Positron emission, beta plus decay, or β decay is a subtype of radioactive decay called beta decay, in which a proton inside a radionuclide nucleus is converted into a neutron while releasing a positron and an electron neutrino (νe). Positron emission is mediated by the weak force. The positron is a type of beta particle (β), the other beta particle being the electron (β) emitted from the β decay of a nucleus.
An example of positron emission (β decay) is shown with magnesium-23 decaying into sodium-23: