In all of these processes--except gamma--elements are transformed into other elements and a significant amount of energy is released. The source of the energy is the small mass loss, Dm, which must occur for any spontaneous nuclear process.

Alpha decay or alpha particle emission is the release of a small particle, generally from a heavy nucleus. The particle consists of 2 neutrons and 2 protons but no electrons. This gives it the same nuclear structure as a helium-4 ion with a charge of +2. Alpha emission is an efficient way for a nucleus to shed excess mass quickly but it alters the neutron : proton ratio only very gradually. The effect of alpha emission is to move the element two spaces back on the periodic table with a mass loss of 4.