Editing Radiocarbon dating (section)

===Physical and chemical details===
{{Main|Carbon-14}}
In nature, [[carbon]] exists as three isotopes. Two are stable and not radioactive: [[carbon-12]] ({{chem|12|C}}), and [[carbon-13]] ({{chem|13|C}}); and [[carbon-14]] ({{chem|14|C}}), also known as "radiocarbon", which is radioactive. The half-life of {{chem|14|C}} (the time it takes for half of a given amount of {{chem|14|C}} to [[Radioactive decay|decay]]) is about 5,730 years, so its concentration in the atmosphere might be expected to decrease over thousands of years, but {{chem|14|C}} is constantly being produced in the lower [[stratosphere]] and upper [[troposphere]], primarily by galactic [[cosmic ray]]s, and to a lesser degree by solar cosmic rays.<ref name=Bowman_9/><ref name=Russel>{{cite book|url=http://theses.gla.ac.uk/2941/1/2011russellphd.pdf|title=Marine radiocarbon reservoir effects (MRE) in archaeology: temporal and spatial changes through the Holocene within the UK coastal environment (PhD thesis)|last=Russell|first=Nicola|publisher=University of Glasgow|year=2011|location=Glasgow, Scotland UK|pages=16|access-date=11 December 2017}}</ref> These cosmic rays generate neutrons as they travel through the atmosphere which can strike [[nitrogen-14]] ({{chem|14|N}}) atoms and turn them into {{chem|14|C}}.<ref name=Bowman_9/> The following [[nuclear reaction]] is the main pathway by which {{chem|14|C}} is created:
: n + {{nuclide|nitrogen|14}} → {{nuclide|carbon|14}} + p
where n represents a [[neutron]] and p represents a [[proton]].<ref name=CES_476>Bianchi & Canuel (2011), p.&nbsp;35.</ref><ref name=LJ_2001/>{{#tag:ref|The interaction of cosmic rays with nitrogen and oxygen below the earth's surface can also create {{chem|14|C}}, and in some circumstances (e.g. near the surface of snow accumulations, which are permeable to gases) this {{chem|14|C}} migrates into the atmosphere. However, this pathway is estimated to be responsible for less than 0.1% of the total production of {{chem|14|C}}.<ref name=LJ_2001/>|group=note}}

Once produced, the {{chem|14|C}} quickly combines with the oxygen (O) in the atmosphere to form first carbon monoxide ({{chem|C|O}}),<ref name=LJ_2001>{{cite journal|last1=Lal|first1=D.|last2=Jull|first2=A.J.T.|year=2001|title=In-situ cosmogenic {{chem|14|C}}: production and examples of its unique applications in studies of terrestrial and extraterrestrial processes |journal=Radiocarbon |volume=43|issue=2B|pages=731–742|doi=10.1017/S0033822200041394|doi-access=free|bibcode=2001Radcb..43..731L }}</ref> and ultimately carbon dioxide ({{chem|CO|2}}).<ref name=Alves2018/>
:{{chem|14|C}} + {{chem|O|2}} → {{chem|14|C|O}} + O

:{{chem|14|C|O}} + OH → {{chem|14|C|O|2}} + H
Carbon dioxide produced in this way diffuses in the atmosphere, is dissolved in the ocean, and is taken up by plants via [[photosynthesis]]. Animals eat the plants, and ultimately the radiocarbon is distributed throughout the [[biosphere]]. The ratio of {{chem|14|C}} to {{chem|12|C}} is approximately 1.25 parts of {{chem|14|C}} to 10<sup>12</sup> parts of {{chem|12|C}}.<ref name=Aitken_56>Tsipenyuk (1997), p.&nbsp;343.</ref> In addition, about 1% of the carbon atoms are of the stable isotope {{chem|13|C}}.<ref name=Bowman_9/>

The equation for the radioactive decay of {{chem|14|C}} is:<ref name=Currie_2004>{{cite journal|last=Currie|first=Lloyd A.|year=2004|title=The remarkable metrological history of radiocarbon dating II|journal=Journal of Research of the National Institute of Standards and Technology|volume=109|issue=2|pages=185–217|doi=10.6028/jres.109.013|pmid=27366605|pmc=4853109}}</ref>
: {{nuclide|carbon|14}} → {{nuclide|nitrogen|14}} + {{subatomic particle|electron}} + {{math|{{subatomic particle|electron antineutrino}}}}
By emitting a beta particle (an [[electron]], e<sup>−</sup>) and an [[Antineutrino|electron antineutrino]] ({{math|{{subatomic particle|Electron antineutrino}}}}), one of the neutrons in the {{chem|14|C}} nucleus changes to a proton and the {{chem|14|C}} nucleus reverts to the stable (non-radioactive) isotope {{chem|14|N}}.<ref>Taylor & Bar-Yosef (2014), p. 33.</ref>