Establishment of terrestrial background radiation dose rate in the vicinity of the proposed Manyoni uranium project, Singida

A study to determine absorbed dose rate in air in the vicinity of the proposed Manyoni uranium mining project located in Singida region, Tanzania has been conducted. The aim was to obtain background radiation dose rate prior to commencement of uranium mining activities which can be used in the future as baseline data. Twenty (20) stations in seven (7) villages were selected so as to cover almost the whole proposed mining area. Each selected station was monitored for six months (from June 2012 to November 2012). This time was found convenient and satisfactory since funds were not enough to conduct the study for the whole year. The absorbed dose rate in air was measured by means of CaF2: Dy thermoluminescent dosimeters (TLD-200) and 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 (396.69 nGy h-1) which was 6.7 times higher than the world average value (59 nGy h-1) was reported at station number 8 (FKF) situated in Mwanzi Village. This value of 396.69 nGy h-1 corresponds to annual effective dose of 0.49 mSv y-1 which is 2 fold lower than the recommended limit of 1 mSv y-1 for a member of the public. Minimum avarage dose rate (30.84 and 30.89 nGy h-1) which were 1.9 fold lower than the world average value were reported in station number 16 (NSF) and 17 (AKF) located in Aghondi village. Their corresponding annual effective dose (0.04 mSv y-1) was 25 times lower than the recomended limit. 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.