Thyroid and Whole-Body Dose Reconstruction in Russia Following the Chernobyl Accident: Review of Progress and Results

Abstract

The results of direct measurements of radioactive iodine content in the human thyroid gland (in Bryansk and Kaluga regions, Russia) and also available data on 131I and 137Cs contamination of the soil were used for investigation of correlations between the mean thyroid dose for adults in settlements and local levels of 137Cs and/or 131I soil contamination. On the basis of this analysis a model was developed showing how to evaluate retrospectively the thyroid absorbed doses. For individual dose reconstruction using an 'age/milk' scale, special questioning of inhabitants was carried out. Mean dose values in the exposed population of each contaminated Russian settlement were evaluated using the model. The total collective dose due to internal exposure of the thyroid gland by iodine radionuclides equates to 106,500 person.Gy in the population of the most contaminated territories of four Russian regions. The maximum value was found in the Bryansk region (73,000 person.Gy). New data concerning the delay in pasturing in different regions as well as time dependencies of the fallout were taken into account. As a result the dose estimations differ from previous published data. Comparisons between the developed method and the other independent approaches indicate a concordance within a factor 3. For application of the EPR tooth enamel dosimetry on a wide scale, estimation of accumulated external doses are demonstrated and analysed. There were about 2500 tooth samples measured from the contaminated region as well as from the non-contaminated territories of Russia. The investigated factors are: (1) effect of solar light on front teeth; (2) correction for the energy dependence of the EPR response; (3) presence in the enamel of some intrinsic signals; (4) age dependent doses due to natural background radiation. The average values of EPR dose with special account taken of correction factors are presented. The tendency of average doses to grow with the level of 137Cs contamination of settlements was found (the linear regression with the slope equates to 2.4 ± 0.5 mGy per Ci.km-2). This tendency is close to that of analytical calculations.