Radiation dose reconstruction and nuclear-explosion dating in the East-Kazakhstan region

Abstract

The radioecological situation in the East-Kazakhstan region was studied by electron paramagnetic resonance (EPR), radiography and nuclear spectroscopy methods. The eastern part of this region borders the Semipalatinsk nuclear test site. Radiation doses for 33 residents of this region were measured by EPR dosimetry in tooth enamel. It was found that for 25% of the residents the measured radiation doses do not exceed the background level. The rest of the doses exceed the background level by a factor of 2–4 on the average. A new method of nuclear explosion dating was developed on the basis of the EPR measurements of the free radical concentration in annual tree rings. Their maximal concentration corresponds to the years when nuclear explosions were executed. The obtained results correlate well with the commonly accepted radiography method. Both methods show a maximum of radionuclide levels in the years of nuclear testing. The plutonium-239 content in residents hair samples was found to be equal to (0.8±0.2)·10−9 g/kg and with activity of 1.9±0.4 Bq/kg. This is by a factor of 20 higher than the permitted content for the population.