Radiological Evaluation of Gold Mining Activities in Ariab (Eastern Sudan)

Abstract

Calculations of individual effective dose per annum have been made from the activity concentrations of dominant gamma-emitting radionuclides from uranium and thorium decay chains in ore, solid waste (spoil heap) and soil samples collected from Adassedakh and Hadal Auatib gold mines in Ariab (Eastern Sudan). Measurements were performed using a high-resolution gamma spectrometer. Independent of location, the data show that the activity concentration for 226Ra and 232Th increases in the order: soil>spoil heap>ore. This order basically confirms that the activity levels in the spoil heap are low relative to natural background (i.e. soil samples), and thus the expected contribution in enhancement of natural background radiation is correspondingly low. The concept of concentration ratio (CR) has been applied to quantify the degree of accumulation of radionuclides in the solid waste (heap). The calculated CR values revealed that 232Th is most accumulated while there is no accumulation of 40K. The absorbed dose rates in air at a height of 1 m as estimated using DRCF from activities of 241Pb, 214Bi, 212Pb, 228Ac, 208Tl and 40K ranges from 6.6 to 32.3 nGy.h-1 (Adassedakh), and 2.2 to 26.1 nGy.h-1 (Hadal Auatib). The principal contributors to the total dose rate are 40K, 214Bi and 228Ac which generate almost 90%. The corresponding annual effective doses fall within the range: 0.04-0.20 mSv.y-1 for Adassedakh and 0.01-0.16 mSv.y-1 for Hadal Auatib. Although, these estimates do not include the internal radiation burden due to inhalation of radon and its decay products, the values obtained are insignificant relative to the dose limit specified for occupational exposure of any worker.