A technique is described for evaluating the shielding properties of spacecraft equipment with respect to cosmic radiation. A gamma-ray source is used in conjunction with a scintillation detector to determine mass-thickness distribution both in plane geometry for equipment units, and in spherical geometry for given points within the spacecraft. Equations are presented for calculating mass-thickness distribution functions, and the results are compared with experimental measurements

Bodin, V. V.

Repin, N. N.

Sakharov, V. M.

Sakovich, V. A.

English

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NASA TECHNICAI MEMORANDUM
	
NASA TM 75593
il-	
EXPERIMENTAL RESULTS ON MASS-THICKNESS DISTRIBUT?ON IN
SPACECRAFT EQUIPMENT
V. V. Bodin, N. N. Repin, V. A. Sakovich and V. M. Sakharov
(ti ASA-TM-75543)	 FXPERIMENTV RESt1L ml CN	 479-12142
MASS-mHICKNESS nISTPI17TION IN SPACFCRAFT
EQUIPMENT (National Aeronautics and Space
Administration)	 13 p HC A02/MF A41 CSCL 2?73	 Dnclas61/18 38481
Translation of "Eksperimental'nyye rezul'taty raspredeleniya tol-
shein materials v oborudovanii kosmicheskikh letatel'nykh appa-
ratov," Report presented at the Second All-Union Scientific Con-
ference on Protection from Ionizing Radiations of Nuclear Instal-
lations, Section 5-M, 1978, 9 pp
o^ILI
 v 3037^^^
`^, Isr ^^42^r
NATIONAL AERONAUTICS A14D SPACE ADMINISTRATION
WASHINGTON, D.C. 20546
	
NOVEMBER 1978
k.
EXPERIME14TAL RESULTS ON 'MASS-THICKNESS DISTRIBUTION IN
SPACECRAFT EQUIPMENT
V. V. Rodin, N. N. Repin, V. A. Sakovich and V. M. Sakharov
One of the approaches to calculating the shielding proper-
	 /1
ties of equipment and devices aboard spacecraft with respect to
cosmic radiations consists in the assumption of a random arrange-
ment of matter in the equipment, which is characterized by cer-
tain distribution functions. In the present study, mass-
thickness distribution functions were obtained experimentally by
means of gamma-radiation thickness measurements both in plane
geometry for equipment units, and in zpherical geometry with re-
spect to given points within the spacecraft.
In both cases gamma radiation which passed through a section
of equipment was registered by a collimated scintillation detector
with Compton-scattering pulse height discrimination. In plane
geometry the collimated beam of gamma quanta with a square cross-
section of 1 x 1 cm was coaxial with the collimator of the detec-
tor, while the piece of equipment under test was discretely moved
with the aid of a scanning stand in order to examine successively
all adjacent sections of the surface.
Measurements of the thickness distribution of equipment
shielding a certain point within the spacecraft were made with the
following arrangement [2]: An isotropic gamma source was placed
at a given point within the spacecraft, and the unscattered radia-
tion passing through the equipment was picked up by a collimated
detector with a NaI(T1) crystal which could be moved outside the
object by a coordinate system over a spherical surface with its
* Numbers in the margin indicate pagination in the foreign text.
1
hk
center at the given point.
When the detector was moved continuously through the azimuth
'+ngle ^ (within prescribed limits) [illegible] of the detector for /2
: ►
 fixed time AT . The periodicity of such measurements was chosen
e,uch that in a corresponding time interval At >> AT the detector
was rnoved iti the azimuth plane by the annular dimeri:,ion of the
rectangular collimator Ado (see Fig. 1). When the detector
reached the limiting angle tP, the measurements were stopped, and
the detector was moved in the polar plane by the angular dimension
of the collimator A0, after which the measuvement cycle t^.gas con-
tinued by moving the detector- through ^ in the opposite direction.
The automatic change in the value of A^ according; to the law
A ► - A D O/sin©allowed the results of individual measurements to
he assigned to the sections of the surface under test which are
adjacent to each other and subtend equal solid angles ASZ = A ► OA©
(where 0 - 90 0 A^ = A VO )•
I	 /i
0-	 U tr:2 /0	 ------ 1	 i /-
90 k
r/Slo"
wlcc.rt; U /irJKGt,
t
Fig. 1. Geometry of measurements
Key: a. Hatch lid
2
The Mot  r i but i on of t he number, of sect Ions examined by the
number of pulse , . was transformed in both cases into a diStrtbut.ton
by thickness based on the calibration of tilt , detector for stan-
dard thicknesses. The main source of error in spherical geometry
is the recording- of radiation scattered by sectiono of equipment
adjacont to till' suction udder test. ThIs can Introduce an orror"
of up to lOro.	 however, a Ca111 1 I-rlt Ion cutWe wa: enrplo,ye.i which
gave the rad lat. :on Intensity :i.; a function of standal-d thickness,
obtained In the pvesenct , of a scattering; layer of kiiown t hlckness.
Ttlu.;, If a calibration curvt , w I t h -I 	 layer of
5 g-/cm 2 lo used, then thickness measurements irl the rango of 1 to
10 g/cm at the thickness of the scatter -ttit- layer (which 1.; prac-
tically equal to tile minimum thickness of spacecraft, edutptrte ► rt.)
lead to an error of ± 0.25 g'/cm 2 . Other sources of error In
spherical geomctr,y are associated with movement of the detector
during, measurements, avid the overlapping of the so- etions under
test and the spaces between them. These errors ;amount to b% and
do not lead to a distortion of the distribution itself'. 	 Oil tilt,
whole, the thickness-measurement, errors amounted to ± 0.3 g/cm2
at a thickness of 1-.' &cm', and ± 0.5-0.6 g/cm 2 at a thickiloss
, , 1' 10-15 g/cm2.
The scuming stand w:ls used to study the 111,.;.3- thickness dls-
tribUt.10IIS in a total of 16 radloelectronle units of v:ivying t'unc-
tion, desi frn and compnsit ion. The re. u.lts of the niOasuremOnts
were smoothed by meads of the Reyle I t-h d i str i but Ion lnw :
( 17Z
whore C(x,::) is the probability density of the	 thickness distr• 1-
bu1.1011 for the geometric.	 dimension	 :•,	 cm, x =	 9/crn 2 ;	 n,Y
	
al'('
/3
3
L
distt.ributtoll
	 parameters,
	 where
	 y	 det'I ►► os the mlr ► trnurn	 constant
thickness	 In the equipment unit;
	 x	 > y; and e(z)
	 is the proba-
bility	 of havintr, a constant thickness
	 In the geometric dimension.
Smoothing of experimental results by the ReyleiErh law w: ► :^
dome by the method of least. squares.
`Pile mean thickness and dispersion values were obtained for
thrL'c- feomrt.ric dimensions 1 ►► Parh u ►► tt, as w^^11 as the value's
of the parameters y arid n associated with them. Analysis of the
results showed that these units can be divided Into three main
groups according to the character of the mass-thickness; distri-
bution (see Table 1), while the values of the distrlbutlo ►► par: ► -
meters could be related to the t.hicktiess in the u ►► It In g/cm'-,
defined as the product of the rnearn ur ► It density p by the f;eo-
metric thickness. Analysis, showed that the mean v:zlu(.' of the
distribution x and dispersion eX 2 0f the unit:, examined are re-
lated by tn, exr.ro sion
Sx2(:;)
= cornst.
	 (2)
x(z)
This equation indicates that the thickness distribution law is
stable. However, the Reylelgh distribution law used by us cannot:
be corn. idered stable. This discrepancy sterns from the fact that
as the mean thickness of the unit increases, the experimentally-
measured distribution earn be smoothed by bath the Reyleigh law
and the normal law, since the preexponential factor Iii expression
(1) changes much more slowly than the exponential factor corres-
ponding to the normal law. In other word ,.-,, the experimental d i s-
tribution laws can also be smoothed by the normal law, but this,
results in marked deviations from experimental values in the
range of small thicknesses.
The f(x,z) functions obtained were used to test the possibility
of calculating the mass-thickness distribution function over
solid angles dx/dW with respect to nn arbitrary point in the
spacecraft., assuming? the distribution function of geometric
dimenslons over solid angles dz/dQ Is known.
The gamma thickness-measuring apparatus wars used to mensuve
experimentally the distribution dx/dS2 with respect to the points
	
of location of tale K-206 and S-1 detectors [1] in the Kosmos-936	 /4
spacecraft. The results of the measurements are presented iri
Fi t;. 2. The distribution function for these points was calcu-
lated by convolution of the distribution law of geometric dimen-
sions over solid angles dz/dQ with respect to selected points
within the sphere and the Reyleigh law f(x,::) according to the
formula
I	 f Max
P 	 ^^z	 (3)
where  	 7 l z1
R is the radius of the sphere (R = 100 cm), and T is the distance
from the point Investigated to the center of the sphere (T =
70 cm, 90 cm) .
Two variants of the parameters of the function f(x,::) were
examined In the calculation: the first, 6x 2 /x = 0.8 g/cm 2 ; the
second, 6x 2 /7 = 5.8 g/cm 2 , where x = 0.7 pz and p = 0.5 g /C1112
for both variants. The results of the calculations are also given
in Fi t;. 2. As can be seen, the calculation with dx 2 /x = 0.8 f, /crrl2
agrees well with experimental results, while t.ho results of the
calculation with 6x 2 /7 = 5.8 g/CU1 2 differ considerably from
5
,.
experimental data, thus indicat ink; the strong influence of the
relation 6x21,x.
The agreement between the results of the calculations and
experimental results in the case where Sx 2 /7 = 0.8 g/cm 2 suggests
a method for determining the dx/dSZ distribution function with
respect to an Arbitrary point in the spacecraft basted on the
experimentally-derived distribution functions f(x,z) for 2-3
points within the craft. To do this, solving the problem which
Is the inverse of (3), it is necessary to find the parameters of
the distribution function f(x,::) arid their dependence on geo-
metric dimension, and then calculate the required distribution
according to formula (3).
In conclusion it must be noted that for many problems it is
necessary to know the thickness of the material shielding a cer-
tain point in the spacecraft in all directions, ratner than the
distribution of thicknesses. Such r-esulcs can be obtained only
with apparatus for performing; gamma thickness measurements.
6
	!	 ORIGINAL PAG'	 f	
fOE PWR QUAJ4TY
I	 ,
I	 i	 (	 /	 .i	 I	
I	 ^	 I	 '	 r.	
F
- 1	 . ►
--	
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i	 I
^ Y	 I ^ I	 I^	 ``	 I	 ^^	 I	 i	 ^	 ^	 1
r. _ 	 1	 I	 I-	 I	 t.._^
	
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	 I	 I	 ^	 I	
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F	 `'	 !	 I	 !	
i 	
I	 I	 tl	 ,	 '	 i
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l
	
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^^^	 i	
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^I	 ^	 ^	 r•	 I	 I	 I	 i	 i	 I	 J	 1	 1
Table 1. Thickness Distribution over 1 1acets for 9-206
1	 go	 0	 .
?	 :'0	 1.o	 11. 0
	
90	 210	 22.0
OU 0	 55.0
180 11
	-	 ^^	 40.0
6	 CU
	 -
	
^ 6.0
C)	 r, :1;1I1j I
..1LQI0ItLI INIJIC;IIAI:,i j .1.;;;11U
 
U .;I)!::. W, J113:;a,
Key: a. Facet no.	 C. Facet 1F to directed perpen-
b.	 6 g/crn 2
	dicular to hatch lid.
Table 2. Distribution of Solid Angles by Thicknesses for K-206
i
> 1U
	 u.'v
Key: a. 6 g/cm 2
	b. steradians
8
L_
Table 3. Thickness Distribution over Facets for K
-206
r	 40	 r ', .;U 1^ .
J ;. 't U .v
^^ ^	 ^ • ^	 1 ^1t^iiJ]"._ ^	 ...	 ....,a^.^..1. :^	 ^)j ^.i=1fL^i ^L )..^ i^
Key: a. d g/cm 2
	b. Facet 7F is directed toward
the hatch lid.
,ORIGINAL PAGE Is
OF, POVK QUM"'CY
9
Table 4.	 Distribution of Solid Angles by Thieknessr,L;
	 for
K-206 in the Range 40 0 	<	 o	 <	 140 0 00	 <	 4,	 <	 360
s	 1'/C; a..
.
•	 ^ ^ v i 1. ^ 'H . ^
KeY
!s . t;,	 — 'r , ll U,:,,, J b.	 g/cm2
c.	 steradians
U
Note:	 Commas in tabu-
lated material are
U ^'-- ; ^<% v,^.	 r' equivalent to decimal
;', N — . U,.,..0 points.
iU v,V ^r .. , L ((	 ``V, /ri•V
tiit:iAl; PACE IS 
POOR QUALITY
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i
is v ,., lJ , ^ 1 —,.J l , 11 (,i , .i U V
V
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I


Experimental results on mass-thickness distribution in spacecraft equipment

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