Editing Neutron (section)

== Composition ==
[[File:Beta Negative Decay.svg|thumb|200px|The principal [[Feynman diagram]] for {{SubatomicParticle|Beta-}}&nbsp;decay of a neutron into a proton, electron, and [[electron antineutrino]] via an intermediate heavy [[W boson|{{SubatomicParticle|W boson-}} boson]]]]
[[File:Electron Capture Decay.svg|thumb|200px|The principal Feynman diagram for {{SubatomicParticle|Beta+}}&nbsp;decay of a proton into a neutron, positron, and [[electron neutrino]] via an intermediate heavy {{SubatomicParticle|W boson+}} boson]]
{{Main|Standard Model}}

Within the theoretical framework of the Standard Model for particle physics, a neutron comprises two [[down quark]]s with charge {{nowrap|−{{sfrac|1|3}}[[elementary charge|''e'']]}} and one [[up quark]] with charge {{nowrap|+{{sfrac|2|3}}''e''}}. The neutron is therefore a [[composite particle]] classified as a ''[[hadron]]''. The neutron is also classified as a ''[[baryon]]'', because it is composed of three [[valence quark]]s.<ref>
{{cite book
|author=Adair, R.K.
|year=1989
|title=The Great Design: Particles, Fields, and Creation
|page=214
|publisher=[[Oxford University Press]]
|bibcode=1988gdpf.book.....A
}}</ref> The finite size of the neutron and its magnetic moment both indicate that the neutron is a [[composite particle|composite]], rather than [[elementary particle|elementary]], particle.

The quarks of the neutron are held together by the [[strong interaction|strong force]], mediated by [[gluon]]s.<ref name=Cottingham>
{{cite book
|author1=Cottingham, W.N. |author2=Greenwood, D.A. |year=1986
|title=An Introduction to Nuclear Physics
|publisher=[[Cambridge University Press]]
|isbn=9780521657334
}}</ref> The nuclear force results from [[Nuclear force#The nuclear force as a residual of the strong force|secondary effects of the more fundamental strong force]].

The only possible decay mode for the neutron that obeys the [[conservation law]] for the [[baryon number]] is for one of the neutron's quarks to change [[flavour (physics)|flavour]] (through a [[Cabibbo–Kobayashi–Maskawa matrix]]) via the [[weak interaction]]. The decay of one of the neutron's down quarks into a lighter up quark can be achieved by the emission of a [[W boson]]. By this process, the Standard Model description of beta decay, the neutron decays into a proton (which contains one down and two up quarks), an electron, and an [[electron neutrino|electron antineutrino]].

The decay of the proton to a neutron occurs similarly through the weak force. The decay of one of the proton's up quarks into a down quark can be achieved by the emission of a W boson. The proton decays into a neutron, a positron, and an electron neutrino. This reaction can only occur within an atomic nucleus which has a quantum state at lower energy available for the created neutron.

[[File:Beta-minus Decay.svg|thumb|A [[schematic]] of the [[atomic nucleus|nucleus of an atom]] indicating {{SubatomicParticle|Beta-}} radiation, the emission of a fast electron from the nucleus. The decay also creates an antineutrino (omitted) and 
converts a neutron to a proton within the nucleus. <br/>
The '''inset''' shows beta decay of a free neutron; an electron and antineutrino are created in this process.]]

===Beta decay===
{{Main|Beta decay}}
Neutrons and protons within a nucleus behave similarly and can exchange their identities by similar reactions. These reactions are a form of [[radioactive decay]] known as [[beta decay]].<ref>{{Cite book |last1=Basdevant |first1=J.-L. |last2=Rich |first2=J. |last3=Spiro |first3=M. |year=2005 |title=Fundamentals in Nuclear Physics: From Nuclear Structure to Cosmology |publisher=[[Springer (publisher)|Springer]] |isbn=978-0-387-01672-6 }}</ref> Beta decay, in which neutrons decay to protons, or vice versa, is governed by the [[weak interaction|weak force]], and it requires the emission or absorption of electrons and neutrinos, or their antiparticles.<ref name=Loveland>{{cite book |last=Loveland |first=W. D. |year=2005 |title=Modern Nuclear Chemistry |url=https://books.google.com/books?id=ZAHJkrJlwbYC&pg=PA199 |page=199 |publisher=[[John Wiley & Sons|Wiley]] |isbn=978-0-471-11532-8 |access-date=2024-05-01 |archive-date=2024-05-01 |archive-url=https://web.archive.org/web/20240501202310/https://books.google.com/books?id=ZAHJkrJlwbYC&pg=PA199 |url-status=live }}</ref> The neutron and proton decay reactions are:
: {{math|{{SubatomicParticle|Neutron0}} → {{SubatomicParticle|Proton+}} + {{SubatomicParticle|Electron}} + {{SubatomicParticle|Electron antineutrino}}}}
where {{SubatomicParticle|Proton+}}, {{SubatomicParticle|Electron}}, and {{math|{{SubatomicParticle|Electron antineutrino}}}} denote the proton, electron and electron anti-[[neutrino]] decay products,<ref>[http://pdg.lbl.gov/2007/tables/bxxx.pdf Particle Data Group Summary Data Table on Baryons] {{Webarchive|url=https://web.archive.org/web/20110910125729/http://pdg.lbl.gov/2007/tables/bxxx.pdf |date=2011-09-10 }}. lbl.gov (2007). Retrieved on 2012-08-16.</ref> and
: {{math|{{SubatomicParticle|Proton+}} → {{SubatomicParticle|Neutron0}} + {{SubatomicParticle|Positron}} + {{SubatomicParticle|Electron neutrino}}}}

where {{SubatomicParticle|Neutron0}}, {{SubatomicParticle|Positron}}, and {{math|{{SubatomicParticle|Electron neutrino}}}} denote the neutron, positron and electron neutrino decay products.

The electron and positron produced in these reactions are historically known as [[beta particles]], denoted β<sup>−</sup> or β<sup>+</sup> respectively, lending the name to the decay process.<ref name=Loveland/>  In these reactions, the original particle is not ''composed'' of the product particles; rather, the product particles are ''created'' at the instant of the reaction.<ref name="Pais1993">{{cite book|author=Abraham Pais|title=Niels Bohr's Times: In Physics, Philosophy, and Polity|url=https://archive.org/details/nielsbohrstimesi0000pais|url-access=registration|year=1991|publisher=Oxford University Press|isbn=0-19-852049-2}}</ref>{{rp|369–370}}

"Beta decay" reactions can also occur by the capture of a [[lepton]] by the nucleon.  The transformation of a proton to a neutron inside of a nucleus is possible through [[electron capture]]:<ref>{{cite book |last1=Cottingham |first1=W.N. |last2=Greenwood  |first2=D.A. |year=1986|title=An introduction to nuclear physics|page=[https://archive.org/details/introductiontonu0000cott/page/40 40] |publisher=[[Cambridge University Press]] |isbn=978-0-521-31960-7 |url=https://archive.org/details/introductiontonu0000cott/page/40 }}</ref>
:{{math|{{SubatomicParticle|Proton+}} + {{SubatomicParticle|Electron}} → {{SubatomicParticle|Neutron0}} + {{SubatomicParticle|Electron neutrino}}}}
A rarer reaction, [[inverse beta decay]], involves the capture of a neutrino by a nucleon.<ref>{{cite journal |year=1997 |title=The Reines-Cowan Experiments: Detecting the Poltergeist |url=http://library.lanl.gov/cgi-bin/getfile?25-02.pdf |journal=[[Los Alamos Science]] |volume=25 |page=3 |access-date=2024-05-09 |archive-date=2013-02-21 |archive-url=https://web.archive.org/web/20130221123519/http://library.lanl.gov/cgi-bin/getfile?25-02.pdf |url-status=live }}</ref>
Rarer still, positron capture by neutrons can occur in the high-temperature environment of stars.<ref name="Fowler">{{cite journal|last=Fowler|first=W.A.|title=The quest for the origin of the elements|journal=Science|volume=226|year=1984|issue=4677 |pages=922–935 |doi=10.1126/science.226.4677.922 |pmid=17737334 |bibcode=1984Sci...226..922F }}</ref>