A long-term study of 137Cs distribution in soil

During a period of ten years, soil samples have been collected at the investigated site and analysed for 137Cs from the Chernobyl accident and from the nuclear weapons tests. The distance between the sampling plots at the different sampling occasions has been no more than three metres. The results show that the depth distribution of 137Cs is practically the same from year to year, indicating that the migration of caesium at this site is very small. The total activity measured in the soil samples have also been compared with the deposition calculated from the amount of precipitation at the site and the results of this comparison shows a good agreement with measured soil caesium. In this calculation is used the previously determined specific activity of 137Cs in the precipitation from nuclear weapons tests and from the Chernobyl accident, based on air activity concentration and the amount of precipitation. For the period 1962 to 1986 the calculated activity of 137Cs amounts to 1.41 kBq/m2 (the decay of all activities has been corrected to 1986) which is to be compared with the measured activity of nuclear weapons fallout in the soil samples, 1.06 kBq/m2 in 1988 and 1.60 kBq/m2 as a mean value of the samples of the first four years. The calculated activity of 137Cs of Chernobyl origin is 0.787 kBq/m2 and the measured activity in the soil samples is 0.789 kBq/m2. For the total activity the mean value of all soil samples give the result 2.28 kBq/m2 which is in good agreement with the calculated 2.20 kBq/m2. (au)