Improved radioxenon detection techniques for use with fluid-based concentration

A portable system that monitors the quantity of radioxenon (/sup 131m/Xe, /sup 133/Xe, /sup 133m/Xe, and /sup 135/Xe) in the atmosphere is being developed. The integrated monitoring system consists of a fluid-based concentration sub-system and a detection sub-system. This study evaluates the performance of different high-efficiency geometries that use NaI(Tl) photon detectors along with with either gas proportional, plastic scintillator, or PIPS detectors to distinguish radioxenon signature emissions and discriminate against radon background. In addition, a NaI(Tl)/CsI(Tl) phoswich detector was investigated as an alternative photon detector. Finally, a dual parameter data acquisition system was demonstrated. Minimum detectable activity (MDA) for a six hour count time of /sup 133/Xe was used as the primary measure of performance. The lowest MDAs were 52/spl plusmn/7 mBq for the gas proportional/NaI(Tl) configuration, 48/spl plusmn/7 mBq for the plastic scintillator/NaI(Tl) configuration and 73/spl plusmn/8 mBq for the PIPS/NaI(Tl) configuration. Based on these results, the performance of a proposed final detection system is predicted to result in a MDA of 12.2 mBq without shielding. This detection system performance compares well to existing radioxenon detection systems and indicates the requirements of the concentration system.