Plutonium and americium in the deep Black Sea bottom sediments

The new data on Pu239+240, Pu-238, Pu-241, Am-241 vertical distribution in the deep western Black Sea sediments was analyzed. The sediment dating, obtained by means of Pu-238/Pu239+240 activity ratio vertical distribution, suggested the upper 3 cm layer of sediments to be formed during 27 years after the Chernobyl accident and the deeper layers to be formed earlier in pre-Chernobyl time (before 1986). The whole data set on profiles of radionuclides studied was shown to reflect the history of their input into the basin and elimination of these radionuclides from the water column. Analysis of inventories of plutonium alpha-emitting nuclides ensured a more significant contribution of Chernobyl fallout into the present total Pu-238 inventory than into Pu239+240 one. The Am-241 inventory after-deposition enhancement due to Pu-241 decay was estimated at 74% in pre-Chernobyl sediment layer and the general contribution of Pu-241 support in the total Am-241 inventory in situ enhancement was estimated at 49%.