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Depth dependence of absorbed dose, dose equivalent and linear energy transfer spectra of galactic and trapped particles in polyethylene and comparison with calculations of modelsA matched set of five tissue-equivalent proportional counters (TEPCs), embedded at the centers of 0 (bare), 3, 5, 8 and 12-inch-diameter polyethylene spheres, were flown on the Shuttle flight STS-81 (inclination 51.65 degrees, altitude approximately 400 km). The data obtained were separated into contributions from trapped protons and galactic cosmic radiation (GCR). From the measured linear energy transfer (LET) spectra, the absorbed dose and dose-equivalent rates were calculated. The results were compared to calculations made with the radiation transport model HZETRN/NUCFRG2, using the GCR free-space spectra, orbit-averaged geomagnetic transmission function and Shuttle shielding distributions. The comparison shows that the model fits the dose rates to a root mean square (rms) error of 5%, and dose-equivalent rates to an rms error of 10%. Fairly good agreement between the LET spectra was found; however, differences are seen at both low and high LET. These differences can be understood as due to the combined effects of chord-length variation and detector response function. These results rule out a number of radiation transport/nuclear fragmentation models. Similar comparisons of trapped-proton dose rates were made between calculations made with the proton transport model BRYNTRN using the AP-8 MIN trapped-proton model and Shuttle shielding distributions. The predictions of absorbed dose and dose-equivalent rates are fairly good. However, the prediction of the LET spectra below approximately 30 keV/microm shows the need to improve the AP-8 model. These results have strong implications for shielding requirements for an interplanetary manned mission.
Document ID
20040172761
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
Authors
Badhwar, G. D.
(NASA Johnson Space Center Houston, TX United States)
Cucinotta, F. A.
Wilson, J. W.
Date Acquired
August 22, 2013
Publication Date
March 1, 1998
Publication Information
Publication: Radiation research
Volume: 149
Issue: 3
ISSN: 0033-7587
Subject Category
Aerospace Medicine
Distribution Limits
Public
Copyright
Other
Keywords
Flight Experiment
STS-81 Shuttle Project
NASA Discipline Radiation Health
NASA Center JSC
short duration
STS Shuttle Project
manned

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