Characterizing a Two-Channel Phoswich Detector Using Radioxenon Isotopes Produced in the Oregon State University TRIGA Reactor

Low concentrations of radioxenon isotopes can be measured with a high sensitivity using beta/gamma coincidence technique. In this technique, a coincidence event is recorded when two signals from beta and gamma detection channels are detected simultaneously. These two coincident signals are then processed to establish a two-dimensional beta/gamma coincidence spectrum in which the four radioxenon isotopes can be measured in the sample. In many beta/gamma coincidence systems, beta and gamma radiations are detected in two separate channels. Another approach is to use a phoswich detector in which both radiations can be detected by one single channel, and simplifying the coincidence system configuration. To expand the solid angle of the radioxenon detection geometry close to 4pi, a two-channel and planar triple-layer phoswich detection system was designed and constructed. In order to characterize the phoswich detection system for radioxenon measurements, we have irradiated enriched stable samples of 132Xe and 134Xe gas with thermal neutrons from the TRIGA reactor at the Oregon State University (OSU). 133mXe, 133Xe, and 135Xe were successfully produced and injected into the detector gas cell using a simple gas transfer manifold system. To enhance the efficiency of coincidence detection between the two phoswich detectors, a synchronization logic mode was added into the previous firmware of our two-channel digital pulse processor system. In this paper, we will describe xenon neutron irradiation conditions, sample transfer procedures, and beta/gamma coincidence measurements results. Also a brief description of our synchronization logic mode will be covered in this paper. Published in Proceedings of the 2010 Monitoring Research Review - Ground-Based Nuclear Explosion Monitoring Technologies, 21-23 September 2010, Orlando, FL. Volume II. Sponsored by the Air Force Research Laboratory (AFRL) and the National Nuclear Security Administration (NNSA). U.S. Government or Federal Rights License