Measurement of radioxenon and radioargon in air from soil with elevated uranium concentration.

Among the most important indicators for an underground nuclear explosion are the radioactive xenon isotopes 131m Xe, 133 Xe, 133m Xe and 135 Xe and the radioactive argon isotope 37 Ar. In order to evaluate a detection of these nuclides in the context of a nuclear test verification regime it is crucial to have knowledge about expected background concentrations. Sub soil gas sampling was carried out on the oil shale ash waste pile in Kvarntorp, Sweden, a location with known elevated uranium content where 133 Xe and 37 Ar were detected in concentrations up to 120 mBq/m3 and 40 mBq/m3 respectively. These data provides one of the first times when xenon and argon were both detected in the same sub soil gas. This, and the correlations between the radionuclides, the sub soil gas contents (i.e. CO2 , O2 , and radon) and uranium concentration in the pile, provide very interesting information regarding the natural background and the xenon concentration levels and can most likely be used as an upper limit on what to be expected naturally occurring.