Weathering and Migration of Chernobyl Fall-out in Sweden

In situ gamma spectrometer measurements of the Chernobyl fall-out in Sweden have been made in the Gävle and Studsvik areas. The main objective of the measurements was to study the weathering effects on typical urban surfaces and migration on permeable surfaces. Measurements were made in May, July and September 1986 and in May 1987. The average remaining fraction after 12 months is about 0.4 (excluding decay). No significant differences between typical urban surfaces were found, except for paving stones, which showed a remaining fraction of 0.8. The depth distribution profiles in soil showed a half-value depth of a few centimetres. Activity was found below 20 cm, which indicated other transport mechanisms than pure diffusion. A similar behaviour of all nuclides with respect to both weathering and migration, indicates that the main part of the activity is bound to carrier particles.