Noble gas migration experiment to support the detection of underground nuclear explosions

A Noble Gas Migration Experiment injected Xe-127, Ar-37, and sulfur hexafluoride into a former underground nuclear explosion shot cavity. These tracer gases were allowed to migrate from the cavity to near-surface and surface sampling locations and were detected in soil gas samples collected using various on-site inspection sampling approaches. Based on this experiment we came to the following conclusions: (1) SF6 was enriched in all of the samples relative to both Ar-37 and Xe-127. (2) There were no significant differences in the Xe-127 to Ar-37 ratio in the samples relative to the ratio injected into the cavity. (3) The migratory behavior of the chemical and radiotracers did not fit typical diffusion modeling scenarios.