Emanometry Radium Radon Ingestion dose a b s t r a c t 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 226 Ra and 222 Rn were determined in natural ground water of the Mandya district, Karnataka State, India. The concentration of 222 Rn in borewell water varies form 6.44 ± 0.20 to 44.83 ± 0.54 Bq l À1 with geometric mean 16.42 ± 0.31 Bq l À1 . Higher radon concentrations were observed at Yettaganahalli and Mandya city. 226 Ra concentration varies form14.26 ± 0.32 to 81.06 ± 0.99 mBq l À1 with geometric mean 27.61 ± 0.43 mBq l À1 . 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 mSv y À1 with a geometric mean of 65.94 mSv y À1 , which is below the prescribed dose limit of 100 mSv y À1 by WHO.

Naturally occurring radionuclide 210 Po which is an element of 238 U decay series, contribute to the radiation that normally people are exposed. Drinking water samples collected from Cauvery river basin of south interior Karnataka State, India were analysed for the activity of 210 Po using radiochemical analysis technique. The estimated concentration of 210 Po in river water ranges from 0.86 to 4.49 mBq l À1 , and its mean value is 2.67 ± 1.09 mBq l À1. The concentration of 210 Po in bore well water ranges from 1.89 to 4.18 mBq l À1 and its mean value is 3.22 ± 0.67 mBq l À1. The dissolved radium concentration in river water varies from 9.09 mBq l À1 to 55.07 mBq l À1 with an average of 32.33 ± 14.16 mBq l À1. Total ingestion dose rate due to 226 Ra and 210 Po varies from 2.61 to 15.00 mSv y À1 with a mean value of 8.95 ± 3.74 mSv y À1 , which is less than the recommended value by ICRP (International commission on radiological protection).

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