber
. . . . .
Polyimide'. . . . . . .
Irradiation-Modified
Polyolefin
Miscellaneous
Organics
. .
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
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. .
. .
. .
. .
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12
16
18
19
20
20
21
22
22
23
24
24
25
26
26
29
. . . . .
29
.
.
.
.
.
30
31
32
33
33
34
. . . .
. . . .
.
.
.
.
.
.
.
.
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.
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.
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.
.
.
.
.
.
. . . . . . . . . .
vii
.
..
.-.
. "
.
_
I
"
.
"
-.-.
,
...................
.
-
TABLE O F CONTENTS
(Continued)
Page
C er amic . . . . .
Miscellaneous
Inorganics
. . . . . . . . . . . .
. . . . . . . . . . . .
35
36
RADIATION E F F E C T S ON ENCAPSULATING
COMPOUNDS . . . . . . . . . . .
.
.
.
.
.
.
36
RADIATION E F F E C T S ON CONNECTORS
AND TERMINALS . . . . . . . .
CAPACITORS
.
.
.
INTRODUCTION .
.
.
.
.
.
.
.
.
40
.
.
.
.
.
.
.
.
46
. . . . . . . . . . . . . . . .
46
.
.
.
.
.
.
.
.
G l a s sa-nPdo r c e l a i n - D i e l e c t r iC
ca p a c i t o r s
. .
Mica-Dielectric
Capacitors
. . . . . . . .
C e r a m i c - D i e l e c t r iC
capacitors
. . . . . . .
P a p e r -a n d Paper/Plastic-Dielectric C a p a c i t o r s .
P l a s t i c - D i e l e c t rCi ca p a c i t o r s
. . . . . . .
Electrolytic
Capacitors
. . . . . . . . .
REFERENCES
INDEX
.
.
. . .
. . .
.
.
.
.
48
50
51
52
60
64
. . . . . . . . . . . . . . . . .
71
.
79
.
.
.
.
.
viii
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
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 p r i m a r y i m p o r t a n c e
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 tole r a n c e of various insulating materials and the degradation of t h e i r e l e c t r i cal properties. Deglladation
of mechanical properties, however, is also
a consideration to the extent that in many applications the mechanical failu r e of an insulator or dielectric will adversely affect its e l e c t r i c a l c h a r a c t e r i s t i c s . If t h e r e a d e r ' s i n t e r e s t i s s u c h t h a t h e r e q u i r e s m o r e
information than is presented herein concerning changes in the basic
m e c h a n i c a l c h a r a c t e r i s t i c s of o r g a n i c i n s u l a t i n g m a t e r i a l s o r t h e d a m a g e
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 c i r c u i t r e q u i r e ments 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
a s temperature and humidity.
The fabrication method used by the manufacturer can also be a factor in
determining the amount of d a m a g e t h a t m i g h t o c c u r . F o r t h e s e r e a s o n s ,
this r e p o r t is limited to generalized "ballpark" type information which
is
applicable to early design considerations. Where information on
a material
i s insufficient for "ballpark" generalization, however, details
of specific
irradiations are presented.
The effects of radiation as p r e s e n t e d i n t h i s r e p o r t a r e o f t e n i d e n t i fied a s d a m a g e t h r e s h o l d a n d / o r 2 5 p e r c e n t d a m a g e d o s e . T h e s e t e r m s
relate to changes in o n e o r m o r e p h y s i c a l p r o p e r t i e s , i . e . , tensile strength,
1
elongation, etc., with damage threshold being the dose where
the change is
first detected. The 2 5 p e r c e n t d a m a g e d o s e is that where a 2 5 p e r c e n t
change in property occurs.
The scope of t h i s r e p o r t h a s b e e n l i m i t e d t o t h e e f f e c t s of steadystate and space radiation and excludes information concerning transient
r a d i a t i o n o r p u l s e - r a d i a t i o n e f f e c t s w i t h t h e e x c e p t i o n of the next few pages
where transient effects are used for illustration. The information presented
i s s e p a r a t e d by the configuration of t h e t e s t item, i. e . , bulk or sheet
materials, wire and cable insulation, encapsulating compounds, connectors
and terminals, and capacitors. Introductory paragraphs on organic and
i n o r g a n i c i n s u l a t o r s d i s c u s s t h e e f f e c t s of r a d i a t i o n i n g e n e r a l t e r m s o n
t h e s e two b a s i c c a t e g o r i e s of insulating materials. Also, the information
on the effects of radiation on bulk or sheet-type specimens is considered
applicable to toher configurations of t h e s a m e m a t e r i a l , k e e p i n g i n m i n d
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 E F F E C T S ON ORGANIC MATERIALS
Organic insulating and dielectric materials experience both temporary and permanent changes in characteristics 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
a r e g e n e r a l l y r a t e s e n s i t i v e w i t h a saturation of the effect at the higher
radiation levels. The enhancement
of the electrical conductivity is the
m o s t i m p o r t a n t of t h e t e m p o r a r y e f f e c t s ; i n c r e a s e s of s e v e r a l o r d e r s of
magnitude are observed. The magnitude
of t h e i n c r e a s e i s dependent
upon s e v e r a l f a c t o r s i n c l u d i n g t h e m a t e r i a l b e i n g i r r a d i a t e d , a m b i e n t
temperature, and the radiation rate.
Absorption of energy, excitation of c h a r g e c a r r i e r s f r o n nonconduc:
ting to conducting states, and the return
of t h e s e c a r r i e r s f r o n c o n d u c t i n g
to nonconducting states are considered responsible for the induced conductivity. S . E . H a r r i s o n , et al, ( l ) have demonstrated that, with steadys t a t e g a m m a irradiationbetweenand
l o 4 r a d s ( H Z O ) / s , t h ee x c e s s
2
conductivity has d i s t i n c t c h a r a c t e r i s t i c s i n t h r e e t i m e i n t e r v a l s w h i c h a r e
denoted as A, B, and C i n F i g u r e 1. The conductivity increases exponent i a l l y i n r e s p o n s e t o a s t e p i n c r e a s e i n g a m m a d o s e r a t e , y, during Interval A and is c h a r a c t e r i z e d by
where
uo = initial conductivity
u
= conductivity at t i m e t
A
= e m p i r i c a lc o n s t a n t
T o = k o j - p = time constant of t h e r e s p o n s e as a function of
gamma dose, gamma equivalent ionizing dose, or
d o s e r a t e ko and p being empirical constants
(see Figure 2 ) .
During Interval B, the induced conductivity is at equilibrium, and
its value is d e t e r m i n e d by t h e r a t e 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 = e m p i r i c a l c o n s t a n t s ( s e e T a b l e 1 ) a n d
i, = g a m m a o r gamma equivalent (ionizing)
exposure rate in rads
(H20)/s.
T h e e q u i l i b r i u m o r s a t u r a t i o n of the radiation induced conductivity is attributed to two conditions: (1) equal rates
of f r e e - c a r r i e r g e n e r a t i o n a n d c a r rier annihilation through recombination, and ( 2 ) t h e r a t e of f r e e - c a r r i e r
capture in trapping states equals that of t r a p p e d - c a r r i e r d e c a y .
The induced conductivity gradually decreases following the termination of t h e i r r a d i a t i o n . T h e m e a s u r e d c o n d u c t i v i t y
of Interval C has been
c h a r a c t e r i z e d f o r s e v e r a l o r g a n i c materials by
3
I
9
"
"
I
I
I
I
00
I
I
I
a
I
I
I
I
I
I
b
Time, t, s
FIGURE 1.
TYPICALBEHAVIOR OF CONDUCTIVITY I N
RESPONSE TO A RECTANGULAR PULSE OF
GAMMA-RAY DOSE RATE(^)
4
5
-
EPOXY1478 - I
4
-
3
-
2
- Below I .7 rads (H,O) /s
I
- No photoconductivityismeasured
I
0
5
4
cn
c
c 3
c
-
2
I
0
5
4
3
2
I
-3
FIGURE 2.
-2
-I
0
2
3
4
i n p, rads (H,O)/s
I
6
7
a
LOGARITHM O F TIMECONSTANTVERSUSLOGARITHM
O F GAMMA-RAY DOSE RATE FOR POLYETHYLENE,
POLYSTYRENE, AND EPOXY 1478-1 AT 38
C('1
5
!I
5
9
TABLE 1. MEASUEDVALUES OF 4, AND 6 FOR EIGHTMATERIAL5 ASDEFINED
Material@)
Polystyrene
Polyethylene
Epoxy 1478 -1
6
38
0.97
49
0.97
4.
o x 10-l7
1.7 x 10'2 to 5 . 0 x 103
60
0.97
4.0
X 10-17
1.7 X 10-2 to 5. o X 103
38
0.74
10-16
5.2
x 10-2
8.3
x1.7
to
Range of; , rads (H20)/s
4. o X 10-17
1 . 7 X 10-2 to 5.0 X 103
x lo3
8.3 x 10'2 to 1.7 x lo3
49
x 6.3
0.74
60
0.74
38
No measurable photoconductivity below f = 1.7
1.6 x
3.3 x 10-17
10-17
3.8
x 7.5
1.0
x
38 Teflon
6.0
to
1.8 1.1 x
1.0
38
X 103
9. o 4.2
to
No measurable photoconductivity below;
60
38
1.74.2
to
3.3 X 10-17
1. 0
3.8 ,0.88
Polypropylene
38
8.3 x 10'2 t o 1 . 7 x l o 3
No measurable photoconductivity below p = 9.0
49
Nylon
pt; d a )
Temperature(c),
C
1.0
H-film
BY (0-ir o ) =
= 7.5 x 101
X 101 to 4.2 X 1 0 3
lo3
1.8
x 10-17
x
5.8
1 . 21.8
x 10-16
X 10-3 to 6.
6.0
to X 10-3
No measurablephotoconductivitybelow
1.3
X 103
10-18
x2.8
8.0
10-20
1.7
8.0
x
X 103
= 8.0
to 6.0 x l o 3
3.0
1. E( xto 10-3
10-16xDiallylphthalate
2.10.3038
o x 103
3.0102
to
x
x 102
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 r e c o v e r y
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 t h r e e b a s i c
c h a r a c t e r i z a t i o n s p r e s e n t e d a b o v e f o r I n t e r v a l s A, B, and C by S. E.
H a r r i s o n , 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)]
T h e c u m u l a t i v e r e s u l t s of the temporary effects pertaining to the
e l e c t r i c a l p a r a m e t e r s of i n s u l a t i n g m a t e r i a l s a r e a reduction in breakdown
and flashover voltages as well a s a n i n c r e a s e i n l e a k a g e c u r r e n t o r c o n d u c tance - the latter also being identified as a d e c r e a s e i n t h e m a t e r i a l s i n sulation resistance. However, these temporary changes in electrical
characteristics are often not large enough to prevent the use
of organic
insulators and dielectrics in
a radiation environment. This is especially
t r u e i f the designer considers these changes and makes allowances to
minimize their effects. Howver, where the designer
is u n d e r s e v e r e
space limitations or the application includes a high radiation-exposure rate,
it m a y b e n e c e s s a r y t o limit insulating-material considerations to the
inorganics since tney tend to have a l a r g e r d o s e t o l e r a n c e t h a n o r g a n i c s
for the same ionizing rate.
P e r m a n e n t e f f e c t s of radiation on organic insulating and dielectric
m a t e r i a l s a r e n o r m a l l y a s s o c i a t e d w i t h 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 t h e m a t e r i a l . A softening of t h e m a t e r i a l , d e c r e a s e s i n t e n s i l e s t r e n g t h a n d m e l t i n g p o i n t , a n d a greater solubility could
be t h e r e s u l t of chain scission. Crosslinking leads to hardening, an increase in strength and melting point, a decrease in solubility, and an
increase in density. Thus, the permanent effects
of radiation on organic
m a t e r i a l s i s predominantly a change in the physical properties. This
7
.. ..
physical degradation, however, may also be disastrous to the electrical
c h a r a c t e r i s t i c s of a component part such a s p r i n t e d c i r c u i t b o a r d s , w i r e i n sulation, and connector s. Radiation-induced embrittlement of insulating
structures, such as these, where the insulation cracks or flakes, 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
i n a radiation environment, i . e . , physical degradation followed by f a i l u r e
of e l e c t r i c a l p r o p e r t i e s . C h a n g e s i n d i e l e c t r i c l o s s o r d i s s i p a t i o n f a c t o r
and insulation resistance have also been recorded as permanent effects
from exposure to a r a d i a t i o n e n v i r o n m e n t . T h e s e c h a n g e s , h o w e v e r , a r e
often quite small, and it would be an uncommon application where they
would offer any problem.
A comparison of t h e r e l a t i v e r e s i s t a n c e of organic insulating materials to permanent effects is p r e s e n t e d i n F i g u r e 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 l e s s t h a n
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 s e r i o u s c o n c e r n e x c e p t f o r o r g a n i c f l u i d s w h e n s u f f i c i e n t p r e s s u r e
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 r u e of the gases produced during the irradiation of halogenated hydrocarbons such a s polytetrafluoroethylene (Teflon) and Kel-F. Although
f a i l u r e f r o m o t h e r . c a u s e s is likely to occur before the corrosion would
become a p r o b l e m , s o m e c o n s i d e r a t i o n i n t h i s a r e a m a y b e a d v i s a b l e w h e n
selecting sealed parts - l i k e m i n i a t u r e r e l a y s - that contain electrical
contacts.
Environmental conditions other than radiation contribute to the
degradation of o r g a n i c i n s u l a t o r s a n d d i e l e c t r i c s . T e m p e r a t u r e a n d / o r
humidity may be important for some materials, and the gaseous content
of the ambient atmosphere is of s e r i o u s i m p o r t t o o t h e r s . F o r e x a m p l e ,
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
I
Phenolic,
laminate
glass
Phendic asbestos filled
Phendi4unfilled
Epoxy, aromatic-type
curing
agent
Polyurethane
Polyester, glass filled
Polyester,mlneralfilled
Diallyl Phthalate, mineral filled
Polyester, unfilled
Mylar
SI Ilcone, glass fllled
Sillcone, minerol filled
Sillcone,unfilled
Melamine- formeldehyde
Urea-formaldehyde
Aniline-formaldehyde
Polystyrene
Utility
Damage
of Organic
Incipienttomild
Nearly always usable
Mild to moderate
Often
satisfactory
Moderate
to
severe
Limited use
I
I
I
r,l/lll-
I
Acrylonltrile/butodiene/styrene (ABS)
Polyimide
Polyvmyl chloride
Polyethylene
Polyvinyl formal
Polyvlnylldene chloride
Polycarbonate
Kel-F Poly trlfluorochloroethylene
Pol vlnyl butyral
CelLose ocetote
Polymeth I methacrylate
PolyomlJe
Vinyl chlorlde-ocetote
Teflon (TFE)
Teflon (FEP)
Noturalrubber
Styrene- butodiene (SBR)
Neoprene rubber
Silicone rubber
Polyprop lene
Polyvinyridene fluoride (Kynor 400)
to5
lo4
10'
106
lo9
108
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
FIGURE 3.
( I rod(C) = 4 x IO' n/cm2)
RELATIVE RADIATION RESISTANCE O F ORGANIC
INSULATING MATERIALS BASED UPON CHANGES
IN PHYSICAL PROPERTIES
9
RADIATION E F F E C T S ON INORGANIC MATERIALS
Inorganic insulating and dielectric materials are, in general, more
resistant to radiation damage than are the organic insulators. Atomic disp l a c e m e n t s a r e r e s p o n s i b l e f o r n e a r l y all of t h e p e r m a n e n t d a m a g e t h a t
occurs in inorganic insulators, but constitutes only
a small p a r t of the
damage in organic insulators.
No new bond f o r m a t i o n s a r e p r o d u c e d by the
i r r a d i a t i o n of t h e i n o r g a n i c i n s u l a t i n g m a t e r i a l s , a n d t h e y a r e l e f t u n a l t e r e d
chemically.
A l a r g e p a r 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 c h a r g e c a r r i e r s i n t h e
inorganic compounds and the excitation-produced quasi-free electrons are
responsible for this photoconductive effect. The generalized expression
for conductivity in insulating materias, Equation
(4),is applicable to the
i n o r g a n i c m a t e r i a l s as well as the organics. The value
of 6 i s a l m o s t
always 1 forinorganicsand
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 c r y s t a l l i n e i n s u l a t o r s d e c r e a s e s
from exposure to fast n e u t r o n s . A m o r p h o u s i n s u l a t o r s , s u c h a s f u s e d
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 characteristics.
A comparison of t h e r e l a t i v e r a d i a t i o n r e s i s t a n c e of inorganic insul a t o r s t o p e r m a n e n t d a m a g e i s p r e s e n t e d i n F i g u r e 4.
10
DZZZZZl
Magnesium oxide
Aluminumoxide
Quartz
Glass
(hard)(<l0I6n
Glass(boronfree)
Sapphire
Forsterite
Spinel
Beryllium oxide
of Inorganic
Utility
Damage
Incipient tomild
Mild to moderate
Nearly always usable
Oftensatisfactory
Limiteduse
Moderate to severe
Gamma Dose, rods(Cfb)
( 0 ) Unsatisfactory
at
n/cm2
(b) Approximate gammadose
(4x 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 E F F E C T S ON SPECIFIC BULK,
SHEET. -AND F I L M INSULATIONS
~~
"
E l e c t r i c a l i n s u l a t i o n s of the bulk, sheet, and
film type have been
investigated as to the effect of radiation on their physical and electrical
p r o p e r t i e s by a number of e x p e r i m e n t e r s . T h i s s e c t i o n
of t h e r e p o r t
s u m m a r i z e d t h e r e s u l t s of t h e s e i n v e s t i g a t i o n s .
11
Polvtetrafluoroethvlene (PTFE)
Polytetrafluoroethylene (commonly identified a s Teflon TFE, but also
including the trades names Halon TFE, Tetran, Fluon, Polyflon and Algoflon) 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 t h e s e p r o p e r t i e s by ionizing radiat i o n i s p r i m a r i l y a t t r i b u t e d t o a prevalence of main-chain scission by liberated fluorine atoms and the production of e n t r a p p e d f l u o r o c a r b o n g a s e s .
Tensile sgrength and ultimate elongation decrease, and the material becomes embrittled through the main- chain scission. The embrittlement
becomes severe with extended irradiation
[ l o 7 r a d s ( C ) ] and the polytetrafluoroethylene crumbles and/or powders. The approximate danage thres
hold and the 25 percent damage dose are 1.
7 x l o 4 rads ( C ) a n d 3 . 4 x lo4
r a d s ( C ) , respectively.
There. is evidence that the damage observed when polytetrafluoroe t h y l e n e i s i r r a d i a t e d i s a function of s e v e r a l f a c t o r s . T h e s e i n c l u d e t h e
various types of p o l y t e t r a f l u o r o e t h y l e n e s u c h a s T F E a n d t h e c o p o l y m e r
FEP, the ambient atmosphere, and the test temperature. It had been
demonstrated that Teflon-FEP is more radiation resistant 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 a i r ,
t h e r e w a s a factor.-of-.l6 difference between the doses at which FEP and
TFE-7 Teflon retained equivalent elongation properties. These differences
a r e i l l u s t r a t e d i n F i g u r e s 5, 6 , and 7 which also give a comparison between
the effects of i r r a d i a t i o n i n v a c u u m a n d a i r a t r o o m t e m p e r a t u r e f o r v a r i o u s
sample thicknesses. The absence
of air or oxygen improves the radiation
r e s i s t a n c e of Teflon. These data
a l s o 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 a f t e r a dose of 2 . 6 x 105 r a d s ( C ) , while the tensile strength dec r e a s e d 40 and 6.0 p e r c e n t a f t e r s i m i l a r d o s e s a t 73 and 350 F . ( 4 )
Polytetrafluoroethylene also experiences changes in electrical prope r t i e s 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 dielectric 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.
COMPARISONOFULTIMATEELONGATIONVALUESOF
VARIOUS THICKNESSES OF TEFLON TFE-7 IRRADIATED
T
FIGURE 7.
I
COMPARISON OF ULTIMATE ELONGATION VALUES OF
VARlOUS THICKNESSES OF TEFLON FEP IRRADIATED
IN VACUUM AND AIR(^)
13
practical applications as long as the materials m e c h a n i c a l i n t e g r i t y is m a i n tained. Therefore, even though changes in electrical properties
do occur,
the degradation of p h y s i c a l p r o p e r t i e s i s t h e c r i t e r i a o f t e n u s e d i n d e t e r mining the acceptability of t h i s m a t e r i a l f o r u s e i n a specific application.
The volume resistivity of polytetrafluoroethylene decreases two or
t h r e e o r d e r s of magnitude from initial values between 5 x 1017 and
1 x 1018 o h m - c m o r g r e a t e r when irradiated under vacuum conditions to
total doses of 106 r a d s ( C ) and higher. The degradation may continue after
the radiation exposure is terminated with an additional decrease
of o n e o r
two o r d e r s of magnitude over a period of s e v e r a l d a y s . R e c o v e r y m a y
also occur with the volume resistivity approaching its p r e i r r a d i a t i o n v a l u e
s e v e r a l w e e k s after t h e i r r a d i a t i o n .
D i e l e c t r i c - c o n s t a n t m e a s u r e m e n t s of polytetrafluoroethylene during
and following exposure to a radiation environment have shown increases
of
l e s s t h a n 15 percent when irradiation in air or vacuum to respective doses
of 8 x l o 6 and lo8 r a d s ( C ) . Recovery i s essentially complete within a day
o r two a f t e r t h e i r r a d i a t i o n . S i m i l a r r e s u l t s h a v e a l s o b e e n o b t a i n e d u n d e r
vacuum conditions at c r y o g e n i c t e m p e r a t u r e s t o a dose of 7 x l o 6
r a d s ( C ) . ( 3 ) H o w e v e r , w h e n t h i s t e s t w a s t e r m i n a t e d at 9 . 5 x l o 7 r a d s ( C ) ,
the greatest value for the dielectric constant during exposure was approxim a t e l y 22 p e r c e n t h i g h e r t h a n t h e i n i t i a l c r y o t e m p e r a t u r e v a l u e . R e c o v e r y
to within 0. 4 p e r c e n t of the initial value occurred after the irradiation
was terminated.
Significant increases of between two and t h r e e o r d e r s of magnitude
occur in the low-frequency dissipation factor (60-100
Hz) or loss tangent
of T e f l o n T F E w h e n i r r a d i a t e d . T h i s
is t r u e f o r i r r a d i a t i o n s at n o r m a l
atmospheric conditions ( a i r ) and in vacuum at r o o m t e m p e r a t u r e as
i l l u s t r a t e d by the example shown in Figure 8. Exposure to radiation in
a n air e n v i r o n m e n t r e s u l t s i n a n i n c r e a s e t o a maximum value which is
then maintained during the irradiation. Irradiation in
a vacuum environment produces a s i m i l a r i n c r e a s e i n d i s s i p a t i o n f a c t o r ; h o w e v e r , u p o n
reaching a m a x i m u m v a l u e , t h i s d i s s i p a t i o n f a c t o r g r a d u a l l y d e c r e a s e s .
The absorbed dose at which the maximum occurs appears to be a function of
t h e e x p o s u r e r a t e i n t h a t t h e b e a k o c c u r s at a higher total dose with an inc r e a s e i n t h e r a t e of exposure.
T h e r e c o v e r y c h a r a c t e r i s t i c s of the dissipation factor of Teflon
i r r a d i a t e d i n air a n d v a c u u m a r e q u i t e d i f f e r e n t . T h a t
of v a c u u m i r r a d i a t e d
Teflon recovers rapidly and is essentially complete a s long a s it r e m a i n s
14
I
I .O
Air
0.I
0.0I
I
I
I
I
I
I
0.001
I-
0
I
FIGURE 8.
2
3
4
5
6
Absorbed Dose, IO6 rads (Ag)
7
a
E F F E C T O F X - R A Y IRRADIATION ON T F E - 6 ( 5 )
15
9
in the vacuum environment, while the dissipation factor
of T e f l o n i r r a d i a t e d
in a n o r m a l a t m o s p h e r e r e c o v e r s g r a d u a l l y o v e r s e v e r a l d a y s o r w e e k s .
If the vacuum-irradiated Teflon is exposed to air o r n i t r o g e n a f t e r i t s r e covery under vacuum conditions the dissipation factor increases sharply.
Following this i n c r e a s e , t h e r e i s a m o r e g r a d u a l r e c o v e r y . E x a m p l e s
of
t h e s e r e c o v e r y c h a r a c t e r i s t i c s a r e p r e s e n t e d i n F i g u r e 9 after the expo s u r e s h o w n i n F i g u r e 8 .
Limited information on the effect of radiation on the dissipation factor
of different Teflon types indicate a difference in sensitivity in radiation.
T h e a - c l o s s c h a r a c t e r i s t i c s 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 r a d s ( A g ) . ( 6 ) It has b e e n a s s u m e d t h a t t h i s d o s e a n d t h a t i n
Figure 8 are in rads silver since the calorimeter target used in measuring
the dose was silver and .no o t h e r m a t e r i a l i s m e n t i o n e d i n t h e d o c u m e n t s
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 e l e c t r o n i r r a d i a t i o n
to a given fluence are both flux and temperature sensitive. ( 7 ) An i n c r e a s e
in temperature or a decrease in electron flux tends to decrease the number
of breakdowns observed. Approximately twice
a s many breakdowns were
observed for a fluence of iO13 e / c m 2 ( E k = 40 keV) and a f l u x of10
e / ( c m 2 . s ) than for a similar fluence and a flux of10 l o e / ( c m 2 . s ) , and the
number of breakdowns at liquid nitrogen temperature was seven to eight
t i m e s g r e a t e r t h a n at r o o m t e m p e r a t u r e .
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 / ( c m 2 . s ) , and a proton fluence of up
to 5 x 1014 p/crn2 did not result in dielectric breakdown
at t h e t e s t t e m p e r a t u r e s of -134 C o r 2 7 C . ( 8 ) A large recombination of t r a p p e d c h a r g e s
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
radiation environment. It
is reported to have a damage threshold of
16
a
I .o
0.I
L
0
+
z
0
c
.-0
t
0.01
0
.-a
v,
.-v,
c)
0.001
4"4
vacuum
0.0001
0
FIGURE 9.
I
5
~~
I
I
IO
15
20
25
Recovery Time, days
I
I
I
30
35
RECOVERYCHARACTERISTICSOFTFE-6SPECIMENS
A F T E R X-RAY IRRADIATION AS SHOWN IN FIGURE 8 ( 5 )
17
1 . 3 x 106 r a d s ( C ) and a 25 percent damage dose of 2 x l o 7 r a d s (C)(4).
The elongation of this m a t e r i a l i n c r e a s e d 47 percent and the impact strength
d e c r e a s e d 16 percent when it was subjected to a t o t a l d o s e of approximately
2 . 4 x l o 7 r a d s ( C ) . (9) The ultimate tensile strength was unaffected.
E l e c t r o n i r r a d i a t i o n with a total of 3. 67 x 1 0 l 6 e / c m 2 ( E = 1. 0 MeV)
at 60 C s o s e r i o u s l y d e g r a d e d a s p e c i m e n of polychlorotrifluorethylene
that it could not be measured as to its p h y s i c a l a n d e l e c t r i c a l p r o p e r t i e s .
The degradation of t h e e l e c t r i c a l p r o p e r t i e s of polychlorotrifluoroethylene from exposure to radiation includes a reduction in volume and
surface resistivity. Decreases
of between one and two orders
of magnitude
have been observed in both of t h e s e p a r a m e t e r s d u r i n g X - r a y i r r a d i a t i o n
to a total dose of 2. 1 x l o 7 rads (Ag) in a vacuum environment.(6) Essentially, no recovery was observed following
the i r r a d i a t i o n .
M e a s u r e m e n t s of dissipation factor during and following the irradiation of t h i s m a t e r i a l h a s a c t u a l l y s h o w n d e c r e a s e s o r i m p r o v e m e n t i n t h i s
c h a r a c t e r i s t i c . Low values of 0 . 001 after 1920 h o u r s of recovery in air
were observed. ( 6 )
A Russian study that included a t o t a l b r e m s s t r a h l u n g d o s e of 5 . 3 x
l o 7 r a d s ( 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 l e s s t h a n
l o 7 r a d s ( C ) . In addition, the tensile strength also increases until approxim a t e l y l o 8 r a d s ( C ) , after which it d e c r e a s e s a n d is 25 p e r c e n t below the
initial value at approximately 1O1O r a d s ( 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 d e g r a d e at lower radiation doses
than thicker films. This difference in behavior
i s attributed, at l e a s t i n
part, to the oxidation
of the polyethylene when it is i r r a d i a t e d . O t h e r
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 1 0 l 6 e / c m 2 ( E = 1. 0 MeV) at 60 C i l l u s t r a t e s t h e d i f f e r e n c e s t h e s e
f a c t o r s m a k e . ( l ) T h e h a r d n e s s a n d s t i f f n e s s i n f l e x u r e of the high-density
m a t e r i a l d e c r e a s e d as a r e s u l t of the irradiation, and the low-density and
carbon-filled materials experienced increases in these properties. The
high-density polyethylene also increased in tensile strength and the others
decreased.
T h e e l e c t r i c a l p r o p e r t i e s of polyethylene also degrade when it is
exposed t o a radiation environment. Measurements
of the insulating qualities such as v o l u m e r e s i s t i v i t y , s u r f a c e r e s i s t i v i t y , a n d i n s u l a t i o n - r e sistance indicate that a d e c r e a s e of up to t h r e e o r d e r s of magnitude occurs
i n t h e s e p a r a m e t e r s d u r i n g i r r a d i a t i o n w i t h p e r m a n e n t d e c r e a s e s of one
o r d e r of magnitude when subject to a total dose of 5. 8 x 1 0 l 6 e / c m 2
( E = 1. 0 MeV). The dissipation factor
at 1 KHz i n c r e a s e s o n e t o two
o r d e r s of magnitude as a r e s u l t of irradiation, and the dielectric constant changes less than *5 p e r c e n t .
Electron-radiation-induced dielectric breakdown in polyethylene
is sensitive to the f l u x to which the polyethylene i s exposed; the number
of o b s e r v e d b r e a k d o w n s i n c r e a s e s w i t h a n i n c r e a s e i n e l e c t r o n f l u x . ( 7 )
E x p o s u r e t o a flux of 1 x 1 0 l 1 e / ( c m 2 .s ) r e s u l t e d i n 20 breakdowns for
a fluence of 2 x 1013 e / c m 2 ( E k = 30 keV) while only
12 breakdowns were
o b s e r v e d f o r a similar fluence at 5 x l o l o e / ( c m 2 . s ) a n d n o n e at 1 x l o l o
e / ( c m 2 *s ) .
P r o t o n i r r a d i a t i o n of polyethylene over a flux range of lO9to 10 10
p / ( c m 2 . s ) f o r a fluence of 1013 p/crn2 at each rate with energies of 1. 1 5
and 1. 6 5 MeV produced no breakdowns in the material. ( 8 )
Polvstvrene
I r r a d i a t i o n s t u d i e s of polystyrene have shown it to be one of t h e m o s t
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 p e r c e n t d a m a g e t o its physical properties below 4 x 109
r a d s ( C ) . P o l y s t y r e n e is subject to postirradiation oxidation that continues
for several weeks, however, oxidation plays little or no part in the radiation damage that o c c u r s .
Electron irradiation to a fluence of 5. 8 x 1 0 l 6 e / c m 2 , ( E= 1. 0 MeV)
at 60 C h a s r e s u l t e d i n d e c r e a s e s of approximately 50 percent in the tensile
strength and ultimate elongation. (11) The hardness and the stiffness in
19
f l e x u r e a l s o d e c r e a s e d 1 percent and 13 percent, respectively, during
this
same s t u d y . T h e s e r e s u l t s i n d i c a t e p o l y s t y r e n e b e c o m e s m o r e f l e x i b l e a n d
s o f t e r a s a r e s u l t of t h e i r r a d i a t i o n .
The insulating quality of polystyrene appears to be the only electrical
property that is affected by e x p o s u r e t o r a d i a t i o n . P e r m a n e n t d e c r e a s e s
of
one and two orders of m a g n i t u d e h a v e b e e n o b s e r v e d i n t h e v o l u m e r e s i s tivity and insulation resistance of this material following doses as low as
4. 5 x l o 6 r a d s ( C ) a n d a s high as 1 x l o 8 r a d s ( C ) . Other electrical parameters, such as dielectric constant and dissipation factor, have shown
l i t t l e o r no change from exposure to a radiation environment within this
r a n g e 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, h o w e v e r , s o m e d i s a g r e e ment concerning the dose at which the trend toward improved physical
p r o p e r t i e s is reversed and degradation begins. Based upon available information, the best estimate for the dose
at w h i c h t h i s r e v e r s a l o c c u r s is
l o 6 to 107 rads (C) for X-ray and reactor irradiation. Radiation exposure
to doses of 108 r a d s ( C ) a n d a b o v e c a u s e s s e v e r e e m b r i t t l e m e n t of polyethylene terephthalate to a d e g r e e t h a t p r o p e r t i e s a r e u n m e a s u r a b l e .
Degradation of t h e e l e c t r i c a l p r o p e r t i e s of polyethylene terephthalate
with the doses described above,
106 to l o 7 r a d s ( C ) , is insignificant.
Changes in the insulation resistance, volume resistivity, and surface resistivity a s a r e s u l t of i r r a d i a t i o n a r e l i m i t e d t o a p p r o x i m a t e l y o n e d e c a d e .
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 / ( c m Z . s ) did not induce
a d i e l e c t r i c b r e a k d o w n i n M y l a r a t t e m p e r a t u r e s 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 e x p e r i e n c e s t h r e s h o l d d a m a g e at a dose of 8 . 6 x lo5 r a d s ( C ) and
25 percent damage at 4 . 7 x l o 6 r a d s ( C ) . T h e s e d o s e s a r e b a s e d u p o n
losses in ultimate elongation and impact strength. Another property
of polya m i d e t h a t d e t e r i o r a t e s f r o m r a d i a t i o n e x p o s u r e i s stiffness in flexure,
which has increased between 52 and 181 percent, depending upon the nylon
type, after exposure to an electron dose
of 5 . 8 x 1016 e / c m 2 ( E = 1 . 0 MeV)
at 60 C( l l ) . This same exposure improved the t e n s i l e s t r e n g t h by 49 to
107 p e r c e n t . T h e s e r e s u l t s a g r e e w i t h o t h e r r a d i a t i o n s t u d i e s w h i c h h a v e
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 d e c r e a s e
of l e s s t h a n a n o r d e r 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 K H z , 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 r e 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 1 0 l 6 e / c m 2
( E = 1.0 MeV) at 60 C .
T h e e l e c t r i c a l p r o p e r t i e s of diallyl phthalate such as dielectric constant, dissipation factor, and insulation resistance are affected
by exposure
to a radiation environment such a s described above. The amount
of d e g r a d a t i o n o r c h a n g e i n t h e s e p a r a m e t e r s b e c a u s e of this exposure i s of little
practical significance. Permanent changes in dielectric constant were
less than 6 percent while the dissipation factor recovered to below the
initial value. Increases in insulation resistance during exposure are followed by complete recovery within approximately 1 h o u r a f t e r t h e i r r a d i ation is terminated.
21
Polypropylene
Polyprolylene i s subject to a s e v e r e l o s s in physical properties when
exposed to a radiation environment. Above
a total dose of 1 x l o 7 r a d s ( C )
t h i s material b e c o m e s e m b r i t t l e d a n d e x T e r i e n c e s d e c r e a s e s i n t e n s i l e a n d
i m p a c t s t r e n g t h s t h a t a p p r o a c h 60 and 75 percent, respectively, at a dose
of 5 x l o 7 r a d s ( C ) . An electron fluence of 5. 8 x 1 0 l 6 e / c m 2 ( E = 1 . 0 MeV)
at 60 C r e s u l t e d i n d e c r e a s e s of 87 to 96 percent in utlimate elongation and
tensile strength. (11) This electron fluence also produced
a decrease in
h a r d n e s s of 2 5 percent which is i n a g r e e m e n t w i t h r e s u l t s f r o m o t h e r
studies where polypropylene became increasingly softer and more flexible
with doses of between 2.6 x lo8 and 8 . 7 x lo8 r a d s ( C ) when lower doses
c a u s e d e m b r i t t l e m e n t of t h e m a t e r i a 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 p l a s t i c i z e d t h e r e m a n d e r 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 l e o r
no practical significance. The dielectric constant decreases slightly and
t h e i n s u l a t i o n r e s i s t a n c e d e c r e a s e s l e s s t h a n a n o r d e r of magnitude.
M e a s u r e m e n t s of a - c l o s s s u c h as power factor and dissipation factor
at
1 KHz to 1 MHz h a v e v a r i e d f r o m no observable change to an increase
from between 0 . 0 0 0 5 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 ) T h e m a x i m u m n u m b e r of breakdowns observed at
r o o m t e m p e r a t u r e w i t h a f l u x of 1 x 1 0 l 1 e / ( c m 2 . s ) f o r a total fluence of
5 x 1013 e / c m 2 ( E k = 30 keV) was 40, while that f o r a flux of 1 x 1010
e / c m 2 w a s 8 f o r 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
d o s e s 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 p e r c e n t ( a physical change)
22
between this dose and 1. 75 x l o 8 r a d s ( C ) indicates the possibility of
approaching a damage threshold. N o information is available above this
dose, with exception of t h e r e s u l t s f r o m a n e l e c t r o n f l u e n c e of 5. 8 x' 1016
e / c m 2 ( E = 1. 0 MeV) at 60 C.( ') Serious deterioration of physical prope r t i e s o c c u r r e d f r o m t h i s r a d i a t i o n e x p o s u r e a n d i n c l u d e d a 67 and 176 p e r cent increase in hardness and stiffness in flexure, respectively.
A 59 p e r c e n t d e c r e a s e i n t e n s i l e s t r e n g t h a n d a 99 p e r c e n t d e c r e a s e i n u l t i m a t e
elongation were also noted following irradiation to this electron fluence.
Information concerning the effect of r a d i a t i o n o n t h e e l e c t r i c a l p r o p e r t i e s of polyurethane is l i m i t e d t o r e s u l t s f r o m two radiation studies:
the electron irradiation mentioned above and a r e a c t o r e x p o s u r e t o 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 a d s ( C ) at 16 C to 29 C. (14) Insignificant permanent changes in
the insulating properties, volume resistivity, or insulation resistance
of
l e s s t h a n o n e o r d e r of magnitude were observed a s a r e s u l 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 t o 0 . 0 4 ) .
T h e o n l y d i s a g r e e m e n t i n t h e r e s u l t s of the two studies was the dielectric
constant which decreased 6-1/4 percent at 1 KHz f r o m t h e e l e c t r o n i r r a d i a tion and increased approximately 16 p e r c e n t f r o m t h e r e a c t o r e x p o s u r e .
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 r a d s ( C ) i n air
or vacuum with no indication of degradation in physical properties except
color change.
An o r d e r - o f - m a g n i t u d e i n c r e a s e i n the radiation dose to 108
r a d s ( C ) a n d a b o v e c a u s e s e m b r i t t l e m e n t a n d l o s s of flexibility and tensile
strength. Low temperature, however, increases the radiation tolerance
of
polyvinylidene fluoride in that doses of this magnitude, lo8 r a d s ( C ) , at
cryogenic temperatures do not reach damage threshold.
Changes in the electrical properties of polyvinylidene fluoride inc l u d e d e c r e a s e s 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
107 r a d s ( C ) i n a n air and a v a c u u m - c r y o t e m p e r a t u r e e n v i r o n m e n t , r e spectively. ( 3 ) A d e c r e a s e of a p p r o x i m a t e l y f i v e o r d e r s of magnitude
occurred with a dose of 2. 1 x 108 r a d s ( C ) i n t h e air a t m o s p h e r e . D i s s i p a tion factor increased less than one decade, and the dielectric constant was
essentially unaffected by the i r r a d i a t i o n .
23
Polvimide
Polyimide (Kapton) has shown little or no change in either its physical
o r e l e c t r i c a l p r o p e r t i e s t o g a m m a d o s e s ( C o 60) of up t o 109 r a d s ( C ) . (15)
T e n s i l e s t r e n g t h r e m a i n e d e s s e n t i a l l y c o n s t a n t w h e n e x p o s e d t o a total dose
of this magnitude but decreased to approximately one-half
its initial value
between 1 x 109 and 6 x 109 r a d s ( C ) . T h e e l e c t r i c a l r e s i s t i v i t y r e m a i n e d
at 1 x 1019 ohm-cm or above and only decreased to 3 x 1 0 l 8 o h m - c m at a
total dose of 1 x 101o r a d s ( C ) , T h i s s a m e d o s e l e f t t h e d i e l e c t r i c c o n s t a n t
essentially unchanged and decreased the breakdown voltage to approximately
75 p e r c e n t of its initial value.
Dielectric breakdown induced in polyimide (Kapton) by e l e c t r o n i r r a diation has been shown to be sensitive to both flux and temperature. (7)
A
total of eight breakdowns on two s a m p l e s w e r e o b s e r v e d a t r o o m t e m p e r a t u r e f o r a f l u x of 1011 e / ( c m 2 . s ) and a fluence of 1013 e / c m 2 ( E k = 30 keV) a factor of f o u r g r e a t e r t h a n t h e n u m b e r o b s e r v e d 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 t h e r e s u l t s 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 / c m 2 ( E k = 30 keV)
at r o o m t e m p e r a t u r e w h i l e 75 and 120 breakdowns occurred with the specim e n s i r r a d i a t e d t o a similar fluence at t h e t e m p e r a t u r e 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 1 0 l 1 p / ( c m 2 . 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
( C o 60). Exposure to high doses
of electron radiation, 1 x l o l o r a d s ( C )
( E = 1 MeV) and 5 x 109 r a d s ( 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 r a d s ( C )
was approximately 70 p e r c e n t g r e a t e r t h a n t h a t of n o n i r r a d i a t e d P y r r o n e ,
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
i n c r e a s e i n d a r k c u r r e n t by a factor of 5 i n P y r r o n e m a d e up of benzophenone tetracarboxylic acid dianhydride (BTDA) and diaminobenzidine (DAB)
while the dark current of a P y r r o n e c o m p o s e d of pyromellitic dianhydride
(PMDA) and diaminobenzidine (DAB) increased approximately two orders
of magnitude.
Dielectric breakdown induced in Pyrrone by e l e c t r o n i r r a d i a t i o n t o a
given fluence is sensitive to both flux and temperature; the number of breakdowns that occur tends to increase with flux and decrease with temperat u r e . ( 7 ) An o r d e r of m a g n i t u d e i n c r e a s e i n e l e c t r o n f l u x , f r o m 109
e / ( c m 2 . s ) to 101o e / ( c m 2 . s ) , resulted in twice as many breakdowns for
similar fluences of
e / c r n 2 (Ek = 30keV) a tr o o mt e m p e r a t u r e .A l s o ,
the number of breakdowns recorded at liquid nitrogen temperature was
m o r e t h a n t w i c e t h a t o b s e r v e d at r o o m t e m p e r a t u r e f o r 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 / c m 2 ( E k = 1.0 and 1. 5 MeV) at t e m p e r a t u r e s
of -134 C and 27 C . ( 8 ) D o s e r a t e s w e r e 109 and 1O1O p / ( c m 2 . s) with specimens subjzcted to each rate for the total fluence.
The exposure of P y r r o n e , both PMDA-DAB and BTDA-DAB, to
a
g a m a d o s e r a t e of 10 to 1000 r a d s / m i n ( C o 6 0 ) p r o d u c e d c u r r e n t d e n s i t i e s
of 1 x
to 6 x
ampere
cm-2
the
in
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 f r e e r a d i a t i o n - i n d u c e d c h a r g e c a r r i e r s m i g r a t i n g i n t h e
electric field.
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 r a d s ( 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 p e r c e n t f r o m p r e i r r a d i a t i o n v a l u e s at 1 x 107 r a d s ( C ) and 50 to 70 p e r c e n t at
1 x 109 r a d s ( C ) . O t h e r e l e c t r i c a l p r o p e r t i e s s u c h
as resistivity, dielectric
constant, and dissipation factor are not degraded significantly
at this total
dose.
25
T h e t e n s i l e s t r e n g t h of epoxy-glass laminates remains unchanged to a
g a m m a d o s e of 1 x l o 7 r a d s ( C ) b u t d e c r e a s e s t o l e s s t h a n 20 p e r c e n t of the
initial value at 1 x 109 r a d s ( C ) . Compressive strength does not change
significantly. A total gamma dose of 101o r a d s ( C ) w i l l c a u s e a n e p o x y g l a s s l a m i n a t e t o b e c o m e b r i t t l e a n d w e a k o r t o l o s e m o s t of t h e r e s i n
binder.
Miscellaneous Organics
Radiation-effects information is available on organic bulk, sheet,
a n d / o r film m a t e r i a l s o t h e r t h a n t h o s e d i s c u s s e d o n t h e p r e c e d i n g p a g e s .
The information, however, is limited to results from only one radiationeffects test of e a c h m a t e r i a l . T h e r e f o r e , t h e s e r e s u l t s a r e l i m i t e d t o t h e
tabular presentations of T a b l e s 2 and 3 . T a b l e 2 is a listing of m a t e r i a l s
t h a t w e r e s o s e r i o u s l y d e g r a d e d 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 c o n s i s t s of t h o s e m a t e r i a l s t h a t
survived exposure to the radiation environment and includes some
of the
particulars concerning changes observed in their physical and electrical
properties.
Ceramics
Ceramic insulating materials, such as silica, Steatite, Alsimag,
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
lo7 rads (C).
Similar results have also been observed with reactor irradiation to doses
a s h i g h a s 1 0 1 7 n / c m 2 ( E > 0 . 1 MeV) and lo9 r a d s ( C ) . P e r m a n e n t d e c r e a s e s of between one and tow orders of magnitude will occur in the
volume and surface resistivity of c e r a m i c i n s u l a t i n g m a t e r i a l s at t h e s e
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 / c m 2 ( E > 0 . 1 MeV) and 9 . 0 x 1010 r a d s ( C ) g a m m a . ( 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 / c m 2
( E > MeV) with temperatures of 800 to 1000 C . (‘l)
26
MISCELLANEOUSORGANIC BULK, SHEET,AND/ORFILMMATERIALSWHICH
LIMITED INFORMATION INDICATE AS UNSATISFACTORY AT THE RADIATION
EXPOSURE INDICATEDW)
TABLE 2.
~
..
~~~
"
"
- .
" -_
.~
- ..
-
-
.~
Identification
Material
"
1.22
-
~
..
-.
-
"
.
.
~
~~
- -
Total Electron Fluence at 60 C
(E = 1 . 0 MeV)
~
x(3.8
resin Acetal
x 108 rads)
e/cm2
Acrylic
plastic,
molding
grade
(rubber
modified)
5.80
x 1016 e/cm2
(1.8
carbonate
Allyl
4.10
plastic,
cast
x e/cm2
1016
( 1 . 3 x l o 9 rads)
x 1016
(1.8e/cm2
5.80
Cellulose
acetate
x l o 9 rads)
x l o 9 rads)
4.10
Cellulose
butyrate
( 1 .e3/ cx m120 l 6
x l o 9 rads)
propionate
Cellulose
4.10 x (1.3 e/cm2
x 109 rads)
Chlorinated polyether
2.90 x 1016 e/cm2 (9 x l o 8 rads)
Polycarbonate
5.80 x 1016 e/cm2 (1.8 x lo9 rads)
Polyfluoroethylenepropylene, Teflon FEP (copolymer)
3.67 x 1OI6 e/cm2 (1.1 x l o 9 rads)
Polymethyl methacrylate, cast
1.22 x
Polymethyl methacrylate, molding grade
4.10 x 1OI6e / c m 2 (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 o 9 rads)
Polyvinyl chloride, rigid
-.
4.10 x 1016 e/cm2 (1.3 x 109 rads)
._-
-
"~
"
-~
- _ _-_ ~-
"
"~
27
e/cm2(3.8
x 108
rads)
TABLE 3.
FL4DJATION.EFFECTS ON MISCELLANEOUSORGANICBULK,SHEET,AND/ORFILM
MATERIALS WHERE ONLY LIMITED INFORMATION IS AVAILABLE
~
~~
Integrated
Identification
Total
Material
~-"-. . -.
-
"
~~
"
,
-
"
"
Remarks
Exposure
Acrylonitrile-butadiene-5.8x1016e/cm2
styrene
at 60 C
Styrene-acrylonitrile
copolymer
creased
C
-
5.8 x 1016 e/cm2
60
(E = 1.0 MeV)Hardnessincreased
13percent;flexibility,tensile strength, and ultimate elongation decreased
49, 58, and93percent,respectively.Dielectric constant increased <1.5 percent and DF
decreased slightly.
IR increased. (11)
(E = 1.0 MeV)
at
Tensile strength and ultimate elongation de34 percent,
and
respectively.
47
Hardness was unchanged and flexibility increased 5 percent. Dielectric constant increased 4 to 6 percent. DF increased to
0 . 0 1 a t 1 KHz and0.40at
1 MHz. I R d e creased one decade. (11)
Styrene-butadiene
(high-impact styrene)
5.8 x 1016 e/cm2
60 at
C
(E = 1.0 MeVj Flexibility and ultimate elongation decreased
percent
90
more
than
and tensile
strength
decreased 35 percent. Hardness increased.
Dielectric constant ipcreased slightly while
DF increased -50 percent.
IR increased. (11)
Styrene-divinylbenzene
significance.
practical
(11)
C
60
5.8 x 1016 e/cm2
at
Polyvinyl chloride
acetate
5.8 x 1016 e/cm2 (E = 1.0 MeV)
at 60 C
Insignificant changes in hardness, tensile
strength,
dielectric
constant,
dissipation
and
factor.Insulationresistancedecreasetwo
decades. Flexibility increased 30 percent. (11)
Polyvinylfluoride
5.8 x 1016 e/cm2
at 60 C
Serious degradation prevented measurement of
physical
degradation.
Dielectric
constant
decreased 7 percent and dissipation factor increased one decade. Insulation resistance did
not change. (11)
Polyester/glass
laminate
2 . 5 x lo6 rads (C)
9 1 -LD Resin/l81 -Volan
A laminates (copper
clad)
2.5 x 1015 n/cm2
at 55 C
Silicone/glass
laminate
5.0 x 1013 n/cm2 (E > 2.9 MeV) 49 percent loss in flexure strength, slight change
at 200 C
thickness,
color,
in
and weight.
(19)
1.0 x 108 rads (C)
(E = 1.0 MeV) Changes
(E = 1 . 0 MeV)
in physical properties were of no
Volume and surface resistivity decreased three
decades. Dissipation factor increased from
0.003 and0.006 to 0.019 and 0.010. No
change in dielectric constant. (6)
(E > 2.9 MeV)
No degradation in physical properties.(l8)
A change o r d a r k e n i n g i n c o l o r i s 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
f o r m s of the material. These data include the evaluation
of physical
damage in a reactor environment for total doses up to
5 x 1013 n / c m 2
( E > 2 . 9 MeV) and 1 x lo8 r a d s at 200 C and of changes in both physical
and electrical properties in a cobalt-60 gamma environment to 1 x 1010
r a d s ( C ) . ( 1 5 , l 9 ) N o 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 p e r c e n t d e c r e a s e i n f l e x u r e s t r e n g t h a t the above reactor
environment.
A glass -bonded mica experienced no change in compressive strength
to a total dose of 1 x 1O1O r a d s ( C ) gamma: the tensile strength decreased
approximately 50 percent with no d e c r e a s e f o r d o s e s up to 1 x l o 7
rads (C). The resistivity was unchanged and the dielectric constant inc r e a s e d l e s s t h a n 10 p e r c e n t f o r t h e s a m e t o t a l d o s e of 1 x 1010 r a d s ( C )
( C o 6 0 ) . Variations in voltage breakdown ranged from 95 to
120 percent
of the initial value to a g a m m a d o s e of 1 x 109 r a d s ( C ) a n d d e c r e a s e d t o
70 percent at 1 x 1O1O r a d s ( C ) .
RADIATION E F F E C T S O N SPECIFIC WIRE
AND CABLE INSULATION
Both organic and inorganic wire insulations have been tested and
evaluated as to their radiation resistance.
A s e r i o u s d e t e r i o r a t i o n of
p h y s i c a l p r o p e r t i e s a s a r e s u l t of irradiation has occurred with some
o r g a n i c s , a n d o t h e r s , d e m o n s t r a t i n g a high level of r a d i a t i o n t o l e r a n c e ,
have survived doses of up to 1 x l o 8 r a d s ( C ) . Special cables and wires
insulated with inorganic materials have shown
similar r a d i a t i o n r e s i s t a n c e
29
I
..
t o d o s e s of 8 . 8 x 109 and 8 . 8 x l o l l rads (C). Changes in the electrical
p r o p e r t i e s of w i r e h a v i n g e i t h e r o r g a n i c o r i n o r g a n i c i n s u l a t i o n a r e g e n e r ally 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 exp o s u r e is t e r m i n a t e d . P e r m a n e n t d e c r e a s e s i n d i e l e c t r i c s t r e n g t h h a v e
also been observed following exposure to radiation
as h a v e i n c r e a s e s i n
dissipation factor and the attenuation of coaxial cables. Details concerning
these and other effects of r a d i a t i o n a r e d i s c u s s e d i n t h e f o l l o w i n g p a r a graphs as they pertain to specific wire and cable insulation.
Polytetrafluoroethylene (PTFE)
Polytetrafluorethylene (Teflon) wire insulation has shown severe
d e g r a d a t i o n i n p h y s i c a l p r o p e r t i e s a s a r e s u l t of exposure to a radiation
environment. The extent
of the damage that occurs is sensitive to total
d o s e a n d v a r i e s f r o m a noticeable decrease in wire flexibility to the complete disintegration of t h e m a t e r i a l .
The lowest total dose at which information on changes in physical
3
c h a r s c t e r i s t i c s is available is 10 r a d s ( 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 M L (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
o c c u r r e d f o r a dose of 6 x 104 r a d s ( C ) with a vacuum of l o e 6 t o r r and
a t e m p e r a t u r e of 150 C . T h e s e r e s u l t s i n d i c a t e two p o s s i b i l i t i e s : t h e T F E
Teflon (polytetrafluoroethylene) insulated wire with the M L coating has a
lower radiation tolerance and/or the
lo3 to 6 x l o 4 r a d s ( C ) total dose is
t h e t h r e s h o l d a r e a f o r d a m a g e t o polytetrafluoroethylene-insulated wire and
damage to the other wire insulations was not yet apparent.
The change in the physical properties of polytetrafluoroethyleneinsulated 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
w i l l appear sound, but will powder and crumble when stressed mechanically
through handling or testing. Failure
of this type in a coaxial cable could be
expected to include shorting between conductors and/or between conductors
30
and the outer sheath or shield when radiation environments reach these dose
levels. This should be
of special concern in applications that include vibrat i o n o r o t h e r m e c h a n i c a l s t r e s s e s as a p a r t of the intended environment.
T h e i r r a d i a t i o n of polytetrafluoroethylene-insulated w i r e a l s o res u l t s i n the degradation of electrical properties. Insulation resistance
measurements performed before and after irradiation have shown little or
no significant change in this parameter. Breakdown voltage has decreased
a s m u c h as 50 percent .between twisted pairs of wire having initial breakdown at voltages a s high as 15.8 to 28. 2 kV.(22, 23) T h e p o s t t e s t r a n g e
was 9 . 1 to 14. 2 K v . S e v e r a l e l e c t r i c a l c h a r a c t e r i s t i c s
of coaxial cables
have shown the effects
of degradation. The attenuation
of a 10-foot length
of RG-225/U at 400 MHz i n c r e a s e d 0 . 20 db while the change for a similar
s a m p l e of RG 142/U was s o g r e a t it could not be measured after a total exp o s u r e of 3 x 1 0 l 6 n / c m 2 ( E> 0 . 1 MeV) and 2 . 3 x lo8 r a d s ( C ) . (24) T h e
RG 142/U cable also experienced larger increases in other measured param e t e r s including VS W R ( 1 . 19: 1 to 2 . 4:l ) , apparent change in electrical
length ( 0 . 224 wavelength), and phase shift (between 0 and t 15 d e g r e e s ) .
Polyethylene
T h e p h y s i c a l a n d e l e c t r i c a l p r o p e r t i e s of wire and cable that inlittle o r no degcorporate polyethylene as the insulating media have shown
radation for total doses up to 107 and l o 8 r a d s ( C ) a t t e m p e r a t u r e s of f r o m
15 C to 100 C . T h i s i s a comparatively high radiation tolerance for plastic
insulated wire. Some degradation is apparent in the physical properties
after a dose of 9 . 6 x l o 7 r a d s ( C ) with the darkening of the polyethylene,
but it still r e m a i n s r e s i l i e n t w i t h no indication of s t i f f n e s s . I t i s e s t i m a t e d t h a t t h r e s h o l d d a m a g e o c c u r s at a p p r o x i m a t e l y 4 . 4 x l o 8 r a d s ( C ) .
Loss of flexibility has been observed, however, after cable insulated
with polyethylene and having outer jackets of e i t h e r E s t a n e o r A l a t h o n
received a total dose of 8. 8 x lo8 r a d s ( C ) . ( 2 5 ) 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 c o a x i a l o r s h i e l d e d t y p e , i n
t h a t s o m e m a t e r i a l s u s e d f o r 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
T h e e l e c t r i c a l p r o p e r t i e s of polyethylene-insulated wire and cable
have shown some degradation during and following exposure to
a radiation
environment. Insulation resistance
is both r a t e a n d d o s e s e n s i t i v e w i t h
changes of o n e t o t h r e e o r d e r s of magnitude observed during exposure. Recovery is essentially complete following the termination
of t h e i r r a d i a t i o n .
T h e c h a r a c t e r i s t i c i m p e d a n c e of coaxial cables has shown some variation
a s a r e s u l t of radiation exposure but the extent of these variations is of
little significance ( 0 . 5 to -10 p e r c e n t ) . L i m i t e d d a t a o n o t h e r c o a x i a l c a b l e p a r a m e t e r s i n d i c a t e t h a t l i t t l e o r no change occurs in attenuation,
VSWR, o r a p p a r e n t e l e c t r i c a l l e n g t h w h e n t h e s e c a b l e s a r e i r r a d i a t e d .
An induced current is a l s o a n e l e c t r i c a l c h a r a c t e r i s t i c t h a t h a s b e e n
o b s e r v e d i n e l e c t r i c a l c a b l e of various insulations. The only steadystate-radiation data concerning this effect are limited to polyethyleneinsulated coaxial cable.(26) Currents
of t h e o r d e r of 1 0 - 8 a m p e r e s w e r e
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 r a d s ( 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 degradiation of its physical properties at d o s e s u p t o 8 . 8 x l o 5 r a d s ( C ) . A
slight change or lightening in color with a barely perceptible loss in
resilience or flexibility has been observed in flat-ribbon multiconductor
wire insulated with this material after an exposure of 8. 8 x 106
r a d s ( C ) . ( 2 7 ) S e r i o u s d e t e r i o r a t i o n of t h e w i r e ' s m e c h a n i c a l q u a l i t i e s
occurs with a total dose of 8 . 8 x l o 7 r a d s ( C ) a n d a b o v e . T h e r e i s
a
definite loss in flexibility, and the silicone rubber insulation will crack
and/or crumble when the wire is s t r e s s e d m e c h a n i c a l l y .
T h e i n s u l a t i o n r e s i s t a n c e of wire insulated with silicon rubber
d e c r e a s e s o n e o r two o r d e r s of magnitude during irradiation with recovery
to within one order of magnitude when the exposure is t e r m i n a t e d . 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
- a n d p o s t i r r a d i a t i o n m e a s u r e m e n t s a f t e r d o s e s of
1 x lo3 and 4 x 10r rea d s ( C ) . ( 2 2 , 2 3 ) These changes in breakdown voltage,
however, include both increases and decreases and are
of little significance.
32
Polyimide
P o l y i m i d e r e s i n film, ML, wire insulation has shown no indication
of d e t e r i o r a t i o n i n p h y s i c a l o r e l e c t r i c a l p r o p e r t i e s u p t o a d o s e 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 characteristics are unaffected with no visible difference between wire
that has been irradiated and that which has not. Measurements of e l e c t r i c a l p a r a m e t e r s s u c h as insulation resistance, capacitance, and dissipation
factor have shown no significant difference between pre- and postirradiation values. Wires with
a combination of g l a s s b r a i d a n d p o l y i m i d e r e s i n
film insulation exhibited a breakdown voltage of approximately 1000 w i r e s
before and after receiving the total exposure indicated above. ( 2 7 )
The absence of degradation at d o s e s up to 1. 5 x l o 8 r a d s ( C ) demons t r a t e s a high level of r a d i a t i o n r e s i s t a n c e f o r t h i s w i r e i n s u l a t i o n w i t h 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 r a d s ( 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 r a d s ( 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,
a s a precautionary procedure,
the designer should allow for a d e c r e a s e of o n e t o t h r e e o r d e r s 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, 2 3 ) The two environmental combinations
* Unidentified as to whether polyethylene or polypropylene.
33
u s e d i n t h i s s t u d y w e r e ( 1 ) a n X - r a y d o s e of 6 x l o 4 r a d s ( C ) with a vacuum
of
t o r r a n d t e m p e r a t u r e of 150 C and ( 2 ) a nX - r a yd o s e
of 1 x 103
r a d s ( C ) w i t h a 5-psi oxygen atmosphere and a t e m p e r a t u r e of 9 0 C. The
stability of the insulating qualities of t h i s m a t e r i a l w h e n i r r a d i a t e d w a s a l s o
demonstrated in another study when wire insulated with this material completed a w e t d i e l e c t r i c - s t r e n g t h t e s t of 2 . 5 kV a f t e r a radiation dose of 5 x
l o 8 r a d s ( C ) .( 2 8 )
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 f e e t when exposed to a total dose of 2 . 9 x l o 8 r a d s ( C )
and 3 . 0 x 1 0 l 6 n / c m - 2 ( E > 0 . 1 M e V ) . ( 2 4 ) At t h e s a m e t i m e t h e r e w a s
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 demonof o t h e r
s t r a t e d a high tolerance for radiation when compared to that
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 e a c h . T h e r e fore, with one exception, this radiation effects information is confined to
the tabular presentation of Table 4.
The single exception is t h e r e s u l t s of a study of e l e c t r o n i r r a d i a t i o n
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 r o o m t e m p e r a t u r e v a r i e d i n v e r s e l y w i t h t h e t o t a l c a p a c i t a n c e i n
the system. The average pulse height decreased from 5.
1 volts at 1. 1 x
f a r a dt ol e s st h a n
0 . 01voltat1.
0 x
farad.Increasingtheload
r e s i s t a n c e f r o m 3 kohms to 300 k o h m s 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 / c m 2 ( E > 60 k e V ) , e l e c t r o n - d i s c h a r g e p a t t e r n s ( L i c h t e n b e r g
f i g u r e s ) w e r e found in the insulation. Rough calculations indicated that
34
I
the power density along the discharge path is adequate to produce the
physical damage observed. The actual pulse height
of t h e d i s c h a r g e s w e r e
possibly as high as 11,000 volts, and power densities
of 3 x 101o w a t t s /
c m 2 w e r e i n d i c a t e d i f a d i s c h a r g e t i m e of 0 . 0 1 m i c r o s e c o n d is acceptable.
The data support a postulate that a portion of the incident electrons a r e
stopped and stored within the dielectric. This charge increases with
i r r a d i a t i o n , a n d at some point in time it is r e l e a s e d a n d t r a n s p o r t e d t o t h e
conductor and is o b s e r v e d a s a voltage pulse.
A surface irregularity or
pin p r i c k i n i t i a t e s the release mechanism. Such pulses could be damaging
to sensitive electronic circuits.
TABLE 4. RADIATIONEFFECTSONMISCELLANEOUS
-
-
~
~~
___
-
Identification
Material
"
.
_, -
~
-
"
~
Total Integrated
Exposure(a)
~
~~
ORGAMC WIRE INSULATIONS
-
_
Remarks
Alkanex
4.6 x l o 7 rads (C), Co-60
Satisfactory performance, 150 C (encapsulated in rigid
epoxy and semirigid silicone). (30)
Silicon-alkyd
4.6 x lo7 rads (C), Co-60
Satisfactory performance, 150 C (encapsulated in rigid
epoxy and semirigid silicone). (30)
Polypropylene
7.1 x lo7
rads
(C),
Unsatisfactory, becomes brittle and crumbles (15
55 C, and 100 C).(31)
Co-60
XE-9003A
n/cm2
4.08 x
(E > 0.5 MeV)
Gamma dose unknown
Ambienttemperature.Unsatisfactory,insulation
too brittle and cracked for postirradiation
testing. (32)
SE-975
4.08 x 1016 n/c&
Ambienttemperature.Unsatisfactory,insulation
cracked and too brittle for postirradiation
testing.
" (32)
~ _ _
_
(E > 0 . 5 MeV)
Gamma dose unknown
I
_
-
-~
~
_
c
_
"-
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 Ceramlt e m p ) , h a s d e m o n s t r a t e d a high tolerance for radiation for total doses up
to 1. 5 x 108 r a d s ( C ) a n d 4.4x 1017 n / c m 2 ( E > 0 . 1 MeV) at r o o m t e m p e r a t u r e . A tendency to powder during stripping tests is the only indication
of
d e t e r i o r a t i o n of physical properties. The stability
of e l e c t r i c a l p r o p e r t i e s
has also been satisfactory with some loss in dielectric strength and insulation resistance being observed.
A d e c r e a s e of approximately 16 p e r c e n t
occurred in breakdown voltage or dielectric strength between pre- and
p o s t i r r a d i a t i o n m e a s u r e m e n t s i n o n e s t u d y . ( 2 7 ) R e s u l t s of other studies
35
have shown a definite difference between the dielectric strength
of i r r a d i a 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
f o r c o n t r o l s p e c i m e n s . ( l 9 ) Considerable difficulty due to the hygroscopic
p r o p e r t y of the ceramic insulation was encountered with these measurem e n t s a n d m a y h a v e c o n t r i b u t e d t o s o m e of the difference. Changes in the
i n s u l a t i o n r e s i s t a n c e a s a r e s u l t of exposure to a radiation environment
have been insignificant.
Miscellaneous Inorganics
Radiation-effects information on seven inorganic wire insulations
o t h e r t h a n t h e c e r a m i c d i s c u s s e d a b o v e i s l i m i t e d t o s i n g l e e v a l u a t i o n s of
t h e r a d i a t i o n r e s i s t a n c e of each wire or cable.
Of the seven wires and
cables tested, four are standard products and three are special or nonproduction items. Because
of the limited information available, information concerning the radiation resistance of t h e s e w i r e s and c a b l e s a r e
p r e s e n t e d i n t h e t a b u l a r f o r m a t of Table 5.
RADIATION E F F E C T S ON ENCAPSULATING COMPOUNDS
Encapsulating compounds that have been evaluated a s to their radiation resistance include epoxy resins, silicone resins, polyurethane, and
aninorganic,calciumaluminate.Thesematerials,generallyexperienced
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 m a t e r i a l s t e s t e d a n d t h e r a d i a t i o n e n v i r o n m e n t
to which they were exposed.
Silicone resin encapsulating materials, such as RTV-501 and Sylgard
19 2 and 183, have not been seriously degraded at radiation exposure doses
of 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
r a d s ( C ) . D e g r a d a t i o n of the physical properties has been limited to a
slight but insignificant weight loss of less than 1 per cent. I n s u l a t i o n r e s i s t a n c e dat.a show permanent decreases of 40 to 50 percent with the
m i n i m u m r e s i s t a n c e of approximately 1 x 1 0 l 2 o h m s a f t e r a total exposure
36
I
TABLE5.
RADIATION EFFECTSONMISCELLANEOUSINORGANIC
Material Identification
~.
WIRE INSULATION
Total Integrated
Exposure(a)
Remarks
~~~
Silica-glass (39001 -1-16)
double shielded coax
1.5 x 108 rads (C)
4.4 x 107 n/cm2
(E > 0 . 1 MeV)
Room temperature. No visible signs of degradation.
electrical tests.(27)
No
Quartz (39Q02-3-26)
multiconductor coax
1.5 x 108 rads (C)
4.4 x 1017 n/cm2
(E > 0 . 1 MeV)
Room temperature. No visible signsof degradation.
electrical tests. (27)
No
Asbestos and fiber (Phosroc
111,RSS -5 -203) lead
wire
9.8 x l o 7 rads (C)
4 . 1 x 1013 n/cm2
(E > 2.9 MeV)
200
No breaking, cracking, or spalling was evident
when subjected to a bend test. Weightloss <0.2 percent. No electrical tests. Slightlydarkerincolor.(lg)
Mica paper-fiberglass
(Mica-Temp, RSS5 -304)
1.1 x 108 rads (C)
4 . 5 x 1013 n/cm2
(E > 2.9 MeV)
200 C. No breaking, cracking, or spalling was evident
when subjected to a bend test. Weight loss ~ 0 . 1 5percent. Slightly darker in color. (19)
S-994 Fiberglass
6.5 x 1O1O rads (C)
I. 5 x 1019 n/cm2
(E > 0.1 MeV)
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 overwhelming factor in determining level of insulation
resistance (-107 ohms). (33934)
Ceramic Kaowool and
Refrasil (power cable)
8.8 x lo9-8. 8 x 1010 Cable met 1200 volt rms dielectric breakdown requirerads(C)(Estimated)ment.
Also, withstood2000 voltrmsbetweencon(35)
3x1019n/cm2ductor
and ground for 5 minutes.
(Energy unknown)
Magnesium oxide
(Rhodium conductor
and platinum sheating)
5x107rads(C)
1.0x1015n/cm2for30
(fission)
much
as
-
C.
Met dielectricstrengthrequirementof1200volts
seconds. Insulationresistancedecreasedas
four orders of magnitude
between
prepostirradiation measurements. (36)
rms
and
"
(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 / c m 2 ( E > 0 . 1 MeV)and1.8 x l o 6 r a d s ( C ) gamma.In
the only study where measurements were performed during irradiation, the
i n s u l a t i o n r e s i s t a n c e d e c r e a s e d by something in excess of o n e o r d e r of
magnitude (> 2 x 1 0 l 2 o h m s to 1 x 1 0 l 1 o h m s ) when the reactor was at its
maximurn power level of 30 k W . (37) An e s t i m a t e of the neutron and gamma
r a t e at this level is 1. 5 x 1 0 l 1 n / c m 2 . s ) ( E > 0 . 1 MeV) and 6 x lo4 r a d s
( C ) / h o u r ,r e s p e c t i v e l y .
Limited information on a polyurethane foam encapsulant indicates
that this material may be more sensitive to radiation exposure than other
encapsulating materials. Decreases in insulation resistance have
a p p r o a c h e d t h r e e o r d e r s 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 r a d s ( C ) h o u r . F u l l
recovery occurred, however, within
3 days after the irradiation was terminated with a total dose of 1. 5 x 1 0 1 5 n / c m 2 ( E > 0 . 1 MeV) and 1.8 x l o 6
r a d s ( C ) g a m m a . (38)
S e v e r a l , b u t n o t n e c e s s a r i l y all epoxy resin encapsulants have shown
a r a d i a t i o n r e s i s t a n c e 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 resistant. Epoxies have
withstood neutron and gamma doses up to 1.
1 x 1 0 l 6 n / c m 2 ( E > 0. 5 MeV)
and 1 x l o 9 r a d s ( C ) f r o m a reactor source without serious deterioration.
S i m i l a r l y , e l e c t r o n i r r a d i a t i o n t o a total exposure of 5. 8 x 1 0 l 6 e / c m 2
( E = 1.0 MeV) at 60 C and cobalt-60 irradiation to 1 x 108 r a d s ( C ) p r o duced 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 ultimate
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
s o u r c e i n e x c e s s of 108 r a d s ( C ) m a y r e s u l t i n f a i l u r e i n s o m e a p p l i c a t i o n s
where the epoxy is under stress. The ultimate 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).
38
TABLE 6.
EPOXIESEXHIBITING SATISFACTORY RADIATION
TOLERANCE AT THE EXPOSJRES INDICATED
Epoxy
Exposure(a)
Integrated
_Identification
_ _Total
~ _ ~- . ~.
.~ . .
Bisphenol A
8.8 x lo7 rads (C) gamma
3.6
n/cm2
x
(E > 0.1 MeV)
Eccobond 182
1 x 108 rads (C) gamma
2 xn/cm2
(E > 0.1 MeV)
Epocast 17B
8.8 x lo7 rads (C) gamma
4.0 x 1013 n/cm2 (E > 0.1 MeV)
Epon 828
4.4 x 106 rads (C) gamma
3.3 x 1015 n/cm2 (E > 0.1 MeV)
Maraset 622-E
1 x lo9 rads (C) gamma
1.1 x 1016 n/cm2 (E > 0.5 MeV)
Novalak
8.8 x lo7 rads (C) gamma
4.0 x 1013 n/cm2 (E > 0.1 MeV)
Scotchcast 5
1 x lo9 rads (C) gamma
1.1 x
n/cm2 (E > 0.5 MeV)
Scotchcast 212
1 x 109 rads (C) gamma
1.1 x
n/cm2 (E > 0.5 MeV)
Stycast 1095
1 x lo8 rads (C) gamma
2 x 1013 n l c m 2 (E > 0 . 1 MeV)
Stycast 2651 MM
4.4 x 106 rads (C) gamma
3.3 x 1015 n/cm2 (E > 0 . 1 MeV)
12-007
1.8 x 106 rads (C) gamma
1.5 x
n/cm2 (E > 0 . 1 MeV)
1 x lo9 rads (C) gamma
412"
1.1 x 1016 n/cm2 (E > 0.5 MeV)
420 -A
1 x lo9 rads (C) gamma
1.1 x 1016 n/cm2 (E > 0.5 MeV)
1126A/B
1.8 x lo6 rads (C) gamma
1.5 x 1015 n/cm2 (E > 0.1 MeV)
CF-8793
9.4 x lo7 rads (C) gamma
3.8 x 1013 n/cm2 (E > 0 . 1 MeV)
CF-8794
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
T h e e l e c t r i c a l p r o p e r t i e s of epoxy encapsulants show some variation
i n r a d i a t i o n t o l e r a n c e b u t a r e g e n e r a l l y of adequate stability for use in
most electronic circuits. The insulation resistance
has d e c r e a s e d by as
m u c h a s two o r d e r s of magnitude during irradiation with a m i n i m u m 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;
t h e l a t t e r s h o w s t h e g r e a t e s t s e n s i t i v i t y t o r a d i a t i o n 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
r a d s ( C).(37) Diglycidylethers of bisphenol A araldite epoxy with an
a l i p h a t i c a m i n e h a r d e n e r r e t a i n e d 84 p e r c e n t of its i n i t i a l d i e l e c t r i c
s t r e n g t h a t 6 . 8 x 108 r a d s ( C ) , b u t w a s s e v e r l y d a m a g e d p h y s i c a l l y
at
109 r a d s ( C ) so that t h e d i e l e c t r i c s t r e n g t h c o u l d n o t b e m e a s u r e d .
The above information is r e p r e s e n t a t i v e of t h e r a d i a t i o n r e s i s t a n c e
of several epoxy encapsulants, but the reader should
be cautioned that one
type of epoxy (358-G) was considered as unsuitable following a t e s t b e c a u s e
it exhibited large variations in volume resistivity during exposure. ( 3 2 )
The extent of these variations is unknown and this information is included
only as precautionary information.
Calcium aluminate, an inorganic encapsulant, w a s e v a l u a t e d a s p a r t
of one study where it was subjected to a total integrated exposure of 1 x l o 8
r a d s ( C ) gamma and 4. 1 x 1013 n / c m 2 ( E > 2 . 9 MeV) at 200 C , ( 1 9 ) No
significant changes occurred between pre-and postirradiation measurem e n t s of capacitance, dissipation factor, and insulation resistance.
Die l e c t r i c s t r e n g t h of control and irradiated specimens was comparable following the radiation expo sur e.
RADIATION E F F E C T S 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
rather than the metals used in these devices. The latter 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
m a y u l t i m a t e l y l e a d t o e l e c t r i c a l f a i l u r e , is a permanent effect and a m a j o r
concern in selecting a c o n n e c t o r o r t e r m i n a l f o r u s e i n a radiation environment. This degradation
of physical properties is manifested in the crumbling or disintegration of some organics that a r e e m p l o y e d as the insulating
media. Thus,
a c o n n e c t o r o r t e r m i n a l t h a t i n c l u d e s a m a t e r i a l of this type
will fail t h r o u g h s t r u c t u r a l c o l l a p s e i n a radiation environment of sufficient
total exposure. Tetrafluoroethylene (Teflon) and
similar fluorocarbon
m a t e r i a l s a r e w e l l known for their lack of radiation resistance and this
mode of f a i l u r e .
Inorganic insulated connectors and terminals of t h e h e r m e t i c s e a l
type, those having glass-to-metal seals, have also experienced physical
damage when exposed to
a radiation environment. This damage is in the
f o r m of cracking and chipping in the glass area immediately surrounding
t h e m e t a l p i n s u s e d a s c o n d u c t o r s ( a n a r e a of h i g h s t r e s s u n d e r n o r m a l
conditions). If this type of d a m a g e i s m o r e e x t e n s i v e t h a n s i m p l e s u r f a c e
f r a c t u r e s , 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
r e p o r t e d by e x p e r i m e n t e r s . T h e c o n s e n s u s i s t h a t t h e s e p a r a m e t e r s a r e
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 m u c h a s 1015-1016 n / c m 2 a n d ( E > 2 . 9 MeV)
and 8 . 8 x 106 r a d s ( C ) g a m m a 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 m a g n i t u d e h a v e o c c u r r e d d u r i n g t h e i r r a d i a t i o n of these connectors with recovery to within one order of magnitude of t h e p r e i r r a d i a t i o n
values within minutes after the irradiation was terminated. Neopreneinsulated connectors have shown a m i n i m u m i n s u l a t i o n r e s i s t a n c e of
approximately 1 x 109 o h m s during exposure to 1.5 x 1 0 l 1 n / c m 2 - s )
( E > 0 . 1 MeV) and 6 . 1 x l o 4 r a d s ( C ) / h r . B u n a - N - i n s u l a t e d c o n n e c t o r s
have exhibited minimums of less than 10 megohms for neutron fluxes and
41
g a m a d o s e r a t e s of 8 . 4 x 1O1O n / c m z . s ) ( E > 0 . 9 MeV) and 6 . 1 x lo4
rads (C)/hr. Results from insulation-resistance measurements on the
neoprene-insulated connectors are presented in Figure 10. Breakdownv o l t a g e m e a s u r e m e n t s o n t h e s e c o n n e c t o r s i n d i c a t e v a l u e s i n e x c e s s of
500 v o l t s d u r i n g i r r a d i a t i o n a n d g r e a t e r t h a n 1000 volts 3 w e e k s l a t e r .
100 I
I
E
40watt
c
0
I
0
-
-0
a,
T
I
LT
C
.o 1.0
4-
0
-
3
10 rads(C) gamma
0.I
IO"
10'2
lot3
1014
loi5
I
I 11
Neutron Fluence, n/cm2(E> 0.1 MeV)
FIGURE10.INSULATIONRESISTANCE
O F NEOPRENEINSULATED CONNECTORS VERSUS TOTAL
EXPOSURE(38, 39)
Physical degradation has resulted in the recommendation that
Buna-N-insulated connectors be r e p l a c e d a f t e r a g a m m a e x p o s u r e of
2 x 106 r a d s ( C ) a t r o o m t e m p e r a t u r e .
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. Connectors having a g l a s s - i n s u l a t e d h e r m e t i c s e a l o r g l a s s - f i b e r f i l l e d d i a l l y l
phthalate insulation have shown superior resistance to radiation damage
42
0'6
when compared to silicon rubber-insulated units after a total exposure of
1 . 6 7 x 1016 n / c m 2 ( E > 2 . 9 MeV) and -7 x lo8 r a d s ( C ) . F e e d t h r o u g h
t e r m i n a l s i n c o r p o r a t i n g the latter for insulating purposes have also been
t e s t e d i n 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 t e m p e r a t u r e ( 5 5 t o 65 C)
a n d r a d i a t i o n h a v e r e s u l t e d i n d e c r e a s e s of four and five orders of magnit u d e . ( l 8 , 26) Minutes after radiation exposures of 1015-1016 n/cm2
( E > 2.9 MeV) and 8.8 x 106 r a d s ( C ) g a m m a at 55 C, the insulation resistance recovered to within one order of magnitude of t h e p r e i r r a d i a t i o n
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 t h e t h r e e
p l a s t i c i n s u l a t o r s t e s t e d a s 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 a t r o o m t e m p e r a t u r e e x p e r i e n c e d d e c r e a s e s 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
r e s i s t a n c e r e m a i n e d f a i r l y c o n s t a n t a t 6 - 7 x l o 7 o h m s during irradiation
at a neutron fluence of 2 . 3 x 101o n / ( c m 2 . s ) ( E > 0 . 5 MeV) and a g a m m a
r a t e of 2 . 6 x l o 5 r a d s ( C ) / h r . w i t h a p r e t e s t r e s i s t a n c e of :1 x 1 0 l 2
o h m s . Capacitance and dissipation factor were fairly independent
of the
altitude and radiation conditions to which the terminals were subjected.
S e v e r a l of t h e t e r m i n a l s f a i l e d b e c a u s e of low corona voltages and insulation resistance: included were
all of the smaller size and
50 p e r c e n t
of t h o s e c l a s s i f i e d a s m e d i u m a n d l a r g e s i z e s .
Radiation-effects information on inorganic insulated connectors inc l u d e t h e g l a s s h e r m e t i c - s e a l t y p e a n d a c e r a m i c ( a l u m i n a ) - i n s u l a t e d AN
type connector. Similar information is also available on ceramic-insulated
feedthrough terminals. Insulation resistance data indicate that both types
of connectors have a d e c r e a s e of a p p r o x i m a t e l y t w o o r d e r s 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 r a d s ( C )
g a m m a at 55 C. Results of i n s u l a t i o n r e s i s t a n c e m e a s u r e m e n t s o n t h e
ceramic-insulated connectors are presented in Figure 11. Combined
effects of radiation and temperature (156 F) h a v e p r o d u c e d d e c r e a s e s of up
t o f i v e o r d e r s of magnitude in insulation resistance during irradiation at a
neutron fluence of 1 . 2 x 1 0 l 2 n / c m 2 . s ) ( E > 2 . 9 MeV) and a g a m m a r a g e of
43
IO''
I
A l l remainingconnectors fall between
the maximum limits of Connector I and
minimumlimits of Connector IO.
IO'
cn
E
r
0
.-cn
cn
Q)
LT
1o9
I oa
0
1.0
Neutron Exposure, n/cm2 (E>0.5MeV)
FIGURE 11.
2.0
x IOl5
INSULATIONRESISTANCE O F C E R A M C 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 t h e i n i t i a l v a l u e s . T h e g l a s s h e r m e t i c - s e a l
,~
type connectors exhibited breakdown voltage characteristics in excess of
500 v o l t s d u r i n g i r r a d i a t i o n a n d g r e a t e r t h a n 1000 volts 3 weeks after the
radiation exposure was terminated. Corona voltage data on the ceramicinsulated AN connector s show a range of 1 . 2 - 1 . 8 kV f o r 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 approxim a t e l y 100 volts while a second connector experienced a d e c r e a s e t o
between 600 and 800 volts in corona ignition voltage.
A radiation study of s e v e r a l t y p e s 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 / c m 2 ( E > 0 . 1 MeV) and 9 . 3 x l o 7
r a d s g a m m a a t 200 C . The insulation resistance was 1014-1015
ohms
before and after the irradiation.
It i s r e c o m m e n d e d t h a t t h e r e a d e r c o n s u l t t h e s e c t i o n o n s h e e t a n d
bulk insulating materials for additional information on the connector insulations discussed above and others
that may be of interest. In addition, the
activation of m e t a l p a r t s p r o v i d e s a continuing source of radiation to the
connector and surrounding electronic parts even after irradiation from the
primary source has terminated. In glass to metal seals, with materials
like Kovar or similar alloys, the interface between the metal and glass,
a
m o s t s e n s i t i v e a r e a , is i n a n a r e a of high radiation concentration and high
p h y s i c a ls t r e s sa n d ,t h u s ,i sm o r es u b j e c t
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
o r g a n i c s , a r e u s e d i n o n e o r m o r e p a r 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 c a p a c i t o r d i e l e c t r i c s is l i m i t e d as little
o r no change i s shown in this property. Therefore, the effect on the dielectric 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 insulation resistance. The ionization effect is the main insulation effect observed during irradiation tests.
I n s u l a t i o n r e s i s t a n c e m e a s u r e m e n t s of p a p e r - d i e l e c t r i c c a p a c i t o r s e x p o s e d
to intense radiation illustrate the effects of both ionization and insulation
breakdowns within the capacitor.
Upon irradiation, the insulation resistance
i m m e d i a t e l y d r o p s a s a r e s u l 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. D e c r e a s e s i n i n s u l a t i o n r e s i s t a n c e w i l l o c c u r w i t h i n c r e a s i n g t e m p e r atures; therefore, any rise in temperature associated with radiation will
contribute to a decrease in the insulation resistance. Capacitors such
a s 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 neutronradiation sensitivity of c a p a c i t o r s a c c o r d i n g t o d i e l e c t r i c m a t e r i a l i s shown
in Figure 12.
46
Mild - to - moderate permanent damage
Moderate- to -severe permanent damage (behavior spread)
Severepermanentdamage
Ceramic
Glass
Mica
Paper and Paper/Plastic
Plastic
Electrolytic
1015
loi4
IO l3
~~~~
~
~~
1017
IOi6
Fast NeutronFluence,
n/cm2
I
I
I
1
I
lo5
IO6
lo7
IO8
lo9
Estimated Ionizing Dose, R
FIGURE 12.
RELATIVE RADIATION SENSITIVITY
O F CAPACITORS
If t h e c a p a c i t o r s a r e going to be used in a system that will operate in
a nuclear or space environment, then temporary changes that occur during
irradiation will be of i n t e r e s t . 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 magnitude. It must be remembered,
however, that the temporary effects are largely dependent
on the f l u x r a t e ,
a n d t h e p e r m a n e n t e f f e c t s a r e m a i n l y t h e r e s u l t of total exposure. More
specific information concerning the various types
of c a p a c i t o r s , a s c l a s s i f i e d
by d i e l e c t r i c material, is presented in the following sections.
47
I
Glass - and
P o r c e l a i n - D i e l e c t rC
i ca p a~citors
"
~~~
~
The basic construction of glass -dielectric capacitors includes alternate
l a y e r s of g l a s s r i b b o n a n d e l e c t r o d e o r p l a t e ( a l u m i n u m ) m a t e r i a l w i t h a n
outer covering of g l a s s . T h e s e l a y e r s a r e s e a l e d t o g e t h e r i n t o
a monolithic
block by high temperature and pressure. Vitreous-enamel (porcelaind i e l e c t r i c ) c a p a c i t o r s a r e of s i m i l a r c o n s t r u c t i o n , w i t h a l t e r n a t e l a y e r s
of
c e r a m i c g l a z e a n d s i l v e r t h a t a r e f u s e d i n t o a monolithic block with an ext e r i o r of the same ceramic glaze. Applications for glass- and porcelaindielectric capacitors include blocking, by-pass, coupling, high-stability
beating oscillators and low-drift R - C o s c i l l a t o r s . T h e y a r e w e l l s u i t e d f o r
c r i t i c a l h i g h R - F applications, within the limitations of t h e i r s e l f - r e s o n a n c e
frequency, and where a m i n i m u m of n o i s e i s r e q u i r e d .
Capacitors having glass- or porcelain- (vitreous enamel) dielectrics
compared to capacitors of o t h e r d i e l e c t r i c m a t e r i a l s , h a v e s h o w n a relatively
high resistance to damage from exposure to
a neutron environment. The
damage or effect of the radiation on the electrical properties of t h e s e c a p a c itors includes both permanent damage and temporary effects. The tempor a r y e f f e c t s a r e a t t r i b u t e d t o i o n i z a t i o n i n the capacitor and i n t h e i m e d i a t e
area surrounding the capacitor and its 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
i n t e m p o r a r y e f f e c t s b e c a u s e of charge equilibration.
G l a s s - and porcelain-dielectric capacitors have exhibited both temporary and permanent changes in capacitance as
a r e s u l t of irradiation.
Changes in dissipation factor and insulation resistance are generally tempor a r y e f f e c t s with recovery to near preirradiation values within a few hours
a f t e r t h e t e r m i n a t i o n of the exposure. The dissipation factor
of porcelain
units, however, has sometimes experienced permanent changes after
a
neutron fluence of
1016 n / c m 2 ( 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 / c m 2 (E > 2.9 MeV)
and total gamma exposures of 7 . 7 x 108 to 3 . 0 x 109 r a d s ( C ) . A m a x i m u m
48
change of only +O. 1 p e r c e n t , w i t h a n a v e r a g e i n c r e a s e of 0.05 p e r c e n t h a s
been observed, however, with a neutron flux and fluence of-4 x 1 0 l 2 n /
( c m 2 - s ) , E > 10 keV, and 8 x 1014 n/cm2, respectively. (40) T h e g a m m a
environment included a r a t e of 5.4 x l o 6 r a d s ( C ) / h r a n d a total dose of
3 x lo6 r a d s (C). S e v e r a l f a c t o r s m a y b e r e s p o n s i b l e f o r t h e d i f f e r e n c e s
in the results reported by various experiments, such as lack
of c l o s e s i m i larity 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 p o r c e l a i n dielectric capacitors during irradiation include a d e c r e a s e of 3. 5 p e r c e n t
a n d a n i n c r e a s e of 2.1 percent. Permanent changes between
- 4 . 0 and +3.5
percent have also occurred.
In m a n y c a s e s , h o w e v e r , t h e c a p a c i t a n c e
r e m a i n s m u c h m o r e s t a b l e w i t h t e m p o r a r y a n d p e r m a n e n t c h a n g e s of l e s s
than 1. 0 p e r c e n t .
In general, the capacitance of g l a s s - a n d p o r c e l a i n - d i e l e c t r i c c a p a c i tors remains stable enough in a radiation environment that they are suitable
f o r m a n y of their intended applications, with the exception of circuits involving critical tuning where precision capacitors are
a necessity. Applications
i n c i r c u i t s of this type require shielding to protect the capacitors against the
radiation environment.
The dissipation factor of g l a s s - a n d p o r c e l a i n - d i e l e c t r i c c a p a c i t o r s
experiences temporary effects from exposure to a nuclear-radiation environment. Glass-dielectric capacitors have shown increases from initial 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
1 0 l 8 n / c m 2 (E = unknown) and 7 . 7 x l o 8 r a d s ( C ) , respectively. The dissipation factor of p o r c e l a i n - d i e l e c t r i c c a p a c i t o r s h a s a p p r o a c h e d 0. 05 during
and after exposure to a n u c l e a r - r a d i a t i o n e n v i r o n m e n t . T h e s e d e v i c e s h a v e
shown both complete recovery to preirradiation values and additional inc r e a s e s when the irradiation was terminated. The maximum, with the posti r r a d i a t i o n i n c r e a s e , h a s n e v e r e x c e e d e d 0. 05, a n d i n s e v e r a l t e s t s t h e d i s sipation 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 / ( c m 2 . s ) (epicadmium),
2 , 1x 1015 n / c m 2 , 2 , 1 x 108 r a d s ( C ) / h r , a n d 3 . 2 x 1 0 l 1 r a d s ( C ) .
T h e i n s u l a t i o n r e s i s t a n c e of g l a s s - a n d p o r c e l a i n - d i e l e c t r i c c a p a c i t o r s
d e c r e a s e s b e t w e e n t w o a n d t h r e e o r d e r s of magnitude when they are subjected
49
I
to a nuclear-radiation environment. This effect is temporary and the insulation resistance recovers when the irradiation is terminated.
Mica-Dielectric Capacitors
T h e i n t e r n a l c o n s t r u c t i o n of m i c a - d i e l e c t r i c c a p a c i t o r s i n c l u d e s a l t e r n a t e l a y e r s of m i c a - d i e l e c t r i c a n d m e t a l l i c e l e c t r o d e s . T h e e l e c t r o d e s o r
c a p a c i t o r p l a t e s m a y b e of m e t a l f o i l o r d e p o s i t e d s i l v e r . T h e d e p o s i t e d
s i l v e r u n i t s , b e c a u s e of the intimate contact between the electrode and dielectric, are used where high-stability capacitors are required, such as in
timing and frequency-determining circuits and other applications where
s t a b i l i t y i s of p r i m a r y i m p o r t a n c e . T h e y a r e n o t , h o w e v e r , r e c o m m e n d e d
for applications that may include high-humidity, high-temperature, and constant d-c potentials. This is due to silver-ion migration, which is accentuated by these conditions. The foil types are less stable than the deposited
s i l v e r ( s i l v e r m i c a s ) , a n d l a r g e r d r i f t s a r e t o be expected with these units,
particularly at elevated temperature.
The capacitance and dissipation factor of m i c a c a p a c i t o r s a r e s u s c e p t ible to permanent damage from irradiation, while changes in insulation
resistance are generally temporary. The permanent changes in capacitance
a n d d i s s i p a t i o n f a c t o r a r e p o s s i b l y due t o c h a n g e s i n t h e p h y s i c a l s t r u c t u r e
of t h e c a p a c i t o r s , s u c h a s s e p a r a t i o n of t h e m e t a l e l e c t r o d e a n d d i e l e c t r i c
layers. Visual examination following exposure has shown severe damage in
t h e f o r m of c a s i n g f r a c t u r e s a s a r e s u l t of the irradiation.
C a p a c i t a n c e m e a s u r e m e n t s 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 / c m 2 (E > 2 . 9
MeV) and 1016 n / c m 2 (E > 0 . 3 MeV) and total gamma exposures of l o 8 r a d s
(C ).
Changes in the dissipation factor of m i c a - d i e l e c t r i c c a p a c i t o r s v a r y
f r o m n o n e , o r no significant effect, to increases where the dissipation
factor was as much as
0. 1 0 a f t e r a neutron fluence of 1 x 1016 n / c m 2
(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
r a d s ( C ) / h r . (41) A s i m i l a r d i s s i p a tion factor (0. 1 0 ) was the result of a t e m p o r a r y i n c r e a s e d u r i n g a d o s e - r a t e
t e s t , a n d d e c r e a s e d t o 0. 04 during a fluence o r i n t e g r a t e d e x p o s u r e t e s t t h a t
was a p a r t of the same study. (42) N o predominant or significant changes
E
50
w e r e r e p- o r t e d i n t e s t s at neutron fluences of 1 x 1014 and 1 x 1015 n/cm2
(E > 2.9 MeV), and total gamma e x p o s u r e s of 1 x l o 7 and 1 x 108 r a d s
(C).( 3 2 3 4 3 )
The insulation resistance of m i c a - d i e l e c t r i c c a p a c i t o r s d e c r e a s e s t o
values in the range of 108 and 109 o h m s during their exposure to a n u c l e a r radiation environment, 109 n/(cm2* s ) (E 1 0 . 5 MeV) and 3 x l o 5 r a d s ( C ) /
hr. Recovery to near preirradiation values,
1010 and 1011 o h m s , o c c u r s
i m m e d i a t e l y following o r s o o n a f t e r t h e i r r a d i a t i o n i s t e r m i n a t e d . T h e
d e c r e a s e i n i n s u l a t i o n r e s i s t a n c e is generally attributed to the ionization
within the capacitor structure and in the near vicinity of t h e c a p a c i t o r , a s
a r e s u l t of the radiation environment.
Ceramic-Dielectric CaDacitors
Basically, a c e r a m i c - d i e l e c t r i c c a p a c i t o r c o n s i s t s of a c e r a m i c d i e l e c t r i c with a thin metallic film, s u c h a s s i l v e r , a p p l i e d t o e i t h e r s i d e a n d
fired at high temperature. The fired metallic
film s e r v e s a s t h e e l e c t r o d e s
o r c a p a c i t o r p l a t e s of t h e d e v i c e . C e r a m i c c a p a c i t o r s a r e a v a i l a b l e a s
two
basic types (general purpose and temperature compensating), with several
bodydesigns:disk,tabular,standoff,andfeedthrough.Thegeneralpurpose units are used in applications where large capacitance changes and
higher losses are not critical. Typical uses are for bypass, filter, and noncritical coupling circuits. The temperature-compensating units are used in
m o r e c r i t i c a l a p p l i c a t i o n s t h a t m a k e u s e of t h e i r t e m p e r a t u r e c h a r a c t e r i s t i c s
t o c o m p e n s a t e f o r p a r a m e t e r c h a n g e s of other elements or components i n the
circuit, These applications include critical coupling and tuning circuits.
Ceramic capacitors have shown various degrees
of sensitivity to
steady-state 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 capacit a n c e c h a n g e s t h a t o c c u r m a y b e a t t r i b u t e d , at l e a s t i n p a r t , t o t e m p e r a t u r e
effects and aging. The latter results in
a gradual decrease in capacitance
with time.
51
The capacitances of g e n e r a l - p u r p o s e c e r a m i c c a p a c i t o r s h a v e d e c r e a s e d d u r i n g i r r a d i a t i o n with but few exceptions, when increases were
observed. These changes in capacitance vary from
a m i n i m u m of 1 o r
2 percent to a m a x i m u m of 2 0 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 c a p a c i t a n c e m a y
possibly be attributable to temperature change, and the permanent effect
m a y 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-dielectric capacitors is limited, and there are
no c l e a r t r e n d s
indicated. The dissipation factor
of t h e s e d e v i c e s h a s i n c r e a s e d d u r i n g a n d
after irradiation, remained rather stable, or even decreased.
(42) The increases observed usually did not exceed 0.02.
The insulation resistance of c e r a m i c - d i e l e c t r i c c a p a c i t o r s d e c r e a s e s
a s m u c h a s t w o t o f i v e o r d e r s of magnitude during irradiation at neutron
fluxes and gamma dose rates of -4 x 108 n / h r ( c m 2 * s ) ( E > 2.9 MeV) and
2 x l o 8 r a d s ( 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 d a y s a f t e r
the discontinuation of the exposure to a neutron flux and fluence of up t o 7. 54
x 1 0 9 n / ( c m 2 . s ) and 3. 11x1015 n / c m 2 (E > 0. 1 MeV), respectively. The
gamma environment included a dose rate of up to 4. 1 x l o 5 r a d s ( C ) / h r a n d
a total dose of 4 . 6 7 x 108 r a d s (C).
PaDer- and PaDer/Plastic-Dielectric C a n a c i t o r s
T h e b a s i c p h y s i c a l s t r u c t u r e of p a p e r - d i e l e c t r i c c a p a c i t o r s c o n s i s t s
of two m e t a l - f o i l s t r i p s o r d e p o s i t e d m e t a l f i l m s ' s e p a r a t e d b y t w o o r m o r e
l a y e r s of p a p e r d i e l e c t r i c . T h e p a p e r i s g e n e r a l l y i m p r e g n a t e d w i t h w a x ,
oil, or synthetic compounds to increase its voltage breakdown and to provide the desired characteristics. The
paper/plastic-dielectric c a p a c i t o r s
are similar in Construction, with the addition of l a y e r s of plastic film i n
the paper layers. Paper and paper/plastic capacitors are used in general
applications involving high voltages and currents at low frequencies, in
52
f i l t e r s a n d n e t w o r k s 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 m a g n i t u d e . P l a i n p a p e r o r p a p e r / p l a s t i c i s
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 oil or other hydrocarbon used to impregnate the dielectric 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 r e s u l t of
this pressure. The ionization
within the capacitor structure and the immediate surrounding area that occurs during irradiation also contributes to
changes i n t h e e l e c t r i c a l c h a r a c t e r i s t i c s of p a p e r a n d p a p e r / p l a s t i c c a p a c i tors. These changes, 'however, are temporary and manifest themselves as
a decrease in the capacitor's insulation resistance.
M e a s u r e m e n t s of capacitance on paper- and p a p e r / p l a s t i c - d i e l e c t r i c
capacitors have shown both increases and decreases during and after capaci t o r e x p o s u r e t o a radiation environment. The maximum changes observed
in the capacitance of units of t h i s c o n s t r u c t i o n a r e a n i n c r e a s e of approxim a t e l y 18 p e r c e n t a n d a d e c r e a s e of 50 percent. The
18 p e r c e n t i n c r e a s e
has been observed with a capacitor type that is molded i n m i n e r a l - f i l l e d
high-temperature plastic.
If the results of two radiation studies i n which
t h e s e e x t r e m e s o c c u r r e d f o r a sample size of two i s d e l e t e d f r o m c o n s i d e r ation, the range of capacitance degradation would be m u c h l e s s , +8. 5 and
- 2 0 p e r c e n t . It is readily understandable that the evolving of gas, with the
a s s o c i a t e d d i s t o r t i o n 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
t h e d i s t o r t i o n m a y a l s o i n s o m e i n s t a n c e s i n c r e a s e t h e e f f e c t i v e a r e a of the
capacitor plates.
The dissipation factor of p a p e r - a n d paper/plastic-dielectric capacit o r s i n c r e a s e s 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
53
1 0 1 1 n / ( c m 2 - s ) ( e p i c a d m i u m ) f oar fluence of 4 x 1 0 l 7 n / c m 2 a n d a g a m a r a t e
and total dose of 8. 7 x l o 5 r a d s ( C ) / h r a n d 3 x l o 8 r a d s (C), respectively.
T h e i n s u l a t i o n r e s i s t a n c e of p a p e r - a n d paper/plastic-dielectric capact o r s d e c r e a s e s a s a r e s u l t of i r r a d i a t i o n . T h e t e m p o r a r y d e c r e a s e t h a t
occurs is generally attributed to the ionization that is produced by the radiation environment. A permanent decrease in the insulation resistance may
be the result of ( 1 ) a d e c r e a s e i n t h e v o l u m e r e s i s t i v i t y of the substance
used to impregnate the device and ( 2 ) t h e p r o c e s s t h a t r e s u l t s i n t h e e m b r i t t l e m e n t of t h e k r a f t - p a p e r d i e l e c t r i c . I n c r e a s e s d u e t o i n t e r e l e c t r o d e d i s t o r t i o n f r o m p r e s s u r e b u i l d u p i s a l s o a strong possibility.
S e v e r a l p r o g r a m s h a v e i n c l u d e d s u f f i c i e n t q u a n t i t i e s of p a p e r - a n d / o r
paper/plastic-dielectric capacitors to provide statistical confidence in the
results. The following discussions
of i n d i v i d u a l t e s t p r o g r a m s a r e p r e sented for this reason.
One hundred CP08AlKE 105M p a p e r - d i e l e c t r i c c a p a c i t o r s w e r e s u b jected to combined environments of h i g h t e m p e r a t u r e a n d n u c l e a r r a d i a tion. (45) The ambient temperature was controlled at 85
C with the reactor
power level limited to 1 m e g a w a t t d u r i n g t h e f i r s t 2 4 h o u r s . T h e r e a c t o r
p o w e r l e v e l w a s t h e n r a i s e d t o 10 megawatts for the duration of t h e e x p e r i ment while the temperature was still controlled
at 85 C. The radiation
environmental conditions for this study included a neutron fluence of 1.4 x
1 0 l 6 n / c m 2 (E > 2. 9 MeV) and a total g a m a e x p o s u r e of 9. 0 x 108 r a d s ( 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 / c m 2 (E > 2 . 9 MeV) and
3.41 x107 r a d s ( C ) . As t h e e x p o s u r e i n c r e a s e d f u r t h e r , t h e r e w a s
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 p e r c e n t t o l e r a n c e l e v e l f o r s e v e r a l
measurements when the capacitors failed catastrophically. Figure
13 i s a
g r a p h i c p r e s e n t a t i o n 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 w e r e s h o r t - c i r c u i t type failures, 9, although not shorted, could
notbe charged, and only
10 c a pacitors were chargeable. The threshold
of failure for the out-of-tolerance
54
I-
I
90
5 80
4
70
x 6 0
Q)
U
5 50
t
'= 40
.-
IO
0
I013
loi4
1015
IOi6
I 017
Average Integrated Neutron Fluence,n/cm*
(E > 2.9 MeV)
I o5
Io6
I o7
I o8
-----
I o9
Average Gamma Dose, rads (C)
FIGURE 13.
RELIABILITY INDEX FORPAPERCAPACITORSFOR
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
n / c m 2 (E > 2.9 MeV) and 3.92 x l o 6 r a d s ( c ) .
A
x 1014
In a n o t h e r i n ~ e s t i g a t i o n ( ~ 6 ) w iat hl a r g e s a m p l e s i z e , a small group
of units was initially stressed in order to obtain conditions for 75 p e r c e n t
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
w e r e p a p e r / M y l a r 0 . 1 pf, 6 0 0 - ~ 0 l t , C P M 0 8 c a p a c i t o r s . T h e c o b a l t - 6 0
s o u r c e u s e d p r o v i d e d a maximum g a m m a e x p o s u r e of 8.77 x 104 r a d s ( C ) / h r .
R e s u l t s of this investigation which included a c o n s t a n t - t e m p e r a t u r e
environment and a temperature-cycled environment are given in Figure
14.
T h e t e m p e r a t u r e - c y c l e d g r o u p w a s s u b j e c t e d t o r o o m t e m p e r a t u r e a n d 135 C
55
Prior ;to -failure
decrease In capacitance
2000 vdc
0 . 5%
160 hr
2000 vdc
Irradiated
6.0 to lO.O%
100 hr
Pulsed 2000 vdc
Irradiated
6.0 to 10.0%
155 hr
Pulsed 2000 vdc
275 hr
l?Tm-y-4%
I
I
7 failed-
‘2””-
636 hr
I
1086 hr
a . Constant 135 C
*Because of equipment malfunction, the units failed
a t 636 h r . If t h e r e h a d
been no t r o n b l e , 7 5 p e r c e n t of the units should have failed by 1086 hr.
2000 vdc
I
15 failed”
2000 vdc
Irradiated
Pulsed 2000 vdc
Irradiated
0
1
2 O/O
566 hr
9 O/O
312 hr
6 Oo/
131 hr
I
Pulsed 2000 vdc
I
Prior-to-failure
decrease in capacitance
I
~~~
1
I
I
I
2 O/O
650 hr
9 failed
b. Temperature -Cycled Units
1.
The pulsed 2000 vdc had a maximum s u r g e c u r r e n t of 3 0 ma
2.
In all c a s e s the sample size equals
FIGURE14.
25 units, Type CPM08
E F F E C T S O F GAMMA RADIATIONON PAPER/MYLAR
CAPACITORS FOR 100 PERCENT SAMPLE-SIZE
FAILURE(46)
56
with 30 m i n u t e s t o s t a b i l i z e at e a c h t e m p e r a t u r e . A total of 90 minutes was
r e q u i r e d a t e a c h t e m p e r a t u r e t o m a k e all n e c e s s a r y m e a s u r e m e n t s . M e a s u r e m e n t s of dissipation factor and insulation resistance for both the constantt e m p e r a t u r e g r o u p a n d t h e t e m p e r a t u r e - c y c l e d g r o u p r e v e a l e d no t r e n d t o ward 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 c a s er u p t u r e s
( 2 ) 6 percent decreases in capacitance
( 3 ) A factor of two increase in dissipation factor
( 4 ) A factor of s e v e n d e c r e a s e in insulation resistance.
Twenty-four units were also operated at 840 vdc and
125 C (no radiation),
a n d w e r e found to be functioning normally after 5, 33 1 h o u r s .
A t h i r d ~ t u d y ( ~included
9)
both paper- and paper/plastic-dielectric
capacitors with deposited metal (metallized) plates or electrodes manufact u r e d a b o u t 1965. Both types were subjected to five environmental conditions
with d-c voltage applied. The paper-dielectric capacitors were also subj e c t e d t o o n e of the environments with no voltage applied. The basic sample
size at each test condition consisted of 20 units for a total of 100 p a p e r /
plastic capacitors and 120 paper capacitors. Each group
of 2 0 s p e c i m e n s
was subjected to one of the environmental conditions indicated in Table 7.
The sixth group of p a p e r - d i e l e c t r i c c a p a c i t o r s ( T e s t G r o u p V I ) was
subjected to the same environmental conditions as Test Group I11 with no
voltage applied.
F a i l u r e - r a t e c o m p u t a t i o n s a t t h e 5 0 , 6 0 , and 90 percent confidence
levels, as shown in Table
8 for the metallized-paper capacitors, indicate
that temperature was the greatest contributor to their failure, since the
c a p a c i t o r s i n T e s t G r o u p V (50 C ) exhibited a m u c h l o w e r f a i l u r e r a t e t h a n
that for any of the other test groups. The units subjected to normal atmos p h e r i c p r e s s u r e , T e s t G r o u p I, a l s o e x p e r i e n c e d a f a i l u r e r a t e a p p r o x i m a t e l y o n e - h a l f t h a t o b s e r v e d f o r u n i t s i n t h e v a c u u m e n v i r o n m e n t s , with the
exception of those in Test Group V. The no-load condition of T e s t G r o u p V I
r e s u l t e d i n a l o w e r f a i l u r e r a t e t h a n t h a t f o r T e s t G r o u p 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
Group
Temperature,
C
I
100
10-5 I1
100
10-5 I11(a )
100
-1013 n / c m 2
(E > 0. 1 MeV)
- l o 7 rads ( C )
10-5 IV (b)
100
-1013 n / c m 2
(E > 0.1 MeV)
- l o 7 rads ( C )
V(4
50
-1013 n / c m 2
(E > 0. 1 MeV)
- l o 7 rads ( C )
Pressure,
torr
None
76 0
Neutron
Fluence
Gamma
Dose
None
( a ) 1 0 , 0 0 0 hours a t 3 x lo5 n/(cm2- s) and 1 x l o 3 rads (C)/hr.
(b) 100 hours a t 3 x 107 n/(cm2. s) and 1x 105 rads (C)/hr followed by 10,000 hours a t 100 C and l o m 5torr
without radiation.
TABLE 8.
T e s t Group
I
I1
I11
IV
V
VI
All test groups
FAILURERATEFORP323ZN105KCAPACITOR,AT50,
60, AND90 PERCENT CONFIDENCE LEVELS(39)
Failure Rate at Indicated Confidence Level,
p e r c e n t / 1000 h r
Percent Recorded
50 P e r c e6n
P0te r c e9n
P0te r c e n t
a s Failed
2. 09
4.86
5.46
4.26
0. 30
4. 56
3 . 19
2.35
5.25
5.88
4.67
0.39
4.97
3.87
3.32
58
3.58
7.03
7. 77
6.41
0.98
6.72
20
50
55
40
0
45
35
ps test
I
T h e e l e c t r i c a l c h a r a c t e r i s t i c s of these capacitors experienced a
g r e a t e r d e g r e e of d e g r a d a t i o n f r o m 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 a r e 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 t h e s e
capacitors.
No failures were observed among 100 m e t a l l i z e d / M y l a r ( p l a s t i c )
capacitors, also manufactured about
1965, that were subjected to the various test conditions in Table 7.
TABLE 9.
~
FAILURE RATE FOR 118P1059252CAPACITORAT
60, AND 90 PERCENT CONFIDENCE LEVELS(39)
50,
~-- .-
T eG
s tr o u p
Failure Rate at Indicated Confidence Level,
Dercent/lOOO h r
Percent Recorded
50 P e r c e n t 6 0 P e r c e n t 9 0 P e r c e n
aFsta i l e d
.
"
I
I1
III
IV
V
All
0.30
0.30
0.30
0.29
0.30
0.06
0.39
0.39
0.39
0.39
0.39
0.08
59
0.98
0.98
0. 98
0.97
0.98
0.20
0
0
0
0
0
0
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
i n t h i s p a r a m e t e r o c c u r r e d i n t h e 1 0 0 C vacuum environments of T e s t
Groups 111,11,
and IV. T h e m a x i m u m l e a k a g e c u r r e n t a p p r o a c h e d 1 . 0
mill i a m p e r e s i n a l l t h r e e of t h e s e t e s t g r o u p s ,
It was concluded from the results obtained that a radiation environm e n t 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 conc e r n e d w i t h t h e d e g r a d a t i o n a s s o c i a t e dwith elevated temperature.
Plastic-Dielectric Capacitors
Most plastic-dielectric materials harden and eventually become brittle
when irradiated. This results in flaking and crumbling especially under
s t r e s s . T h e e l e c t r i c a l p r o p e r t i e s of M y l a r a r e s t a b l e t o a n a b s o r b e d d o s e
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 s p e c i m e n t o a p p r o a c h a quiescent
state after irradiation. Dielectric constant and dielectric
l o s s show no p e r manent dose-rate effect. Some properties
of Mylar do exhibit a d o s e - r a t e
effect that is generally less at higher dose rates. For example, dielectric
strength is considerably reduced at lower dose rates,
but at higher dose
r a t e s t h e c h a n g e i s not n e a r l y a s g r e a t .
Plastic-dielectric capacitors are similar in construction to the paper
a n d p a p e r / p l a s t i c c a p a c i t o r s , w i t h t h e e x c e p t i o n t h a t t h e d i e l e c t r i c i s a thin
p l a s t i c film r a t h e r t h a n p a p e r o r p a p e r a n d p l a s t i c . M a t e r i a l s c o m m o n l y
u s e d a s t h e d i e l e c t r i c film are polystyrene, polyethylene, polycarbonate,
and Mylar (polyethylene terephthalate).
In general, low-voltage units are
manufactured without impregnation or liquid f i l l . H o w e v e r , f o r h i g h e r
voltages, a liquid f i l l i s r e q u i r e d t o r e d u c e c o r o n a a n d i n c r e a s e v o l t a g e flashover limits. Applications for plastic-dielectric capacitors are the
same as those for the paper and paper/plastic capacitors.
Radiation-effects testing of p l a s t i c - d i e l e c t r i c c a p a c i t o r s h a s e s s e n tially been limited to devices employing Mylar as the dielectric
film. T h e r e fore, the following discussion of radiation effects on p l a s t i c - d i e l e c t r i c c a p a c i t o r s i s c o n c e r n e d with o r l i m i t e d t o M y l a r c a p a c i t o r s .
60
E x p e r i m e n t s t o d e t e r m i n e t h e e f f e c t of nuclear radiation on plasticdielectric capacitors have shown that these organic dielectrics experience
m o d e r a t e - t o - s e v e r e p e r m a n e n t d a m a g e at a radiation fluence an order of
magnitude less than the inorganics,
i. e . , g l a s s , c e r a m i c , a n d m i c a .
As in
t h e c a s e f o r p a p e r - a n d 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 exterior case or enclosure.
T h i s r u p t u r e m a y b e t h e p u s h i n g o u t o f t h e g l a s s - t o - m e t a l e n d s e a l s s o that
the material used to impregnate the capacitor leaks out, or, if there is a
sufficient buildup of pressure, the end seal may even be blown completely
f r e e of the capacitor, with the capacitor element extending beyond the limits
of i t s e n c l o s u r e . S u c h a violent rupture occurring in an actual application,
o f f e r s , i n a d d i t i o n t o e l e c t r i c a l f a i l u r e , a p h y s i c a l h a z a r d to other component
parts in the vicinity of the capacitor.
The capacitance of p l a s t i c - d i e l e c t r i c ( M y l a r ) c a p a c i t o r s s u b j e c t e d t o a
r a d i a t i o n e n v i r o n m e n t h a s both i n c r e a s e d a n d d e c r e a s e d when pre- and postirradiation measurements are compared.
In g e n e r a l , t h e s e c h a n g e s a r e
within *4 p e r c e n t of the preirradiation value at neutron fluences of l O 1 5 n / c m 2
( E 2 . 9 MeV) and 10l6 n/cm2
(E > 0.3 MeV). However, decreases
of a s
m u c h a s 10 p e r c e n t a n d a s s m a l l a s <1 p e r c e n t h a v e a l s o b e e n r e c o r d e d f o r
similar capacitors and fluences. The differences
i n the sensitivity to a r a d i ation environment may possibly be the result of differences i n the Mylar and
i t s t r e a t m e n t b e f o r e o r d u r i n g t h e m a n u f a c t u r e of the capacitors, or differe n c e s i n t h e m a t e r i a l u s e d t o 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.
The dissipation factor of plastic-dielectric (Mylar) capacitors remains
stable with a negligible amount of change. The change,
i f i t o c c u r s , i s not
detectable because of t h e m e a s u r e m e n t a c c u r a c y a n d / o r t h e d i s s i p a t i o n f a c t o r
of the long leads required between the test capacitors in the radiation environment and the instrumentation used to measure their electrical characteristics. The maximum observed increase in dissipation factor is
6 0 percent
of t h e i n i t i a l v a l u e m e a s u r e d b e f o r e t h e c a p a c i t o r s w e r e i n s e r t e d i n t h e r e actor. This increase occurred at
a neutron fluence of 6 x 1017 n / c m 2
(epicadmium) and a total gamma dose of 4.4 x 108 r a d s ( C ) .
T h e i n s u l a t i o n r e s i s t a n c e of p l a s t i c - d i e l e c t r i c c a p a c i t o r s d e c r e a s e s
when they are exposed to nuclear radiation. Permanent changes in the insulation resistance may be due to the chemical breakdown process that occurs
61
in the oil or wax substances used to impregnate the capacitor or
a change in
theplastic-dielectric-materialscharacteristics.Theinsulationresistance
of capacitors having a M y l a r d i e l e c t r i c d e c r e a s e s a s m u c h a s t h r e e a n d f o u r
o r d e r s of magnitude, with minimum values as low as
10 megohms. Recovery
after the irradiation is terminated normally returns the insulation resistance
t o n e a r p r e i r r a d i a t i o n v a l u e s , i. e., within an order
of magnitude.
Two p r o g r a m s h a v e i n c l u d e d q u a n t i t i e s o r s a m p l e s i z e s of M y l a r d i e l e c t r i c c a p a c i t o r s t o p r o v i d e a higher than usual statistical confidence in
the results. The following discussions
of i n d i v i d u a l t e s t p r o g r a m s a r e p r e sented for this reason.
One hundred Hyrel Mylar capacitors, rated at
1. 0 pf, were subjected
to a combined environment of high temperature and nuclear radiation. (45)
The ambient temperature was controlled at
85 C, with the reactor power
limited to 1 m e g a w a t t d u r i n g t h e f i r s t 24 h o u r s . T h e r e a c t o r p o w e r w a s t h e n
i n c r e a s e d t o 10 megawatts for the duration of the experiment. The neutron
1
Io5
Average Integrated Neutron FIuence,n/cm*
( E > 2.9 MeV)
-
Io6
10’
Average Gamma Dose,rads(C)
FIGURE 15.
I
J
IO*
Io9
----
RELIABILITY INDEX F O R MYLARCAPACITORS F O R
A 95 PERCENT CONFIDENCE LEVEL, BASED O N A
SAMPLE SIZE O F 98 UNITS (CAPACITANCE AND
CATASTROPHIC FAILURE)(45)
62
ps test
fluence and total gamma exposures to which these Mylar capacitors were
subjected were 1.32 x 1 0 l 6 n / c m 2 (E 7 2.9 MeV.) and 8.5 x lo8 r a d s ( C ) ,
respectively. The capacitance values
of the Mylar capacitors exhibited very
little change for an extended period of radiation; a g e n e r a l i n c r e a s e w a s
o b s e r v e d t o w a r d t h e e n d of t h e t e s t . At the end of t h e t e s t s e v e r a l u n i t s e x ceeded the 10 p e r c e n t t o l e r a n c e l e v e l s p e c i f i e d f o r t h e c a p a c i t o r . P r i o r t o
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 outof-tolerance occurrence. Postirradiation examination
of the Mylar capacit o r s r e v e a l e d t h a t 94 units had failed catastrophically and 81 had ruptured
a s a r e s u l t of the test conditions. One capacitor that exhibited
a nonshorted
condition could not be charged, and
18 units of t h e e n t i r e t e s t g r o u p w e r e
chargeable,
The second study that included a l a r g e s a m p l e s i z e of Mylar capacitors
consisted of subjecting them t o 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
t o t a l s a m p l e s i z e of 140 Mylar capacitors manufactured about 1965.
Failure-rate computations, Table
10, show that the combination
of
radiation exposure and 100 C t e m p e r a t u r e , T e s t G r o u p s 111 and IV, r e s u l t e d
TABLE 10.
FAILURERATE
FOR 683G10592W2CAPACITOR AT 50,
6 0 , AND 90 PERCENT CONFIDENCE LEVELS(39)
Failure Rate at Indicated Confidence Level,
e r c e n t / 1000
hr
.
_ _ _ _ _ _ ~.pP e r c e nR
t ecorded
50 Percent 6 0 Percent
90 P e r c eF
ansat i l e d
""
'
T eG
s tr o u p
-.
.
~
~-
-
I
I1
1.23
0.30
36.70
18.76
0.30
0.30
0.30
III
IV
V
VI
VI1
. .
All
.. __
."
. .
"
".
.
~
"
"
..
~-
. ..
- .~
63
. .
2.44
0.98
48.38
25.53
0.98
0.98
0.98
1.43
0.39
38.85
20.02
0.39
0.39
0.39
10
0
95
75
0
0
0
25.7
in exceptionally high failure rates. The results for the capacitors in Test
Group V, radiation and 5 0 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
f o r T e s t G r o u p 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 capacitors are quite susceptible to radiation
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
5 0 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
t h i s i s of p r i m e c o n c e r n . A m a j o r d i s a d v a n t a g e of e l e c t r o l y t i c c a p a c i t o r s i s
that they are polar, and applications of n o n p o l a r c a p a c i t o r s r e q u i r e t w o
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 t h e e l e c t r o lytic capacitor, which as stated above is its major advantage.
The construction of an electrolytic capacitor includes an electrode
o r c a p a c i t o r p l a t e of some form that has been anodized on one side to form
a d i e l e c t r i c film or insulating layer.
A wet or dry electrolyte is provided
between this anodized surface and the other terminal of the capacitor.
Tantalum and aluminum are the commonly used metals for the anodized
e l e c t r o d e s i n 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 i n c r e a s i n g l e a k a g e c u r r e n t s a n d d e creasing breakdown voltages during shelf life or operation at below-rated
voltage. The .aluminum units experience greater degradation because they
64
deform (the thickness of the oxide layer is r e d u c e d ) at a m o r e r a p i d r a t e t h a n
that for the tantalum. Applications for electrolytic capacitors include filtering 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 e q u i p m e n t m a y
be required. This is due to the activation
of the tantalum when subjected to
t h e r m a l n e u t r o n s a n d t h e l o n g h a l f - l i f e , 112 d a y s , a s s o c i a t e d w i t h t h e r e sulting radiation from the tantalum isotope Ta-182. This hazard is not
associated with the aluminum units because of the very short half-life of
2. 3 minutes for the aluminum isotope A1 -28. The aluminum units also have
the possibility of an isotopic reaction, A1-27 (n, a)Na-24, when exposed to
a high level of fast neutrons. The sodium isotope has
a half-life of 15 h o u r s .
T h e e l e c t r i c a l c h a r a c t e r i s t i c s 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 nearly complete recovery to preirradiation values when the irradiation is terminated. Some
of t h e e l e c t r o l y t i c c a p a c i t o r s a l s o e x p e r i e n c e p h y s i c a l d a m a g e b e c a u s e of t h e i r c o n s t r u c tion. These are the types that employ Teflon
i n the construction of the end
s e a l s of t h e c a p a c i t o r c a s e . T e f l o n i s v e r y s e n s i t i v e t o t h e n u c l e a r radiation environment, especially if oxygen is present in the atmosphere
during the irradiation. It also suffers damage
i f exposed to oxygen after
b e i n g i r r a d i a t e d i n a vacuum or inert atmosphere. The Teflon end plugs
of
tantalum-electrolytic capacitors have popped out because of this sensitivity
of Teflon to radiation, and the inner rubber seal protrudes.
The capacitance of tantalum- and aluminum- electrolytic capacitors
h a s both increased and decreased during radiation-effects experiments.
The changes in capacitance have varied between the maximums of -25 and
+20 p e r c e n t f o r t a n t a l u m t y p e s a n d b e t w e e n t h e m a x i m u m s of -2 and $65 p e 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 capacitance during irradiation may be
due to temperature effects from gamma heating. The permanent changes or
t h o s e t h a t s h o w r e c o v e r y o v e r a n e x t e n d e d p e r i o d of t i m e would be indicative
65
The dissipation factor of tantalum and aluminum electrolytic capacitors
has shown both temporary and permanent effects from exposure to a n u c l e a r radiation environment. The dissipation factor
of high-capacity aluminumelectrolytic 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 / c m 2 (E > 0.5 MeV) and 7.1 x
l o 5 r a d s (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 / c m 2 ( f a s t ) a n d 6 x108 r a d s (C). T h e d i f f e r e n c e i n t h e s e r e s u l t s i s v e r y
likely due to the large volumetric difference in the capacitors, and should
be
a consideration in what to expect in the application of s i m i l a r d e v i c e s .
The dissipation factor of t a n t a l u m - e l e c t r o l y t i c c a p a c i t o r s m a y i n c r e a s e
to where it exceeds 0. 5 0 during irradiation. These high values or large inc r e a s e s o c c u r when the Teflon end seals fail and there is
a l o s s of e l e c t r o lyte. Maximum increases in dissipation factor remain below
0. 10 i f t h e r e
is no l o s s of electrolyte and may not exceed 0.05 with neutron and gamma
flux and total exposure levels as high as
3 x 1 0 l 1 n / ( c m 2 *s ) and 6 x 1017
n/cm2 (epicadmiurn), and 8.7
x l o 5 r a d s ( C ) / h r a n d 4 . 4 x108 r a d s ( C ) ,
respectively.
T h e l e a k a g e c u r r e n t of aluminum- and tantalum-electrolytic capacitors
increases during irradiation by one o r two o r d e r s of magnitude at neutron
fluxes and gamma dose rates of 2.5 x 101o n / ( c m 2 - s ) E > 0 . 5 MeV and 3.6 x
105 r a d s ( C ) , respectively. It h a s i n c r e a s e d t o v a l u e s a s h i g h a s
1000 m i c r o amperes for large capacitors such as
47 mfd and 100 Vde. S m a l l e r c a p a c i tors experience lower leakage currents since there is
a direct proportionality
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 req u i r e a period of several days.
Two programs on tantalum capacitors have included sufficient quantit i e s 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 h i g h t e m p e r a t u r e a n d n u c l e a r r a d i a t i o n i n o n e p r o g r a m . ( 4 5 ) T h e a m b i e n t
t e m p e r a t u r e w a s c o n t r o l l e d a t 8 5 C with the reactor power limited to
1 megawatt during the first 24 h o u r s . T h e r e a c t o r p o w e r w a s t h e n i n c r e a s e d t o
10 megawatts for the duration of t h e e x p e r i m e n t w h i l e t h e t e m p e r a t u r e c o n tinued to be controlled at
85 C. The neutron fluence and total gamma expos u r e t o w h i c h t h e s e c a p a c i t o r s w e r e s u b j e c t e d i n c l u d e d 2. 0 x 1016 n / c m 2
(E > 2. 9 MeV) and 7.3 x 108 r a d s ( C ) , respectively. The capacitance and
dissipation factor of t h e t a n t a l u m c a p a c i t o r s i n c r e a s e d v e r y e a r l y i n t h e
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 r a d s
(C). This change can be observed in Figure 16, where the reliability indices
I 013
I
105
I 014
loi5
I Ol6
Average Integrated Neutron Fiuence,n/cm2
(E>-~
2.9MeV)I
I06
lo7
108
I 017
I
to9
Average Gamma Dose,rads (C)----FIGURE 16.
RELIABILITY INDEX FORTANTALUMCAPACITORS
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 c a t a s 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 a t l e a s t 1 . 6 x 1016 n / c m 2
(E > 2. 9 MeV) and 5. 1 x l o 8 r a d s ( C ) . P o s t i r r a d i a t i o n e x a m i n a t i o n of the
t a n t a l u m c a p a c i t o r s r e v e a l e d 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 ( ~that
9 ) 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
t a n t a l u m c a p a c i t o r s w e r e a l s o s u b j e c t e d t o o n e of the environments with no
voltage applied. These additional capacitors, Test Group
(VI), weresubjected to the same environmental conditions as Test Group
111, Table 7.
T h e b a s i c s a m p l e s i z e of each test condition consisted of 20 units, for a
total of 120 of the wet-foil-type and 1 0 0 of the wet-slug-type capacitor.
N o f a i l u r e s w e r e o b s e r v e d f o r 120 wet-foil tantalum capacitors, and
no
leakage or physical damage was detected during the final visual inspection.
F a i l u r e - r a t e c o m p u t a t i o n s a r e p r e s e n t e d i n T a b l e 11 f o r t h e s e c a p a c itors. The minor difference between the failure rates for Test Group
IV and
TABLE 11.
T eG
s tr o u p
I
II
I11
IV
V
VI
groups
test All
FAILURERATEFOR
5K106AA6 CAPACITOR AT 50,
6 0 , AND 90 PERCENT CONFIDENCE LEVELS(39)
Failure Rate at Indicated Confidence Level,
percent/ 1000 h r
Percent Recorded
50 P e r c e n t 6 0 P e r c e n t 90 P e r c e aF
nsta i l e d
0.30
0.30
0.39
0.29
0.30
0.30
0. 05
0.39
0.39
0.39
0.39
0.39
0.39
0. 06
68
0.98
0 . 98
0. 98
0.97
0.98
0.98
0. 16
0
0
0
0
0
0
0
p-
t h o s e f o r t h e o t h e r test groups is due to the additional operating time associated with the 100 h o u r s of high-flux radiation that these components received
p r i o r t o t h e b e g i n n i n g of the 10, 000-hour life test.
The range of capacitance remained well within the specified
lirnit. A
g e n e r a l i n c r e a s e w a s o b s e r v e d i n t h e d i s s i p a t i o n f a c t o r f o r all t e s t g r o u p s ,
with the exception of T e s t G r o u p 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 p a r t i c u l a r p r o b l e m
in the application of t h e s e c a p a c i t o r s .
Twenty-five failures were observed in a total sample of 1 0 0 of the wetslug tantalum capacitors that were subjected to the five operating conditions
of this study. Three
of these failures were not confirmed by final measurem e n t s . Two of the remaining 22 indicated a high leakage-current condition
(approaching short circuit), and 2 0 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 ( 1 0 0 C, a t m o s p h e r i c
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 t h e c a s e h a d m e l t e d
on four capacitors.
Failure-rate computations for these units, Table
12, indicated a m u c h
higher failure rate for the capacitors in Test Groups
I and I1 (nonradiation
environments). The higher values for Test Group
I were attributed, at l e a s t
in part, to the fact that the plastic cover was left
on the capacitors in this
t e s t g r o u p b u t w a s r e m o v e d f r o m all others as offering a possible outgassing
problem in the vacuum-environments. The plastic covers were considered
a s 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
f a i l u r e r a t e f o r t h e c a p a c i t o r s i n T e s t G r o u p I1 (compared to that of T e s t
Groups III and I V ) , 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.
69
5groups test
TABLE 12.FAILURERATE
FOR HP56C50D1CAPACITORAT50,
60, AND 90 PERCENT CONFIDENCE LEVELS(39)
-
-~
~~
.~
~
~
-
F a i l u r e R a t e at Indicated Confidence Level,
p e r c e n t / 1000 h r
- . __
Percent Recorded
90 P e r c eF
ansat i l e d
"~
T eG
s tr o u5Pp0e r c e6P
n0te r c e n t
~~
__
~~~
I
I1
I11
IV
V
~
-
~~
11.82
7.31
0.30
0.75
0.75
12. 56
85
307.81
0.39
0.89
0.90
15.80
10.05
0.98
1.74
1.72
0
5
5
All
The results obtained on t h e s e c a p a c i t o r s s h o w t h a t t h e y c a n s u r v i v e t h e
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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INDEX
C a s i n gF r a c t u r e
50
CellulosAcetate 9 , 27
CelluloseBytyrate
27
C e l l u l o s eP r o p i o n a t e 27
Cements/Bonding/ 26
C e r a m i cC a p a c i t o r 46, 47, 51, 52
C e r a m i cG l a z e 48
C e r a m i c i t e 35
C e r a m i t e m p3 5
C h a i nS c i s s i o n 7,12,
22
C h a r g eE q u i l i b r a t i o n4 8
Chemical Breakdown 6 1
ChemicalChange 66
ChlorinatedPolyethers27
C h r o m e - P l a t i n g 26
Circuits48-51,53,65
CompressiveStrength26,
29, 33,
38
Conductance - See Also Conductivity 7
Conductivity2-7,10,24,25
Conductors 26, 4 1
ConfidenceLevel59,62,68,
70
Constant D-C P o t e n t i a l 50
Copper26,
28
CoronaVoltages41,45,
60
C o r r o s i o n8 ,
33
Cracking8,31,32,41
Crosslinking 7
C r y o g e n i cT e m p e r a t u r e s1 4 ,1 6 ,
23-25
D a m a g eT h r e s h o l d s
1, 2, 9, 11, 12,
16,18,
19, 21-23,31
D a r k C u r r e n t 25
Density 7, 29
Diallylphthalate 6 , 9 , 21,42,43
DielectricBreakdowns16,19,
20
22,24,25,37,
46
DielectricConstant12,14,19-26,
28,29,40,46,52,60
91-LDResin 28
A c e t a l R e s i n 27
A-C LOSS 16,22
A c r y l i cR e s i n s
27
Acrylonitrile Butadiene Rubber
41,42
Acrylonitrile Butadiene Styrene
Rubber 9 , 28
Activation 40, 6 5
Aging
51,
52
Air Environment 12- 17,
23
Alkanex35
A l l y lC a r b o n a t eP l a s t i c
27
Alox 26
Alsimag 26
Aluminum33,48,
64, 65
Aluminum Capacitor 64-66
AluminumIsotope 6 5
Aluminum Oxide 11, 26, 43
AnilineFormaldehyde
9
Annealing 59
Anodized64
AppliedVoltage 66
A s b e s t o3
s7
AtomicDisplacements
10
Audio F r e q u e n c y 53
BerylliumOxide11
BiologicalHazard40,65
Blocking
48
B o r a t eE l e c t r o l y t e 46
BreakdownVoltage7,24,25,29,
31-33,35,36,41-43,45,52,64
Buna-N - UseAcrylonitrileButadiene Rubber
CalciumAluminate36,40
Capacitance33,34,40,43,46,
48-54,57,60,
61, 63-69
C a p a c i t o r Plate 46, 50, 51, 53,
64
C a r r i e rC h a r a c t e r i s t i c s
2, 3,10,25
79
D i e l e c t r i c Film 64
D i e l e c t r i c L o s s - - See a l s o D i s s i p a tionFactor8,60
D i e l e c t r i cS t r e n g t h 12, 30,34-37,
40, 60
DimensionalChanges
29, 46
Disintegration12,30,32,41,
60
DissipationFactor8,12,14-23,25,
28,30,33,40,43,46-53,57,60,
61,65-69
66,
DoseRateEffect3-5,60,
Electrode46,50,51,53,54,
57
Electrolyte46,64-66
Electrolyte Leakage 69
ElectrolyticCapacitor46,47,64-70
Elongation
12,
13,
18,
19,
21-24
28,38
Embrittlement8,12,20,22,23,26,
31, 35, 54,60
Encapsulation36,38-40,48,
69
EpoxyResins5,
6 , 9 , 25, 26, 35,
36,38-40
FailureRate59,63,68,
69
F i b e r g l a s3s 7
F i l l e dP o l y m e r s 9 , 18,21,39,42
43) 53
60
Flaking - See Also Disintegration
FlashoverVoltage7,
60
FlexureProperties19-23,28-33,38
F o r s t e r i t e 11
F u s e d Q u a r t z 10
GammaHeating46,65
GasEvolution 8 , 33,46,53,
6 1, 69
Gl.assCapacitor46-48
G l a s s e s 10,
11,
29,
33,
37,
42,
43,48
G l a s sL a m i n a t e s
9 , 25,26,
28
G l a s s - t o - M e t a lS e a l s4 1 ,4 5
H a r d n e s s7 ,
19,21-23,28,38,
60, 69
Heat Dissipation 69
HermeticSeal41-43,45
H - F i l m - U s e Polyimides
80
ImpactStrength
18, 21, 22
Induced Conductivity - Use Photoconductivity
InsulationResistance7,8,19-23,
26,28,30-33,35-38,40-46,4854,57,60-62
IonizationEffect46,48,
51, 53,
54
Kaowool37
Kapton - Use Polyimides
K e l - F - U s e Polytrifluorochloroethylene
Kovar
45
LeakageCurrent7,60,64-66,68,
69
L e a k a g eR e s i s t a n c e4 7
L i q u i dF i l l e r
60
LowFrequencyCurrent
52
Lucalox
26
MagnesiumOxide11,37
M e l a m i n eF o r m a l d e h y d e 9 , 42
Melting 69
Melting Point 7
Mica29,37
MicaCapacitor46,47,50,51
M i r r o r s3 3
M y l a r 9 , 20, 34,60,62
MylarCapacitor60-64
NaturalRubber
9
Neoprene Rubber 9 , 41, 42
Network 53
Nylon 6 , 9 , 20
O i lI m p r e g n a t e d 52,53,61,62
Open Circuit Failure
69
O r l o n 21
Oscillators
48
Oxidation
18,
19
PaperCapacitor46,52-60
P a p e r / M y l a rC a p a c i t o r5 5 - 6 0
P a p e r / P l a s t i cC a p a c i t o r4 7 ,5 2 - 6 0
PhenolFormaldehyde42
P h e n o l i cR e s i n s 9
Phosphate-BondedCements
26
P h o s r o c I11 ,37
Photoconductivity 2-6, 10,25,32
PlasticCapacitors47,52.-64
P o l y c a r b o n a t e s 9 , 27,60
P o l y e s t e rR e s i n s 9 , 28
Polyethylene5,
6,9,
18, 19, 31,
32,34,60
P o l y e t h y l e n e T e r e p h t h a l a t e - Use
Mylar
Polyimidazopyrrolone - U s e P y r r o n e
Polyimides6,
9 , 24,30,33
PolymethylMethacrylate 9 , 27
Polyolefins,Radiation-Modified33,34
Polypropylene 6 , 9 , 22,35
P o l y s t y r e n e 5, 6 , 9 , 19,20,60
Polytetrafluoroethylene - Use
Teflon
P o l y t r i f l u o r o c h l o r o e t h y l e n e 8, 9 ,
16, 18
P o l y u r e t h a n e s 9 , 2 2 , 23,36,38
PolyvinylButyral 9
PolyvinylChloride9,
27
Polyvinylfluoride 28
P o l y v i n y lF o r m a l 9
Polyvinylidene Chloride 9
PolyvinylideneFluoride 9 , 23
P o r c e l a i nD i e l e c t r i cC a p a c i t o r4 8 ,
49
Potting - Use Encapsulation
P r e s s u r eB u i l d u p4 6 ,
53,54,
61
P y r o c e r a m 26
P y r r o n e 24, 25
Quartz10,11,37
R e c o v e r y C h a r a c t e r i s t i c s 1 4 , 16- 18,
30,32,38,40,41,43,45,48,49,
51, 52
R e f r a s i l 37
ReliabilityIndices54,55,58,62,
63,67
Resistivity - U s e Conductivity
R - F A p p l i c a t i o n 48
Rupture 54, - 61, 63
81
S a p p h i r e 11
S e a l i n gP r o p e r t i e s4 1
Seals41-43,45,
53, 65, 66, 69
Shielding 49
Short Circuit Failure
54
Silica 26, 37
Silicone-Alkyd 35
SiliconeResins
9 , 28, 36
SiliconeRubbers 9 , 32,35,36,38,
41,43
Silver48,50,51
S i l v e r -Ion Migration 50
SodiumIsotope65
S o f t e n i n gP o i n tT e m p e r a t u r e
18
Solder 69
Solubility 7
Spinel
11
Steatite 26
S t r e s s 60
StyreneAcrylicCopolymer
27
StyreneAcrylonitrileCopolymer
28
StyreneButadieneRubber9,
28
StyreneDivinylbenzene
28
SurfaceResistivity18-20,
26, 28
Swelling 46
Tantalum64,65
TantalumCapacitor64-70
TantalumIsotope65
Teflon 6 , 8,9,12-17,
2 7 , 30,31,
41,65,
66
T e m p e r a t u r e C y c l i n g 55-57
T e m p e r a t u r e E f f e c t s 12,24,25,
32,34,46,50-52,54,59,
62,
64-67
TensileStrength7,12,18,19,
21-24,26,
28, 29,38
U r e aF o r m a l d e h y d e 9
Vacuum12-17,
23, 3 0 ,3 4
VinylChloride-Acetate
9 , 28
V i t r e o u s Enamel Capacitor48
VolumeResistivity12,14,18-20,
23, 26, 28, 40
E
VolumetricEfficiency64
W a x Impregnated48,
52,61,62
Weight L o s s 22, 28, 36-38
Yield Strength 24
82
NASA-Langley, 1971
- 9 CR-1787