Assessment of Gamma Dose Rate over a Suspected Uranium Mineralisation Area of Jebel Mun, Western Sudan

Abstract

This study was conducted at the request of authorities in western Darfour State, to address the public concern about the levels of radioactivity in the area of Jebel Mun situated at Sudan-Chad international boundaries. It has been identified as a high background radiation area through aerial geological surveys conducted in late 1970s. The ambient gamma dose in the area was measured with the aid of a hand-held dose rate meter (Mini-Rad, Series 1000) and the surface rock samples were collected and analysed for their radioactivity content using a high-resolution gamma spectrometry equipped with HPGe with relative efficiency of 18%. The activity concentrations of 238U, 232Th and 40K were found to range from 39-253 Bq.kg(-1), 41-527 Bq.kg(-1) and 77-3027 Bq.kg(-1), respectively. From the values of the standard deviation it was concluded that the activity concentration of the considered primordial radionuclides was highly scattered (localised) which in turn indicates non-uniformity in the geological features and/or formations. 238U activity concentration corresponds to equivalent mass concentration of 7.77+/-6.12 ppm (3.19-20.73 ppm), which is of no economic importance. Samples are enriched in thorium relative to uranium as reflected by the Th:U mass ratio which ranges from 3 to 17. The absorbed dose rate in air as estimated from the measured activity concentrations of the primordial radionuclides using the DRCFs (dose rate conversion factors) falls within the range of 70-522 nGy.h(-1) with an average of 221+/-130 nGy.h(-1). It corresponds to an annual effective dose equivalent averaged of 0.27 mSv. The regression analysis has shown that the correlation between calculated and the measured ambient dose rate is marginally significant (r2 = 0.59). The 232Th series is the major producer of the surface radioactivity followed by 40K as they contribute 48% and 32% of the total absorbed dose, respectively.

Investigations of the Radioactive Presence and Heavy Metallic Materials in Merowe Dam Area

“…From the results of the measurements of radionuclide activity concentrations in the soil at various locations in Sudan, the average exposure was found to be 45 nGy·h −1 , corresponding to the annual dose equivalent of 278 mSv·y −1 [10]. Also in the western region, Darfur state, specifically in Jebel Mun, the activity concentrations of 238U, 232Th and 40K were found to range from 39 -253 Bq·kg −1 , 41 -527 Bq·kg −1 and 77 -3027 Bq·kg −1 , respectively [11]. In additions, in Sinnar State, measurements were carried out using high-resolution gamma-spectrometry; on average, the activity concentrations obtained were 38 ± 8 (232Th), 17 ± 2 (226Ra), 174 ± 19 (40K) and 0.9 ± 0.2 Bq·kg −1 for the fallout radionuclide 137Cs.…”