Assessing the need for radiation protection measures in artisanal and small scale mining of tantalite in Oke-Ogun, Oyo State, Nigeria

Abstract

There is concern that work scenarios on the tantalite mining sites in Oke-Ogun, Oyo State, Nigeria may cause occupational radiation exposure of workers due to enhanced concentrations of naturally occurring radionuclides in some process materials. A prior radiological assessment of the mining activities was carried out to determine if and which exposure scenarios may require radiation protection measures. Samples of the materials involved, comprising tantalite (tantalum ores), soil and waste rock were collected and analyzed for activity concentrations of ⁴⁰K, ²²⁶Ra, ²³⁸U and ²³²Th using a hyper pure germanium detector gamma-ray spectrometer. Radon concentrations in the mines were also measured using a continuous radon monitor - Radon-Scout Plus (Sarad, GmbH). Activity concentrations of ⁴⁰K are below 10 Bqg^-1 in all the samples but all the tantalite samples contain more than 1 Bqg^-1 of ²²⁶Ra and ²³⁸U. Hence tantalite is regarded as naturally occurring radioactive material (NORM) and the mining activity as a practice. The requirements for planned exposure situations apply to all the mining sites but, on the basis of graded approach, the optimum radiation protection measures vary from one mine to another, ranging from exemption to authorization. Exposures to radon in the underground mines pose the greatest radiological risks and portend the greatest need for regulatory control in the mining operations. The results further underscore the need to integrate radiation protection with the other health and safety measures in the mining sector.