Carbon-14 content in surface soils near atmospheric and below ground nuclear detonations

Global and regional releases of ¹⁴C have resulted from nuclear weapons testing activities; assessment of the chemical behavior and mechanisms of environmental transport and deposition of this radionuclide can assist remediation strategy development efforts and provide insights into global carbon cycling processes. This work reports a systematic evaluation of ¹⁴C in surface soils taken from the Nevada National Security Site. Surface soil samples are derived from above- and underground test locations, with underground test sites representing a range from near complete containment to uncontrolled radioactive releases. Only one surface soil taken from a underground test location (i.e. the Baneberry shot) shows elevated ¹⁴C concentrations (319 ± 9 pMC) in addition to elevated concentrations of ¹³⁷Cs, ⁶⁰Co and ¹⁵²Eu above regional backgrounds. Surface soils from above-ground test locations show extremely high ¹⁴C content (~1000 to 10,000 pMC); elevated concentrations of ¹⁵²Eu and ⁶⁰Co for these soils are also observed, with ¹³⁷Cs at or below background levels. Taken together, these data suggest that ¹⁴C in surface soils from above-ground tests is primarily derived from in-situ neutron activation of the native soil material, whereas ¹⁴C in surface soils from underground tests may be from either recondensed particulate material or soil activation.