Radiological and chronological studies on black shales from Budaa area, southwestern Sinai, Egypt

The study measured the activity concentrations of various radionuclides (U-238, U-234, Th-230, Ra-226, Rn-222, Th-232, K-40, and U-235) using gamma-ray spectrometry in 11 black shale samples from three trenches and a wall in Budaa area, southwestern Sinai, Egypt. The samples were taken from different parts of Magharet El Meyiah Formation (top, middle, and base) to understand radionuclide migration processes. The average activity concentrations of U-238, Th-232, and Ra-226 in all samples were higher than the worldwide averages, while K-40 levels were lower. Isotopic ratio relationships showed accumulation of radionuclides in most samples except one sample lies in uranium leaching sector from the base layer of the wall. Uranium-Thorium (U-Th) dating revealed varying ages of uranium deposition: 42.43-119.90 ka in trench 1, 40.09-85.37 ka in trench 3, 63.92 ka in trench 2, and 106.50 and 325.80 ka in the top of wall, suggesting differential mobility of uranium. Hazard parameters like external radiation hazards (H-ex < 1) were minimal and annual effective dose rates within acceptable limits, while, internal radiation hazards (H-in > 1) were a concern for samples from the top layers. All samples had absorbed dose rates higher than the global average, indicating elevated background radiation levels.