Long-term Availability of Sr-90 in Foodstuff after Nuclear Fallout

Among the many radionuclides possibly released in a severe reactor accident or a nuclear weapons detonation 137Cs and 90Sr are of particular importance. Due to their long physical half-life of 30 and 28,5 years respectively, the exposure of the population by these nuclides will last for decades and has to be taken into account in estimating the total 50 year-exposure caused by the fallout and in evaluating coutnermeasures with regard to land utilization. However, their effective decrease in the environment with regard to the population exposure follows a much shorter half-life reducing the exposure of the public much quicker than estimated from the physical half-life and therefore, permits an earlier re-utilization of a higly contaminated territory. A thorough knowledge of the decrease in availability of these nuclides in foodstuffs relevant to the ingestion dose, therefore, is of great importance. While for Cs this was investigated before, this work concentrated on the effective decrease in 90Sr. The long-term availability of 90Sr in milk was investigated as a main indicator of the environmental behavior of this radionuclide in the environment and as the most important foodstuff with regard to 90Sr-intake of the infant. An estimate of the dose in infants and the adult in central Europe 35 years after the end of atmoshperic nuclear wapons testing and 14 years after the reactor accident in Chernobyl is presented and compared to the dose of other long-lived radionuclides in the environment. Since 137Cs is easier to determine and therefore often used as main indicator for the contamination of the environment, ratios of 90Sr to 137Cs are given for the period after the wapons tests and after the Chernobyl accident up to the present time. The variation in this ratio with time and its causes as well as the differences in environmental decay of these two radionuclides are discussed.