Determination of the Radiological Risk Associated with Naturally Occurring Radioactive Materials (NORM) at Selected Quarry Sites in Abuja FCT, Nigeria: Using Gamma-Ray Spectroscopy

Abstract

The concentrations of natural radionuclides (238U, 232Th and 40K) in the granite rocks of major quarry sites in Federal Capital Territory, (FCT), Abuja was determined by gamma ray spectroscopy using a well calibrated NaI (Tl) detector system. The range of activity concentrations of (238U, 232Th and 40K) were found to be (37.41 ± 5.41 to 110.16 ± 7.50, 64.13 ± 15.99 to 349.11 ± 69.44 and 323.99 ± 3.73 to 2727.95 ± 14.69) Bq.kg-1 r respectively. The total average of 238U, 232Th and 40K were found to be 74.74 ± 5.67. 199.23 ± 43.30 and 1021.27 ± 7.14 Bq.kg-1 respectively, which are high when compared with worldwide average of 33, 45 and 412. The high value is attributed to geology of the areas where the granites is mined and varies from different quarry sites. The radium equivalent activity concentration was found in the range from 331.50 to 529.91 Bqkg-1, the absorbed dose rate was found to be in the range from 148.72 ± 30.69 to 243.78 ± 30.49 nGyh-1 with an average value of 197.45±29.06 nGyh-1, and the outdoor annual effective dose equivalent (AEDE) was found to vary from 0.13 to 0.38 mSvy-1, which is below the safety limit of 1 mSv.y-1 as recommended by International Commission on Radiological Protection [19]. Also, the internal and external hazard indices were found to be more than unity, suggesting that workers and people living in such site could be exposed to radiological hazard.