Study of Sensitivity Fading of CR-39 Detectors during Long Time Exposure

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Study of Sensitivity Fading of CR-39 Detectors
during Long Time Exposure

• D. Zhoua, b, D. OSullivanc, 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
• 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 Astronauts
• Dominated 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 (gt 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.

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• A correction formula was found
• Sc So/(1-(abT))
• where So etch rate ratio before correction
• Sc corrected value of etch rate
  ratio
• Sc1 So1/(1-(abT1))
• Sc2 So2/(1-(abT2))
• 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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Table 2 Comparison of LET before and
aftercorrection of CR-39 sensitivity
Major / Minor LET 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
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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
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• 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
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• 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

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• 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
  .