Assessment of the influence of radioxenon releases from radiopharmaceutical isotope production in the Southern Hemisphere on measured air concentrations at CTBTO IMS stations using atmospheric transport modeling (ATM)

Monitoring atmospheric radioxenon concentration is crucial for verifying compliance with the Comprehensive Nuclear-Test-Ban Treaty (CTBT) and may confirm the nuclear nature an underground explosion. The International Monitoring System (IMS) collects and analyzes air samples to determine the activity concentrations of radioxenon releases in the environment. Medical isotope production facilities contribute significantly to the background levels of radioxenon. This can potentially mask signals from a nuclear explosion. The understanding of the influence of known emissions on the observed radioxenon level is of crucial importance for treaty verification. This study used radioxenon observations at two IMS radionuclide sampling locations (AUX04, BRX11) to estimate the contribution of Southern Hemisphere medical isotope producers to the ¹³³ Xe background. The source strength of South Africa is the least well-known parameter so far, but it is thought to be the strongest source worldwide. This study also reveals that radioxenon is constantly being released by the medical isotope facility in Indonesia (INUKI). As a result, we have determined the upper range of daily discharges from all medical isotope production facilities in the Southern hemisphere.