Evaluation of natural radioactivity in rocks of Nilgiri hills and their radiation hazard to mankind

Twenty three rock samples were collected from various altitudes of Nilgiri hills, Tamil Nadu, India. A survey was carried out to determine the activity concentration of selected radionuclides ( 238 U, 232 Th, 40 K) by means of gamma-ray spectroscopy using NaI (Tl) detector. From the measured spectra, the mean activity of 238 U, 232 Th, 40 K are 7.13 Bq kg -1 , 30.47 Bq kg -1 and 346.06 Bq kg -1 , respectively. To evaluate the radiological effects, the absorbed dose rate, effective absorbed dose rate, radium equivalent activity, external and internal hazard indices, and radioactivity level index are also calculated. The mean absorbed dose rate of gamma radiation ranged from 11.90 nGy h -1 to 108.22 nGy h -1 . The activity concentration of 238 U, 232 Th, 40 K and the various radiological effects are below the internationally recommended maximum values.