11/12/2015NASA-JSC and DIAS1 Study of Sensitivity Fading of CR-39 Detectors during Long Time Exposure D. Zhou a, b, D. O’Sullivan c, E. Semones a, N. Zapp.

04/20/23 NASA-JSC and DIAS 1

Study of Sensitivity Fading of CR-39 Detectors during Long

Time ExposureD. Zhoua, b, D. O’Sullivanc, E. Semonesa,

N. Zappa, E.R. Bentond

aJohnson Space Center - NASA, 2101 Nasa Parkway, Houston, TX 77058, USA

bUniversities Space Research Association, 3600 Bay Area Blvd, Houston, TX 77058, USA

cDublin Institute for Advanced Studies, 5 Merrion Square, Dublin 2, Ireland

dEril Research Inc., 1110 Innovation Way, Suite 100, Stillwater, OK 74074, USA

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The Role of CR-39 Detectors

in Space Studies

Measurement of

(1) LET (Linear Energy Transfer)

(2) Dose and Dose Equivalent

(3) Charge Spectrum of GCR

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Radiation Field in Low Earth Orbit

GCR (Galactic Cosmic Rays)

Solar Energetic Particles

SAA (South Atlantic Anomaly)

Albedo Neutrons

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Radiobiological Impact on AstronautsDominated by high LET (≥ 5 keV/µm water)

CR-39 detectors are most appropriate

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Some Space Missions

Which Employed CR-39 Detectors

LDEF (5.8 Years)

EUROMIR (6 Months)

Matroshka-1 (616 Days)

Matroshka-2 (367 Days)

ISS Expeditions (> 6 Months)

DOBIES (15-400 days)

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Photo of Matroshka in Space

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Fading of CR-39 Sensitivity Was observed for all CR-39 detectors

with long time exposure.

Compared to TEPC data, results measured

with CR-39 are low.

Results must be corrected for fading of

latent tracks irrespective of source. Use

“Fe peak” of exposed detector events

compare with accelerator data.

04/20/23 NASA-JSC and DIAS 8

A correction formula was found:Sc = So/(1-(a+bT))

where So = etch rate ratio before correction

Sc = corrected value of etch rate ratio

Sc1 = So1/(1-(a+bT1))

Sc2 = So2/(1-(a+bT2))

for exposure times T1 and T2

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Table 1: Fading Comparison

for different exposure time

T (a + bT) 1 – (a + bT) Sc/So

(Month)

6 0.0242 0.9758 1.0248

12 0.0388 0.9612 1.0404

24 0.0682 0.9318 1.0731

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Major / MinorLET

before Correction

LET

after Correction

(µm) (keV/µm water) (keV/µm water)

Matroshka-1

33.3 / 23.3

39 / 7

115.45

116.04

135.83

136.47

33.8 / 21 116.88 137.38

36.5 / 17

38 / 21

118.05

117.20

138.64

137.72

ISS-Expedition 12

37.5 / 20.7 128.5 136.82

37.7 / 12 129.76 138.12

Table 2: Comparison of LET before and aftercorrection of CR-39 sensitivity

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Table 3: Radiation measured without and with fading correction for CR-39 sensitivity (values include background)

Mission

(Time)

Exposure

Position

Absorbed Dose

(≥10keV/µm water)

Dose Equi. (ICRP60)

(≥ 10 keV/µm water)

Q

Factor

(Days) (mGy) (mSv)

Matroshka-1

(616)

P1

Eye

Stomach

R1

R2

29.90^/ 36.94*

14.94 / 21.60

14.96 / 18.89

13.90 / 17.93

13.85 / 17.55

270.97^/ 437.00*

176.59 / 274.82

156.95 / 246.13

148.74 / 217.31

135.29 / 215.04

9.06^/ 11.83*

11.82 / 12.72

10.49 / 13.03

10.70 / 12.12

9.77 / 12.25

Matroshka-2

(367)

P1

Eye

Stomach

R2

10.86 / 12.90

9.13 / 10.99

8.40 / 9.66

11.23 / 12.97

121.10 / 150.66

106.88 / 134.48

96.23 / 118.82

123.85 / 152.16

11.15 / 11.68

11.71 / 12.24

11.46 / 12.30

11.03 / 11.73

Expedition 12

(190)

TEPC

TESS

SMP327

SMP442

5.31 / 6.19

4.92 / 6.22

5.31 / 6.83

7.99 / 10.59

60.06 / 69.03

59.21 / 68.89

68.98 / 78.48

89.05 / 105.61

11.32 / 11.15

12.04 / 11.08

12.98 / 11.49

11.14 / 9.97

Expedition 13

(183)

TEPC

TESS

SMP442

4.90 / 6.23

4.55 / 6.18

7.98 / 9.31

65.33 / 74.20

64.09 / 73.39

94.90 / 109.95

13.33 / 11.91

14.09 / 11.88

11.89 / 11.81

04/20/23 NASA-JSC and DIAS 12

Table 4: A comparison of radiation quantities measured with JSC-TEPC and CR-39

(Fading correction applied to CR-39,ICRP60)

Space Mission

Absorbed

Dose

(TEPC / CR-39)

Dose Equivalent

(TEPC / CR-39)

Q

Factor

(TEPC / CR-39)

(µGy/d) (µSv/d)

Expedition 12 31.70 31.39 346.56 / 348.18 10.93 / 11.09

Expedition 13 31.31 / 30.54 356.58 / 359.97 11.39 / 11.79

Matroshka-2 (R2) ~ 34 / 33.08 ~ 390 / 388.39 11.47 / 11.74

04/20/23 NASA-JSC and DIAS 13

Charge Identification (G-Seff Method)For two points separated by x and with etch rate VT1 and VT2, G and Seff are:

Seff = Veff / Vg

Where Vg is the bulk etch rate and Veff, the effective etch rate is

For a track with 2n equally spaced etched cone, the overall value of G is given by:

And the overall value of Veff is

xVV

VVG

TT

TT

)(

)(2

12

12

21

212

TT

TTeff VV

VVV

n

ii

n

iiiiniiin

w

xVVwVVG

1

11212 /2

n

iiniini

eff

VVVV

nV

11212 2/

04/20/23 NASA-JSC and DIAS 14

Figure: Charge identification with G-Seff method for test events.

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We wish to thank all those who assisted us in the ISS, Matroshka and Dobies space missions.

DIAS wishes to thank the ESA PRODEX office for support of this work .