Assessment of 226Ra, 232Th and 40K in soil with gamma dose rates from quarries of the Mandya district, Karnataka, India.

Naturally occurring radionuclides (226Ra, 232Th, and 40K) are commonly found in quarry fields, and the use of quarry-derived materials in construction can increase indoor radiation levels. The presence of these radionuclides increases background radiation, which prolongs health risk as indicated by WHO and ICRP guidelines. Therefore, assessing their radioactivity is crucial for public health and safe construction use. In the current study, soil samples collected from 21 quarry sites in Mandya district, Karnataka, India, and their activity concentration is measured using HPGe γ-ray spectrometer. The mean activity concentrations of 226Ra, 232Th and 40K were found to be 39.5, 81.5 and 656 Bq kg-1, respectively. The average activity concentration ratios were calculated as 232Th/226Ra (2.05), 40K/226Ra (16.65), and 40K/232Th (8.15). The average values of Raeq, Iγr, Hex and Hin were found to be 206.5 Bq kg-1, 1.52, 0.56 and 0.66, respectively. In addition, the ambient γ-radiation levels measured using a calibrated ER-709 portable dosimeter yielded average values of 89.06 nGy h-1 for absorbed γ dose rate, 0.11 mSv y-1 for annual effective dose, 0.38 × 10-3 for excess lifetime cancer risk and 671.22 μSv y-1 for annual gonadal dose equivalent. These results collectively indicate low radiological risk within internationally accepted safety limits. The study also provides baseline data for future soil radioactivity monitoring and radiological assessments.