The radionuclide station network of the IMS

Most of the 241 stations incorporated in the global monitoring network of the IMS are based on wave technologies – seismic, infrasound and hydroacoustic – to be able to detect and localise any nuclear explosions anywhere around the world. Although these techniques can identify explosions, they cannot differentiate between chemical and nuclear explosions. This is the job of the radionuclide measuring network with its 80 trace measurement stations around the world for detecting radioactivity in the air. They are used to unequivocally confirm whether an explosion has a nuclear character. Air mass analysis is carried out to confirm the presence of radionuclides released by nuclear explosions which are not otherwise naturally present. One of the stations in the global network at Schauinsland near Freiburg – station RN33 is operated by the Federal Office for Radiation Protection (BfS) on behalf of the German government. Together with another 39 stations, this station is also equipped with sensors to measure the presence of noble gas isotopes in the air which enables the unequivocal identification of underground or underwater nuclear explosions.

The world topographic map shows the location of the 80 radionuclide stations which are marked with squares. RN33 is the German station near Freiburg. Source: BGR

The sample in the sensor is removed only once a day after more than 1000 cubic metres of air have been filtered. This is done to ensure that the analysis is as reliable and precise as possible. This means that a clear interpretation of whether a critical event is caused by a chemical or a nuclear explosion can take several days given that the transport of radioactive isotopes in the troposphere is strongly dependent on the weather conditions. However, analysis of the radioactive elements in the air is so sensitive that e.g. the improper handling of weakly radioactive material in a hospital in southern France set off an alarm at RN33.

Example of a radionuclide spectrum Source: BGR