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

Information included in auxiliary signals, i.e. incoherently and coherently scattered signals and transmitted beam intensities in x-ray fluorescence a nalysis (XRF), a selected channel in the scattered white synchrotron radiat ion and in the contents of selected bremsstrahlung channels in electron mic roprobe analysis (EMPA), can be extracted and exploited to complete the res ults of analyses. Such additional information is much more detailed when th e devices are operating in the microprobe mode; however, this is not a nece ssary condition. The theoretical basis for the use of the auxiliary signals , in the sense proposed in this paper, is discussed. In situations where th e main component is of essentially constant chemical composition but with v ariable density through the sample (wood of living trees, petrified wood, s talactites, coral structures-in general natural periodic structures) or wit h inclusions inside, the application of two kind of signals is preferable i n XRF: the transmitted and scattered signal. For light organic matrices (ce llulose, plastics), the information included in the Rayleigh or Compton sig nal is reversed in relation to the information from the transmission signal s. The selected bremsstrahlung signal or the signal from the secondary elec tron spectrum can serve the same purpose if EMPA analysis is performed. In general, these signals provide auxiliary knowledge about the density of obj ects. 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 petrified wood with respect to the distribution of the cellulose in the original wood. Many original results of analyses are shown. Intercomparison s of the transmission images with the reversed scattered scans in light mat rices are still scarce, while the observation of bremsstrahlung or secondar y electron scans (in EMPA) and their scattered or transmission analogues (i n XRF) for objects and their chemical negatives is demonstrated for the fir st time. Comprehensive results of the analyses of petrified wood and stalac tites (EMPA and XRF) are presented. Copyright (C) 1999 John Wiley & Sons, L td.