Electron microprobe quantification: A new model based on electrons rather than on mass

Abstract

Conventional models for reduction of electron probe microanalysis (EPMA) data are based improperly on mass. A unique set of electron microprobe measurements shows no significant differences between the intensities of characteristic x rays emitted from natural and enriched isotope pairs of Cu, Ni, and Mo. This observation and fundamental physical precepts both indicate that mass does not affect the generation of characteristic x rays, the basis of the EPMA technique. We offer instead a mass-independent, atomic-number based approach, which features electron fractions, the proportion of electrons in a compound contributed by each element. In this model, the initial estimate of the intensity of characteristic x rays emitted by each element in a compound is the intensity of the emission from each pure element times its electron fraction (instead of its mass fraction) in the compound. Published characteristic x-ray data, culled to provide 655 measurements of binary compounds which require only minor corrections (less than 2% each) for fluorescence and absorption, yield initial estimates of compositions closer to the measured values when calculations are based on electron fractions rather than on mass fractions. Thus, when fitted to an appropriate correction scheme, the electron-fraction model ultimately should yield a simplified and physically based method of data reduction which will simplify and improve the accuracy of electron microprobe quantitation.