Speaker
Description
For on-site inspection the radioactive noble gas isotope 37Ar is a definitive and unambiguous indicator of an underground nuclear explosion. In order to distinguish between natural and artificially elevated 37Ar the location-specific activity range in soils, rocks and the atmosphere were identified. Periodic atmospheric air measurements collected worldwide revealed a background level in the order of 1-5 mBq/m3air in agreement with former findings and theoretical calculations. Those calculations also indicated that the intrusion of stratospheric air masses may lead to elevated tropospheric 37Ar concentrations up to 8-10 mBq/m3air. From CARIBIC flights, a passenger aircraft with a special air freight container filled with scientific equipment in the cargo compartment, tropospheric air samples were analyzed for 37Ar and 85Kr. Selected samples taken up to now in the vicinity of nuclear power plants revealed no significant deviation from the natural background. The natural 37Ar production in soils and the rock basement underlying the alluvium is investigated by means of insitu measurements of different isotopes, theortical calculations and irradiation experiments on selected rock samples. This will help to resolve the temporal evolution and/or constancy of the natural 37Ar background and allow for an interpretation in terms of the identification of clandestine nuclear explosions.
