At present, the most widely used non-enucleation therapy is radiation. 125 I , encapsulated in titanium, is gaining wide use for implants in radiotherapy and is used in this study. The 125 I irradiation of choroidal melanoma results in a low radiation dose to ocular structures adjacent to the tumor. I decays exclusively by electron capture to an excited state of 125 Te, which spontaneously decays to the ground state with the emission of a 35.5 keV gamma photon. In the process of electron capture the nucleus captures an orbital electron, almost always from the K shell.
Energy is emitted in the form of a neutrino and characteristic x-rays.
Auger electrons, which are emitted by the daughter product when the resulting orbital electron vacancy is filled, are also emitted. The conversion electrons refer to orbital atomic electrons that are sometimes ejected from the atom in place of the gamma ray that would normally be emitted. This process of internal conversion is often thought of as a type of internal photoelectric effect in which the gamma ray is emitted by the nucleus but hits an orbital electron on its way out of the atom. The electron is ejected and is then called a conversion electron to distinguish it from beta particles which might also be emitted. The chief difference between a conversion electron and a beta particle is the fact that internal conversion electrons are monoenergetic, whereas beta particles exhibit a spectrum of energies.