Assessment of natural radioactivity and radiation hazard indices in soil samples of East Khasi Hills District, Meghalaya, India

The Activity Concentrations of naturally occurring radionuclides such as 40K, 238U and 232Th were determined from 20 (twenty) villages of East Khasi Hills District of Meghalaya, India using gamma-ray spectroscopy. This District is adjacent to the South-West Khasi Hills District located in the same state where heavy deposit of uranium has been identified [1]. The measured activities of 40K, 238U and 232Th were found ranging from 93.4 to 606.3, 23.2 to 140.9 and 25.1 to 158.9 Bq kg−1 with their average values of 207.9, 45.6 and 63.8 Bq kg−1, respectively. The obtained value of activity concentration for 40K is lower than the world average value 400.0 Bq kg−1 while for 238U and 232Th, the average concentrations are above the world average values 35.0 and 30.0 Bq kg−1, respectively. The calculated Absorbed Dose Rate gamma-radiation of the natural radionuclides ranged from 37.4 to 186.5 nGy h−1 with an average of 71.3 nGy h−1. The outdoor Annual Effective Dose Rate received by an individual ranged from 50.0-230.0 µSv y−1 with an average value of 87.5 µSv y–1. The physical and chemical properties of the soil have no effects on the naturally occurring radionuclides concentrations. This has been revealed by the results obtained as there is no positive correlation between physical/chemical parameters and the radionuclides concentrations in the soil samples [2]. It is observed that good positive correlations among the radionuclides concentrations and with the measured dose rate prevail. The findings show that the values of external and internal hazard indices resulting from the measured activity concentrations of natural radionuclides in soil from the collected sampling areas are less than the International Recommended safety limits of 1 (unity) with the exception of Mylliem (1.12) where the External hazard index is slightly higher.