Study of distribution of 226Ra, 232Th and 40K in different rock formations and their dose estimation in and around Chickmagalur, India

The concentrations of radionuclides like 226Ra, 232Th and 40K and the dose rate are measured in igneous and metamorphic rock formations in and around Chickmagalur. A total of 236 samples from 13 different locations around study area were analyzed. The activity concentrations of the three radioactive elements were determined for mean period of 25000 s using HPGe (GMX - 10190) detector and the dose calculations were made using standard formulae. The mean activity concentrations in igneous rocks recorded were 36.6 Bqkg-1, 73.2 Bqkg-1 and 992.3 Bqkg-1 for 226Ra, 232Th and 40K respectively. The mean activity concentrations in metamorphic rocks were 17.2 Bqkg-1, 28.1 Bqkg-1 and 617.8 Bqkg-1 for 226Ra, 232Th and 40K respectively. Assuming 20% occupancy factor, the corresponding mean annual effective dose due to igneous and metamorphic rocks were 169.6 µSv and 90 µSv respectively. The concentrations of radionuclides were found to be in similar with global and Indian average (1-3).