Editing Beta decay (section)

==Electron capture (K-capture/L-capture)==
{{main|Electron capture}}
[[File:Electron-capture.svg|alt=Leading-order EC Feynman diagrams|thumb|309x309px|The leading-order [[Feynman diagram]]s for [[electron capture]] decay. An [[electron]] interacts with an [[up quark]] in the nucleus via a [[W and Z bosons|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.]]
In all cases where {{SubatomicParticle|Beta+}}&nbsp;decay (positron emission) of a nucleus is allowed energetically, so too is [[electron capture]] allowed. This is a process during which a nucleus captures one of its atomic electrons, resulting in the emission of a neutrino:

: {{Physics particle|TL={{mvar|A}}|BL={{mvar|Z}}|X}} + {{SubatomicParticle|Electron}} → {{Physics particle|TL={{mvar|A}}|BL={{math|''Z''−1}}|X′}} + {{math|{{SubatomicParticle|Electron Neutrino}}}}

An example of electron capture is one of the decay modes of [[krypton-81]] into [[bromine-81]]:
:{{nuclide|Krypton|81}} + {{subatomic particle|electron}} → {{nuclide|Bromine|81}} + {{math|{{subatomic particle|electron neutrino}}}}

All emitted neutrinos are of the same energy. In proton-rich nuclei where the energy difference between the initial and final states is less than 2{{math|''m''<sub>e</sub>''c''<sup>2</sup>}}, {{SubatomicParticle|Beta+}}&nbsp;decay is not energetically possible, and electron capture is the sole decay mode.<ref name="Zuber" />

If the captured electron comes from the innermost shell of the atom, the [[Electron shell|K-shell]], which has the highest probability to interact with the nucleus, the process is called K-capture.<ref name="Jevremovic2009">{{cite book
 |last=Jevremovic |first=T.
 |year=2009
 |title=Nuclear Principles in Engineering
 |url=https://books.google.com/books?id=tEM9TCfAe7EC&pg=PA201
 |page=201
 |publisher=[[Springer Science + Business Media]]
 |isbn=978-0-387-85608-7
}}</ref> If it comes from the L-shell, the process is called L-capture, etc.

Electron capture is a competing (simultaneous) decay process for all nuclei that can undergo β<sup>+</sup> decay. The converse, however, is not true: electron capture is the ''only'' type of decay that is allowed in proton-rich nuclides that do not have sufficient energy to emit a positron and neutrino.<ref name="Zuber">{{cite book
 |last=Zuber |first=K.
 |year=2011
 |title=Neutrino Physics
 |page=466 |edition=2nd
 |publisher=[[CRC Press]]
 |isbn=978-1-4200-6471-1
}}</ref>