Measurement of natural radioactivity and radon exhalation rate from rock samples of Jaduguda uranium mines and its radiological implications

The Singhbhum shear zone is a 200 km long arcuate belt in Jharkhand state situated in eastern India. The central part between Jaduguda-Bhatin-Nimdih, Narwapahr-Garadih-Turamdih is rich in uranium. Presence of uranium in the host rocks and the prevalence of a confined atmosphere within mines could result in enhanced concentration of radon (Rn-222) gas and its progeny. Inhalation of radon daughter products is a major contributor to the radiation dose to exposed subjects. By using high resolution gamma-ray spectroscopic system various radionuclides in the rock samples, collected from different places of Jaduguda uranium mines have been identified quantitatively based on the characteristic spectral peaks. The activity concentrations of the natural radionuclides, uranium (U-238), thorium (Th-232) and potassium (K-40) were measured in the rock samples and radiological parameters were calculated. Uranium concentration was found to vary from 123 +/- 7 Bq kg(-1) to 40,858 +/- 174 Bq kg(-1). Activity of thorium was not significant in the samples, whereas, few samples have shown potassium activity from 162 +/- 11 Bq kg(-1) to 9024 +/- 189 Bq kg(-1). Radon exhalation rates from these samples were also measured using "Sealed Can technique" and found to vary from 4.2 +/- 0.05 to 13.7 +/- 0.08 Bq m(-2) h(-1). A positive correlation was found between the radon exhalation rate and the uranium activity. The absorbed dose rates vary from 63.6 to 18876.4 nGy h(-1), with an average value of 7054.2 nGy h(-1). The annual external effective dose rates vary from 0.7 to 23.2 mSv y(-1). Radium equivalent activities (Ra-eq) varied from 134.3 to 40858.0 Bq kg(-1). Value of external hazard index (H-ex) varied from 0.4 to 110.4 with an average value of 41.2. (C) 2008 Elsevier B.V. All rights reserved.