Activity distribution of fission products in the surface water of the Adriatic Sea

Abstract

The activity concentrations of ^Sr and '^Cs in the surface waters of the Adriatic Sea were investigated twice a year (in April and October, if possible) over the 1963 - 1997 period at four locations (towns of Rovinj, Rijeka, Split and Dubrovnik). The fallout samples were collected monthly in the town of Zadar. An exponential decline of radioactivity in sea water as well as in fallout samples followed the nuclear moratorium. After the nuclear accident at Chornobyl, higher levels of *^Cs were detected again, while the activity concentrations of *°Sr, that is less volatile than radiocaesium, have not been significantly increased. The coefficient of correlation between *°Sr activity concentrations in fallout and sea water was found to be fairly good, representing the fact that approximately 85% of man-made radioactive contamination in the Mediterranean Sea comes from fallout. The long term measurements were used to model the mean residence time of *°Sr in sea water. No significant variations of mean residence time on different locations were found, implying the uniform distribution of *°Sr through the mixed layer of the Adriatic Sea.