Comparison of near-background concentrations of Argon-37 and Xenon-133 in the atmosphere

Radioisotopes of the noble gases xenon and argon can be important indicators of underground nuclear explosions. The Comprehensive Nuclear-Test-Ban Treaty (CTBT) includes monitoring capabilities to identify potential nuclear explosions conducted in violation of the CTBT. This monitoring currently focuses on measurement of the xenon isotopes 131mXe, 133Xe, 133mXe, and 135Xe. However, it is predicted that within 100 days of an underground nuclear explosion (UNE) 37Ar would be released to the atmosphere at higher concentrations than xenon and with a higher signal to background ratio, depending on the radioxenon background levels. Therefore, inclusion of 37Ar measurement capabilities at atmospheric International Monitoring System (IMS) stations may represent an improvement in the capability to detect a nuclear explosion.