Application of auxiliary signals in x-ray fluorescence and electron microprobe analysis for density evaluation

Abstract

Information included in auxiliary signals, i,e. incoherently and coherently scattered signals and transmitted beam intensities in x-ray fluorescence analysis (XRF), a selected channel in the scattered white synchrotron radiation and in the contents of selected hremsstrahlung channels in electron microprobe analysis (EMPA), can be extracted and exploited to complete the results of analyses. Such additional information is much more detailed when the devices are operating in the microprobe mode; however, this is not a necessary condition. The theoretical basis for the use of the auxiliary signals, in the sense proposed in this paper, is discussed. In situations where the main component is of essentially constant chemical composition but with variable density through the sample (wood of living trees, petrified wood, stalactites, coral structures-in general natural periodic structures) or with inclusions inside, the application of two kind of signals is preferable in XRF: the transmitted and scattered signal. For light organic matrices (cellulose, plastics), the information included in the Rayleigh or Compton signal is reversed in relation to the information from the transmission signals. The selected hremsstrahlung signal or the signal from the secondary electron spectrum can serve the same purpose if EMPA analysis is performed. In general, these signals provide auxiliary knowledge about the density of objects. An especially interesting situation is when the object is a chemical negative of the original, such as the distribution of silica in some kinds of petrilied wood with respect to the distribution of the cellulose in the original wood. Many original results of analyses are shown. Intercomparisons of the transmission images with the reversed scattered scans in light matrices are still scarce, while the observation of bremsstrahlung or secondary electron scans (in EMPA) and their scattered or transmission analogues (in XRF) for objects and their chemical negatives is demonstrated for the first time. Comprehensive results of the analyses of petrified wood and stalactites (EMPA and XRF) are presented.