127Xe Quantification Method Development and Intercomparison Exercise

Monitoring of the atmosphere for fission products (131mXe, 133mXe, 133Xe, and 135Xe) is performed by various laboratories to detect nuclear explosions. Quantification of 127Xe is not routinely performed by laboratories measuring atmospheric radioxenon because it is not a fission product. 127Xe was recently detected by a ground-based beta-gamma air monitoring system. When measured using beta-gamma coincidence detector systems, such as those in use on the International Monitoring System (IMS) of the Comprehensive Nuclear-Test-Ban Treaty (CTBT), 127Xe can interfere with the quantification of fission product radioxenon due to overlap of the 127Xe beta-gamma coincidence signatures with those of fission product radioxenon. This work demonstrates quantification of 127Xe at different laboratories with different measurement techniques. Production and purification of 127Xe was performed by neutron activation of enriched 126Xe. The purified 127Xe was then split between laboratories, and detection and quantification methods were developed. At Idaho National Laboratory, a quantification method involving high purity germanium detectors was devised that included self-attenuation correction. At AWE, a beta-gamma coincidence counting method, as used in support of the IMS, was modified to enable the measurement and analysis of the 127Xe samples. Corrections were made for self-attenuation, which showed a strong xenon volume dependency, for some coincidence signatures. The gas sample activity concentration was used as the comparison metric and it showed excellent agreement between the methods.