Natural radionuclides and hazards of rock samples collected from Southeastern Nigeria

Gamma radiation from natural radionuclides in thirty eight rock samples collected from Southeastern Nigeria was measured using gamma-ray spectrometry method. The activity concentrations varied from 13.1 ± 1.6 Bq kg−1 (ferrogeneisis shale) to 129 ± 38 Bq kg−1 (granite) for 226Ra, 42.4 ± 4.5 Bq kg−1 (siltstone) to 150 ± 23 Bq kg−1 (pegmatite) for 232Th and 64.5 ± 6.3 Bq kg−1 (ferrogeneisis shale) to 882 ± 298 Bq kg−1 (granite) for 40K. Hazard indices were used to determine the suitability of the rock samples for building in the context of radiological hazard. The results obtained for the radium equivalent activity and the external hazard index show that two of the samples, granite and pegmatite exceeded the recommended limits of 370 Bq kg−1 and 1, respectively. However the results of the gamma index were below the recommended limit. The dose rates and the annual effective dose calculated ranged from 0.012 to 0.042 μGy h−1 and 0.06–0.21 mSv, respectively.