gems, gem testing, gemology, advanced gemology, advanced testing

In 1948, Raymond Castaing, then a student of A. Guinier, presented to the University of Paris a doctoral thesis entitled “Application of Electron Beams to a Method of Local Chemical and Crystallographic Analysis.” The instrument he described had been produced by modifying an electron microscope, using an electron beam focused to a diameter of less than a micrometer (1 µm = 10⁻⁶ m) to excite X-rays within a microscopic region on the specimen surface. Spectral analysis of these X-rays provided information about the composition of the excited region, while the crystalline structure of the area could also be investigated using the Kossel-line X-ray diffraction technique. Castaing’s electron probe microanalyzer has since become the most important tool for elemental microanalysis, distinguished by its high spatial resolution, nondestructive operation, quantitative potential, wide elemental detection range, and compatibility with a variety of specimen types.