A reexamination of absorption and enhancement effects In X-ray fluorescence trace element analysis

摘要

In this paper, sample mass-absorption corrections for X-ray fluorescence trace element analysis are reexamined and a new approach is presented that is more accurate and more versatile than current methods. A method based on Compton scattering of a tube line is widely used because it is simple and does not require knowledge of the complete sample composition. The equivalent-wavelength method is sometimes used instead, especially if there is a major element absorption edge between the wavelengths of the Compton peak and the characteristic analyte radiation. Both methods suffer from difficulties in correcting for absorption edges and for enhancement by secondary fluorescence. In addition, the necessary assumption that the ratio of mass-absorption coefficients of any two elements is approximately independent of wavelength is surprisingly inaccurate. A series of examples demonstrates that in some cases large analytical errors may result. Methods based on the new approach completely and automatically correct for absorption edges and secondary fluorescence, without introducing such errors. In contrast to current methods, a complete major element analysis is not necessary. Thus, rapid determination of concentration ratios, such as Cr/Fe and V/Fe in oxide ores, Ba/Fe in Fe-rich hydrothermal deposits, and Sr/Ca in carbonates, is possible. In an experimental test, accuracy of better than 1 percent was demonstrated for analysis of V in Fe-rich samples. A proposed coefficient approximation was shown to give accuracy of 2 percent or better (excluding experimental errors) for Rb, Ni, Ba, and Cr over an extremely wide range of sample compositions.