RESUMEN
The distribution of natural nuclide gamma-ray activities and their respective annual effective dose rates, produced by potassium-40 (4°K), uranium-238 (²³8U), thorium-232 (²³²Th), and radium-226 (²²6Ra), were determined for 14 oilfield scale samples from the Middle East. Accumulated radioactive materials concentrate in tubing and surface equipment, and workers at equipment-cleaning facilities and naturally occurring radioactive materials (NORMs) disposal facilities are the population most at risk for exposure to NORM radiation. Gamma-spectra analysis indicated that photo-gamma lines represent the parents of 10 radioactive nuclides: ²³4Th, plutonium-239, actinium-228, ²²6Ra, lead-212 (²¹²Pb), ²¹4Pb, thallium-238 (²°8Tl), bismuth-212 (²¹²Bi), ²¹4Bi, and 4°K. These nuclides represent the daughters of the natural radioactive series ²³8U and ²³²Th with 4°K as well. The mean activity concentration of ²³8U, ²³²Th, and 4°K were found to be 25.8 ± 11.6, 18.3 ± 8.1, and 4487.2 ± 2.5% Bq kg⻹ (average values for 14 samples), respectively. The annual effective dose rates and the absorbed doses in air, both indoor and outdoor, for the samples were obtained as well. The results can be used to assess the respective hazard on workers in the field and represent a basis for revisiting current engineering practices.