Distribution and disequilibrium of natural radionuclides in the black shale from Wadi Naseib area, Southwest Sinai, and their environmental hazard indices

Abstract

Several radionuclides of the 238U (or its decay daughters such as 234Pa, 234U, 230Th, 226Ra, 214Pb, and 214Bi), 232Th (228Ac, 208Tl, and 212Bi), and 235U decay series have been measured. The 234U/238U activity ratios (ARs) are >1 for most rock samples indicating preferential abundance of 234U relative to 238U from the rock due to prevailing reducing conditions. The 226Ra/238U ratios are ranging between 0.04 and 0.6 and averaging 0.4 which show disequilibrium in the direction of uranium concentrations. 230Th/238U and 230Th/234U ARs for all studied samples are less than unity, suggesting that all 230Th are produced by in situ decay of 234U and there is no allogeneic or initial 230Th. Exposure rate, dose rate, radium equivalent activity, external hazard index, internal hazard index, and radioactivity level index are determined.

Keywords

• Gamma spectrometry
• radiometric indices
• radionuclides concentrations
• shale rocks