What is Electron microprobe, wavelength-dispersive spectrometry?

An electron microprobe is an instrument that focuses a beam of electrons on a spot of a polished section and measures the characteristic X-rays emitted there, giving a quantitative analysis of a volume a few micrometres across. In wavelength-dispersive spectrometry, the X-rays fall on an analytical crystal that reflects to a detector only the wavelength satisfying Bragg’s law at its angle; crystal and detector move together on a circle (the Rowland circle) to select each element’s line in turn.