Positron emission or beta plus decay (β decay) is a particular type of radioactive decay and a subtype of beta decay, in which a proton inside a radionuclide nucleus is converted into a neutron while releasing a positron and an electron neutrino (ν_e). 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.