Sedimentation of cobalt-60 and caesium-137 released in Träven, a Baltic bay

The amounts of cobalt-60 and caesium-137 bound in the sediment in a bay off the Studsvik research station were determined. Of the cumulative released activity during 22 years, 19% of ⁶⁰Co and 1.8% of ¹³⁷Cs were found in the sediments within an area of 23 km². The rate of input through sedimentation and the loss rate through physical decay were of the same order in 1981 and were close to steady state for ⁶⁰Co while for ¹³⁷Cs they had only reached 30% of that level. The sedimentation coefficients calculated for the bay were 6·5 year⁻¹ for ⁶⁰Co and 0·49 year⁻¹ for ¹³⁷Cs, higher values than many published previously. Cobalt-60 seemed to precipitate close to the outlet and to migrate near the bottom as bed-load.