Measurement of gamma radiation levels in soil samples from Thanjavur using γ-ray spectrometry and estimation of population exposure

This study assesses the level of terrestrial gamma radiation and associated dose rates from the naturally occurring radionuclides (232)Th, (238)U and (40)K in 10 soil samples collected from Thanjavur (Tamil Nadu, India) using γ-ray spectrometry. The activity profile of radionuclides has clearly showed the existence of low level activity in Thanjavur. The geometric mean activity concentrations of (232)Th, (238)U and (40)K is 42.9±9.4 Bq.kg(−1), 14.7±1.7 Bq.kg(−1) and 149.5±3.1 Bq.kg(−1) respectively are derived from all the soil samples studied. The activity concentration of (232)Th, (238)U and (40)K in soil is due to the presence of metamorphic rocks like shale, hornblende-biotite gneiss and quartzofeldspathic gneiss in these areas. Gamma absorbed dose rates in air outdoors were calculated to be in the range between 32 nGy.h(−1) and 59.1 nGy.h(−1) with an arithmetic mean of 43.3 ±9 nGy.h(−1). This value is lesser than the population weighted world-averaged of 60 nGy.h(−1). Inhabitants of Thanjavur are subjected to external gamma radiation exposure (effective dose) ranging between 39.2 and 72.6 μSv.y(−1) with an arithmetic mean of 53.1±11 μSv.y(−1). The values of the external hazard index determined from the soil radioactivity of the study area are less than the recommended safe levels.