Spatial patterns and ratios of 137Cs, 90Sr, and Pu isotopes in the top layer of undisturbed meadow soils as indicators for contamination origin

Spatial distribution of activity concentrations of Cs-137, Sr-90, and Pu-239,Pu-240 in the top layer of undisturbed meadow soils was compared between two regional transects across Lithuania: one in the SWregion, more affected by the Chernobyl radioactive fallout, and the other in the NE region. Radiochemical, gamma-, alpha-, beta-, and mass spectrometric methods were used to determine the radionuclide activity. Our results validate that higher activity concentrations in the top soil layer were present in the SW region, despite the fact that sampling was performed after 22 years of the Chernobyl Nuclear Power Plant (NPP) accident. Using the activity concentration ratio Cs-137/Pu-239,240(global), the contribution of the Chernobyl NPP accident to the total radiocesium activity concentrations in these meadow soils was evaluated and found to be in the range of 6.5-59.1 %. Meanwhile, the activity concentration ratio Pu-238/Pu-239,Pu-240 showed that Chernobyl-derived Pu occurred at almost half of the sampling sites. The locations with maximal values of 47 % of Chernobylderived Pu material were close to northeastern Poland, where deposition of most of non-volatile radioisotopes from the Chernobyl plume was determined.