Electron capture

This process thereby changes a nuclear proton to a neutron and simultaneously causes the emission of an electron neutrino.

Usually, a gamma ray is emitted during this transition, but nuclear de-excitation may also take place by internal conversion.

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 sometimes included as a type of beta decay,[1] because the basic nuclear process, mediated by the weak force, is the same.

The theory of electron capture was first discussed by Gian-Carlo Wick in a 1934 paper, and then developed by Hideki Yukawa and others.

It is hypothesized that such elements, if formed by the r-process in exploding supernovae, are ejected fully ionized and so do not undergo radioactive decay as long as they do not encounter electrons in outer space.

Electron capture happens most often in the heavier neutron-deficient elements where the mass change is smallest and positron emission is not always possible.

Scheme of two types of electron capture. Top : The nucleus absorbs an electron. Lower left : An outer electron replaces the "missing" electron. Electromagnetic radiation equal in energy to the difference between the two electron shells is emitted. Lower right : In the Auger effect, the energy absorbed when the outer electron replaces the inner electron is transferred to an outer electron. The outer electron is ejected from the atom, leaving a positive ion.
Leading-order EC Feynman diagrams
The leading-order Feynman diagrams for electron capture decay. An electron interacts with an up quark in the nucleus via a W boson to create a down quark and electron neutrino . Two diagrams comprise the leading (second) order, though as a virtual particle , the type (and charge) of the W-boson is indistinguishable.