Abstract
The results of reconstruction of the radionuclide composition of the Chernobyl fallout in the territories of Russia is presented. Reconstruction has been carried out by means of statistical analysis of the gamma spectrometry data on 2867 soil samples collected in the territories of Ukraine, Byelarus and Russia from 1986 to 1988. To verify the data, aggregated estimates of the fuel composition of the 4th block at the moment of the accident (available from the literature) have been used, as well as the estimates of activity released to the atmosphere. As a result, correlation and regression dependences have been obtained between the activities of the radionuclides most contributing to the dose (137Cs, 134Cs, 131I, 140Ba, 95Zr, 95Nb, 103Ru, 106Ru, 141Ce, 144Ce, 125Sb). Statistically significant regression relations between different pairs of radionuclides (including analysis of the 'noise' contribution to the data) depending on the distance between the point of sample collection and the power station are presented for the 'north-east track' - the northern part of the 30 km zone and southern part of the Gomel district (Byelarus) and the Briansk, Kaluga, Tula and Orel districts (Russia). A methodology is also described for reconstruction space-time characteristics of the contamination of the territories by major dose-forming radionuclides released from the Chernobyl NPP 4th unit. This methodology is based on the results of modelling atmospheric dispersion of radionuclides released between the time of the accident and 20 May 1986, on data from gamma spectrometry of soil samples collected around the populated areas in 1986-1988, and on available data for exposure dose rates in the populated areas. Based on the developed model of 'local effective precipitation' volumetric concentrations and deposition rates of major radionuclides (including short-lived ones) are reconstructed and these are then used to derive a time dependence of exposure rate. Account is taken of vertical migration of radionuclides and attenuation by snow cover. The data obtained are further used to assess external absorbed doses from depositions and passing radioactive plumes.
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