Dual attenuation of X-rays for measurement of the concentration of metals in solution

Abstract

This study examines the feasibility of dual energy attenuation metering to measure the concentration of two elements in aqueous solution, in a pipe of fixed thickness. Photon energies between 20 and 30 keV were selected in order to be able to determine mg L⁻¹ metal concentrations. Pairs of elements from a group with atomic numbers between 24–82 (Cr, Cu, Zn, Hg and Pb) were used to test the methodology. The sensitivity of measurement for a mixture of two elements was predicted from the ratios of the attenuation coefficients at 20 keV to the ratios at 30 keV. Experimental results confirmed that the sensitivity was greatest for the mixture of Cr and Pb, since those elements have the largest ratio of attenuation coefficients (1.108) and it was possible to accurately analyse a solution containing 0.15 g L⁻¹ of Cr and 0.13 g L⁻¹ of Pb. Other pairs of elements with ratios at 1.074 and 1.078 (Cu/Pb, Cu/Hg,) could only be determined at g L⁻¹ concentrations. It was not possible to differentiate between the pairs of elements with attenuation coefficient ratios below 1.03 (Cr/Zn and Cr/Cu) in this study.