Re-evaluation of thyroid doses in Russia after the Chernobyl accident

Abstract

Immediately after the Chernobyl accident, the team of Medical Radiological Research Center (MRRC) specialists carried out wide-scale measurements of iodine-131 content in the thyroid gland of 27 887 inhabitants of the Kaluga region. This initial information was presented only as official reports to governmental structures. Similar work was done by local specialists for 1441 inhabitants of the Bryansk region. The data of direct measurements provided us the basis for further individual thyroid dose estimations, where we exploited the developed model and personal interviews. This paper presents the results of updated dose evaluations, including the additional factors, such as dynamics of fallout and data on the pasture period. According to new estimations, the median of individual dose values in the Kaluga database (seven districts) vary from 30 mGy for children to 8 mGy for adults (geometric standard deviation of about 2.6). In the database of Bryansk (five raions), the median dose values are ranging from 140 mGy for children to 30 mGy for adults (geometric standard deviation of about 2.7). The obtained data were used for the validation of the semi-empirical model for thyroid dose reconstruction. This allowed the reconstruction of the mean doses for the settlements where I-131 measurements were not performed. The collective thyroid doses for the Bryansk and Kaluga regions were estimated as 72 600 and 3400 persons-Gy (for population of 1 137 100 and 213 500 inhabitants).