Beta decay
There are two types of beta decay: beta plus decay and beta minus decay. Only beta minus decay, however, occurs naturally.
Beta minus decay occurs in unstable nuclei with too many neutrons. One of the neutrons becomes a proton in a process that involves the release of a β- particle (a high energy electron) and an antineutrino. The result is the nuclei of a different element. This element is located one box to the right of the original element on the periodic table.
Beta plus decay occurs in unstable nuclei with too many protons. One proton becomes a neutron with the release of a β+ particle (a positron) and a neutrino. The result of this decay is the nuclei of a different element, which is located one box to the left of the original element on the periodic table.