 Electron capture is an example of weak interaction, one of the four fundamental forces.Electron capture is the primary decay mode for isotopes with a relative superabundance of protons in the nucleus, but with insufficient energy difference between the isotope and its prospective daughter (the isobar with one less positive charge) for the nuclide to decay by emitting a positron.Electron capture is always an alternative decay mode for radioactive isotopes that "do" have sufficient energy to decay by positron emission.