Migration of Sulfur in the X-Ray Fluorescence Analysis of Rocks

Resumo

The intensity of the analytical SKα line in the determination of the concentration of sulfur in rocks by X-ray fluorescence spectrometry constantly increases in the course of measurements. The reason for such change may be the directed drift of sulfur ions to the sample surface under the influence of primary X-radiation. This phenomenon is visually demonstrated by an experiment in which a sample is measured first on one side and then on the other side. The intensity of the analytical line from the back side of the tablet in this case begins to increase just from the same level as in the initial measurement from the fore side. A mechanism of the directed drift of sulfur to the sample surface is proposed. A positive potential forms at the sample−vacuum interface because of the lack of negative sulfur ions near the surface, part of which primary X-ray photons knock out of the sample. Under the effect of this potential, sulfur ions from the lower sample layers and also ions escaped from it come to the surface layer of the sample. To ensure the reliability of the results of the quantitative determination of sulfur, one should measure the intensity of its analytical line from two sides of the sample and use the average value as the result.