ABSTRACT

During radioactive decay, the unstable atoms can become a different element via a process known as transmutation. This is the case in radioactive processes that result in the emission of alpha particles (a, or 4He2+), electrons (b-), or positrons (b+). As an example, fluorine-18 (18F) has nine protons and nine neutrons in its nucleus and is a positron emitter; on spontaneous decay a positron is emitted and, consequently, one of the protons becomes a neutron. The newly formed element, which has eight protons and ten neutrons, is oxygen-18 (18O). Radioactive decay can also occur via electron capture (when a nucleus captures an orbiting electron, thereby converting a proton into a neutron with consequent transmutation), by emission of gamma ( g) rays, by emission of a neutron, or by ejection of an orbital electron due to interaction with an excited nucleus in a process called “internal transition”. In the latter three decay modalities, the atoms before and after radioactive decay correspond to the same element because the number of protons remains unchanged and transmutation does not occur.