Implications of conflicting cross sections for the 40 Ca(n,α) 37 Ar reaction as applied to nuclear explosion monitoring

Radioactive 37 Ar produced mainly from the 40 Ca(n,α) reaction is relevant for nuclear explosion monitoring. However, the 40 Ca(n,α) 37 Ar thermal neutron cross section is poorly understood. The JEFF-3.3 and JENDL-4.0 cross section libraries have differing models in the thermal region for the 40 Ca(n,α) 37 Ar reaction causing a difference in the predicted 37 Ar yield from a potential nuclear detonation. MCNP and SCALE were used to model the production of 37 Ar from a one kiloton detonation in several rock types and revealed that the elemental composition of rock affects the impact of thermal neutrons on 37 Ar yield. Thus, further examination of the 40 Ca(n,α) 37 Ar reaction is recommended.