Estimating uncertainties in external and internal radiation doses in people resided in contaminated regions of Russia after the Chernobyl accident with the use of instrumental data

The paper presents the results estimation of uncertainties in doses to the thyroid, from external and internal exposure to radiation following the Chernobyl accident. For the estimation the database of radiometry activities of 134+137Cs in the body and 131I to the thyroid in 1986 for 28,311 residents of Kaluga region and 16,470 residents of Bryansk region. Whole body radiation spectrometry measurements made for 167,325 residents of Bryansk region from 1990 through 1994 were used. The computational model for reassessment of 131I activities into individual exposure doses is an analytical relationship that describes the relative dynamics of radionuclide activities in a chain consisting “vegetation”, “milk”, “thyroid” and “inside the human body”, that is the chain of successive single-chamber models with time-constant transition rates between chambers and depending on the age of a person after single deposition of radionuclides on vegetation. The dynamics of specific activities of 131I, 134+137Cs in the vegetation chamber is calculated according to the agroclimatic model, with account of the dynamics of precipitation, the growth of forage and food vegetation biomass according to the data of the annual variation of average daily air temperatures in the surface layer of the atmosphere. The official methodology was used to calculate external exposure doses and reassess whole body radiation spectrometry measurements into internal exposure doses. Based on the results of the studies, uncertainty estimates were obtained in terms of standard geometric deviations in the year of the accident - for individual, average in populated areas and integral dose estimates: (minimum/average/maximum) doses of internal thyroid and whole body exposure, respectively (1.1/2,0/3.0), (1.2/1.5/2.3) and (1.3/2.9/3.3); for doses since 1987, respectively (1.2/1.9/4.0), (1.2/1.9/2.1) and (1.4/5.2/8.2). The uncertainty of the calculation model for internal doses since 1987 is estimated at 2.1 times; the uncertainties estimated from the data of individual dosimetry of external and internal exposure of the population with the allocation of critical groups are equal to 1.5 and (1.9-2.2) times, respectively.