| Summary: | Radium is naturally occurring radioactive element in the earth's crust. It is chemically similar to calcium and absorbed from soil by plants, passed up the food chain to humans. The occurrence and the distribution of radioactivity in water depend on the local geological characteristics of the source, soil, rock and other factors that control the occurrence and distribution of radionuclides in ground water and the hydro geological condition and the geochemistry of radionuclides. Activities of the naturally occurring radionuclides 226Ra and 222Rn were determined in natural ground water of the Mandya district, Karnataka State, India. The concentration of 222Rn in borewell water varies form 6.44 ± 0.20 to 44.83 ± 0.54 Bq l−1 with geometric mean 16.42 ± 0.31 Bq l−1. Higher radon concentrations were observed at Yettaganahalli and Mandya city. 226Ra concentration varies form 14.26 ± 0.32 to 81.06 ± 0.99 mBq l−1 with geometric mean 27.61 ± 0.43 mBq l−1. It is observed that the radon concentration is high in ground water around the granitic rock exposures and similarly observation of high values of radon is reported in sheared gneiss which covers major portion of the Mandya district to phyllites and schists. The total dose due to ingestion and inhalation varies from 26.31 to 178.53 μSv y−1 with a geometric mean of 65.94 μSv y−1, which is below the prescribed dose limit of 100 μSv y−1 by WHO. Keywords: Ground water, Emanometry, Radium, Radon, Ingestion dose
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