Modeling of the Shuttle Tissue-Equivalent Proportional Counters Using Computer Automated Design Techniques and Radial Frequency Distributions

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.