Auger effect

(atomic physics) A two-electron process in which an electron makes a discrete transition from a less bound shell to a vacant electron shell and the energy gained in this process is tranferred via the electrostatic interaction to another bound electron which escapes the atom. Also known as Auger transition; internal absorption; internal photoionization.

One of the two principal processes for the relaxation of an inner-shell electron vacancy in an excited or ionized atom. The Auger effect is a two-electron process in which an electron makes a discrete transition from a less bound shell to the vacant, but more tightly bound, electron shell. The energy gained in this process is transferred, via the electrostatic interaction, to another bound electron which then escapes from the atom. This outgoing electron is referred to as an Auger electron and is labeled by letters corresponding to the atomic shells involved in the process. For example, a KL_IL_III Auger electron corresponds to a process in which an L_I electron makes a transition to the K shell and the energy is transferred to an L_III electron (illus. a). By the conservation of energy, the Auger electron kinetic energy E is given by E = E(K) − E(L_I) − E(L_III) where E(K,L) is the binding energy of the various electron shells. Since the energy levels of atoms are discrete and well understood, the Auger energy is a signature of the emitting atom. See also Electron configuration.

radiative process in which an L_II electron fills the K-shell vacancy with the emission of a K_α2 photon.">
Two principal processes for the filling of an inner-shell electron vacancy. (a) Auger emission; a KL_IL_III Auger process in which an L_I electron fills the K-shell vacancy with the emission of a KL_IL_III Auger electron from the L_III shell. (b) Photon emission; a radiative process in which an L_II electron fills the K-shell vacancy with the emission of a K_α2 photon.

The other principal process for the filling of an inner-shell hole is a radiative one in which the transition energy is carried off by a photon (illus. b). Inner-shell vacancies in elements with large atomic number correspond to large transition energies and usually decay by such radiative processes; vacancies in elements with low atomic number or outer-shell vacancies with low transition energies decay primarily by Auger processes. See also Atomic structure and spectra.