Part of the International Monitoring System (IMS) for the Comprehensive Nuclear-Test-Ban Treaty (CTBT) is a network of highly sensitive radionuclide stations sniffing for tiny traces of fission and activation products in the atmosphere. All IMS radionuclide stations have a high volume sampler for the detection of particulate radionuclides, some are equipped with noble gas systems for the measurement of radioxenon. The specific radioactive xenon isotopes are more likely to escape from underground nuclear explosions and have less complex features in atmospheric transport. There are also radioxenon background emissions from legitimate nuclear facilities. Isotopic ratio analysis allows to a certain extend for source characterization and timing. Atmospheric Transport Modelling (ATM) in backward and forward mode is applied to connect the measurements in space and time with potential releases. Noble gas systems at IMS radionuclide stations used to operate with 24 or 12 hours sampling time. The next generation noble gas systems utilize shorter sampling periods. At station RN33 on Mount Schauinsland, Germany, a SPALAX system with 24 hours sampling is operated by BfS. In the phase II testing a “Xenon International” system with six hours sampling time and better sensitivity to Xe-135, Xe-133m and Xe-131m was installed in parallel from July 2021 to April 2022. The main contributing emitter to elevated xenon activity concentrations at RN33 is the medical isotope production facility at Fleurus, Belgium.We investigated how the increase in time resolution in sampling and ATM changes the location capability of backward ATM. For that, the Lagrangian Particle Dispersion model HYSPLIT (NOAA-ARL) is applied driven by GFS meteorological data for all samples of the test phase. Calculation of expected Xe-133 contributions from Fleurus derived by ATM backward sensitivities and emission data show generally good agreement. As the Xenon International system also allows for additional detections particularly of Xe-135 and isomers Xe-133m and Xe-131m, the sensitivity to unknown additional sources is potentially improved and analysed. A coincidence analysis of repeating or in respect to isotopic composition remarkable detections which could not be well explained by emissions from Fleurus show several other potential source regions pointing to several Nuclear Power Plants and research reactors.

Station RN33 on Mount Schauinsland near Freiburg, Germany, is part of the International Monitoring System monitoring radioxenon in air (131mXe, 133Xe, 133mXe, and 135Xe) for verification of the Comprehensive Nuclear Test Ban Treaty. Here, we present data from phase II testing of a new system, Xenon International at RN33, July 14th, 2021 to Jan 22nd, 2022, together with SPALAX data from the same time period. Radioxenon could be detected in 473 of 719 samples, among them many multiple isotope detections. Activity concentrations of spiked and selected environmental samples were verified by laboratory reanalysis. The sensitivity of Xenon International for radioxenons is up to one order of magnitude better for the metastable isotopes than that of the SPALAX, with a shorter sampling duration of 6 h.

We present a model written in python to evaluate data from comprehensive 85Kr collection schemes comprising 11 datasets from different monitoring stations around the globe. The model is designed to (1) calculate atmospheric input functions for the application of 85Kr as a dating tracer and (2) to investigate atmospheric circulation based on a two-box model of the atmosphere. Different functions were implemented, to (1) filter the data, (2) fit polynomials and running means, (3) extrapolate fits from the northern to the southern hemisphere, (4) calculate interhemispheric exchange times and 85Kr emission rates and (5) export data to a csv file.Although the model is designed to evaluate atmospheric 85Kr datasets, some functionality and basic concepts can be applied to other dating tracers, like tritium and SF6. • Standardized method to systematically analyse atmospheric 85Kr activity concentration time series for dating water and ice and to investigate atmospheric circulation. • Easily modifiable python script to adapt functions for similar data analysis procedures.