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A. K. Sam, D. A. Sirelkhatim

Comparative study on the evaluation of gamma-dose rate above uranium mineralisation areas in Western Sudan

Absorbed dose rate received from natural external irradiation in uranium mineralisation areas at Jebel Uro, Jebel Kurun and Jebel Mun was evaluated from the measured activity concentrations of ²³⁸U, ²³²Th and ⁴⁰K in rock samples. The analyses were performed using alpha-spectrometry and high-resolution gamma-ray spectrometry. A great spatial variability was observed in activity concentration of the primordial radionuclides indicating complexity in geological features. Converse to Jebel Mun, Uro and Kurun deposits exhibit very high U: Th mass ratio, the feature that characterized vein deposits. The resulting absorbed dose rate at 1m above bedrock level as estimated using dose rate conversion factors (DRCF) fall within the range of 70-500nGy/h (Mun), 600-6000nGy/h (Uro) and 80-300nGy/h (Kurun). At maximum, it corresponds to annual effective dose rate of 0.6mSv, 8mSv and 0.4mSv, respectively. Uranium is the principal producer of the surface radioactivity at Uro and Kurun as it contributes 99.6 and 95 of the total absorbed dose whereas, in Jebel Mun the cause of radioactive anomaly is due to ⁴⁰K and ²³²Th. Regression analysis showed no correlation between uranium concentration and other radionuclides. Although, radioactive equilibrium is not likely to occur in surface and near-surface geological environments, however, daughter/parent activity concentration ratios along uranium series, viz. ²³⁴U: ²³⁸U, Ra:U, ²³⁰Th:U, ²¹⁰Po:U do not differ from unity in both Uro and Kurun deposits.

Radiochimica Acta, Oldenbourg Wissenschaftsverlag

Print ISSN: 0033-8230
Volume: 91, 07/2003
Pages: 409

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