Distribution of the radiation doses in South Urals of former Soviet Union investigated by Electron Spin Resonance dosimetry of mammal teeth

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After the World War II, former Soviet Union constructed its first plant complex in South Ural, which produces plutonium, starting its operation in 1948. There were three major accidents, such as contamination of Techa river, associated with this plant complex. This region of South Ural has been contaminated with huge amount of radioactive nuclei from nuclear waste, especially with Strontium-90. Strontium replaces calcium of bones and teeth, therefore, it is taken into hydroxyapatite of tooth enamel and dentin which are examined by the present research project, giving internal doses. In the present study, 25 cow teeth from Ozersk in which the plant complex is located and from surrounding villages were examined to obtain the concentrations of Strontium-90 and radiation doses. Imaging plates sensitive to beta rays were used to obtain the concentrations. The teeth were cut in half and were placed on an imaging plate for a week in a low background lead cave. The images of the Strontium-90 distribution were obtained by the imaging scanner from the imaging plate. Quantitative measurement was available by measuring the standard samples of dentin containing known concentrations of Strontium-90. The images were found for 5 teeth of those samples. The concentrations of Strontium-90 were low in enamel but higher in the region between dentin and enamel. The maximum concentration was about 15 Bq/g. Teeth from highly contaminated area have higher Strontium-90 concentrations but with some variations. The radiation doses given to tooth enamel were measured by ESR method. Nominal doses of 300 to 400 mGy were obtained for 4 teeth samples, however, these should be considered to be tentative values because these may be overestimated due to larger background signal which is different from human teeth. Another scheme to obtain doses from cow teeth should be developed with considering the species-specific background signal.