Measurement of radioxenon and radioargon in soil gas collected in the region of Kvarntorp, Sweden.

Over 40 soil gas samples were collected both in post-industrial areas as well as in undisturbed areas in the region of Kvarntorp, Sweden. Radioxenon (133Xe) was detected in 15 samples and radioargon was detected in 7 from 10 samples analysed. The concentration of radioxenon and radioargon in soil gas ranged up to 109 mBq/m3 and 19 mBq/m3, respectively. During sample collection other soil gases such as radon, CO2 and O2 were also measured and soil samples were taken along with dose rate measurements. The field experiment presented here shows that it is possible to detect naturally occurring radioxenon and radioargon in soil gas simultaneously.

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 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.

Radioxenon detections in the CTBT international monitoring system likely related to the announced nuclear test in North Korea on February 12, 2013.

Observations made in April 2013 of the radioxenon isotopes (133)Xe and (131m)Xe at measurement stations in Japan and Russia, belonging to the International Monitoring System for verification of the Comprehensive Nuclear-Test-Ban Treaty, are unique with respect to the measurement history of these stations. Comparison of measured data with calculated isotopic ratios as well as analysis using atmospheric transport modeling indicate that it is likely that the xenon measured was created in the underground nuclear test conducted by North Korea on February 12, 2013, and released 7-8 weeks later. More than one release is required to explain all observations. The (131m)Xe source terms for each release were calculated to 0.7 TBq, corresponding to about 1-10% of the total xenon inventory for a 10 kt explosion, depending on fractionation and release scenario. The observed ratios could not be used to obtain any information regarding the fissile material that was used in the test.