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

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 a , E.R. Benton d a Johnson Space Center - NASA, 2101 Nasa Parkway, Houston, TX 77058, USA

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

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  1. Study of Sensitivity Fading of CR-39 Detectors during Long Time Exposure D. 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 NASA-JSC and DIAS

  2. 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 NASA-JSC and DIAS

  3. Radiation Field in Low Earth Orbit GCR (Galactic Cosmic Rays) Solar Energetic Particles SAA (South Atlantic Anomaly) Albedo Neutrons NASA-JSC and DIAS

  4. Radiobiological Impact on Astronauts Dominated by high LET (≥ 5 keV/µm water) CR-39 detectors are most appropriate NASA-JSC and DIAS

  5. 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) NASA-JSC and DIAS

  6. Photo of Matroshka in Space NASA-JSC and DIAS

  7. 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. 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 NASA-JSC and DIAS

  9. Table 1: Fading Comparison for different exposure time NASA-JSC and DIAS

  10. Table 2: Comparison of LET before and aftercorrection of CR-39 sensitivity NASA-JSC and DIAS

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

  14. Figure: Charge identification with G-Seff method for test events. NASA-JSC and DIAS

  15. 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 . NASA-JSC and DIAS

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