The azimuthal angle distribution and the charge and energy spectra of selected light-heavy (5 less than or equal to Z less than or equal to 8) stopping particles were measured in a single layer of CR-39 plastic nuclear track detector (PNTD) from the stack of the A0015 experiment located on the Earth-end of the LDEF satellite. The directional incidence of the trapped protons is studied by comparing the azimuthal angle distribution of selected recoils, obtained in the LDEF detectors, to that obtained through calibrations of PNTD's with exposures performed with 200 MeV proton beams from different directions

Benton, E. R.

Benton, E. V.

Csige, I.

Soundararajan, S.

English

NASA Technical Reports Server

N93-29638
LIGHT-HEAVY ION MEASUREMENTS IN CR-39 LOCATED ON THE EARTt_I SIDE OF LDEF *
I. Csige, E. V. Benton, S. Soundararajan and E. R. Benton
Eril Research Inc. P. O. Box 150788
San Rafael, CA 94915-0788
Phone: 415-666-2333, Fax: 415-454-4089
SUMMARY
The azimuthal angle distribution and the charge and energy spectra of selected light-heavy (5 < Z _<
8) stopping particles were measured in a single layer of CR-39 plastic nuclear track detector (PNTD) from
the stack of the A0015 experiment located on the Earth-end of the LDEF satellite. The directional
incidence of the trapped protons is studied by comparing the azimuthal angle distribution of selected
recoils, obtained in the LDEF detectors, to that obtained through calibrations of PNTDs with exposures
performed with 200 MeV proton beams from different directions.
INTRODUCTION
The purpose of the A0015 Free Flyer Biostack experiment was to measure the total absorbed doses
and particle LET spectra as a function of depth in shielding material at different positions on the surface of
the LDEF satellite[ 1,2,3,4,5,6,7].
Cosmic ray charged particles contribute to the health risk of crew members and high LET particles
can cause single event upsets (SEUs) in microelectronics. In the present study the charge and energy
spectra of selected high LET particles (mostly heavy recoils) were measured in order to compare with
model calculations. The contribution of high LET recoils to the LET spectra seems to be more significant
than previously thought. Their flux in the inner radiation field is much higher than the flux of the high LET
primary cosmic ray particles under the same shielding conditions. To measure the LET spectra, plastic
nuclear track detectors are widely used. A standard technique is developed to measure the LET spectra in
regular STS flight. This technique, however, has a range threshold about 30-40 #m, therefore recoil
particles with a range shorter than that threshold could not be detected. Hence, short range recoils are not
included in regular LET spectra measurements performed in STS flights. This range cut-off value,
however, is proportional to the etching time which had to be much shorter in the case of the LDEF samples
because of the expected high track density. Also, the fluence of these relatively long range recoils is much
higher in the case of the LDEF samples because of the long duration exposure. Heavy recoils, satisfying
*Work partially supported by NASA contract No. NAS8-38610 (NASA-Marshall Space Flight Center,
Huntsville).
181
https://ntrs.nasa.gov/search.jsp?R=19930020449 2020-03-17T04:28:25+00:00Z
certainselectioncriteria,canbe identifiedin CR-39PNTDsby measuringthegeometricalparametersof
their single-surfaceetchedtrack.Detectionefficiencyof theseparticlescanbecalculatedandexperimental
andtheoreticalresultscanbecomparedin thefuture.Thisgivesagoodopportunityto validatemodel
calculations.
Thedirectionalitydistributionof theseparticleswasmeasuredandcomparedwith calibration
measurementsperformedwith 200MeV protonbeams.Someconclusionsaboutthedirectionalityof the
primarytrappedprotonradiationenvironmentaredrawn.
EXPERIMENT
Detectorstacksfilled two Biostackcontainersandpartially filled a third in theA0015experiment.
DetectorstackNo. 1(Earth-side)andNo. 2 (nonLEarth'slde)werepositionedin thecenterof AI canisters.
Eachcanisterwassealedfrom theoutsideenvironmentbymeansof anO-ring. Theinnerwall of each
canisterwascoveredby anacryliclayer. _
Two layersof CR-39 from theEari-h±side:stackandtwo iayers-from:then0n-Earth-sideStackwere
selectedfor analysis.Theminimumshieldingof theselayerswas10.0g/cm2for theEarth-sidelayersand
4.2g/cmefor thenon-Earth-sidePNTDs.Thelayerswereetchedin a6.25N NaOHsolutionat50 °C for
36hours.A thicknessof 8-10 _m wasremovedfrom eachsurface.
i
1
Measurement of Charge and Energy of "Energetic" Recoil Particles
A layer from the Earth-side stack was selected for these measurements of the charge and energy of
selected energetic recoil particles. The minimum shielding distance (from the outer surface of the canister)
for this layer was 10.3 g/cm2: The surface of the layer was parallel with the surface of the Earth. That side
ofthe-iayer nearest the satellite was scanned. The scanned area was 4.32 cm 2 and was located at the center
of the l_iyer, 400 undercut, rounded tracks were measured in the scanned _ea and_2_ of thesewere
Selected for charge and energy dete_ination. The range of the p_icies in the CR-39 layer and the
red__ rate ratio ( VT/VB - 1 ) along the particie's _acks were determined from track geometry
measurements of eiched tracks using the assumption of constant etch rate ratio. The particles were
identified using an internai calibration technique and the REL (Restricted Energy Loss) model Of track
formation with a threshold energy of 200 eV. The internal calibration is based on the assumption that recoil
particleSwith thehigties_charge are Oxygen because there are no particles with larger charge in the
composition Of the CR-39 material The corresponding charge distribution is shown in Figure 1.
The track selection criteria were determined in such a way as tO ensure that only "energetic" recoil
particles were measured, the range of which had to be greater than _ 15-20/zm depending on the charge of
the pmicies. Currently, a detailed detection efficiency calculation is under way to convert this data into
charge, energy and LET fluence spectra.
22
182
25
LDEF, AO015, C20 200 particles
0
t_
13.
0
.13
E
z
2O
15
10-
5-
0 ¸ i
4
i i i
'5' 6 7 8 9
Charge, Z [e]
Figure 1: Number of energetic recoil particles as a function of charge measured in a CR-39 layer from the
LDEF A0015 Earth-side stack.
Directionality of Recoil Particles
In addition to charge and energy spectra measurements, the directionality distribution of recoil
particles was measured. Figure 2 shows the azimuthal angle distribution of the 400 measured tracks. The
azimuthal angle in this case is the angle of the projection of the particle trajectory onto the detector surface
measured from an arbitrary x-axis on the detector sheet.
Similar measurements have been performed on calibration samples of CR-39 exposed to 200 MeV
protons at different angles of incidence. The corresponding azimuthal angle distributions are presented in
Figure 3. The comparison of these distributions with that obtained from the LDEF sample confirm the
anisotropic nature of the primary proton fluence by which these energetic heavy recoils were produced in
the case of the LDEE
CONCLUSIONS
Charge and energy spectra of selected energetic recoil particles can be measured in CR-39 samples
with acceptable charged resolution in the case of the LDEF samples. Together with detailed detection
efficiency calculations these spectra can be compared with theoretical results to validate model calculations.
183
35
co
,¢,
k,,.
O
E
Z
30-
25-
20-
15-
10-
_
0
j j
m
'' _,_ ' 9d' ' '''''''0 i35 i8() 225 270 315
Azimuthal angle, [degree]
i
Figure 2: Azimuthal angle distribution of 400 tracks of energetic heavy recoils in a CR-39 layer from the
LDEF A0015 Earth-side stack. The anisotropy reflects the anisotropy of the high energy trapped proton
i fluence by which these recoils were produced.
184
t.o
v
t..)
¢O
L
0
E
Z
4O
35
30
25
20
t5
10
5
0
4O
35
3O
25
2O
15
10
5
0
6O
5O
4O
3O
2O
10
0
o 4s 90 _35 _8o zzs 270 3_s
Azimuthal angle (degrees)
Figure 3: Azimuthal angle distributions of 300 energetic recoils produced by 200 MeV protons incident on
CR-39 at various dip angles. Anisotropy of recoils show the directionality of the primary proton beam in
the case of 45 ° and 0 ° dip angles.
185
It is found through calibration experiments that the directionality of energetic recoil particles reflects
the directionality of the primary high energy proton beam by which the recoils were produced. The
analysis of the azimuthal angle distribution of energetic recoils in an LDEF sample confirms the anisotropic
nature of the high energy trapped proton fluence in the case of the LDEF.
Similar experiments are under way in a sample from the non-Earth-side stack to study the location
dependence of the charge and energy spectra of energetic recoils. Also, a directionality study of energetic
recoils is under way in samples with surfaces parallel with the East-West direction. The directionality of
recoils in these samples is expected to be more definite as the majority of the trapped protons is expected to
have arrived from the West direction. These experiments will be also used for validation of directionality
of trapped proton radiation environment models.
REFERENCES
1. Armstrong, T. W.; and C01born, B, L.: Radiation model predictions and validation using LDEF data.
Second LDEF Post-Retrieval Symposium, NASA CP-3194, 1993.
2. Benton, E. V.; Heinrich, W., Parnell, T. A.; Armstrong, T. W.; Derrickson, J. H.; Fishman, G. J.;
Frank, A. L.; Watts, J. W.; and Wiegei, B.: Ionizing radiation exposure of LDEF: Pre-recovery
estimates. Nuclear Tracks and Radiation Measurements, Vol. 20, No. 1 1992, pp. 75-100.
3. Benton, E. V.; Frank, A. L.; Benton, E. R.; Csige, I.; Parnell, T. A.; and Watts, J. W. Jr.: Radiation
exposure of LDEF: Initial Results. LDEF-69 Months in Space." First Post-Retrieval Symposium,
NASA-CP 3134, Part 1, Washington DC, 1991, pp. 325-338.
4. Csige, I.; Benton, E. V.; Frank, A. L.; Frigo, L. A.; Benton, E. R.; Parnell, T. A.; and Watts, J. W. Jr.:
Charged particle LET-spectra measurements aboard LDEE LDEF-69 Months in Space." First
Post-Retrieval Symposium, NASA-CP 3134, Part 1, Washington DC, 1991, pp. 339-346.
5. Harmon, B. A.; Fishman, G. J.; Parnell, T. A.; Benton, E. V.; and Frank, A. L.: LDEF radiation
measurements: preliminary results. Nuclear Tracks and Radiation Measurements, Vol. 10, No. 1,
1992, pp. I31-136.
6. Watts, J. W. Jr.; Parnell, T. A.; Derrickson, H. J.; Armstrong, T. W.; and Benton, E. V.: Predictions of
LDEF ionizing radiation environment. LDEF_59 Months in Space." First Post-Retrieval Symposium,
NASA-CP 3134, Part 1, Washington DC, 1991, pp. 213-224.
7. Reitz, G.; Bticker, H.; Facius, R.; Horneck, G.; Schaefer, M.; Schott, J. U.; Bayonove, J.; Beaujean,
R.; Benton, E. V.; Delpoux, M.; Heilmann, C.; Heinrich, W.; Kranz, A. R.; Planel, H.; Gasset, Y.;
Gaubin, G.; Portal, G.; Graul, E. H.; Rtither, W.; Schopper, E.; Tobias, C. A.; and Yang, T. C. First
biological and dosimetric results of the free flyer biostack experiment A0015 on LDEE LDEF--69
Months in Space." First Post-Retrieval Symposium, NASA-CP 3134, Part 1, Washington DC, 1991,
pp. 1639-1642.
iS6


Light-heavy ion measurements in CR-39 located on the Earth side of LDEF

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