[01] H. O. Shittu, Department of Science Infrastructure, National Agency for Science and Engineering Infrastructure (NASENI), Abuja, Nigeria. [02] I. O. Olarinoye, Department of Physics, Federal University of Technology, Minna, Niger State, Nigeria. [03] A. N. Baba-Kutigi, Department of Physics, Federal University Dutsema, Katsina State, Nigeri. [04] S. F. Olukotun, Department of Physics and Engineering Physics, Obafemi Awolowo University, Ile-Ife, Nigeria. [05] E. O. Ojo, Department of Science Infrastructure, National Agency for Science and Engineering Infrastructure (NASENI), Abuja, Nigeria. [06] A. Egga, Department of Science Infrastructure, National Agency for Science and Engineering Infrastructure (NASENI), Abuja, Nigeria.

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 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.

Natural Radionuclides, Gamma Spectrometry, Quarry Site, Granite Rock, Abuja FCT

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