Editing Radiocarbon dating (section)

===History===
In 1939, [[Martin Kamen]] and [[Sam Ruben|Samuel Ruben]] of the [[Lawrence Radiation Laboratory|Radiation Laboratory at Berkeley]] began experiments to determine if any of the elements common in organic matter had isotopes with half-lives long enough to be of value in biomedical research. They synthesized {{chem|14|C}} using the laboratory's cyclotron accelerator and soon discovered that the atom's [[half-life]] was far longer than had been previously thought.<ref name=renamed_from_20_on_20200701175743>Taylor & Bar-Yosef (2014), p. 268.</ref> This was followed by a prediction by [[Serge A. Korff]], then employed at the [[Franklin Institute]] in [[Philadelphia]], that the interaction of [[w:neutron temperature|thermal neutrons]] with {{chem|14|N}} in the upper atmosphere would create {{chem|14|C}}.{{#tag:ref|Korff's paper actually referred to slow neutrons, a term that since Korff's time has acquired a more specific meaning, referring to a range of neutron energies that does not overlap with thermal neutrons.<ref name=Korff_1949>{{cite journal|last1=Korff|first1=S.A. |year=1940|title=On the contribution to the ionization at sea-level produced by the neutrons in the cosmic radiation|journal=Journal of the Franklin Institute |volume=230|issue=6|pages=777–779|doi=10.1016/s0016-0032(40)90838-9|bibcode=1940TeMAE..45..133K }}</ref>|group=note}}<ref name=taylor269>Taylor & Bar-Yosef (2014), p. 269.</ref><ref name=acs>{{Cite web|url=https://www.acs.org/content/acs/en/education/whatischemistry/landmarks/radiocarbon-dating.html|title=Radiocarbon Dating – American Chemical Society|website=American Chemical Society|access-date=2016-10-09}}</ref> It had previously been thought that {{chem|14|C}} would be more likely to be created by [[deuteron]]s interacting with {{chem|13|C}}.<ref name=renamed_from_20_on_20200701175743/> At some time during World War II, [[Willard Libby]], who was then at Berkeley, learned of Korff's research and conceived the idea that it might be possible to use radiocarbon for dating.<ref name=taylor269/><ref name=acs/>
[[File:Willard Libby in Lab (cropped).jpg|alt=The head of a man wearing glasses, looking at the camera|thumb|Willard Libby, the inventor of radiocarbon dating]]
In 1945, Libby moved to the [[University of Chicago]], where he began his work on radiocarbon dating. He published a paper in 1946 in which he proposed that the carbon in living matter might include {{chem|14|C}} as well as non-radioactive carbon.<ref name=Bowman_9>Bowman (1995), pp.&nbsp;9–15.</ref><ref>{{cite journal|last=Libby|first=W.F.|year=1946|title=Atmospheric helium three and radiocarbon from cosmic radiation|journal=Physical Review|volume=69|issue=11–12|pages=671–672|bibcode=1946PhRv...69..671L|doi=10.1103/PhysRev.69.671.2}}</ref> Libby and several collaborators proceeded to experiment with [[methane]] collected from sewage works in Baltimore, and after [[Isotope enrichment|isotopically enriching]] their samples they were able to demonstrate that they contained {{chem|14|C}}. By contrast, methane created from petroleum showed no radiocarbon activity because of its age. The results were summarized in a paper in ''[[Science (journal)|Science]]'' in 1947, in which the authors commented that their results implied it would be possible to date materials containing carbon of organic origin.<ref name=Bowman_9/><ref name=Anderson_1947>{{cite journal|last1=Anderson|first1=E.C.|last2=Libby|first2=W.F.|last3=Weinhouse|first3=S.|last4=Reid|first4=A.F.|last5=Kirshenbaum|first5=A.D.|last6=Grosse|first6=A.V.|year=1947|title=Radiocarbon from cosmic radiation|journal=Science|volume=105|issue=2765|pages=576–577|bibcode=1947Sci...105..576A|doi=10.1126/science.105.2735.576|pmid=17746224}}</ref>

Libby and [[James R. Arnold|James Arnold]] proceeded to test the radiocarbon dating theory by analyzing samples with known ages. For example, two samples taken from the tombs of two Egyptian kings, [[Zoser]] and [[Sneferu]], independently dated to 2625 BC ± 75 years, were dated by radiocarbon measurement to an average of 2800 BC ± 250 years. These results were published in ''Science'' in December 1949.<ref name=libby49>{{cite journal|last1=Arnold|first1=J.R.|last2=Libby|first2=W.F.|year=1949|title=Age determinations by radiocarbon content: checks with samples of known age|url=http://hbar.phys.msu.ru/gorm/fomenko/libby.htm|journal=Science|volume=110|issue=2869|pages=678–680|bibcode=1949Sci...110..678A|doi=10.1126/science.110.2869.678|jstor=1677049|pmid=15407879}}</ref><ref name=Aitken_60>Aitken (1990), pp.&nbsp;60–61.</ref>{{#tag:ref|Some of Libby's original samples have since been retested, and the results, published in 2018, were generally in good agreement with Libby's original results.<ref name=LJ_2018>{{cite journal|last1=Jull|first1=A.J.T.|last2=Pearson|first2=C.L.|last3=Taylor|first3=R.E.|last4=Southon|first4= J.R. |last5=Santos |first5=G.M. |last6=Kohl |first6=C.P. |last7=Hajdas |first7=I. |last8=Molnar |first8=M. |last9=Baisan |first9=C. |last10=Lange |first10=T.E. |last11=Cruz |first11=R. |last12=Janovics |first12=R. |last13=Major |first13= I.|year=2018|title=Radiocarbon dating and intercomparison of some early historical radiocarbon samples|journal=Radiocarbon |volume=60|issue=2|pages=535–548|doi=10.1017/RDC.2018.18|bibcode=2018Radcb..60..535J |s2cid=134723966|url=https://escholarship.org/content/qt8tm2p64f/qt8tm2p64f.pdf }}</ref>|group=note}}  Within 11 years of their announcement, more than 20 radiocarbon dating laboratories had been set up worldwide.<ref>{{Cite web|url=http://www.c14dating.com/int.html|title=The method|website=www.c14dating.com|access-date=2016-10-09}}</ref> In 1960, Libby was awarded the [[Nobel Prize in Chemistry]] for this work.<ref name=Bowman_9/>