scoping estimates of the ldef satellite induced radioactivity · 2013-08-30 · a : m k = e scoping...

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Scoping Estimates

of the

LDEF Satellite Induced Radioactivity

Scietce Al_ications International _tion

An Employee-Owned Company

by

T. W. ArmstrongB. L. Colborn

Report No.SAIC-90/1462

INu

r

Work Performed for

NASA Marshall Space Flight CenterSpace Science Laboratory, Astrophysics Division

Huntsville, AL.

Contract No. NAS8 - 38427

September 1990

Route 2, Prospect, Tennessee 38477

https://ntrs.nasa.gov/search.jsp?R=19910006743 2020-04-28T22:21:24+00:00Z

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Table of Contents

1. Introduction ........................................................................................ 1

2. Calculational Method .............................................................................. 6

3. Results of Transport Calculations ............................................................... 12

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4. Approximate Estimate of Activation Anisotropyand Comparison with LDEF Data ............................................................... 18

5. References .......................................................................................... 22

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Appendix A

Appendix B

Appendix C

Appendix D

Appendix E

Appendix F

Sources of LDEF Ionizing Radiation Exposure

Dose Response Functions

Activation Cross Sections

Additional Fluence Results

Additional Dose Results

Results for Radioisotope Production from Stainless Steel

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1. Introduction

The Long Duration Exposure Facility (LDEF) satellite was recovered in January 1990 after

almost six years in space. LDEF was well-instrumented with ionizing radiation

dosimeters, including thermoluminescent dosimeters (TLD's), plastic nuclear track

detectors (PNTD's), and a variety of metal foil samples for measuring nuclear activation

products, l In addition, the induced radioactivity produced in various spacecraft

components provides information on the radiation exposure. 2 Analysis of these LDEF

data by several groups is in progress under coordination of the LDEF Ionizing Radiation

Special Investigation Group:

The extensive LDEF radiation measurements (Fig. 1) provide the type of radiation

environments and effects data needed to evaluate and help resolve uncertainties in present

ionizing radiation models and calculational methods (Fig. 2). The LDEF data are

particularly important to improving models for addressing radiation issues associated with

Space Station Freedom since LDEF had the same altitude range (_. 350 - 500) and orbit

inclination (28.5 °) as planned for the Space Station. In conjunction with the LDEF data

analysis, a calculational program has been established at the NASA MSFC to provide

calculational support to aid in LDEF data interpretation and to utilize LDEF data for

assessing the accuracy of current models. A summary of the calcuiational approach is

given in Fig. 3. The present report describes some initial results from this LDEF

calculational study.

The purpose of the calculations reported here is to provide some initial results to aid in the

LDEF data interpretation -- namely, to obtain a general indication of: (a) the importance of

different space radiation sources (trapped protons, galactic protons, albedo protons, and

albedo neutrons), (b) the importance of secondary particles, and (c) the spatial dependence

of the radiation environments and effects expected within the spacecraft. These are only

seoping estimates because several important approximations have been made in this initial

work -- e.g., a one-dimensional (aluminum slab) model of the LDEF spacecraft is used,

and the angular variation of the incident radiation (particularly the trapped proton

anisotropy) is not accurately simulated. Subsequent calculations are planned which will

remove these approximations.

The calculational method (described in Sec. 2) uses the High Energy Transport Code

(HETC) 4 to estimate the importance of different sources and secondary particles in terms

Fig. 1. Ionizing radiation measurements aboard the LDEF satellite.

Radiation Quantity Dosimeters Employed

Total Absorbed Dose

Dose in MicroscopicVolumes

LET Spectra

Neutron Fluence & Spectra

Heavy Ion Fluence & Spectra

Proton l_uence & Spectra

Trapped Proton Direcfiona/ity

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TLD's(a)

Microspheres

PNTDCO)

Fission Foils, Activation( c)

PNTD

PNTD, Activation(c)

TLD's, Activation(c)

(a)

Co)

(c)

Thermoluminescent Dosimeters

Passive Nuclear Track _t___rs _

ActiV_onma_eriaisinclude specific me'samples for activation meas_ements (e.g,

Ni, Co, V, Ta) and selected spacecraft components (e.g., Al structure, stainless steeltrunions)

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of fluence, absorbed dose in tissue and silicon, and induced radioactivity as a function of

depth in aluminum. Radioisotope production from aluminum and stainless steel is

computed for varying aluminum shielding thicknesses. Results from these transport

calculations are given in Sec. 3.

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As indicated earlier in Fig. 2, the LDEF spacecraft had a fixed orientation, which allows

measurement of the trapped proton anisotropy in the South Atlantic Anomaly region

because the anisotropy is not "averaged out" by spacecraft motion as is usually the case. A

model describing this anisotropy has been developed recently by Watts, et al. at MSFC. 5

LDEF data should enable a definitive test of the model, and detailed transport calculations

using a 3-D spacecraft model and anisotropic trapped proton spectra are planned to compare

with the LDEF data. However, the induced radioactivity very near the spacecraft surface

should be relatively insensitive to spacecraft geometry, and some approximate 1-D

calculations have been made of the anisotropy of near-surface activation and comparisons

made with preliminary LDEF data. These preliminary anisotropy comparisons are given in

See. 4.

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2. Caiculationai Method

Radiation transport calculations have been performed to obtain Scoping estimates of the

depth dependence of fluence, dose, and induced radioactivity produced in the LDEF

spacecraft due to ionizing radiation exposure.

The radiation sources considered are trapped (Van Allen belt) protons, galactic protons, and

"albedo" neutrons and protons emanating from the earth's atmosphere due to cosmic ray

bombardment. The source spectra used as input for the transport calculations are shown in

Fig. 4, and the procedure used in estimating these spectra is described in Appendix A.

(The trapped electron spectrum is shown in Fig. 4 for comparison only. Since the trapped

electrons axe of low energy and produce effects very near the spacecraft surface, they are

not considered in the transport calculations here.)

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Spectra for the different sources were assumed incident isotropically on one side of a slab

of aluminum 100 g/cm 2 in thickness. This is, of course, an important approximation, not

only because it neglects the 3-D shielding effects of the spacecraft but also because the

actual angular distribution of the incident radiation is very different for the different

sources, as illustrated in Fig. 5.

The transport calculations were carried out using the SAIC version 6 of the HETC code. 4

This code uses Monte Carlo methods to obtain a detailed simulation of the radiation

transport (Fig. 6). At each nuclear collision during the transport process, a calculation of

particle transport inside the nucleus is performed using a high-energy intranuclear-cascade-

evaporation (ICE) model 7 to obtain the multiplicity, direction, and energy of all secondary

particles (Fig. 7). For low-energy neutron (< 20 MeV) transport the high-energy ICE

model is not applicable, but various experimental data libraries and transport codes are

available in this low-energy region. For the calculations here, the low energy neutron

source computed by HETC is coupled to the MORSE Monte Carlo s code for low-energy

neutron transport (Fig. 8).

The main output obtained from the transport calculations is depth-dependent fluence

spectra. These spectra are folded with the response functions given in Appendix B to

estimate the absorbed dose in tissue and silicon as a function of aluminum shielding

thickness. While HETC provides radionuclide production directly as a natural outcome of

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Trapped Protons

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DIFFERENTIAL Spectra

(Cummulative over LDEF Mission)"I

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INTEGRAL Spectra

--- _Protons (Cummulative over LDEF Mission) -

Galactic Protons

Albedo Neutrons ', \ Albedo Protons

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Fig. 4. LDEF exposure to ionizing radiation. Shown are cummulafive, orbit-average differential and

integr_ fiuence spec_a over _e 5.8 yr. duration of file LDEF nfission.

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(conehalf-angle= 110° at 450 kin.)

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Atmospheric Neutrons

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Fig. 5. Illustration of the nonuniform angular variation of LDEF exposure to ionizing radiation. Trappedproton exposure occurs in the South Adantic Anomaly region where the flux is highly anisotropic at LDEFaltitudes, with protons confined mainly in planes perpendicular to magnetic field lines and with in-plane

asymmetry due to the East-West effect. Galactic protons are blocked out from below by the shielding effect ofthe earth. The angular distribution of albedo neutrons emanating from the earth's atmosphere is also

geometrically constrained clue to earth shielding.

Input

I Nuclear Data Files

* partlcle-partlcle crosssections [ n-p, p-p, etc. )

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Target ConflguraUon ]• geometry (1-D. 2-D. 3-D]* materials (arbitrary)

Sour_ Description

partlcle.type.: _ distribution

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Overview of the High Energy Transport Code (HETC).

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code for computing secondary particles from high-energy Cspalladon") nuclear collisions.

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the ICE model calculation, the statistical accuracy is generally poor when the product

nucleus mass is far removed from the target nuclear mass. Since large target-product mass

differences are of interest in the present problem (e.g., 7Be from Fe in stainless steel), we

have used an alternate procedure in which the I-IETC (and MORSE) computed fluence

spectra are folded with available activation cross sections to estimate radionuclide

production. Radioisotope production from aluminum and stainless steel were calculated

using the cross sections given in Appendix C.

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3. Results of Transport Calculations

Results from the transport calculations are arranged to show the contributions of different

radiation sources and the contribution of secondary particles in terms of various effects. A

summary of the results are given in this section, with additional results given in

Appendixes D-F. The table below is a guide to the location of various results in the report.

Fluence Tissue Silicon Aluminum S. SteelFluence _ Dose Do_ _ Activation

• Radiation SourceContribution Fig. 9 App. D Fig. 10 Fig. 10 Fig. 11 App. F

• Secondary ParticleContribution App. D App. D App. E -- Fig. 12 App. F

The spatial dependence of the results are in terms of the areal density depth in aluminum

from 0 to 100 g/cm 2. To roughly relate these thicknesses to LDEF, the spacecraft diameter

is 32 g/cm 2, and the length is 68 g/cm 2. (This is based on an average density obtained

from the overall dimensions of 14 ft. diameter x 30 ft. long, a spacecraft structure weight

of 8,000 lb., and a weight of 13,400 lb. for the experimentsl.)

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Figure 9 compares the proton and neutron fluences (over all energies) for all sources. For

the trapped proton environment, the fluence from secondary neutrons exceed the proton

fluence for penetration depths _> 10 g/cm 2. The magnitude, and spatial dependence, of

secondary neutrons from galactic protons is comparable to the secondary neutrons from

trapped protons.

Dose

Figure 10 compares the importance of different sources in terms of the absorbed dose in

tissue and in silicon. The trapped proton source dominates for penetration depths <_5 0

g/cm 2. The albedo sources contribute at most a few percent. Additional results for

secondary particle contributions to the absorbed dose are given in Appendix E.

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Depth in Aluminum (g / cm2 )

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Ga/actic Proton Source:

Per Cent Contribution by Source

Absorbed Dose in Tissue.... Absorbed Dose in Silicon

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0 20 40 60 BO 100

Depth in Alumlnun, ( g / cm 2 )

Fig. I0. Impocumce of various radiation sources in terms of absorbed dose in _sue and silicon forthe total dose over the duration of the LDEF mission (top graph) and as a per cent of the total dose at

each depth from all sources (bottom graph).

14

Activation

Figure 11 compares the contribution of different sources to _Na and to 7Be production

from aluminum. The galactic source contribution exceeds the trapped source contribution

for depths _ 50 g/cm 2 for 22Na production and > 25 g/cm 2 for 7Be production. The

relative importance of the galactic source, which has a harder spectrum, is expected to be

higher for the higher threshold activation products, which is consistent with these 7Be

vs. _Na results. Figure 12 shows that for the trapped proton source and the case of 22Na

production the secondary neutron contribution becomes important at depths _ 30 g/cm 2 .

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Results from calculations of radioisotope production in stainless steel are given in

Appendix F.

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- _ Al_o Proton Source

103 _ J _ I , I .... _ I J I J I , I _ I a I ,0 20 40 60 80 100

Depth in Aluminum (g / cm 2)

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A/bedo Proton Source

0 20 40 60 80 100

Depth it1Alumi_rn _ g / _ 2

Fig. 11. Importance of different sources in terms of 22Na and 7Be production from aluminum.

The production is normalized for the total lifetime of the LDEF mission.

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Depth in Aluminum (g / cm 2 )

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secondary neutrons

Fig. 12. Contribution of secondary particles in producing 22Na from aluminum by incident

trapped protons; top graph for production over LDEF mission, bottom graph as percentage oftotal production from primary and-secondary particles by tra_ pr0tons.

17

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o Approximate Estimate of Activation Anisotropy

and Comparison with LDEF Data

We consider here the directional dependence of induced radioactivity near the LDEF

spacecraft surface due to anisotropy of the trapped proton exposure.

The results for 22Na production from aluminum shown previously (Figs. 11 and 12)

based on a 1-D geometry (with irradiation from one side) indicate that the dominate

production mode near the surface is from primary gapped protons. While for the actual

spacecraft geometry there may be some contribution from radiation entering the "opposite

side", we neglect this contribution for now and assume a 1-D geometry model of

effectively infinite thickness.

We have used anisotropic trapped proton spectra based on the Watts, et al. 5 model (Fig.

13) and modified the 1-D MSFC straight-ahead proton transport code of Burrell Il to

compute activation products (using the activation cross sections of Appendix C) and to

estimate the anisotropy of 22Na production at small depths in aluminum. The results

(Fig. 14) show a West/East anisotropy ratio for 22Na production that varies from about

a factor of 2 near the surface to a factor of 3.5 at 10 g/cm 2 depth.

These results are compared in Fig. 15 with recent preliminary measurements by Harmon, et

al. 1° for the 22Na activation of LDEF aluminum clamp plates. (These plates are

relatively thin, 1.29 g/cm 2, and located on the surface of the spacecraft.) Based on an

approximate fit we have made to the data points (Fig. 15), the measured West/East

anisotropy is 1.8 compared to a calculated ratio of 2.0. In comparing absolute

magnitudes, the calculations are higher than the measurements by about 30% for directions

in the vicinity of East, and higher by about 50% for directions in the vicinity of West.

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Anlaotropy of Trapped Proton Spectra

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Spectrum Looking West

Spectrum Looking East

10 -6 _ ' ' ' .... 1

101 102 103

Proton Energy (MeV)

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Fig. 13. (Top) Predicted anisotropy of trapped proton flux > 100 MeV , from Re£ 9, using theanisotopy model of Watts, et al 5 (Bottom) Trapped proton spectra in a differential solid anglelooking West and looking East and the West/East ratio of the two spectra. Both graphs for orbit-average spectra (283 ° inclination, 450 kan.altitude, solar minimum).

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Predicted Directionality of 22Na Production in Aluminum Due to Trapped Proton Anisotropy

Orbit Parameters:

• 450 kin., circular• 28.5 ° inclination

• solar minimum

• 5.8 yr. mission

4._; _ : I I I

EastL I

0 = 45 •

0.01

North West SouthI I I I I I

90 ° 135 ° 180 ° 225 o 270 ° 315 °

Angle from East

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4.0 - Magnitude of Predicted 22Na Activation DirectionalityBased on 1- D LDEF Spacecraft Model

3.5C

._ 3.0b

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2.0

1.5 [ i I , [ = I i I i . I i I . I , 1 . I

1 2 3 4 5 6 7 8 9 10

Dep_ in Aluminum (g / cr_

Fig. 14. Approximate calculation of 22Na acfivadon of aluminum from LDEF exposure to trapped protons in the

South Atlantic Anomaly using a I-D spacecraft model. The anisotropy of the trapped proton spectra ts taken into

account using the model of Watts. et alS. The top graph shows the depth dependence of the activation as a function

of angle in the horizona] plane (90 ° from zenith) perpendicular to the spacecraft axis. The bottom graph shows the

predicted increase in directionality with depth in terms of the activation on the West vs. East side of the spacecraft.

20

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22Na Activation of LDEF Aluminum clamp Plates

8 / ' ' I ' ' I , , i , , 1 , , i , , I " ' I ' '

• Measured (Preliminary);Harmon, et al., MSFCApprox. CalculationUsing MSFC Anisotropy Model of Watts, et al. i

_, 7 (1-D LDEF Geometry Model, 0.64 g/cm 2 Depth, 450 km.)

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East North West South East iI , = I = , I , , I l , I = J I I l I , i I i , I

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Angle from LDEF Leading Edge (East) i

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Fig. 15. Comparison of approximate calculations for 22Na activation of LDEF aluminum Clamp plates (used on outer

surface of spacecraft to secure experimental trays) with the preliminary measurements of Harmon, et al.10 The

calculated activation is at the mid-depth (0.64 g/cm 2) of the clamp and based on a : -D model of the spacecraft. The

measured anisotropy (activation on West vs. East side of spacecraft) based on the aproximate data fit shown is 1.8;the calculated anisotropy at this depth is 2.0.

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5. References

Lenwood G. Clark, William H. Kinard, David J. Carter, Jr., and James L. Jones,

Jr., "The Long Duration Exposure Facility (LDEF), Mission 1 Experiments", NASA

SP-473, 1984.

G. J. Fishman, T. A. Parnell, and B. A. Harmon,,_'Long Duration Exposure Facility(LDEF) - Induced Radioactivity Analysis Plan , Proc. LDEF Ionizing Radiation

Special Investigation Group Meeting, NASA Marshall Space Flight Center,December 1989.

T. A. Parnell, "Overview of LDEF Ionizing Radiation SIG", Proc. LDEF Ionizing

Radiation Special Group Meeting, NASA Marshall Space Flight Center, December1989.

T. W. Armstrong and K. C. Chandler, "The High-Energy Transport Code HETC",

Nucl. Sci. Engr. 49, 110 (1972).

J. W. Watts, T. A. Parnell, and H. H. Heckman, "Approximate Angular Distribution

and Spectra for Geomagnetically Trapped Protons in Low-Earth Orbit"; SanibelIsland, FL 1987 Conf.: "High-Energy Radiation Backgrounds in Space", A. C.Rester, Jr., and J. I. Trombka (Eds.), AIP Conf. Proc. 186, Am. Inst. Phys., New

York, 1989.

T. W. Armstrong and B. L. Colborn, "A Thick-Target Radiation Transport Code forLow Mass Heavy Ion Beams, HETC/LHI", Nucl. Instr. Meth. 169, 161 (1980).

T. W. Armstrong, "The Intranuclear-Cascade-Evaporation Model", Chapter 20 inComputer Techniques in Radiation Transport and Dosimetry, Walter R. Nelson andTheodore M. Jenkins (Eds.), Plenum Press, New York, 1980.

E. A. Straker, P. N. Stevens, D. C. Irving, and V. R. Cain, "The MORSE Code - A

Multigroup Neutron and Gamma-Ray Monte Carlo Transport Code", ORNL-4585,

September, 1970.

T. W. Armstrong, B. L. Colborn, and J. W. Watts, "Trapped Proton Anisotropy",Minutes of SSF Ionizing Radiation Working Group Meeting, NASA Marshall Space

Flight Center, May 1-3, 1990.

B. A. Harmon, G. J. Fishman, and T. A. Parnell, "LDEF Induced Radioactivity

Analysis", Proc. LDEF Ionizing Radiation Special Investigation Group Meeting,

NASA Marshall Space Flight Center, July 1990.

Martin O. Burrell, "The Calculation of Proton Penetration and Dose Rates", NASA

TM X-53063, August 1964.

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Appendix A

Sources of LDEF Ionizing Radiation Exposure

uTrapped Protons (Omnidirectional)

The omnidirectional trapped proton spectrum calculated by Watts t was used as the trapped

proton source for the HETC transport calculations. These spectra are based on the

AP8MIN and AP8MAX trapped proton environment models 2 and the IGRF 1965.0 80-

term magnetic field model projected to 1964, the epoch of the proton models. The

cumulative flux over the duration of the LDEF mission was estimated by Watts by

performing orbit average calculations (28.5 ° inclination, circular) at altitudes of 258.5,

255.0, 249.9, 230.0, and 172 nautical miles, which took place on mission days 0, 550,

1450, 1950, and 2105. A linear variation is assumed between time points. At altitudes of

230 and 170 nautical miles, the solar maximum model (AP8MAX) was used, with the solar

minimum model (AP8MIN) usedfor other altitudes.

The resulting omnidirectional, altitude-average differential and integral cumulative trapped

proton flux spectra over the duration of the LDEF mission are shown in Fig. A- 1. For the

one-dimensional transport calculation, one-half of this fluence was assumed to be incident

isotropically on one side of the slab of material. While isotropy is a reasonable

compromise for use in a one-dimensional approximation, the actual angular distribution is,

as shown in the Sec. 4, highly anisotropic.

Trapped Electrons

The trapped electrons are of such low energy that they contribute significantly to the dose

only at small penetration depths (< 0.5 g/cm 2) (Ref. 1) and do not contribute at all to

radionuclide production. Thus, transport calculations for trapped electrons have not been

made here, but the trapped electron spectra are given in Fig. A-2 for comparison with

trapped protons. These trapped electron spectra were computed by Watts I using the

AE8MIN and AE8MAX trapped electron environment models 3'4 and the same mission-

averaged method as for the trapped protons given above.

A-1

Galactic Protons

For the galactic proton spectrum we start with the analytic fit given by Adams, et al. 5 for

the exomagnetospheric, time-dependent spectrum, which at solar minimum and solar

maximum reduces to ............... _:

F(E) = 10 m (E/117500) a

where m = 6.52 exp{- 0.8 (logl0E) 2} - 4.0

a = -2.2{ 1 - exp [-b (logl0E) 2"75])

b = 0.1 !7 at solar minimum and b = 0.079 at solar maximum. Here F has units of protons

m'2 steradian" 1 MeV x and E is in MeV. This fit to the galactic Spectrum (multiplied by

4x steradians, converted to cm "2, and multiplied by the LDEF mission duration of 2114

days) is shown as the "exomagnetosphere" spectrum in Fig. A-3. "

I

tim

Ill

mmtim

mm

,7

To take into account the effect of geomagnetic shielding at the LDEF orbit, we have used

the geomagnetic field "transmittance fraction" given in Adams, et al.6 for 30 ° inclination at

400km altitude, which is based on the cosmic ray trajectory tracing calculations of Shea

and Smart for effective geomagnetic cutoffs over a world-wide, longitude-latitude grid at

400 km altitude and the orbit averaging method of Heinrich and Spill 7. This fraction of the

exoatmosphedcgalacticprotons transmitted through the geomagnetic field is sh6wn fia Fig.

A-4, and the result of applying this transmission factor to the exomagnetospheric spectrum

gives the curves labeled "LDEF orbit" in Fig. A-3.

Another factor influencing LDEF's exposure to galactic protons is the shielding effect of

the earth's "shadow". The solid angle occulation is

__ 2ST _ :

An=2x{1-[(Re+h) 2-Ri]It2/(Rea , e+h)}

where Re is the earth's radius (6371 km) and h is the orbit altitude. For an average LDEF

altitude of about 450 km, A D./4x = 0.32. Thus, 32% of the 4x solid angle is blocked by

the earth, and the incident proton directions are within + 110 ° about the zenith direction. In

the transport calculations, the incident galactic proton flux was assumed incident

isotropically over 5:90 ° about the target surface normal.

A-2

mz

II

m

I

2

===.

It

ZI

!

The galactic proton integral and differential energy spectra over the LDEF mission duration

are given in Fig. A-5.

Albedo Protons*

Secondary protons produced in the earth's atmosphere by cosmic rays can escape upward

as "splash albedo" and become trapped in the earth's magnetic field when the proton energy

is below the geomagnetic cutoff. These protons are guided by the field to impact with the

atmosphere in the hemisphere opposite to their formation, providing a "re-entrant" albedo.

The splash albedo spectrum has been measured by several balloon flights at different

latitudes. In particular, Wenzel, et al.s and Pennypacker, et al 9 measured the albedo

spectrum in the 4 MeV to 1 GeV energy range at about 4 g/cm 2 residual atmosphere over

Palestine, TX (42 ° N geomagnetic latitude, 4.5 GV geomagnetic cutoff). Measurements of

the proton albedo by the Cosmos-721 satellite (polar orbit, 210-240 km) have been

reported by Kuznetsov, et al.10 For a 4.5 GV cutoff they find a similar spectral shape as

for the balloon flights but a factor of 4 higher intensity, which Kuznetsov, et al. attribute as

possibly due to the dffferent angular distribution of albedo protons at satellite vs. balloon

altitudes.

For the splash albedo calculations in the present work we have used a fit to these satellite

and balloon measurements, with the magnitude of the balloon data increased by a factor of

4 and the reported measurements per steradian multiplied by 2Ir to obtain an

omnidirectional flux. These data and the fit used are shown in Fig. A-6, with the fit being

= 0.00113 exp (- 0.0095E), 10 < E < 115 MeV

= 0.79 E - 1.61 115 < E < 2000 MeV

where _ has units cm -2 s- 1 MeV - 1 This differential flux multiplied by the LDEF

mission duration, together with the corresponding integral fluence, is shown in Fig. A-7.

* We wish to thank J. Adams, Naval Research Laboratory, for providing background material on albedoproton measurements.

A-3

w

Neutron Albedo

Some of the neutrons produced in the earth's atmosphere by cosmic-ray

bombardment escape the top of the atmosphere to constitute a neutron albedo. Several

measurements and calculations of the neutron albedo near the top of the atmosphere have

been made -- e.g., Fig. A-8. The results of Fig. A-8 are for the upward moving flux at 45

km altitude, 42 ° N geomagnetic longitude, and solar minimum. We have fit the calculated

spectrum as:

_(E) = 0.047E" 2.88,i0 5 < E <0.1

= 0.40 exp (- 0.97E), ........... O:!:_:E <!:0 ..........

where _ has units cm'2 s" 1 MeV-1

- 0.15 E" 1.34 1.0 < E < 10

= 0.0086 exp(- 0.tN5E),+ 0.0021 exp(- 0.0085E), 10 _< E < 200

= 1.95 E 1.61 200 < E N 3000

arid E is in MeV.

The analytic fit of Fig. A-7 is scaled as follows to obtain an estimate of LDEF exposure to

albedo neutrons. The maximum geomagnetic latitude reached by the LDEF orbit is 2_n =

40 °, which is approximately the latitude corresponding to the spectrum of Fig. A-7. From

measurements of the i-10 MeV albedo flux dependence on magnetic latitude, the variation

of the albedo flux over LDEF orbits (ratio of flux at 7_m = 40 ° to flux at L m = 0 °) is about a

factor of 3, and the ratio of the maximum albedo flux to the 28" inclination orbit-average

flux is estimated to be a factor of -- 2. Thus, while a detailed orbit integration has not been

carried out to obtain the average LDEF exposure to albedo neutrons, the _'m - 42°

spectrum of Fig. A-7 is multiplied by 0.5 as an estimate of the orbit-average exposure. To

take into accouni aifitude differences, 1/r 2 scaling is assumed and the 45 km spectrum of

Fig. A-7 is multiplied by 0.88 to obtain the spectrum at 450 km, which is approximately

the average LDEF altitude. Finally, the flux of Fig. A-7 is multiplied by the LDEF on-orbit

time (2114 days) to obtain the albedo neutron fluence over the duration of the LDEF

mission. The product of these scale factors (8 x 107 ) times the analytic fit curve of Fig. A-

7 gives the estimate used for LDEF exposure to albedo neutrons (Fig. A-9).

I

mI

II

mI

m

m

|

Ill

mZ

I

Ill

II

I

m

I

mmI

m

Z

I

A-4 i

i

At altitudes of about 450 km the albedo neutron directions are restricted within a cone half-

angle of 70 ° about the zenith because the earth shields neutrons of other directions. Thus,

in the transport calculations only neutron directions within + 70 ° about the slab normal were

allowed.

=

m

Summary

Table A- 1 below summarizes the energy range and normalization for the different sources

used as input for the transport calculations. Also indicated is the angular distribution range

assumed in computing the source spectra per unit solid angle.

Table A-I. Source parameters used for transport calculations.

Source

Trapped Protons

Galactic Protons

Albedo Protons

Albedo Neutrons

MinimumIncident

Energy

15 MeV

3.2 GeV

15 MeV

1 keV

Maximum

Incident

Energy

600 MeV

100 GeV

3.5 GeV

3.0 GeV

Omnidirectional Integral

Ruence above E rr_

(crn" 2, over LDEF Mission)

4.3 X 10 9

2.8 x 10 7

2.3 x 10 7

7.4 x 10 7

Range ofAngular

Distribution

(steradians I

4_

2/¢

4/¢

1.3g

References for Appendix A

1. J.W. Watts, "LDEF Dose Predictions and Measurement", LDEF Ionizing Radiation Special Investigation

Group Meeting, NASA/MSFC, July 1990.

2. Donald M. Sawyer and James I. Vette, "AP-8 Trapped Proton Environment for Solar Maximum and Solar

Minimum", National Science Data Center, Goddard Space Flight Center, NSSDC/WDC-A-R&S 76-06,

1976.

3. Michale J. Teague and Iames I. Vette, "A Model of the Trapped Electron Population for Solar Minimum",

National Science Data Ceter, Goddard Space Flight Center, NSSDC 74-03, 1974.

4. Michael J. Teague, King W. Chart, and J. I. Vette, "AE6: A Model Environment of the Trapped Electrons forSolar Maximum", National Science Data Center, Goddard Space Flight Center, NSSDC/WDC-A-R&S 76-04,

1976.

5. L H. Adams, Jr., R. Silberberg, and C. H. Tsao, "Cosmic Ray Effects on Mieroelectronics, Part I: The Near

Earth Environment", N'RL Memorandum Report 4506, August 1981.

6. J.H. Adams, Jr., J. R. Letaw, and D. F. Smart, "Cosmic Ray Effects on Microelectronics, Part II: The

Geomagnetic Cutoff Effects", NRL Memorandum Report 5099, May 1983.

7. W. Heinrich and A. Spill, "Geomagnetic Shielding of Cosmic Rays for Different Satellite Orbits", J.

Geophys. Res. 84, 4401 (1979).

A-5

.

.

10.

11.

12.

13.

K. P. Wenzel, E. C. Stone, and R. E. Vogt, "Splash Albedo Protons Between 4 and 315 MeV at High andLow Geomagnetic Latitudes", J. Geophys. Res. 80, 3580 (1975).

C. R. Pennypacker, G. F. Smoot, A. Buffington, R A. Mu, H. Smith, "Measurement of Geomagnetic CutoffNear Palestine, Texas", J. Geophys. Res. 78, 1515 (1973).

S. N. Kuznetsov, Yu I. Logachev, S. P. Ryumin, and G. A. Trebuckhovskaya, "AIbedo of Galactic cosmicRays from the COSMOS-721 Data", MG-28, p.161.

T. W. Armstrong, K. C. Chandler, and J. Barish, "Calculations of Neutron Flux Spectra Induced in theEarth's Atmosphere by Ga/actic Cosmic Rays", I. Geophys. Res. 78, 2715 (1973).

A. M. Preszler, G. M. Simnett, and R. S. White, "Earth Albedo Neutrons from 10 to 100 MeV", Phys. Rev.Lett. 28, 982 (1972).

R. S. White, S. Moon, A. M. Preszler, and G. M. Simnett, "Earth Albedo and Solar Neutrons", Rept. IGPP-UCR-72-16, U.C. Riverside, 1972.

U

Ill

U

m

m

U

b

mU

i

u

im

g

z

m

U

m

m

I

A-6

i

m

mmm

U

1011i i , i ,ill] b = i _ _ i_ i , i i _ i i _, I i _ = p , i_

I Trapped Proton Spectra

Integral

i ......

10 5 ' ' 10 5

10 -1 10 0 101 10 2 103

Proton Energy (MeV)

Fig. A-1. LDEF exposure to uapped protons, averaged over LDEF altitudes and cummulative over the LDEF

mission duration, calculated by Wattsl using the APSMAX and APSMIN environment models.2 Shown

here are omnidirectional spectra; as discussed in the text, the trapped proton spectra at the LDEF altitude and

orbit inclination are actually highly anisotropic.

,. 1011

i

.,....

LL

==.u(:3

1014

1 0TM

1012

1 011

1010

lo9

lO8

lO7

lO610 -1

, i

Differential

Integral

Trapped Electron Spectra

10 0

Electron Energy (MeV)

1014

1013

10 TM 3"

1011

1010 "_

106101

Fig. A-2. LDEF exposure to trapped elecu'ons, averaged over LDEF altitudes and cummulative over the LDEF

mission duration, calculated by Watts 1 using the AE8MIN and AEMAX environment models.3,4

A-7

10 3 ......... I ........ I ' '

102

101

_'E I0°

_ I0 Iv

X

10 -2

3

10_3

10 -4

Outside Earth's

Magnetosphere

I _ ==¢ iii _ i i i i i,

Galactic Proton spectra

solermaximum

..... solarminimum

At .'_

10.5 .... ,,,,j. ..... ,,Jl ...... I j _ L., ,,,

101 102 103 104 105

Proton Energy (MeV)

Fig. A-3. Galactic proton spectra in interplanetary space (from Adams, et al.5) and at LDEF orbit

after attenuation by geomagnetic field.

m

i

i

i

I

i

i

m

1 , ' ' ..... I , t , , , , i

Geomagnetic Transmission0.9 (30 _, 400 kin.) 0.9

0.8 0.8

0.7 0.7

0.6 0.6

he 0.5 0.5

"6 0.4 _ 0.4

i 0.3 o.s

0.2 0.2

0.1 0.1

0 I i_"_, .... _ I I. I I I I , , , 0

10 3 10 4 105

Proton Energy (MeV)

Fig. A-4. Transmission factor for galactic proton penetration of geomagnetic fielcii averaged over 30 °

inclination, circular orbit at 400 Ion. altitude (adapted from Adams, et al. 6),

A-8

i

i!l

=

i

mzmm

m

m

!

i

=

m

m

i

m

i

i

=

1011

A

> 109:EI

tqE0

(/)t-

O 07

v

0t-

I1

105

a

103

101

%

i I I ] il,l i i i i I I Ill I

Integral,

Exomagnetosphere

%

\ ",,Differential, "

%

Exomagnetosphere "%

I I I ! IIII I I I I I I II

GalacticProton Spectra

Cummula_eoverLDEFMissionDuration

%

%_w _

/ • \

/iOi#orontial, ,

at LDEFOrbit _t

I

] I I [ll]lt t 1 J I IIIlt 1 I I ] I 11111 II

I

1011

109

107

o=

80

05 _0

3v

10a

I I I ] 1]1

lo1 lO2 lO3 lO4 lo5

101

E,Energy(MeV)

Fig. A-5. Cummuladve galactic proton spectra over the duratio, of the LDEF mission.

A-9

10 .2

10 _

i

O4

10 -4

X

n-10 5

10 -6

10 0

+ r I I I r +_1 t r 1 I I i II I * I ! I I I I , 1

Albedo Proton Data

• Cosmos 72i Measurements (Kuznetsov, et al.)

0 Balloon Measurements of Wenzel, et al. (x 4)[] Balloon Measurements of Pennypacker, et al. (x 4) \

-- Fit used here

I L I i t i i i I t i i • i IlL] I i i i i _ t I I

lo _ lo2 lo3Energy (MeV)

10 .2

I 0 -3

10 .4

10 -5

10-6

Fig. A-6. Measurements of the "splash" proton albedo specman at balloon '7, 8 and satellite 9 altitudes.

('The balloon data have been multiplied by a factor of four to get agreement with the magnitude of the

satellite data.) Also shown is a fit m the data used here as input for the Uansport calculations.

108

10 6

i 104

c_

102

• , , i i i + i i , i = _ _ i I , _ i _ , , = ,-

Albedo Proton SpectraCummulative over LDEF Mission Duration

Integral

Differenfial

I i i i i i i i [ i 1 t i i = I [ i i i i i i i i

101 102 103 104

Fig. A-7. Cummuladve albedo proton spectra over the duration of the LDEF mission.

10 8

lo 6 _--n

10 4 _

102

A-IO

I

l

zI

m

!

I

m

I

I

i

I

I

m

I

Ill

i

I

[][]

m

I

ZI

[]

mB

!

..j-- r-- PRESENT CALCULATIONS

• MEASURED UPWARD MovING

FLUX, PRESZLER, et <T/. (t972)• MEASURED UPWARD MOVING

CURRENT, WHITE, e/ oA (t972)

' i

J I

__L__

Fig. A-8. HETC code calculations of the neutron albedo spectra from cosmic-ray bombardment of the

earth's atmosphere. 11 Shown are flux (0) and current (J) spectra for the upward moving (21r) and

omnidirectional (4n) neutrons at 5 ,#cm 2 residual atmosphere, 42 ° N geomagnetic latitude, and solar

minimum conditions. Also shown are data from balloon flight measuremenL_ by Preszler, et al. 12 andby White, et al. 13.

A-11

W

1011

_" 10 9i

e-2

e-

8 10 7

U_

o_

._ I tlllU I

©\

.m

a

10 5

10 3 ' "'''''_

10 `5

I II,llll I i I lilill I i rilH_i I _ i _lli,i I r i1_Tiln i I i ,lhH I I I I_

Differential

0\

x

Q\

\

\

\

Integral

l ¢lJlilll I i llliliJ

10 -3

Aibedo Neutron SpectraCummulat_veover LDEF Mission Duration

Im

, _ ,Lm,l J ! ]iIiil[ | i illi|lJ [ i [l_il_ I I iIJilJl _ i i llml

%

1 0"1 101 1 03

Neutron Enemy {MeV)

1011

10 9 _

-13

3

lO70

o')

3

10 5

10 3

Fig. A-9. Cummuladv¢ neutron albedo spec_'a over the dura[lon of the LDEF mission. The points (open

circles) are from HETC code calculations of the differential spectrum at the top of the atmosphere (from Fig. A-

S), which have been renormal;zed for the LDEF orbit.

A-12

m

i

i

I

i

J

iR

iI

g

!B

m

g

B

i

m

m

I

mmm

J

m

u

m

m

mm

Dose

Appendix B

Response Functions

To estimate depth dependent doses the flux spectra at various depths from the transport

calculations were folded with dose response functions. The response functions used (Figs.

B-1 and B-2) are "surface doses" for protons or neutrons incident normally on a slab of

tissue or silicon.

For protons incident on tissue, the response function was estimated using the stopping

power approximation of Burrell I below 60 MeV and the transport calculation results of

Zerby and Kinney 2 in the range from 60 to 400 MeV, Alsmiller, et al. 3 from 400 MeV to

3 GeV, and Armstrong and Chandler 4 from 3 GeV to 100 GeV. For neutrons incident on

tissue, results from Irving, et al 5 were used below 60 MeV, from Alsmiller, et al 3

between 60 MeV and 3 GeV, and from Armstrong and Chandler 4 between 3 GeV and 100

GeV.

_mmr

For protons incident on silicon, the Burrell _ stopping power approximation was used

below 200 MeV with the HETC code kerma factor calculations of Zazula, et al. 6 used

above 200 MeV. The response to neutrons is based on the DLC-31 data library 7 below 20

MeV and the Zazula, et al. 6 calculations at higher energies.

References for Appendix B

1.

2.

3.

4.

5.

6.

.

Martin O. Burrell, "The Calculation of Proton Penetration and Dose Rates", NASA TM X-53063, August1964.

C. D. Zerby and W. E. Kinney, Nucl. Instru. Meth. 36, 125 (1965).

R. G. Alsmiller, Jr., T. W. Armstrong, and W. A. Coleman, "l'he Absorbed Dose and Dose Equivalent fromNeutrons in the Energy Range 60 to 3000 MeV and Protons in the Energy Range 400 MeV to 3000 MeV",Nuel. Sci. Engr., 42, 367 (1970).

T. W. Armstrong and K. C. Chandler, "Calculation of the Absorbed Dose and Dose Equivalent fromNeutrons and Protons in the Energy Range from 3.5 GeV to 1.0 TeV", Health Phys. 24, 277 (1973).

D. C. Irving, R. G. Alsmiller, Jr., and H. S. Moran, "l'issue Current-to-Dose Conversion Factors forNeutrons from 0.5 to 60 MeV", ORNL-4432, August 1967.

J. M. Zazula, P. Cloth, D. Filges, and G. Sterzenbach, "Secondary Particle Yield and Energy Release Datafrom Ia,.'ranuclear-Cascade-Evaporation Model Calculations of High Energy (20 - 1100 MeV) NeutronInteraction with Elements of Shielding and Biological Importance", Nuel. Instr. Melh. BI6, 506 (1986).

DLC-31, "37 Neutron, 21 Gamma Ray Coupled Multigroup Library", Radiation Shielding InformationCenter, r_ata Library Collection DLC-31/(DPL-1/q:EWG1), Oak Ridge National Laboratory, 1976.

B-1

10"5

10-6

E(3

(3•_ 10-7

10.8

0

10 -9

10 -1°

t0 -3

10 -5

0-7E I(3

cL

_. 10 9

o 10.11r',,

10 "13

10 .2

Protons

Neurons

10 -2 10 "1 10 0 101 10 2 10 3 10 4 10 5

Energy (MeV)

Fig. B-1. Flux-to-dose conversion factors used for absorbed dose in tissue.

10 6

| r I I I IH I I ! i iiitl_ 1 I i I Jill I i _ _ i$iii i #" i i ii$ii_ "-F T_ i 'i if ii

p

Silicon

I I l i ii]lJ I I i Zlllll I i i IIlll| 1 I llZlll| 1 I I I III1| i ] I I I IIIj l LI ']llJ

10 "1 10 0 101 10 2 10 3 10 4 10 5

Energy (MeV)

Fig. B-2. Flux-to-dose conversion factors used for absorbed dose in silicon.

B-2

W

i

I

m

U

m

I

I

I

g

I

J

88

mg

I

i

iai

I

mmm

88

|

Appendix C

Activation Cross Sections

Michel and co-workers (e.g., Ref. 1) have developed a set of activation cross sections for

neutrons and protons incident on various elements by using a combination of experimental

data, semi-empirical methods, and nuclear models. Predictions of the spatial dependence

of radioisotope production in thick composite targets using the Michel, et al. cross section

set folded with flux spectra calculated by the HETC transport code are in very good

agreement with experimental data for high-energy proton irradiations 2. Thus, in these

initial calculations we have used the Michel, et al. 2 activation cross sections shown in Figs.

C-1 through C-3.

References for Appendix C

1. R. Michel and R. Sti/ck, J. Geophys. Res. 89, B673, (1984).

° D. Aylmer, et al., "Monte Carlo Modelling and Comparison with Experiment of the Nuclide Production inThick Stony Targets Isotropically Irradiated with 600 MeV Protons", CERN SC96 Experiment,Kernforschungsanlage Julich GMBH, Report Jul-2130, May 1987.

C-1

10 2

E

E 101c._o

10 °

101

22 Na from AI

1"4

L__ _L I i I | I i J t t

10 2

Energy (MeV)

I u n | t |

101

,__ 10 0

EE0

10-1

i !

7Be from AI

101 103

I I I I L I t | I i L I t. [ I

10 2

Energy (MeV)

Fig. C-1. Cross sections for 22Na and 7Be woduction _om aluminum; solid ]hie by Immms, dash_

line by neurons.

C-2

i

roll

i

Ii

i

_-J

=__

i

i

I

m

i

i

Ill

lib

I

i

!1

III

w

w

lO2

E

,oE

v

o

looU)

2o

10 -1

103

A

102

E01c: 1

o

_ 10°2

0

I 0 "1

s7 Co from

|

O1

p i

Fe

i i , i t i _ I ! 1 i i i

10 2 10 3

Energy (MeV)

1C

101

E

._ 100

E

co

®_ 10 -1

0

10 "2

54 Mn from

ix

s

, i , I I.]___ L l , i , t I i I i

101 10 2

Energy (MeV)

I

7 Be from Fe

i 1 i i i I , , , , i , , ,I 02

Energy (MoV)

,.

10 3

0 3

Fig. C-2. Cross sections for 57Co, 54Mn and 7Be production from iron; solid line by protons,

dashed line by neutrons.

C-3

10 2

JE

_1o 1 -

100 -

101

: ' ' ' ' ''1 ' ' ' ''

S4Mn from Ni

:'', / ",i " : ",

' "":t " ........

i ! ! I

102 103

En_gy (MeV)

103--

102-

1101

100-

101

SICo from NI

I 1%_.

.........

, , i i i l:l _

lO 2

Energy(MeV)

103

mm

BE

Ill

,,m

im

BE

m

IB

103- , , ,,,,,; , , , ' ''"l i -, , , ,,,

l 02-

100 I

10°

STCo from Ni ,'"

I

, ,,I

r I Ii

!

¢

i

iI

i

ei

i i i r i sml

lO 1

"l

I

103-_ ; ' ' '''''l

SlCo from Nl

I

#n

il 02

_ t

t

¢_ 101-

10 3

/, ,L .... I , 100 , ....... z

1_ 10 0 101

it° _,l _

°f i,.

7, ..... J i ....... t

Energy (MeV) Energy (MeV)

Fig.C-3.Crossmctionsfor54Mn,56Co,57Co and 58Coproductionfromnickel;solidline by protons,dashed

lineby neutrons.

C-4

lO 3

=

m

m

g

IB

Zm

m

m

lib

im

!m

lg

|

Appendix D

Additional Fluence Results

Figs. D-1 through D-4 compare the depth dependent fluences (over all energies) for

primary and secondary particles for LDEF exposure to trapped proton, galactic proton,

albedo proton, and albedo neutronsources.

Fluence spectra of protons and neutrons from all sources are compared for 10 and 50 g/cm 2

aluminum shielding depths in Figs. D-5 and D-6.

w

D-1

w

10 lo

t

8t-¢D

Tf-

.gt/)

LLUJ

..J

109

10 8

10 7secondary protons

I

Trapped

secondary neutrons

primary protons

Proton Sou rce

I

iu

I

I

i

106

0 2O

Fig. D-I.

40 60

Depth in Aluminum (g/cm 2)

8O

Secondary particle production for _apped proton source.

100

I

iI

m

I

1010

._. 109 _O4

l

E_o

8

I , ' -i l I ' ' T I ' a

Galactlc

I i t !

Proton Source

secondary neutrons

ii secondary protons

107-J

F1 06 f I 1., I , , , I • , ,

0 20 40

primary protons

[ i i i I

60 80

I I I


100

Fig. D-2. Secondary particle production for galactic proton source.

D-2

=

I

i

i

i

I

i

I

I

i

I

m

I

II

108 ' ' ' I "_ ' ' I ' ; ' I ' ' ' I ' ' '

Albedo Proton Source

'_ 107

10 6 _

q

105

secondary neutrons

I , , , I , ,.._, I. , , , I , , _ I , , ,

0 20 40 60 80

Depth in Aluminum {g/cm 2)

Fig. D-3. Secondary particle production for albedo proton source.

100

u

109

...,. 10804

Eo

ID_ 10 7U.

106

1 05

' ' ' l ' ' ' l ' ' ' J ' '

Albedo

g

I I I I ,

0 20

primary + secondary neutrons

secondary protons0

! | i g I

Neutron Source

O

, , I , L , I , i , I ,

40 60 80


I I

100

Fig. D-4. Secondary particle production for albedo neutron source.

D.3

I I " I I I_ [ IIIIII I I IIIIII I I IIIIII I I IIIIit I I IIIIII I |

®

//

o/

I

,,,,,,,,,p....,LI,,,,,,,,,,,,,,,,,, ........ ,.......,I I I I

( I. - Aal#I ;_.'w0 ) eJ|:::_d9 a0uanl-.l u0!ss!l_ :1:107

O

o

D-4

e,')o'v--

O.I vO >,

_)f-LU

'l"-"

O,r,,

O'i-'.'

,-;-,O

vl

o=",,,_iiii

_QI,)

ra.,

i

.Sl,e.,1

.5

III

IIII:

O

W

IE

lib

El

Ill

11

lib

BII

II

IE

!I

II

II

mmgmmllll

lie

imI!!

l

II

II

i.

,,,,,_, ......,,'_,,,_,?,,,,_,,,,,,,,_,,,,,,,,,......,, ,,,,,,,,, _,,,,,,,,,,,,,,,,,I I I I I I I I

0"_ r,,. 14") cO0 0 0 0

( L.^e_ __ uJ0 ) e_ods a0u0nl_-Iu0!sS!lAI=130"1

O

IDO

'T"

O

I.U

°O

,6

O,q,.,.

D-5

ul

z

!I

11!

II

Ill

111

IB

=_

Ill

nIII!

II

II

m

III

m

U

II

i

IIs

111

llr

ul

Ill

Appendix E

Additional Dose Results

Figs. D-1 through E-4 compare primary vs. secondary particle contributions to the

absorbed dose in tissue for each of the LDEF exposure sources considered.

L

.i,.m,

k=.

w

E-1

.... • • r

(IP

t-

.on

I=UJ

1 O3

io2

101

1 0 °

10-1

primary protonsTotal

/ protons

secondary neutrons

0 20 40 60 80

Depth in Aluminum (g/cm 2}


100

Fig. E-I. Secondary particle contribution to absorbed dose in tissue for capped proton source.

101

!1 00

' ' ' I ' ' ' I _ '" ' I ' ' * I ' _' '

GaJactic Proton Source

__ Total

secondary neutrons

, , a I • _ _ I , , , I z z , I

0 20 40 60 80


s i

100

Fig. E-2. Secondary particle contribution to absorbed dose in tissue for galactic proton source.

E-2

im

m

J

t

mUW

g

i

w

IB

III

i

m

i

IB

i

i

i

I

R

iQ

101

,.- 00

t.=

10 1

LL

LU

c)-,J

10.2

0

Fig.E-3.

Albedo Proton Source

Tota/

primary protons

secondary neutrons

secondary protons

i , I I , , I i ] L I

20 40 60 80

Depth in Aluminum (g/cm2)

Secondary particle contribution to absorbed dose in tissue for albedo proton source.

10C

A

!9

10°

10"1

I ' ' ' I ' ' ' 1 ' ' ' I


Tota/Q 41, __

_ primary +secondary neutrons

__econdary protons

I , , , I , i s I , , ,= I ,

20 40 60 80

Depth inAluminum (g/cm2)

100

Fig. E-4. Secondary particle contribution to absorbed dose in tissue for albedo neutron source.

E-3

g

II

Ill

i

m_ii

!ll

II

m

II

m

II

II

iI

i

II

II

z

m

ill

m

qlll

_mII

!t!

II

imi

II

=il

w

Appendix F

=

Results for Radioisotope Production from Stainless Steel

Induced radioactivity measurements are being made for several LDEF components which

are made of stainless steel, and calculated results are given here for several radioisotopes

produced in thin stainless steel samples behind varying thicknesses of aluminum shielding.

The stainless steel composition used in the calculations (75.3% Fe, 15.4% Cr, and 4.3%

Ni, by weight) is based on post-flight x-ray fluorescence measurements (made at MSFC,

and provided by A. Harmon, MSFC/SSL) of segments of the LDEF trunion.

Figures F-1 through F-3 compare the contributions from different sources to each of the

radioisotopes considered. Figures F-4 through F-8 compare the primary vs. secondary

particle contributions to the production of each isotope for trapped proton and galactic

sources.

m

w

F-1

r0

0

"02

(3.

lO5

lO4

lO3


' I ¢ ' • I ' ' '

SSCo from S Steel

Galactic Proton Source

AlbedoNeutronSource

Al:_JdoProton Source

0 20 40 60 80 100


g

"102Q.

10 6 _- ' '--=7- ' ' ' I ' ' ' I ' ' ' I ' ' '

I S7Co from S Steel 1

104

10 3

10 2

0 20 40 60 8_) 100


Fig. F-1. Con_ibution of various space radiation sources to _e production of 5_Co (top graph) and

57 Co Cootmm graph) _om st_nless steel, normalized for LDEF mission duration.

w

I

all

ill

BI;

Ill

m

i

iI

l

m

B_

ii

i

m

mm

m

!

gB

m

u

i

1-2II

=_=

im

l!

= =

,05f 1S6Co from S Steel

o 103O. _ x -" u Albedo Neutron Source l

]

0 20 40 60 80 100.

Depth in Aluminum (g/cm2)

L

F

107

106

105

(3.

104

' ' ' I ' ' ' I ' ' ' I ' '' I ' ' '

54Mn from S Steel

Ga/actic Proton SourceC

x x x _A/Albedo Neutron Source

103 = _ i I , , , ! , , t I , , , I , l ,

0 - 20 40 60 80


100

Fig. F-2. Contribution of various space radiation sources to the production of 56Co (top graph) and

54 Mn (bottom graph) from stainless steel, normalized for LDEF mission duration.

F-3

j-

iJ

Jr

j"

qlm

!

m

IB

104

i 1 03 -

1 02

7Be from S Steel

ped Proton Source

Galactic Proton Source i-"

_ron Source N.----.--.

e--.... A/bedo Proton Source.-e---...

101 l I I 1 = L l I i * , I = = I I = A,

0 20 40 60 80


Fig. F-3. Conu'ibution of various space radiation sources to the production of 7Be from stainlesssteel, normalized for LDEF mission duration.

10(

z_

m

!II

II

II

!11

i

III

BI

==_==i

J

!11

F-4

11

lib

lib

=ail

=

los

lO4

A

t-O

lO2

101

primary pro tons

secondary protons

58Co from S Steel


I ' J

2O

I = ,= = I ,

40 60


8O 100

w

lOs

104-

At_

_o

lO2

' ' ' I ' ' ' ! ' I t I =

e

secondary protons

__..primary protons

! i I = _ =

58Co from S Steel


101 _ _ _ I _ _ , I = J = I i J [ I _ =0 20 40 60 8O


I

100

Fig. F-4. Secondary particle contribution to 58Co production from stainless steel by trapped

proton (top) and galactic proton (bottom) sources, normalized for LDEF mission duradon.

F-5

A

2t-O

106 I ' ' ' I ' ' ' I ' ' ° I ' i

io5

1o4

1o3

1o2

primary pro tons

57Co from S Steel


neutrons

protons

0 20 40 60 80 100

Dep_ in Aluminum {g/cm 2)

1 _v I i l a80 100

_, 57Co from S Steel -

Galacdc Proton Source

__ , , I , , i I , A,, _ I , i L

0 2O 4O 60

Deoth in Aluminum (o/cm2_

D

m

IB

BE

EB

i

IB

IB

lib

il

IB

B

mim

Fig. F-5. Secondary particle contribution to 57Co production from stainless Steel by _:appedproton (top) and galactic proton (bottom) sources, normalized for LDEF mission duration.

F-6

m

Ii

m

II

v

lo5

lo'

lo2

101

C

o.

primary protons

secondary protons

I Trappe56Cofrom S Steel

d Proton Source

0 20

neutrons

40 60


8O 100

w

104

lO3A

2CO

' ' ' I ' ' ' I ' ' ' I '

56Co from S Steel


I I I I I

20

0

a __ --

101 = , I , , _ I , , = I , ,0 40 60 80 100


Fig. F-6. Secondary particle contribution to 56Co production from stainless steel by trapped

proton (top) and galactic proton (bottom) sources, normaJized for LDEF mission duration.

F-7

1_ l ,. , , I , , ' ' ' ' ' ° ' ' J ' ' ' I

i lo_ _ neutrons

_o4

103 0 20 _80 10040 ..... 60

Depth in Aluminum (g/crn 2)

w

m

BB

i

=

IB

lm

IB

neutrons _ = • .

In3v , I i0 100

secondary protons _ o

54Mn from S Steel


I J = I J I , I , , L I J = I I

20 40 60 80


BIll

mi

BB

im

!!

lib

m

'i

m

m

IB

Fig. F-7. Secondary particle contribution to 54Mn product/on from stainless steel by _'apped

proton (top) and galactic proton (bottom) sources, normalized for LDEF mission duration.

F-8

m

R

m

I

=

m

R

w

104

lO3

A

102e-

101

lo0

primary protons

7Be from S Steel


neuVons

secondaryprotons

0 20 40 60 80

DepthinAluminum(_cm 2)

100

=

w

7Be from S Steel


101 _ = _ I _ , , I = = , I , = J I ,

0 20 40 60 80


100

Fig. F-8. Secondaryparticle contribution to 7Be production from stainless steel by trapped

proton (top) and galactic proton (bottom) sources, normalized for LDEF mission duration.

F-9

±

qP

U

U

HI

[]

z

g

IB

Ni

alp

mqP

U

RB

I

mm

II

m_

I

z

m

scoping estimates of the ldef satellite induced radioactivity · 2013-08-30 · a : m k = e scoping...

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