Internal conversion is an electromagnetic process, by which a nuclear excited state decays by the direct emission of one of its atomic electrons. Note that, the high energy electrons resulting from internal conversion are not called beta particles, since the latter come from beta decay, where they are newly created in the nuclear decay process. These electrons are known as internal conversion electrons.
The internal conversion electron (ICE) energy, is the transition energy, Etransition, minus the binding energy of the orbital electron, Eb.e., as:
For example, 203Hg is beta radioactive nuclide, which produces a continuous beta spectrum with maximum energy 214 keV. This decay produces an excited state of the daughter nucleus 203Tl, which then decays very quickly (~ 10-10 s) to its ground state emitting a gamma ray of energy 279.2 keV or an internal conversion electron. If we analyze a spectrum of beta particles, we can see the typical continuous spectrum of beta particles as well as narrow peaks at specific energies. These peaks are produced by internal conversion electrons (ICE). Since the binding energy of the K electrons in 203Tl amounts to 85.5 keV, the K line has an energy of:
Te (K) = 279.2 – 85.5 = 194 keV
Because of lesser binding energies, the L- and M-lines have higher energies. Since the internal conversion process can interact with any of the orbital electrons, the result is a spectrum of internal conversion electrons which will be seen as superimposed upon the electron energy spectrum of the beta emission. These relative intensities of these ICE peaks can give information about the electric multipole character of the nucleus and about the decay process.
Special reference: Kenneth S. Krane. Introductory Nuclear Physics, 3rd Edition, Wiley, 1987, ISBN 978-0471805533