Establishment of background radiation dose rate in the vicinity of the proposed Manyoni Uranium Project, Singida

Abstract

The absorbed dose rate in air in the vicinity of the proposed Manyoni uranium mining project located in Singida region, Tanzania, was determined so as to establish the baseline data for background radiation dose rate data prior to commencement of uranium mining activities. Twenty stations in seven villages were selected and monitored for six months from June 2012 to November 2012. The absorbed dose rate in air was measured by means of CaF2:Dy thermoluminescent dosimeters (TLD-200). The annual effective dose was estimated using outdoor occupancy factor of 0.2 and conversion coefficient factor of 0.7 SvG y^-1. The mean dose rate was found to range from 16.68 - 507.00 nGy h^-1  with an average of 74.86 nGy h^-1. Maximum average dose rate of 396.7 nGy h^-1  was found at station number 8 situated in Mwanzi Village which was about 7 times higher than the world average value of 59 nGy h^-1  (UNSCEAR 2008) corresponding to annual effective dose of 0.5mSv y^-1. This value is 2 fold lower than the recommended limit of 1 mSv y^-1  for a member of the public (ICRP 1990). Minimum avarage dose rates of 30.9 nGy h^-1  was found in station number 16 and 17 located in Aghondi village, corresponding to annual effective dose of 0.04 mSv y^-1. This implies that prior to commencement of uranium mining activities in the proposed area the external exposure rates due to the natural background radiation are lower than the world recommended value.

Keywords:  Absorbed dose rate, Uranium mining, Background radiation, Thermoluminescent dosimeter, Annual effective dose