The temporal course of the internal radiation exposure after the Chernobylsk reactor accident

Most of the radionuclides released with a reactor accident such as Chernobyl possess short half-lives of a few hours to several days and weeks. Only two of the more relevant radionuclides, 134Cs and 137Cs, have half-lives of 2 and 30 years, respectively. Due to the high fixation of these two nuclides in soil, however, a significantly steeper decline of the availability in the environment is observed than corresponds to the radioactive decay. As a consequence the 137Cs-activity concentration in all relevant foodstuff decreased significantly faster than the physical half-life. The effective half-life of 137Cs in foodstuffs is about 1.5 - 2 years. This results in virtually unmeasurable activity concentrations in foodstuffs in 1999. By specific sampling, special sample preparation and long-term measurements efforts were undertaken to determine the presently remaining activity concentrations and the theoretically resulting ingestion dose. From these measurements an ingestion dose of 3.9 μSv for the adult and 1.8 μSv for the 5 year infant is derived in Austria 12 years after the fallout. This is equivalent to 1 % of the exposure in the first year after the reactor accident or to 0.1 % of the natural annual radiation exposure in Austria, respectively. Refs. 21 (author)