Interpretation and use of inter-element correlation graphs obtained by scanning X-ray fluorescence micro-beam spectrometry from individual particles. Part I — theory

Two-dimensional scanning micro-beam X-ray fluorescence measurements of homogeneous particles with simple geometrical shapes are modeled in this study. Characteristic X-ray line intensities of different elements were calculated as a function of beam position for spheres, spherical shells and rectangular blocks with a SiO2 or carbon matrix. When self-absorption of the fluorescent radiation is important, inter-element correlation plots showing the intensity of an element as the function of another, may differ significantly from single-valued narrow curves. The shape of a given correlation plot is characteristic for the topology of the particle: its slope depends on the concentration ratio of the investigated element-pair and its width varies with the composition and density of the matrix. The model calculations were verified by scanning glass micro-spheres of standard reference material NIST SRM K961 using a synchrotron micro-beam. Good agreement was obtained between the experimental results and theory.