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

A Noble Gas Migration Experiment injected 127 Xe, 37 Ar, 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) SF 6 was enriched in all of the samples relative to both 37 Ar and 127 Xe. (2) There were no significant differences in the 127 Xe to 37 Ar 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.