Assessment of Natural Radionuclide Distribution Pattern and Radiological Risk from Rocks in Precambrian Oban Massif, Southeastern Nigeria

A gamma spectrometric analysis of rock samples collected from the Precambrian Oban Massif, southeastern Nigeria, was performed to determine some primordial radioelements' activity concentrations: U-238, Th-232, and K-40, and their associated radiological hazards. The mean activity of the primordial radionuclides was determined to be 1073.06 +/- 0.65, 160.74 +/- 1.32, and 250.76 +/- 0.91 Bq center dot kg(-1) for K-40, U-238, and Th-232, respectively, showing that they are inhomogeneously distributed, with activity changing with the rock type and location. The activity concentrations are highest in biotite garnet schist, quartz diorite, and biotite gneiss rock domains. The mean values of the radiological hazards are 0.08 Bq center dot kg(-1) (alpha index), 2.15 Bq center dot kg(-1)(gamma index), 2.06 Bq center dot kg(-1)(internal) and 1.63 Bq center dot kg(-1) (external4.30 Bq center dot kg(-1)(representative level index6), 602.23 Bq center dot kg(-1), (radium equivalent), 780 nGy center dot h(-1) (total absorbed dose rate), 270.91 nGy center dot h(-1) (indoor), 509.78 nGy center dot h(-1) (outdoor), 624.99, 1329.07 and 1954.06 mSv center dot yr(-1) (outdoor, indoor and total annual effective dose equivalent, respectively), 6448.40 (cumulative excess lifetime cancer risk) and 248.94-3761.47 Bq center dot kg(-1) (annual gonadal dose equivalent). These results are higher than their various permissible limits (except at Ako Community) and suggest that rocks in the area may be unsuitable for constructing dwelling places. It is strongly advised that basic safety standards and precautionary measures recommended by the European Commission should be strictly adhered to while dealing with these rocks.