Hussam Khalily

ABSTRACT This study focused on the evaluation of self-attenuation correction factors (Cf) and linear attenuation coefficients (μ) of scale samples, produced from the oilfields. This was performed using a 152Eu point source at the optimal 3 mm geometry. Scale samples had density values between 1.04 and 3.08 g cm−3. The results illustrated that self-attenuation correction values were as high as 5.08 for the most dense samples at the γ-energy line of 45.5 keV. High correlation was observed by a Pearson matrix between the self-attenuation correction factor and sample density (correlation coefficient of 0.967 at γ-energy 45.5 keV). A simplified model of the relationship between these variables was proposed that when scale sample density increased, self-absorption extended to occur at higher energy lines. Hence, the self-attenuation correction was negligible at γ-energies of 122, 222, and 344 keV for densities between 1.04 and 1.41, 1.45 and 2.04, and 2.12 and 3.08 g cm−3, respectively. Since the linear attenuation coefficient is material sensitive, it was calculated for each sample. Analysis of variance (ANOVA) reflected the linear relationship between the linear attenuation coefficient and sample density up to 344 keV. The data obtained allowed an accurate determination of the concentrations of γ-emitters in scale samples.

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 (226)Ra, (228)Ra and (210)Pb 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 (226)Ra, (228)Ra and (210)Pb, 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 (226)Ra 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.