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The Average Quality Factors by TEPC for Charged ParticlesThe quality factor used in radiation protection is defined as a function of LET, Q(sub ave)(LET). However, tissue equivalent proportional counters (TEPC) measure the average quality factors as a function of lineal energy (y), Q(sub ave)(Y). A model of the TEPC response for charged particles considers energy deposition as a function of impact parameter from the ion s path to the volume, and describes the escape of energy out of sensitive volume by delta-rays and the entry of delta rays from the high-density wall into the low-density gas-volume. A common goal for operational detectors is to measure the average radiation quality to within accuracy of 25%. Using our TEPC response model and the NASA space radiation transport model we show that this accuracy is obtained by a properly calibrated TEPC. However, when the individual contributions from trapped protons and galactic cosmic rays (GCR) are considered; the average quality factor obtained by TEPC is overestimated for trapped protons and underestimated for GCR by about 30%, i.e., a compensating error. Using TEPC's values for trapped protons for Q(sub ave)(y), we obtained average quality factors in the 2.07-2.32 range. However, Q(sub ave)(LET) ranges from 1.5-1.65 as spacecraft shielding depth increases. The average quality factors for trapped protons on STS-89 demonstrate that the model of the TEPC response is in good agreement with flight TEPC data for Q(sub ave)(y), and thus Q(sub ave)(LET) for trapped protons is overestimated by TEPC. Preliminary comparisons for the complete GCR spectra show that Q(sub ave)(LET) for GCR is approximately 3.2-4.1, while TEPC measures 2.9-3.4 for QQ(sub ave)(y), indicating that QQ(sub ave)(LET) for GCR is underestimated by TEPC.
Document ID
20060023353
Acquisition Source
Johnson Space Center
Document Type
Conference Paper
Authors
Kim, Myung-Hee Y.
(Wyle Labs., Inc. Houston, TX, United States)
Nikjoo, Hooshang
(Universities Space Research Association Houston, TX, United States)
Cucinotta, Francis A.
(NASA Johnson Space Center Houston, TX, United States)
Date Acquired
August 23, 2013
Publication Date
January 1, 2004
Subject Category
Man/System Technology And Life Support
Meeting Information
Meeting: 9th Workshop on Radiation Monitoring for the International Space Station
Location: Vienna
Country: Austria
Start Date: September 8, 2004
End Date: September 10, 2004
Sponsors: Wien Univ.
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.

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