Plutonium Contamination Level and Isotopic Composition in Soils around St. Petersburg

Plutonium isotopic composition including ²³⁸Pu, ²³⁹Pu, ²⁴⁰Pu, and ²⁴¹Pu and the Pu contamination level are determined in soils around St. Petersburg using an advanced procedure involving radiochemical separation stage followed by the -ray spectrometric and mass spectrometric determination. The Pu specific activity in surface horizons (0-25 cm) ranges from 0.2 to 0.44 Bq kg^-1. The mean ²³⁸Pu/239,240Pu activity ratio is found to be 0.033±0.007. The Pu contamination level of the surface horizon (0-25 cm) is 62±5 Bq m^-2. The ²³⁸Pu/²³⁹Pu, ²⁴⁰Pu/²³⁹Pu, and ²⁴¹Pu/²³⁹Pu isotopic ratios are (2.0±0.5)×10^-4, 0.172±0.004, and 0.003±0.002, respectively. These ratios are close to the values typical of plutonium from the global radioactive fallout due to nuclear weapons tests in the atmosphere. The effect of the Chernobyl accident and regional potential contamination sources, including the Leningrad NPP, on the Pu isotopic composition and contamination level in the soil is insignificant.