Delayed coincidence technique for 133gXe detection

Delayed coincidence techniques show promise of significant improvements for a Xe counting system which will be a key element in monitoring the Comprehensive Test Ban Treaty. We have previously developed a beta–gamma counting system for 131mXe, 133mXe, 133gXe, and 135gXe as part of an automated system for analyzing Xe in air. Depending on background levels, higher sensitivity for 133gXe can be achieved by use of the delayed coincidence between beta particles that feed the 81 keV state in 133Cs and the conversion electrons produced in the deexcitation of the 81 keV state (t1/2=6.36 ns). In the delay time region, only the 31 keV X-ray associated with 133gXe decay is observed. This technique detects 133gXe with extremely low background and distinguishes 133gXe from 131mXe and 133mXe.