High sensitivity detection of /sup 133g/Xe via delayed coincidence counting

Sensitive detection of Xe fission products is needed for monitoring the Comprehensive Test Ban Treaty. Pacific Northwest National Laboratory has developed an automated system for separating Xe from air which includes a beta-gamma counting system for /sup 131m/Xe, and /sup 133g/Xe, /sup 133m/Xe, and /sup 135g/Xe. Even greater sensitivity for /sup 133g/Xe can be achieved by use of the delayed coincidence between beta particles which feed the 81-keV state in /sup 133/Cs and the in conversion electrons produced in the deexcitation of the 81-keV state (t/sub 1/2/=6.36 ns). Besides the ability to detect /sup 133g/Xe with 0 background, this technique distinguishes /sup 133g/Xe from /sup 131m/Xe and /sup 133m/Xe.