Similar Processes
This internal conversion process is also not to be confused with the similar photoelectric effect, which also may occur with gamma radiation associated electron emission, in which an incident gamma photon emitted from a nucleus interacts with an electron, expelling the electron from the atom. Thus, gamma photoelectric effect electron emission may also cause high-speed electrons to be emitted from radioactive atoms without beta decay. However, in internal conversion, the nucleus does not first emit an intermediate real gamma ray, and therefore need not change angular momentum or electric moment.
Also, electrons from the gamma photoelectric effect show a spread in energy, depending on how much energy has been imparted to the ejected electron by the gamma ray which interacts with it—an amount which is variable depending on the angle of gamma photon scattering from the electron (see Compton scattering). Further, a gamma ray is still emitted in photoelectric processes, but one which possesses a fraction of the energy than the gamma ray which left the nucleus. By contrast, in internal conversion, as noted, no gamma ray is emitted at all and the electron energy is fixed at a single, typical value.
Auger electrons, which may also be produced after an internal conversion, arise from a mechanism that is different from that of internal conversion, but is analogous to it. Internal conversion electrons arise when an intense electric dipole field inside the nucleus accelerates an electron which has penetrated the nucleus, to remove it from the atom. Auger electrons similarly arise when an electric field is produced within an atom's electron cloud due to loss of another electron, and this field again induces the acceleration and removal of yet another of the atom's atomic orbital electrons. Like internal conversion electrons, Auger electrons also emerge in a sharp energy peak.
The electron capture (EC) process also involves an inner shell electron, which in this case is retained in the nucleus (changing the atomic number) and leaving the atom (not the nucleus) in an excited state. The atom can relax by X-ray emission and/or by Auger electron emission. Unstable nuclei can usually decay through both IC and EC processes.
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