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.