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The accumulation of scales in the production pipe lines is a common problem in the oil industry, reducing fluid flow and leading to costly remediation and disposal programmes. Thus, an accurate determination of the activity of the radionuclides in scale samples is essential for environmental protection. The present study focuses on the characterization of naturally occurring radioactive materials (NORM) in scales generated from the petroleum industry to develop a suitable NORM waste management plan. The activity concentrations of 226Ra, 228Ra and 210Pb in 32 representative samples, collected from a number of drums at the NORM Decontamination Facility storage, were determined using gamma spectrometry. It was found that the highest concentrations were 2922, 254 and 1794 Bq g(-1) for 226Ra, 228Ra and 210Pb, respectively. A comparison to the reported worldwide values was made. Statistical approaches, namely Box plot, ANOVA and principal components analysis were applied on the total results. Maximal correlation was demonstrated by 226Ra activity concentration and count per second (cps) to density ratio. To obtain an accurate characterization of the radionuclides studied in the scale samples, method validation of gamma measurement procedure was carried out, in which minimum detectable activity, repeatability, intermediate precision and assessment of uncertainty were the parameters investigated. The work is a forefront for the proper and safe disposal of such radioactive wastes.

The sorption of radium 226 ((226)Ra) on different clay materials (bentonite, illite and a mixture of bentonite-illite) was studied. Clay materials are used in the construction of disposal pits for technically enhanced naturally occurring radioactive materials (TENORM) wastes (i.e., contaminated soil and sludge) generated by the oil and gas industry operations. Experimental conditions (pH, clay materials quantity, and activity concentrations of (226)Ra) were changed in order to determine the optimal state for adsorption of (226)Ra. The results showed that the concentration of adsorbed (226)Ra on clay materials increased with time to reach an equilibrium state after approximately 5 h. More than 95 % of the radium was adsorbed. The mixture of bentonite-illite (1/9) exhibited the greatest adsorption of radium under all experimental conditions.

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& This study focuses on the evaluation of self-attenuation correction factors (C f ) and linearÀ attenuation coefficients (l) of scale samples, produced from the oil fields. This was performed using 152 Eu point source at the optimal geometry found (i.e., 3 mm). The scale samples were of apparent density ranging 1.04 À 3.08 g cm À3 . The results illustrated that self-attenuation correction values were as high as 5.08 for the most dense samples at c-energy line of 45.5 keV. High correlation was observed by Pearson matrix between self-attenuation correction factor and sample density (correlation coefficient of 0.967 at c-energy of 45.5 keV). A simplified model of the relationship between these variables was proposed. The remarkable finding was that when scale sample density increased self-absorption extended to occur to a higher energy line. Hence, self-attenuation correction was negligible at c-energies of 122, 222, and 344 keV for samples with density ranging 1.04-1.41, 1.45-2.04, and 2.12-3.08 g cm À3 , respectively. Since linear attenuation coefficient is material sensitive, it was calculated for each sample. Analysis of variance (ANOVA) reflected the linear relationship between linear-attenuation coefficient and sample density up to 344 keV which disappeared thereafter. The data obtained allowed an accurate determination of the concentrations of c-emitters in scale samples within the energy range of 45.5-1408 keV.