ИСТИНА

A relatively high level of the 239,240Pu isotopes’ total activity was discovered. Pu activity in two series of lake bottom sediments (sediment layers 0.0–0.5 and 0.5– 1.0 cm). In the surface layer, the specific activity of the 239,240Pu isotopes varied from 162.3 to 191.2 Bq kg-1 in the two series of samples, while in the 0.5-1 cm layer, its concentration was as low as 7.9-13.7 Bq kg-1. To separate the isotopes (239 and 240), ICP-MS analysis was conducted. The mass spectrometric analysis results confirmed the plutonium isotopes’ activity concentration levels, revealing a 239Pu level of 85 ± 2 ppt and a 240Pu level of 14 ± 2 ppt. Plutonium isotopes 241 and 238 were not detected, i.e., in both cases, the 238,241Pu specific activity and concentration levels were below the detection limit.