“Zero Point” Background Screening of 137cs and Pu Isotopic Composition for Radiation Environment in Eastern Lithuania

Detection of environmental concentrations of radionuclides is the next step to complement data on abnormal events recorded by seismic, hydro-acoustic and infrasound station networks prior to asking for the approval of the on-site inspection. Radionuclides can travel hundreds of kilometres away from their source and under favourable meteorological conditions, be detectable in the air and when deposited on the ground. In order to determine and assess contributions to the anthropogenic radionuclides in the environment and to firmly distinguish it from previous global nuclear tests or emissions from nuclear facilities, it is essential to screen the background “zero point” of the anthropogenic radionuclides. This is especially important around existing sources e.g. nuclear power plants. In this work the radiochemical separation of radionuclides, alpha-, gamma- and mass-spectrometry measurement techniques were combined to determine concentrations and compositions of anthropogenic radionuclides in soil samples within 70 km radius around the Belarussian nuclear power plant in Astravec, on the territory of Lithuania. Gamma spectrometric measurements were performed with state-of-the-art alpha spectrometers and gamma spectra were acquired using an HPGe coaxial detector. Radionuclide isotopic ratios were measured by a sector field mass spectrometer combined with a high-sensitivity APEX sample introduction system. In this work 137Cs/239,240Pu, 238Pu/239,240Pu, 240Pu/239Pu isotopic “fingerprint” values revealed that previous nuclear weapon tests in the Northern hemisphere are prevailing in most of the sampling sites within a 70 km radius around Astravec NPP on the Lithuania territory.