What’s Still Missing with the Fluorescence Corrections and Should We Care?

Of the corrections employed for quantitative electron microprobe analysis, the correction for effects of fluorescence by characteristic x-ray lines has changed the least since the early re-parameterization of Castaing’s original correction by S.J.B. Reed in 1965 [1], and formal correction for the effects of continuum fluorescence is still seldom applied with no consensus parameterization employed by the standard software provided for EDS and WDS analysis systems. With regard to the characteristic fluorescence correction, part of the reason for the lack of change is the brilliance of Reed’s formulation of a useful set of equations. However, although he noted in his original paper that a number of simplifications had been made due to lack of fundamental measurement data and to aid in calculation and he and others later proposed substitution of better data sets and equations [e.g., 2,3], most correction programs still retain the original simplified expressions. Alternate methods have been proposed based on use of parameterized expressions for the primary φ(ρz) distribution coupled with numerical integration of the fluorescing and fluoresced x-ray path lengths [e.g., 4-6] and from Monte Carlo calculations [e.g., 7-10]. These alternate expressions can be used or modified to calculate correction for fluorescence in thin films, layered specimens, particles, inclusions, and across phase boundaries. But none of these are yet in common use and most still involve assumptions or simplifications to avoid the very extensive set of calculations a truly rigorous fluorescence correction would require. Moreover there are virtually no sets of measurements of k-ratios in well characterized systems where fluorescence effects are important to determine if the various correction algorithms actually work [e.g. 11].