Introduction

Qualitative X-ray analysis entails the identification of the elements present in a given sample, or the identification of phases from the elements which they contain. Of the two available sorts of X-ray spectrometer, the ED type is far better for qualitative analysis, owing to its ability to record complete spectra rapidly (major elements and their approximate relative concentrations are apparent in only a few seconds). Occasionally, though, ambiguity in the identification of peaks closely similar in energy requires the better resolution obtainable with a WD spectrometer.

For quantitative analysis X-ray line intensities emitted from the specimen are measured and elemental concentrations are calculated from the ratios of these intensities to those from standard samples with known concentrations. Methods of measuring intensities and correcting for background differ in WD and ED analysis, which are therefore treated separately below. The ‘matrix’ (or ‘ZAF’) corrections required in order to allow for the effect of the difference in composition between standard and specimen on the emitted intensities are common to both methods of analysis.

Pure-element X-ray spectra

The origin of characteristic X-rays is described in Section 2.5.2. The K lines of elements of atomic number 11–30 (Na–Zn) lie within the energy range 1–10 keV. Elements of higher atomic number can be identified from their L or M lines, which lie in the same range. With a thin-window ED detector (Section 5.2.1), the atomic-number range can be extended down to 4 (Be).