The Auger effect (/oʊˈʒeɪ/; French pronunciation: [ˈ/o.ʒe/]) or Auger−Meitner effect is a physical phenomenon in which the filling of an inner-shell vacancy of an atom is accompanied by the emission of an electron from the same atom.[1] 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.[2] This second ejected electron is called an Auger electron.[3] For heavier atomic nuclei, the release of the energy in the form of an emitted photon becomes gradually more probable.