Auger effect

Two views of the Auger process using the Bohr model of the atom. (a) illustrates sequentially the steps involved in Auger deexcitation. An incident electron (or photon) creates a core hole in the 1s level. An electron from the 2s level fills in the 1s hole, and the transition energy is imparted to a 2p electron, which is emitted. The final atomic state thus has two holes, one in the 2s orbital and the other in the 2p orbital. (b) illustrates the same process using X-ray notation, KL1L2,3. The Meitner–Auger effect is a physical phenomenon in which atoms eject electrons. It occurs when an inner-shell vacancy in an atom is filled by an electron, releasing energy that causes the emission of another electron from a different shell of the same atom.

When a core electron is removed, leaving a vacancy, an electron from a higher energy level may fall into the vacancy, resulting in a release of energy. For light atoms (Z<12), this energy is most often transferred to a valence electron which is subsequently ejected from the atom. This second ejected electron is called an Auger electron. For heavier atomic nuclei, the release of the energy in the form of an emitted photon becomes gradually more probable.