Electron capture (K-electron capture, also K-capture, or L-electron capture, L-capture) is a process in which the proton-rich nucleus of an electrically neutral atom absorbs an inner atomic electron, usually from the K or L electron shells. This process thereby changes a nuclear proton to a neutron and simultaneously causes the emission of an electron neutrino. p + e− → n + νe or when written as a nuclear reaction equation, ν Electron capture is an example of weak interaction, one of the four fundamental forces.