INVESTIGATING ISOTOPIC RATIO DISTRIBUTIONS AT IMS RADIONUCLIDE
STATIONS USING EMISSIONS FROM NUCLEAR FACILITIES WITH DECAY
CORRECTION BASED ON THE ATMOSPHERIC TRANSPORT TIME
DISTRIBUTIONS FOR ONE YEAR

The isotopic ratios of radioxenon can be useful for the discrimination between CTBT-relevant radioxenon detections related to nuclear testing and emissions from nuclear facilities. The typical isotopic ratios of radioxenon released from nuclear facilities are well known. However, due to the short half-life of some of the relevant radioxenons, the isotopic ratios have changed when reaching the International Monitoring System (IMS) radionuclide stations. For a better understanding of the expected isotopic ratios at the IMS stations, the isotopic ratio distributions of emissions from the nuclear facilities are evaluated first. Secondly, the source receptor sensitivity (SRS) fields calculated operationally with atmospheric transport modelling (ATM) are utilized to determine for these radionuclides the distributions of the travel times for one year between these facilities and the IMS stations. Then, the isotopic ratio distributions that can be expected for measurements at IMS stations can be calculated by folding these two kinds of distributions (emission and atmospheric transport time) while applying the radioactive decay equations. Finally, we compare these calculated isotopic ratio distributions of measurements at IMS stations with the real isotopic ratio distributions of measurement at IMS stations. This investigation can help to develop methods for screening by distinguishing between normal (based on known sources) and anomalous isotopic ratios. It may also be useful for discrimination between CTBT-relevant radioxenon detections and estimated observations based on emissions from known nuclear facilities as part of the effort of developing a Xenon Background Estimation Tool (XeBET).