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A higher fidelity shield model and response model have been developed for the Shuttle TEPC. The shield model was built using a CAD package in conjunction with a ray tracer. The response model considers the spatial restriction on the mean-energy imparted and the variance for direct particle effects and combines the radial distribution of the electron energy and flux about incoming ions with the distribution of electron frequencies from Monte Carlo simulations. The latter model accounts for secondary electrons entering the sensitive area of the TEPC. The new models are compared against measurements of a variety of shielding depths of aluminum and polyethylene that were acquired on the Shuttle during STS-81 and STS-89. Good agreement is obtained between the models and the measurements for trapped proton effects.

A new Green’s function code (GRNTRN) capable of simulating HZE ions with either laboratory or space boundary conditions is currently under development. The computational model consists of combinations of physical perturbation expansions based on the scales of atomic interaction, multiple scattering, and nuclear reactive processes with use of the Neumann-asymptotic expansions with non-perturbative corrections. The code contains energy loss due to straggling, nuclear attenuation, nuclear fragmentation with energy dispersion and downshifts. Recent publications have focused on code validation in the laboratory environment and have shown that the code predicts energy loss spectra accurately as measured by solid-state detectors in ion beam experiments. In this paper emphasis is placed on code validation with space boundary conditions.

The highly inclined orbit of the International Space Station Alpha exhibits significant radiation exposure contributions from the galactic cosmic rays penetrating the earth's magnetic field. In the absence of an accepted method for estimating the corresponding astronaut risk, we examined the attenuation characteristics using conventional LET dependent quality factors (as one means of representing RBE) and a track-structure repair model fit to cell transformation (and inactivation) data in the C3H10T1/2 mouse cell system obtained by T. C. Yang and coworkers for various ion beams. Although the usual aluminum spacecraft shield is effective in reducing dose equivalent with increasing shield thickness, cell transformation rates are increased for thin aluminum shields providing increased risk rather than protection to large shield thickness.