Man-made plutonium radioisotopes in the salt lakes of the Crimean peninsula

摘要

Investigations of 239+240Pu and 238Pu in the surface layer(0-5 cm)of bottom sediment in the Crimean 10 salt lakes from 4 geographical groups were carried out for the first time.The 239+240Pu varied widely between regional geographical groups of lakes as well as within groups too and ranged from 11±4 to 451±43 mBq239+240Pu/kg.The highest levels of 239+240Pu—419±27,443±24 and 451±43 mBq/kg were observed in the Yevpatoriya(Lake Kyzyl-Yar),the Tarkhankut(Dzharylhach)and the Kerch group(Tobechik),respectively.The lowest values of 239+240Pu were identified in three lakes of the Perekop group and were 20±12,24±6 and 48±6 mBq/kg.In all lakes 238Pu was an order of magnitude lower than 239+240Pu and varied from 4.8±2.6 to 30.7±5.5 mBq/kg.The 238Pu activity was decay-corrected to 1986.The characteristic ratio of the 238Pu/239+240Pu activities in the sediment and percentage of the Chernobyl-derived Pu was calculated.The largest percentages of the Chernobyl-derived Pu were observed in the Evpatoriya group(Lake Sasyk-Sivash)-16.2%±8.26%,the Tarkhankut group(Dzharylhach)-8.4%±2.10%and the Kerch group(Aktash)-10.5%±5.56%.The study of the depth distribution of plutonium in the Lake Kyzyl-Yar bottom sediment core(0-25 cm)was fulfilled.It was shown that 239+240Pu was high enough in all studied layers of bottom sediment,but the highest activity ratio 238Pu/239—240Pu(0.062±0.020)was found in the deepest layer of 15-20.5cm and the percentage of Chernobyl-derived Pu was estimated at 6.8%±2.85%in this layer.