A comparison of long-term 37Ar and 39Ar transport and implications for 39Ar as a persistent indicator of underground nuclear explosions

Measurements were first made in 2016 of legacy 39Ar gas from the decades-old Barnwell underground nuclear explosion site within the Nevada National Security Site. This has raised the question of the ubiquity of the radionuclide 39Ar following underground nuclear explosions in general locations. This work presents a high-level evaluation of the scientific case for using 39Ar as a long-term indicator of underground nuclear explosions. Assessment is made based on a broad set of assumptions to reasonably estimate the persistence of 39Ar in the subsurface environment following an explosion to establish potential detectability years to decades after the originating event.