On peculiarities of vertical distribution of ~(239,240)Pu, ~(238)Pu and ~(137)Cs activity concentrations and their ratios in lake sediments and soils

摘要

Distributions of ~(239,240)Pu, ~(238)Pu and ~(137)Cs activity concentrations in the cores of sediments in the shallow lake, flooded and upland forest soils taken in the vicinity of Vilnius city were analyzed. The radiochemical, α-spectrometric and mass spectrometric methods were used for the plutonium evaluation and γ-spectrometry was used for the radiocesium evaluation. The only peak of enhanced radionuclide activity concentrations was determined for the lake bottomsediments, whereas vertical profiles of the radionuclide activity concentrations in flooded and upland forest soil cores were distinguished by two peaks. The obtained values of the activity concentration ratio ~(238)Pu/~(239,240)Pu and the isotopic ratio ~(240)Pu/~(239)Pu indicated that the global fallout was a source of plutonium in the investigated environment. Chernobylderived radiocesium was detected solely in the surface layers (2–11 cm) of the studied sample cores.The contribution of the Chernobyl deposits amounted to about 2.26, 6.11 and 20.9 % of the total radiocesiuminventory in the bottomsediments, the upland soil and flooded soil, respectively.