A multi-channel beta-gamma coincidence counting system using well-HPGe and plastic scintillation detectors for radioactive Xenon measurements

A new type of multi-channel beta-gamma coincidence counting system was developed for the analysis of radioactive Xenon samples with low-level radioactivity. The proposed system consists of a state-of-the-art well-HPGe detector with a large well volume ((sic) 28 mm x 40 mm) and a cylindrical plastic scintillation detector with an interior volume of 8.8 cm(3). A two-dimensional beta-gamma coincidence histogram was obtained, and the beta-gamma coincidence counting efficiency was estimated using gaseous radioxenons and Monte Carlo simulation with the MCNP code. The energy resolution of the plastic scintillation detector for the 129.4 keV internal conversion electron was 29%, and the minimum detectable concentration for (131)mXe,Xe-133, Xe-133m, and Xe-135 was calculated as 0.27 mBq/m(3), 0.23 mBq/m(3), 0.16 mBq/m(3) and 0.24 mBq/m(3) under the assumed conditions of a 20000 s measurement and a 10 m(3) air sample with the beta-gamma coincidence mode, respectively.