Distribution of radon activity in the atmosphere above Wzgórza Niemczansko-Strzelinskie (South-WestPoland) and its dependence on uranium and thorium content in the underlying rock and indirect ground basement

Radon activity in the atmosphere and its behavior in the environment have been investigated using LR-115 nuclear track detector. The complex geological structure of Wzgórza Niemczansko-Strzelinskie (south-west Poland) enabled this problem to be studied in various geological conditions. The eU and eTh content in rocks and soil was measured by gamma-spectrometer GR-320. Uranium content of bedrock reached its maximum value of 15 ppm in the case of quartz-graphite schist. Thorium reached its maximum value of 35 ppm in the case of granodiorite. Radon activity was measured by means of long-term exposure of LR-115. The mean value of atmospheric radon activity was 21 Bqm-3 in the air 2 m above the ground surface. The highest radon activities were measured in the area of granite and quartz-graphite schist outcrops and in the area of mylonitic rocks of the Niemcza Zone. Radon activity in close to ground cup detectors varies from 25 to 300 Bqm-3, these values depend on uranium and thorium content in indirect ground basement (soil and weathered rocks). Not only uranium and thorium content but also rock disintegration due to tectonic events (shear zones) influenced atmospheric radon activity. Seasonal variation is not strong, although higher values were measured in the autumn- winter period