An evaluation of radioxenon detection techniques for use with a fluid-based concentration system

A portable monitoring system to measure the quantity of radioxenon (/sup 131m/Xe, /sup 133/Xe, /sup 133m/Xe, and /sup 135/Xe) in the atmosphere is being developed which incorporates a fluid-based concentration system with a detection system. To this end a number of radioxenon detection techniques have been evaluated to determine the best method of analyzing the output of the concentration system, which may contain significant amounts of radon in addition to concentrated xenon. Three detector configurations have been tested to measure the characteristic electron/photon coincidence radiation: plastic scintillator/NaI(Tl), gas proportional detector/NaI(Tl), and liquid scintillator/NaI(Tl). In addition to standard coincidence measurements, some additional gating criteria were also used: pulse height discrimination, pulse shape discrimination, and delayed coincidence. While the lowest relative minimum detectable activity was achieved using the liquid scintillator with delayed coincidence gating, the best performance for fieldable detection systems depends on the ratio of xenon to radon in the output of the concentration system. A high ratio favors the use of a gas proportional/NaI(Tl) detector using coincidence gating with pulse height discrimination. The use of a plastic scintillator/NaI(Tl) detector using coincidence eating with pulse shape discrimination is preferred when the ratio is low.