Editing Neutron (section)

{{Short description|Subatomic particle with no charge}}
{{About|the subatomic particle|other uses|Neutron (disambiguation)}}
{{Distinguish|Neuron|Neutrino}}
{{pp-move}}
{{Infobox particle
| classification  = [[Baryon]]
| name            = Neutron
| image           = [[File:Quark_structure_neutron.svg|250px]]
| caption         = The [[quark]] content of the neutron. The color assignment of individual quarks is arbitrary, but all three colors must be present. Forces between quarks are mediated by [[gluons]].
| group           = [[Hadron]]
| num_types       =
| composition     = 1 [[up quark]], 2 [[down quark]]s
| statistics      = [[Fermionic]]
| generation      =
| interaction     = [[Gravity]], [[weak interaction|weak]], [[strong Interaction|strong]], [[electromagnetic interaction|electromagnetic]]
| antiparticle    = [[Antineutron]]
| theorized       = [[Ernest Rutherford]]<ref name="chemed.chem.purdue.edu">[http://chemed.chem.purdue.edu/genchem/history/rutherford.html Ernest Rutherford] {{Webarchive|url=https://web.archive.org/web/20110803083616/http://chemed.chem.purdue.edu/genchem/history/rutherford.html |date=2011-08-03 }}. Chemed.chem.purdue.edu. Retrieved on 2012-08-16.</ref> (1920)
| discovered      = [[James Chadwick]]<ref name="1935 Nobel Prize in Physics">[http://nobelprize.org/nobel_prizes/physics/laureates/1935/ 1935 Nobel Prize in Physics] {{Webarchive|url=https://web.archive.org/web/20171003030602/http://nobelprize.org/nobel_prizes/physics/laureates/1935/ |date=2017-10-03 }}. Nobelprize.org. Retrieved on 2012-08-16.</ref> (1932)
| symbol          = {{SubatomicParticle|Neutron}}, {{SubatomicParticle|Neutron0}}, {{SubatomicParticle|Nucleon0}}
| mass            = {{physconst|mn}} {{physconst|mnc2_MeV|unit=MeV/''c''<sup>2</sup>}}<br />{{physconst|mn_Da}}
| mean_lifetime   = {{val|878.4|(5)|u=s}} ([[Free neutron decay|free]])<ref name="PDG Live: 2020 Review of Particle Physics">{{cite web |last1=Zyla |first1=P. A. |title=n MEAN LIFE |url=https://pdglive.lbl.gov/DataBlock.action?node=S017T |website=PDG Live: 2020 Review of Particle Physics |publisher=Particle Data Group |access-date=25 February 2021 |date=2020 |archive-date=17 January 2021 |archive-url=https://web.archive.org/web/20210117164505/https://pdglive.lbl.gov/DataBlock.action?node=S017T |url-status=live }}</ref>
| electric_charge = {{val|0|u=[[elementary charge|''e'']]}}<br />
{{val|-2|±8|e=-22|u=[[elementary charge|''e'']]}} (experimental limits)<ref name="PDGLIVE"/>
| electric_dipole_moment  = < {{val|1.8|e=-26|u=''e''⋅cm}} (experimental upper limit)
| electric_polarizability = {{val|1.16|(15)|e=-3|u=fm<sup>3</sup>}}
| magnetic_moment = [[Neutron magnetic moment|{{val|-0.96623650|(23)|e=-26}}]]&nbsp;[[Joule|J]]·[[Tesla (unit)|T]]<sup>−1</sup><ref name="2014 CODATA">Mohr, P.J.; Taylor, B.N. and Newell, D.B. (2014), [http://physics.nist.gov/constants "The 2014 CODATA Recommended Values of the Fundamental Physical Constants"] {{Webarchive|url=https://web.archive.org/web/20131009032049/http://physics.nist.gov/constants |date=2013-10-09 }} (Web Version 7.0). The database was developed by J. Baker, M. Douma, and [[Svetlana Kotochigova|S. Kotochigova]]. (2014). National Institute of Standards and Technology, Gaithersburg, Maryland 20899.</ref><br /><!--
   -->{{val|-1.04187563|(25)|e=-3|u=[[Bohr magneton|''μ''<sub>B</sub>]]}}<ref name="2014 CODATA"/><br /><!--
   -->{{val|-1.91304273|(45)|u=[[Nuclear magneton|''μ''<sub>N</sub>]]}}<ref name="2014 CODATA"/>
| magnetic_polarizability = {{val|3.7|(20)|e=-4|u=fm<sup>3</sup>}}
| spin            = {{sfrac|1|2}}&nbsp;[[reduced Planck constant|''ħ'']]
| isospin         = −{{sfrac|1|2}}
| parity          = +1
| condensed_symmetries    = ''[[Isospin|I]]''(''[[Total angular momentum|J]]''<sup>''[[Intrinsic parity|P]]''</sup>)&nbsp;=&nbsp;{{sfrac|1|2}}({{sfrac|1|2}}<sup>+</sup>)
}}

The '''neutron''' is a [[subatomic particle]], symbol {{SubatomicParticle|Neutron}} or {{SubatomicParticle|Neutron0}}, that has no electric charge, and a [[mass]] slightly greater than that of a [[proton]]. The [[Discovery of the neutron|neutron was discovered]] by [[James Chadwick]] in 1932, leading to the discovery of [[nuclear fission]] in 1938, the first self-sustaining [[nuclear reactor]] ([[Chicago Pile-1]], 1942) and the first [[nuclear weapon]] ([[Trinity (nuclear test)|Trinity]], 1945).

Neutrons are found, together with a similar number of [[protons]] in the [[atomic nucleus|nuclei]] of [[atom]]s. Atoms of a [[chemical element]] that differ only in neutron number are called [[isotopes]]. Free neutrons are produced copiously in [[nuclear fission]] and [[nuclear fusion|fusion]]. They are a primary contributor to the [[nucleosynthesis]] of chemical elements within [[star]]s through fission, fusion, and [[neutron capture]] processes. [[Neutron star]]s, formed from massive collapsing stars, consist of neutrons at the density of atomic nuclei but a total mass more than the Sun.

Neutron properties and interactions are described by [[nuclear physics]].  Neutrons are not [[elementary particle]]s; each is composed of three [[quark]]s. A free neutron spontaneously decays to a proton, an [[electron]], and an [[antineutrino]], with a [[Exponential decay#Mean lifetime|mean lifetime]] of about 15 minutes.

The neutron is essential to the production of nuclear power. 
Dedicated [[neutron source]]s like [[neutron generator]]s, [[research reactor]]s and [[spallation|spallation sources]] produce free neutrons for use in [[irradiation]] and in [[neutron scattering]] experiments.  Free neutrons do not directly ionize atoms, but they do indirectly cause [[ionizing radiation#Neutrons|ionizing radiation]], so they can be a biological hazard, depending on dose. A small natural "neutron background" flux of free neutrons exists on Earth, caused by [[cosmic rays]], and by the natural radioactivity of spontaneously fissionable elements in the [[Crust (geology)#Earth's crust|Earth's crust]].