Natural Radioactivity Associated with Mining of Rare Metal Pegmatite of Oke-Ogun Field, Sepeteri, Southwestern, Nigeria I. A. Tubosun 1 , P. Tchokossa 2* , G.A. Okunlola 3 , F.A. Balogun 1 , M.K. Fasasi 1 , S. Ekhaeyemhe 4 1 Centre for Energy Research and Development, Obafemi Awolowo University, Ile-Ife, Osun State, Nigeria. 2* Department of Physics, Obafemi Awolowo University, Ile-Ife, Osun State, Nigeria (E-Mail:ptchokos@yahoo.com) 3 Department of Geology, University of Ibadan, Nigeria 4 Department of Geology, Obafemi Awolowo University, Ile-Ife, Osun State, Nigeria Abstract Within and around major cities of Southwestern Nigeria, there are scores of mining activities whose constitute menace into the immediate environments. In this study, a combined techniques using a portable survey meter (Gamma-Scout SN 038439) for in-situ investigation and a well-calibrated NaI(Tl) detector system were used for the measurement of the average radioactivity concentration in some rocks associated with mining of rare metal pegmatite of Oke-Ogun field, Sepeteri, Oyo state of Nigeria. The average dose rate obtained for gamma and beta exposure vary between 0.1 – 0.24 Sv hr -1 with a mean of 0.18 Sv/hr and between 0.01 – 0.08 Sv/hr with a mean of 0.03 Sv hr -1 respectively. With the exception of 40 K and the anthropogenic 137 Cs, all the radionuclides detected are traceable to the pre-medial series of 238 U and 232 Th. The specific activity value obtained for 238 U, 232 Th and 40 K varied from 26.06 to 97.10 Bq kg -1 with a mean value of 58.04 ±12.78 Bq kg -1 , 17.65 to 85.65 Bq kg -1 with an average of 29.04 ± 9.49 Bq kg -1 and 194.87 to 1035.56 Bq kg -1 with an average of 586.23 ± 88.56 Bq kg -1 respectively. The mean value obtained for the Representative levels index (I ), the radium equivalent (Raeq), the total absorbed dose rate (ADR) were 1.07; 144.71 Bq kg -1 and 68.80 nGy h -1 respectively. The discrepancies of our data can be attributed to several factors such as geological formation, transport process, etc. Although our results are just some fractions of the international standard limit, but still within the same ranges when compared with those obtained elsewhere. This results also will serve as a baseline data for future investigations. Keywords: Radioactivity, Mining, Hazards, Gamma Spectrometry 1 Introduction Radiation of natural origin at the earth’s surface consists of two components namely cosmic rays and radiation from the radioactive nuclides in the earth’s crust. The latter component is the terrestrial radiation, which mainly originates from the so-called primordial radioactive nuclides that were made in the early stage of the formation of the solar system. Long-lived radioactive elements of interest, which are the main elements contributing to natural terrestrial radioactivity (UNSCEAR, 2000) include uranium, thorium and potassium and any of their radioactive decay products, such as radium and radon. The radioactive waste generated in mining and milling activities, especially those involving uranium and thorium (U, Th) ores, differs from that generated at nuclear power plants and most other industrial operations and medical facilities. They contain only low concentrations of radioactive material but it is generated in large volumes (IAEA, 2002). These elements have always been present in the earth’s crust and within the tissues of all living species. Studies of terrestrial natural radiation are of great importance for various reasons. They serve as useful tracers for atmospheric variation studies. It is usually realized that natural environmental radiation mainly depends on geological and geographical conditions. Also, an understanding of natural radioactivity was used to determine the age of the earth using the radioactive decay of 238 U to 206 Pb and 235 U to 207 Pb. The heat produced by radioactive disintegration is an important source of thermal energy