The current status of model prediction and comparison with LDEF radiation dosimetry measurements is summarized with emphasis on major results obtained in evaluating the uncertainties of present radiation environment model. The consistency of results and conclusions obtained from model comparison with different sets of LDEF radiation data (dose, activation, fluence, LET spectra) is discussed. Examples where LDEF radiation data and modeling results can be utilized to provide improved radiation assessments for planned LEO missions (e.g., Space Station) are given

Armstrong, T. W.

Colborn, B. L.

Watts, John W.

English

NASA Technical Reports Server

N95- 23819
STATUS OF LDEF RADIATION MODELING
John W. Watts
ES84, NASA Marshall Space Flight Center
AL 35812
Phone: 205/544-7696, Fax: 205/544-7754
T. W. Armstrong and B. L. Colborn
Science Applications International Corporation
Route 2, Prospect, TN 38477
Phone: 615/468-2603, Fax: 615/268-2676
ABSTRACT
The current status of lnodel prediction and comparison with LDEF radiation (h)silnefry
nleasurelnents is sunlmarized with emphasis on major results obtained in evaluating the uncer-
tainties of 1)resent radiation environment model. The consistency of results and conclusi(ms ol)-
tained from model comparison with different sets of LDEF radiation data (dose, activation, flu-
ence, LET spectra) is discussed. Examples where LDEF radiation data and lnodeling results can
be utilized to provide improved radiation assessments for planned LEO missions (e.g., Space
Station) are given.
INTRODUCTION
The return of LDEF has provided a. unique opportunity to test current ionizing radiati(m
models with a. great variety of measurements. Figure 1 (ref. 1) describes the characteristics (_f
the LDEF mission and measurements that are important for these coml)arisons and figure 2 (ref.
1) shows the models and t)rograms whose outputs have been compared to the measurements of
various LDEF experiments.
PROTON DOSE
There were a number of exl)erinients (ref. 2, 3) which contained therni()huninescent dosime-
ters (TLD) with sufficient shielding so that the geomagnetically trapped protons contril)ute,l
nearly all the accumulated dose observed. These measurements provide a good test of the Vette
tra l)ped proton model AP8MIN and APSMAX(ref.6). Figures 3, 4, and 5 fl'om (ref. 7) show
coml)arisons of measurements with predictions both as ratios (Figures 3 and 5) and missi(m d()se
(Figure 4). The Figure 3 ratios suggest that the Vette models predict fluxes that are about 0.6 ()f
the actual fluxes. Energy dependence of the ratio is not evident since the ratio is c(,nstant ()ver a
large range of effective shield thicknesses. Figure 5 shows a test of the directional model(ref. 8)
against measurements. The higher observed ratios suggest that the proton scale heights used in
217
https://ntrs.nasa.gov/search.jsp?R=19950017399 2020-06-16T08:31:24+00:00Z
the model are low. The comparisons are somewhat complicated by the effects of shielding geom-
etry. Both a comI)lex geometry model of tile spacecraft and accounting of tile l)rot(,n directional-
ity are required to match the trends observed in the measurements. One is not sufficient with, rot
the other.
ELECTRON DOSE
TLD measurements behind thin shields (< 1.Og/cm 2) provide a test of the AE8MIN and
AE8MAX geomagnetically trapped electron models(ref. 9). These were a nl.llll])er of measure-
ments on LDEF that meet this requirement(ref. 4, 5). In Figure 6 fl'om (ref. 7) these measure-
ments are COml)ared to predicted values fi)r a l)lane slab shielding geometry(tel. 10) with gen-
erally good agreement considering the difficulty of the measurements fi)r very thin geometries.
The high predictions at the thinnest shielding may reflect an excess of low energy electrons in the
models or geometry effects where the detector thicknesses are comparable with the shield thick-
heSS.
PROTON ACTIVATION
The LDEF measurements of activation samples for so many location and shiehling del)ths on
a single satellite with a long-term stable attitude is unique. The 2_Na. activation measurements
of the tray clamps are little confllsed by geometry and the surface is well mal)l)ed by munerous
samples. In Figure 7 fl'om (ref. 11) these measurements(ref. 12, 14) are compared with the di-
rectional flux model(ref. 8, 11, 12) confl)ined with botl, detailed and siml)le geometrical shielding
models. The predictions are h)wer than the measurements l)y about the same ratios seen in the
TLD versus predicted (h)se comparisons, again suggestit,g that the Vette proton flux model(ref.
6) predicts low fluxes for low orbital altitudes. The anisotropl,y of the proton flux is more evi-
dent in these measurements than in any otllers on LDEF.
Table 1. Ratio of 1)redicted-to-measured activity
at recovery for nickel activation smnples from (ref. 11)
Isotope Exp. P0006
Saml)le Location on LDEF
Exp. A0114 Exp. M0002 Exp. M0001
Sc-40 0.29
Mn-54 0.62 0.34
Co-56 0.66 0.69
Co-57 0.49 0.48
Co-58 0.71 0.69
Co-60 0.84 0.49
0.73 0.33
1.24 0.59
0.46 0.63
0.55 0.56
Average 0.60 0.54 0.74 0.53
Average fi)r all saml)les: 0.60±0.15
Tables 1 and 2 from (ref. 11) show intentional sample measurements fin' nickel (Table 1) and
vanadimn (Table 2) a.t a. variety of shielding del)ths. Again the mea.surements are higher than
218 ORIGINAL PAGE IS
OF POOR QUALITY
the model predictions with most of the ratios near those observed for dose and 'Z2Na activation.
Some of tile other ratios may 1)e explained by contributions from galactic cosmic rays or lmcer-
tainties in activation cross sections used ill the models. The general trend supp()rts the conclu-
sion fi'om the other ccmlparisons that the \,)tte flux predictions(ref. 3) are low.
Tal)le 2. C(mlparison of Sc-46 activation in vanadiunl samples
fl'om (ref. 11 )
Saml)le Location
Exp. Tray Position
Activity at Recovery (picocnries/kg) Ratio
Measllred C alculat ed h Ieas. / C alc.
P0006 F2 trailing edge 17+1.1 (a) 7.00 0.40
21-t-2.7 (1_) 0.33
A0114 C9 leading edge 20-t-1.5 (b) 7.65 0.38
M0001 H12 space end 20+13 (b) 8.76 0.44
22-t-6.8 (b) 9.50 0.44
M0002 G12 earth end 16+1.3 (b) 9.16 0.57
16+1.4 (c) {I.58
Average 0.46-t-0.16
LET SPECTRA
The long mission exl)osure ()n LDEF allowed tile measurement of the Linear Energy Trans-
fer (LET) spectra to 1)e extended to higher LET with 1)etter statistical accuracy than has l_een
achieved previously(ref. 15). Measurements at higher LET are significant because 1)artMes with
higher LET are more likely to produce Single Event Upsets (SEU)s of microelectronic devices
(an iml)ortant problem for spacecraft al)plicati(ms). Figure 8 from (ref. 16) shows coml)aris(ms
1)etween model(ref. 17) and measured LET sl)ectra. At high LET the measurements are sig-
nificantly higher than the model. At low LET where 1)rotons are the most common 1)article the
lnodel results are higher. This suggest the possibility that not all the prot()ns are l)eing (letected
due to their very thin tracks. The differences at high LET are more difficult to exl)lain, lint the
modeling al)l)roach ignores nuclear interactions and tile 1)roduced fission fl'agments.
h'on nuclei fluxes are of interest because these particles have the largest charges and there-
fi:)re largest LET of any 1)articles that are fairly abundant. (elemelltal abundances takes a ma.ior
step downward just 1)eyond iron.) Figure 9 fl'om (ref. 18) show LDEF measurements ()f the ir()n
energy spectra. The excess over fluxes expected from galactic cosmic rays in the energy range
(100-800 MeV) has been attributed to particles arriving during the large solar particle events
in the fall of 1989. F(,r iron nucM in this ellergy range to arrive at the LDEF _)rl)it through tile
Earth's magnetic field they must not have 1)een coml)letely stril)ped of electrons altd the results
suggest a charge near +12-13 similar to iron in the corona. In Figure 10 from (ref. 11. 19) the
219
LDEF measured Fe fluxes are used to replace the Fe fluxes used in CREME(ref. 17) for a 500 km
altitude orl)it at 28.5 °. (The flux is not strongly dependent on altitude.) The result su_;est that
CREME 1)redicts high fluxes of tile 1,,w energy component of the heavier 1)articles.
SUMMARY
The LDEF ionizing radiation measurements continue to 1)rovide a unique Ol)l)ortunity to test
the current models ,,f tile pa,'ticle environment that will not 1)e rel)eated in the foreseeable fu-
ture. Carefid use of the models considering the details of shielding geometry and particle
alfisotrol)hy, and model assumptions are required to explain so,he of the trends observed in the
measurements. Only with this attention to detail can we locate where the models have significant
pr()blems describing the environment or the measurenients ha.re observation difficulty.
REFERENCE
.
.
.
.
.
.
,
.
,
Armstrong. T. W..; Colborn, B. L. and Watts, J. W.: Radiation Calculations an(l Coml)ar-
isons with LDEF Data. First LDEF Post-Retrieval Symposium, NASA CP-3134, 1991, pl ).
347-36O.
Bent(:m. E. V.; Frank, A. L.; Bent(re, E. R.; Csige, I.; Parnell, T. A. and Watts, J. W.: Ra-
diati(:)n Exposure of LDEF: Initial Results. First. LDEF Post-Retrieval Sylnp()siunl, NASA
CP-3134, 1991, pp. 325-338.
Frank, A. L.: Bent.oiL E. V.; Armstrong, T. W. and Colborn, B. L.: Abs(n'])ed D(_se and
Predicti()ns on LDEF. Second LDEF Post-Retrieval Symposium, NASA CP-3194. 1992, pp.
163-170.
B(,urieau, J.: LDEF: Dosimetric Measurements Results (A0138-7) Experiment. Sec()n(1
LDEF Post-Retrieval Symposium, NASA CP-3194, 1992, pp. 157-162.
Blake. J. B. and hmnamoto, S. S.: A Measurenient of tile Radiation Dose to LDEF by Pas-
sive Dosimetry. Second LDEF Post-Retrieval Syml)osium , NASA CP-3194, 1992, pp. 147-
155.
Sawyer. Donald M. and Vette, James I.: AP-8 Trapped Proton Em'iromnent for Solar Max-
imum and Solar Minimum. National Science Data C,enter, Goddard Space Fligl,t Center,
NSSDC/WDC-A-R& S 76-06, 1976.
Armstrc,ng, T. W. and (',)ll_(_rn. B. L.: Radiation Model Prr, li,'ti(,ns and Validati()l, Using
LDEF Satellite Data.. Second LDEF Post-Retrieval Symposium, NASA CP-3194, 1992, pp.
207-220.
Watts, J. W.; Parnell, T. A.; and Heckman, H. H.: Approximate Angular Distril)ution and
Spectra for Geomagnetically Trapped Protons in Low-Earth Orl)it. High Energy Radia-
tion Backgromld in Space, Proceedings of AlP Conference, Sanil)el Island, Florida, Vol. 186,
1989, pp. 75-85.
Vette. J. I.: The AE8 Trapl)ed Electron Model Enviromnent. National Space Science Data
Ce, lter, God(lard S1)ace Flicht Center, NSSDC/WDC-A-R&S 91-24, 1991.
220
10. Watts, J. W.; Parnell, T. A.; Derricksom J. H.; Armstrong, T. W.,; and Benton, E. V.: Pre-
diction of LDEF Ionizing Radiation Enviromnent. First LDEF Post-Retrieval Synqmsium.
NASA CP-3134, 1991, pp. 213-224.
11. Armstrong, T. W. and Colborn, B. L.: Prediction of LDEF Induced Radi_mctivity and Ccml-
parison with Measurements. Third LDEF Post-Retrieval Symposium, NASA CP-3275,
1995.
12. Colborn; B. L. and Armstrong; T. W.: Development and Al_plication of a 3-D
Geometry/Mass Model for LDEF Satellite Ionizing Radiation1 Assessments. Second LDEF
Post-Iletrieval Symposium, NASA CP-3194, 1992, pp. 195-206.
13. Harmon, B. A.; Fishman, G. J.: Parnell, T. A.; and Laird, C. E.: Induced Radioactivity in
LDEF Components. First LDEF Post-Retrieval Symposium, NASA CP-3134, 1991, 1)p. 301-
312.
14. Harmon, B. A.; Fishman, G. J.; Parnell; T. A. and Laird; C. E.: Induced Activati_m Study
of LDEF. Second LDEF Post-Retrieval Symposium, NASA CP-3194, 1992, pp. 125-136.
15. Benton, E. V.; Csige, I.; Odin K.; Henke, I/. P.; Frank, A. L.; Benton, E. I1.; Frig_, L. A.:
Parnell, T. A.; Watts, J. W. Jr.; and Derrickson. J. H.: LET Spectra Measurements ,)f
Charged Particles in the P0006 Experiment of LDEF. Second LDEF Post- Retrieval Sympc_-
sium, NASA CP-3194, 1993.
16. Arnlstrong, T. W. and Colborn, B. L.: Prediction of LET Spectra Measured on LDEF.
Thir(l LDEF Post-Iletrieval Symposium, NASA CP-3275, 1995.
17. Adams, J. H. Jr.: Cosmic Ray Effects on Microelectronics, Part IV, Naval Research Lal_()ra-
tory NRL Memorandunl Report 5901, December 1986.
18. Tylka. A. J.; Adams, J. H.; Beahm, L. P.; Boberg, P. R. and KMs, T.: Results from the
HIIS Experiment on the Ionic Charge State of Solar Energetic Particles. Thir(l LDEF
Post-Retrieval Symposium, NASA CP-3275, 1995.
tion. )
19. Space Station Ionizing Radiation Emission and Susceptibility for Ionizing Radiation Envi-
romnent Compatibility. SSP 30512, National Aeronautics and Space Administrati(m, 1991.
221
I Unique Features
of
LDEF Mission
• Well-
instrumented
for
ionizing
radiation
measurements
• Long
mission
duration
• Fixed
orientation
(< 0.2"",t,o0ble
Importance to
Ionizing Radiation
Data Collection
• Extensive radiation dosimetry:
6 different types of dosimetry
mu/tip/e dosimeters of each type
(= 200 TLD's, > 500 PNDT's,
> 400 activation samples)
- multiple dosimetry locations (in
16 different experimental trays)
• High statistical accuracy of
dosimelry results
• Allows measurement of
trapped proton anisotropy
Importance to
Model/Coda Validation
• Data sufficiently extensive and
detailed to allow variety of
rnoclelincjchecks - e.g:
- aOsorbed dose
- proton and heavy ton fluence
- energy spectra
- LET spectra
. secondary neutron fluence
and spectra
• Unprecedented data accuracy
Ior checking model predictions
of high-LET radiation from
high-Z cosmic rays and nuclear
recoi_
• Unprecedented data for testing
models of trapped proton
anisotropy
Importance to
Future LEO Missions
• Allows benchmarking and
imwovements of predictive
methods for addressing
ionizing radiation issues:
dose to astronauts
electronics upsegburnout
- male,;ai_ dam_oe
- radiations backgrounds ;u
sensitive instrumentatpon
• High-LET radiation component is
of key importance in assessing
"single-hit" phenomena:
- biokxjcal effects
Sing/e-Event-Upsets
of electronics
• Trapped prolon anisotropy
important for LEO, fixed-orientation
spacecrait (such as Space Slation
Freedom, EOS)
Figure 1. Significance of LDEF data for validation of ionizing radiation models from (ref. 1).
Figure 2.
.-__ ........................... _.=F.x_m_ F.nm _ .....................................
LOEFMM_GeometryMo0al [ Trl_pWPmlBm TrmpN_ GalaclePm_= [ _=
• 1-O MOdg Lied lot Initial EsammlN AI_ F_X Model AEII Flux MOdW NRL CREME Flu= Model
• _-0 MoOa unoer Oevmo_nent lot ; i
Trans0otl Code I_ Pv0tonl Cooe for NeOllron an0 Ahead Code for I I-D Pro[_ an0 H_ Ion :
S_ P_ Gamm,='¢-Ray Traflslpofl Protons [Elecvc : _,cl Fw,_-_ I Trsn¢,Ooct ] [
:: =:-,:-..-----..-.--------.-:-:e ........................................................:
• -- S_ (N' Co V T. In) [ Compatts_t..Fiss_onFol, ] [ _-- ] [ ComD.if, on.6_ I• $4_¢11d LDEF Sl_cture SamDl_ • e g,: and Se_cted IsoloQe Mealt_emenll PNTO Mllluremen= TLD k4_m,_m_
T_, Tray CJalr_l
Eva_u._e Accuracy of Model= & Predictive Metho¢ls
Prov_e Radiation Environmont$ to Aid LDEF Data AnaJys*s
Deletmine Im_lcations for Future Mluions
...................................... ... ................................ J
Overview of approach and models for LDEF ionizing radiation calculations from (ref.
1).
222
Figure 3.
(D
='-_ 1.2-
t_
Q_
1
(D
.__ 08
O6-
n" 0.4
0
a 0.2-
o
o
Exp. MO004, Tray F8; Frank, et al. measurements
Exp. P0004, Tray F2; Frank, et al. measurements
----e---- Exp. P0006, Tray F2; Frank, et al. measurements
---er---- Exp. A0015, Tray G2; Frank, et al. measurements
Exp. A0015, Tray G2; Reitz measurements
Exp. A0015, Tray C2; Reitz measurements
,I,l,l,l,''''''t'''''l'l'l'l'l'l, , , , , ,
2 4 6 8 10 12 14 16
Shielding (g/cm 2)
Ration of predicted-to.measured radiation dose (in tissue)due to trapped proton envi-
ronment based on LDEF data from thermoluminescent dosimeters from (ref. 7).
Figure 4.
(D
o3
v
<D
O
a
c-
O
U'}
u_
W
a
-J
800 --,
,
700 . ----a--- Measured, P0004 (Frank et al.)
__, ---o-- Measured, P0006 (Frank et al.)...... Pre-Recovery Predictions (Watts)"
600 _ ----e-- Present Calc., Exp. PO004
_... _ Present Calc., Exp. PO006
500 i __
400 -_
3 0 0 - ] Measured
"=o....
200
"',.._ , -_ Catcuated. "....Sphere .... -
"" ..... _1 3-0 Geometry, Pre-Hecovery
1O0 ......... d Anisotropy Predictions,
....................... Plane Ommdirect_onal
o ,',,',,I,','l'l",'l'l't",",'I",':",'l",", ',",'t'l :'I
0 3 6 9 12 15 18 21 24
Shielding (g/cm 2)
Influence of geometry model and environment anisotrophy on predicting LDEF dose
from trapped protons from (ref. 7).
223
O"O
LM
C
.m
O
._1
O
o')
LLI
¢-
I.-
i5
,w
n-
o
O
E3
.0--
,5 -!
r
L
2.0-'
T
1.5- !
r il
\
Measured,
1.0 _ M0003,
Tray D3/
Tray D9
0.50 .... t
i
0 1
I--..°
"°--.°°..
"'''0
Data Sources:
Exit. PO004.P0006,M0004: Frank et al.
Exp. A0015: Reltz
Exp. MO003: Blake and Imam•to
Exp. A0138o7: B0urneau
Measured, P0004(Tray F2)/M0004(Tray F8)
Measured, P0006(Tray F2)/M0004(Tray F8)
,&-o°..
-°...
-°.
Et
\
Measured,
A0138-7(Tray B3),extrapolated/M0004(Tray F8)
Measured, A0015(Tray C2)/M0004(Tray F8)
Predicted, P0004 (Tray F2)/M0004 (Tray F8)
Predicted, P0006(Tray F2)/M0004(Tray FS)
t .... t .... t .... .... t
2 3 4 5 6
Shielding (g/cm 2)
Figure 5. Radiation dose anisotrophy on LDEF due to the directionality of the trapped proton
environment. Shown are predicted and measured values of the ratio for the dose on the
trailing (west) side LDEF to the dose on leading (east) side from (ref. 7).
A
o
_0
co
&
23
v
o
o9
o
a
o
U_
U.I
a
_ L
1 0 2
10 2
105-=.
.7] Exp. MOO03 (Blake and Imam•to)
x
t- •-i Exp. A0138-7 _ou,"e3u_
_ _ ---I-l-- electrons- PlaneSh,eld.
- _ _ -- i Pre-Recovery
A _ _ ----- prolons i Predation s
10a
....... i 'i
10 "1 100
Shielding (g/cm 2)
Figure 6. Compazison of measured and predicted absorbed dose for thermoluminescent dosimeters
having thin shielding where the dose is due to the trapped electron enviromTaent from
(ref. 7).
224
22Ha Activation of LDEF Aluminum Tray Clamps
8-i-
O)
O "1"
6 7(1)
rr" T
a ' 5
-a-_ 5
(1' t- . °
from Harmon (NASA/MSFC)
Initial Scoplng Calculations:
Single AlituOe (450 knl), _ (:3e0_
E o 4 "-_-+
._ ._ 3-D Geomalry Model
'_I_ <1-- D PreOicled: Hollow-Cykn0er
<:: 2 E PreOictea: 3-D Geometry, incldom
Flux lrom Exle_or Only
Z
'T
East North West South Easl
0 L , ,
(7 45 ° 90 ° 135" 180 ° 225 ° 270 ° 315° 360°
Angle from LDEF Leading Edge (Easl)
Figure 7. Preliminary comparison of predicted vs. measured effect (ref. 13, 14) of trapped proton
anisotrophy in terms of 22Na radioactivity induced in aluminum damps of LDEF exper-
iment trays from (ref. 11).
LET Spectra - Exp. P0006
...J
t, 10 _-[-
% 1C -r-
E
C-..- 1 U -"
IC _ :
L.--
-_ 10_
E 10
104' -_
1 042 "
10'
LET Measured in CR-39
al deDII1 of 6,5 Q/on "2 T
m Main Demctor'Slack
T
lO' I ......... i
1 0 ¢ _ . Predicted
.q _._ - _. incIudmo 3-D ShlelO_ng fOr
_ _-' -1P. /" LDEF ,_acecraft and" Deleclo_
;' _ "-.. _" • nuclear teco.s nogle¢lo£1
,_ Io-_ ......... T
1 0 :" -_- """'"'. Measured (Benlon el al, USF)
', q
"It-
""'"'.... T
T
1 0_ 1O: 10" 1 0 s
LET [MeVltg/cm')]
Figure 8. Comparison of LDEF predictions of Linear Energy Transfer (LET) spectra and interim
results from measured spectra in experiment P0006(ref. 15). The predictions were made
using the CREME code(ref. 17) and a 3-D shielding geometry from (ref.16) .
225
10 -5 _
10 -6
10 -7
I
X
c
o
u
o
e) e)
I I -8
,.. 10
C u')
0 I
I
LDEF
"E i ,',K,.,
_ I0-9 o Siegen
10 -I°
10
from Adams, et al. (NRL)
! I ! I _ I I
Fe
l l I I I I I I
I 1 I_L
50 100 500 1000
Kinetic Energy (MeV/nucleon)
Figure 9. Measured low energy Fe spectra measured by HIIS experiment on LDEF from (ref. 18).
lO,_ 
105_
"" 103
"T
"O
E 101
to
X
10-I
I.L,..
m 10 .3
e-
10 "s
10 -7
10 .3
_ ss_c_=,,,,,- F_-.t_,_ ._
/ _tmm Be*rigUsed
_ CREM_.x_ t
10 .2 10 "1 10 ° 101 102 103
LET (MeV cm2tmg)
Figure 10. Comparison of Space Station Freedom Requirement document SSP 30512 (ref.
tra vs. LET and measured results from the HIIS experiment on LDEF from
(ref. 16).
19) spec-
226


Status of LDEF radiation modeling

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