Beta-plus decay is a type of decay that converts an unstable atom into a more stable configuration via the emission of a neutrino and a positron. In beta-plus decay, a proton in the nucleus is converted to a neutron. The atom then equalizes charges by emitting a positron and a neutrino, both of which are expelled from the nucleus.
Beta-plus decay reduces the number of protons in an atom and increases the number of neutrons by one. Because of this conversion, the total number of particles in the nucleus remains unchanged. The number of protons has dropped, however, so the element transitions to the next-lightest element on the periodic table.
An example of beta-plus decay is the transition of magnesium-23 to sodium-23. In this decay event, the unstable isotope of magnesium loses a proton and gains a neutron, forming a daughter atom of sodium-23. The atomic mass remains unchanged, but the element has been transmuted. To avoid a net imbalance of forces inside the atom, the nucleus sheds a positron in the process.
Beta-plus decay is not to be confused with beta-minus decay. In a beta-minus interaction, one neutron transitions into a proton, and the atom sheds an electron and an antineutrino. In the process, which also conserves the atomic mass, the decayed atom is the next-higher element on the periodic table.