Long-term external and internal irradiation of inhabitants in an area highly contaminated by the Chernobyl accident

From 1990 to 1998, estimations of the effective dose from external and internal irradiation due to l 3 7 Cs and >,ACs were carried out for inhabitants in rural villages in theBryansk region, Russia, highly contaminated due to the Chernobyl accident in 1986. Yearly expeditions were conducted in autumn. The external effective dose was estimated from measurements with thermoluminescent (TL)dosemeters worn by the participants during one month each year. The internal effective dose was estimated from measurements of the urinary concentration of caesium radionuclides, together with measurements of the body content using a portable detector. The mean effective dose from external and internal irradiation varied between 1.2 and 2.5 mSv per year between 1990 and 1998. The total mean effective dose decreased, on average, 7% per year, while the mean external dose decreased by 15% per year. The dose rate from internal irradiation decreased more slowly than the dose rate from external irradiation, showing large variations from year to year depending to a great extent on dietary habits. The contribution from the external dose to the total dose was between 50-70%, depending on the village. The cumulated effective dose for the 70-year period after the accident was calculated to be 100 mSv with the assumption that both internal and external dose will decrease by 2% per year.