Natural Radionuclides in Soils from Selected Regions in Bulgaria Affected by Natural and Anthropogenic Processes

The content of natural radionuclides 40K, 235U, 238U, 232Th and 226Ra in soils from two regions of past uranium mining in Bulgaria were determined and analyzed and results of radiation monitoring summarized. Soil samples from three other regions in the country: North Bulgaria - plane region (around “Kozloduy” Nuclear Power Plant and the Danube River) – 40 samples; semi-mountainous - (Sofia field) – 5 samples and South Bulgaria – mountainous (Rhodope massif) – 25 samples, were analyzed for comparison. Evaluation of possible radiation hazard to the population in the respective regions was made by calculatingthe average radium equivalent activity (Raeq) and the external hazard index (Hex). It was found that content of natural radionuclides in the studied soils, both plain and mountainous, is within normal background levels and is not hazardous to the population