An Etymological Dictionary of Astronomy and Astrophysics
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The → emission of an → electron when an → atom transits to a less → excited state. More specifically, → ionization of an atom by a very energetic photon can bring about the ejection of an inner electron of the atom. Consequently, the atom becomes unstable and rapidly undergoes a → spontaneous transition. As a result, an outer electron moves inward and fills the → vacancy produced in the inner orbit. Energy conservation requires that this transition be accompanied by the emission of a photon or a peripheral electron. The latter is called the → Auger electron. Knowing the electron energy leads us to characterize the atom from which it was ejected. This effect is used, in the Auger spectroscopy, to analyze the surface compositions of materials.

This effect was discovered in 1923 Lise Meitner (1878-1968) and in 1925 independently by Pierre Auger (1899-1993).