An assessment of natural radioactivity levels and radiation hazards in the soil of Coonoor, South India

The concentration of naturally existing primordial radionuclides (²³⁸U, ²³²Th and ⁴⁰K) in the soil at various locations in Coonoor, South India has been determined from the gamma spectrum of soil recorded using a low-background NaI(Tl) detector coupled to 8 K multichannel analyzer system. The average concentration of ²³⁸U, ²³²Th and ⁴⁰K radionuclides in the soil has been found to be 41.5, 78.0 and 295.6 Bq kg⁻¹, respectively. The mean concentration of ²³²Th and ²³⁸U estimated in the soil of the study area is found to be 2.6 and 1.2 times the corresponding value reported as the world average. The absorbed gamma dose rate in the air at 1 m above the soil due to these radionuclides has been calculated as 78.6 nGy h⁻¹ and it is found to be 1.54 times the world average value. The radium equivalent activity (Ra_eq) of soil has been calculated and it is found to be 175.9 Bq kg⁻¹. The external hazard index (H _ex) and the internal hazard index (H _in) of soil are estimated as 0.47 and 0.59, respectively. Ra_eq, H _ex and H _in of soil in the study area are found to be less than recommended level and it is safe to live in the study area. The variation in the activity concentration of primordial radionuclides with depth is also studied. It has been found that their concentration decreases with depth. The annual outdoor and indoor effective dose equivalent is found to be 96.45 and 385.79 μSv year⁻¹, respectively.