Spectrum evaluation

Spectrum evaluation is a crucial step in x-ray analysis, as much as sample preparation and quantification. As with any analytical procedure, the final performance of x-ray analysis is determined by the weakest step in the process. Spectrum evaluation in energy-dispersive (ED) analysis is certainly more critical than in wavelength-dispersive (WD) spectrometry because of the relatively low resolution of the solid-state detectors employed. As a result, most of the research done in the field of spectrum evaluation was and still is situated in ED spectrometry. Although in WD spectrometry for a long time rate meters and/or strip-chart recorders have been employed, the processing of ED spectra by means of computers has always been more evident because of their inherent digital nature. For some of the techniques discussed here, the foundations have been laid in γ-ray spectrometry; for others (notably spectrum fitting procedures), ED x-ray analysis has developed its own specialized data-processing methodology. The availability of relatively cheap and fast microcomputers together with the implementation of mature spectrum evaluation packages on these machines has brought sophisticated spectrum evaluation within the reach of each x-ray spectrometry laboratory. In this chapter various methods for spectrum evaluation are discussed, with emphasis on energy-dispersive x-ray spectra. Most of the methods are relevant for x-ray fluorescence, particle-induced x-ray emission, and analytical electron microscopy x-ray spectra. The principles of the methods and their practical use are discussed. Least-squares fitting, which is of importance not only for spectrum evaluation but also for quantification procedures, is discussed in detail in Section IX. Computer implementations of the main algorithms are presented in Section X. 85 refs., 36 figs, 11 tabs