Microdosimetry Studies at the BMRR and the MITR-II Using Miniature Tissue-Equivalent Proportional Counters

Abstract

Conventional dosimetry methods for BNCT measure the macroscopic absorbed dose, but give no information about its microscopic nature or radiation quality. A low pressure tissue-equivalent proportional counter (TEPC) is capable of providing this information by supplying the complete single event charged particle spectrum depositing the dose in a simulated microscopic site. Miniature TEPCs have been designed to overcome the limitations in spatial resolution and dose rate of conventional Rossi counters. They are small enough to provide excellent spatial resolution and to be used in the high flux beams used for BNCT with a total deadtime of only a few percent and negligible pulse pile-up. A pair of TEPCs, made of A-150 tissue-equivalent plastic and A-150 loaded with 200µg/g 10B, with sensitive volumes of 0.01 cm3 have been constructed and characterized. Another TEPC has been constructed to investigate the effect of differences between A-150 plastic and brain tissue-equivalent plastic on the secondary charged particle spectrum. Collaborative arrangements have been made with Brookhaven National Laboratory and Massachusetts Institute of Technology to make microdosimetric measurements at the BMRR and the MITR-II. The results of these measurements are presented.