Editing Carbon-14 (section)

===Natural production in the atmosphere===
[[File:Carbon 14 formation and decay.svg|right|thumb| 1: Formation of carbon-14 <br>2: Decay of carbon-14 <br>3: The "equal" equation is for living organisms, and the unequal one is for dead organisms, in which the C-14 then decays (See 2).]]
Carbon-14 is produced in the upper [[troposphere]] and the [[stratosphere]] by [[thermal neutron]]s absorbed by [[nitrogen]] atoms. When [[cosmic ray]]s enter the atmosphere, they undergo various transformations, including the production of [[neutron]]s. The resulting neutrons (n) participate in the following [[(n-p) reaction|n-p]] reaction (p is [[proton]]):

:{{chem|14|7|N}} + n → {{chem|14|6|C}} + p + 0.626 MeV

The highest rate of carbon-14 production takes place at altitudes of {{convert|9|to|15|km|ft}} and at high [[geomagnetic latitude]]s.

The rate of {{sup|14}}C production can be modeled, yielding values of 16,400<ref name="Kovaltsov-2012">{{cite journal | vauthors = Kovaltsov GA, Mishev A, Usoskin IG |title=A new model of cosmogenic production of radiocarbon 14C in the atmosphere |journal=Earth and Planetary Science Letters |volume=337–338 |year=2012 |pages=114–20 |issn=0012-821X |doi=10.1016/j.epsl.2012.05.036 |arxiv=1206.6974 |bibcode=2012E&PSL.337..114K |s2cid=118602346}}</ref> or 18,800<ref name="Poluianov-2016">{{cite journal | vauthors = Poluianov SV, Kovaltsov GA, Mishev AL, Usoskin IG |title=Production of cosmogenic isotopes 7Be, 10Be, 14C, 22Na, and 36Cl in the atmosphere: Altitudinal profiles of yield functions |journal=Journal of Geophysical Research: Atmospheres |volume=121 |issue=13 |year=2016 |pages=8125–36 |doi=10.1002/2016JD025034 |arxiv=1606.05899 |bibcode=2016JGRD..121.8125P|s2cid=119301845 }}</ref> atoms of {{chem|14|C}} per second per square meter of Earth's surface, which agrees with the global [[Emissions budget|carbon budget]] that can be used to backtrack,<ref name="Hain-2014">{{cite journal | vauthors = Hain MP, Sigman DM, Haug GH |title=Distinct roles of the Southern Ocean and North Atlantic in the deglacial atmospheric radiocarbon decline |journal=Earth and Planetary Science Letters |volume=394 |year=2014 |pages=198–208 |issn=0012-821X |doi=10.1016/j.epsl.2014.03.020 |url=https://earth-system-biogeochemistry.net/wp-content/uploads/2021/05/Hain_et_al_2014_EPSL.pdf |bibcode=2014E&PSL.394..198H |url-status=live |archive-url=https://web.archive.org/web/20151222120109/http://www.mathis-hain.net/resources/Hain_et_al_2014_EPSL.pdf |archive-date=2015-12-22}}</ref> but attempts to measure the production time directly ''in situ'' were not very successful. Production rates vary because of changes to the cosmic ray flux caused by the heliospheric modulation (solar wind and solar magnetic field), and, of great significance, due to variations in the [[Earth's magnetic field]]. Changes in the [[carbon cycle]] however can make such effects difficult to isolate and quantify.
<ref name="Hain-2014"/><ref name="Ramsey-2008">{{cite journal | year=2008 | author=Ramsey, C. Bronk | journal =Archaeometry | volume=50 | pages=249–75 | doi=10.1111/j.1475-4754.2008.00394.x | issue=2 | title=Radiocarbon Dating: Revolutions in Understanding}}</ref>
Occasional spikes may occur; for example, there is evidence for [[774–775 carbon-14 spike|an unusually high production rate in AD 774–775]],<ref>{{cite journal | vauthors = Miyake F, Nagaya K, Masuda K, Nakamura T | title = A signature of cosmic-ray increase in AD 774-775 from tree rings in Japan | journal = Nature | volume = 486 | issue = 7402 | pages = 240–242 | date = June 2012 | pmid = 22699615 | doi = 10.1038/nature11123 | url = http://sciences.blogs.liberation.fr/files/c14-774-apr%C3%A8s-jc.pdf | url-status = dead | s2cid = 4368820 | bibcode = 2012Natur.486..240M | archive-url = https://web.archive.org/web/20150706121714/http://sciences.blogs.liberation.fr/files/c14-774-apr%C3%A8s-jc.pdf | archive-date = 2015-07-06 }}</ref> caused by an extreme
solar energetic particle event, the strongest such event to have occurred within the last ten millennia.<ref name="Usoskin-2013">{{cite journal | year=2013 | vauthors = Usoskin IG, Kromer B, Ludlow F, Beer J, Friedrich M, Kovaltsov GA, Solanki SK, Wacker L | display-authors = 6 | journal =Astron. Astrophys.| volume=552 | pages=L3 | doi=10.1051/0004-6361/201321080 | title=The AD775 cosmic event revisited: the Sun is to blame | bibcode=2013A&A...552L...3U|arxiv=1302.6897|s2cid=55137950 }}</ref><ref name="Mekhaldi-2015">{{cite journal | vauthors = Mekhaldi F, Muscheler R, Adolphi F, Aldahan A, Beer J, McConnell JR, Possnert G, Sigl M, Svensson A, Synal HA, Welten KC, Woodruff TE | display-authors = 6 | title = Multiradionuclide evidence for the solar origin of the cosmic-ray events of ᴀᴅ 774/5 and 993/4 | journal = Nature Communications | volume = 6 | pages = 8611 | date = October 2015 | pmid = 26497389 | pmc = 4639793 | doi = 10.1038/ncomms9611 | bibcode = 2015NatCo...6.8611M }}</ref> Another "extraordinarily large" {{sup|14}}C increase (2%) has been associated with a 5480&nbsp;BC event, which is unlikely to be a solar energetic particle event.<ref>{{cite journal | vauthors = Miyake F, Jull AJ, Panyushkina IP, Wacker L, Salzer M, Baisan CH, Lange T, Cruz R, Masuda K, Nakamura T | display-authors = 6 | title = Large 14C excursion in 5480 BC indicates an abnormal sun in the mid-Holocene | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 114 | issue = 5 | pages = 881–884 | date = January 2017 | pmid = 28100493 | pmc = 5293056 | doi = 10.1073/pnas.1613144114 | doi-access = free | bibcode = 2017PNAS..114..881M }}</ref>

Carbon-14 may also be produced by lightning<ref>{{Cite journal | doi=10.1029/JB078i026p05902| bibcode=1973JGR....78.5902L| title=Production of radiocarbon in tree rings by lightning bolts| year=1973| vauthors = Libby LM, Lukens HR | journal=Journal of Geophysical Research| volume=78| issue=26| pages=5902–5903}}</ref><ref>{{cite journal | vauthors = Enoto T, Wada Y, Furuta Y, Nakazawa K, Yuasa T, Okuda K, Makishima K, Sato M, Sato Y, Nakano T, Umemoto D, Tsuchiya H | display-authors = 6 | title = Photonuclear reactions triggered by lightning discharge | journal = Nature | volume = 551 | issue = 7681 | pages = 481–484 | date = November 2017 | pmid = 29168803 | doi = 10.1038/nature24630 | bibcode = 2017Natur.551..481E | arxiv = 1711.08044 | s2cid = 4388159 }}</ref> but in amounts negligible, globally, compared to cosmic ray production. Local effects of cloud-ground discharge through sample residues are unclear, but possibly significant.