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

A Noble Gas Migration Experiment injected 127Xe, 37Ar, 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 37Ar and 127Xe. (2) There were no significant differences in the 127Xe to 37Ar 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.