Electron and proton induced x-ray spectrometry: Two complementary spatially resolved analytical techniques in mineralogy

Spatially resolved quantitative analysis by means of the electron probe micro analyzer (EPMA) is now well-established as a routine analytical method for point chemical analysis of a variety of mineral materials. Modern computer controlled EPMA are most often equipped with wavelength dispersive spectrometers (WDS). Quantitative analysis are generally carried out according to a standard based approached, i.e. the x-ray intensities measured at the surface of the unknowns are normalized to those measured at the surface of reference specimens. By the use of energy dispersive spectrometry (EDS) a standardless, quantitative-based method is preferred when the incident beam current is not accurately known, as for the case of EDS analysis coupled to scanning electron microscopy (SEM). The accuracy of point analysis by means of electron beam induced x-ray spectrometry will be discussed emphasizing the x-ray intensity measurement procedures and the data reduction scheme accounting for the electron-solid and x-ray-photon interactions respectively. Proton induced x-ray emission (PIXE) complements this electron induced x-ray emission for the localization of elements present at trace levels. The experimental procedure used for quantitative analysis by means of PIXE will be illustrated emphasizing the use of a limited number of reference materials for deriving quantitative data from the raw PIXE spectra. The complementarity of EMPA/SEM and PIXE techniques will be illustrated for the case of rare-earth bearing natural and synthetic doped zircon crystals (SiZrO4). It will be shown that cathodoluminescence and ionoluminescence may offer other approaches to x-ray spectrometry of such minerals.