Natural Radioactivity in Soil and Radiological Risk Assessment in Lisava Uranium Mining Sector, Banat Mountains, Romania

The specific activity and spatial distribution of U-238, Th-232 and K-40 were determined in the surface soil from the Lisava uranium mining sector. This sector belongs to the Banat district, an historically important uranium mining area in Romania (an area with closed uranium mines and a radioactive waste dump). Gamma-ray spectrometry using a high-purity germanium (HPGe) detector was used to measure the activity of naturally occurring radionuclides in the soil. The average specific activities of U-238, Th-232 and K-40 in the soil were 197.21 Bq/kg for U-238, 16.21 Bq/kg for Th-232 and 543.21 Bq/kg for K-40. The mineral contents of selected waste rock samples (sandstones) were examined using a scanning electron microscope (SEM), which revealed that brannerite, pitchblende and coffinite were the most important uranium-bearing minerals. The means of the radiological hazard parameters were calculated to be 262.22 Bq/kg radium equivalent activity (Raeq), 123.72 nGy/h absorbed gamma dose rates (DR), 0.7 external hazard index (Hex) and 1.8 representative level index (RLI). The spatial distribution of the risk assessment indices associated with the investigated soils exceeded the median values provided by UNSCEAR and reflected the geological settings and influences of anthropic activities such as uranium mining practices and the tipping of radioactive mining waste.