Beta-gamma counting system for Xe fission products

A beta-gamma coincidence counting system has been developed for automated analysis of Xe gas samples separated from air. The Xe gas samples are contained in a cylindrical plastic scintillator cell located between two NaI(T1) scintillation detectors. The X-ray and gamma spectra gated by coincident events in the plastic scintillator cell are recorded for each NaI(T1) crystal. The characteristic signatures of the^131mXe,^133gXe,^133mXe, and^135gXe isotopes of interest for nuclear test-ban verification as well as the procedures and results of absolute efficiency measurements are described. A NaI(T1) crystal with provision for 4 sample cells has been implemented for the system to be deployed in the field. Examples of data on ambient air samples in New York City obtained with the field prototype are presented.