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

Highlights: • Sub soil sampling in an area with known high uranium content. • Detection of both radioxenon and radioargon in sub soil gas. • The study provides interesting information regarding natural background of radioxenon. - Abstract: Among the most important indicators for an underground nuclear explosion are the radioactive xenon isotopes ^131mXe, ¹³³Xe, ^133mXe and ¹³⁵Xe and the radioactive argon isotope ³⁷Ar. 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 ¹³³Xe and ³⁷Ar 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.