Editing Willard Libby (section)

==Radiocarbon dating==
After the war, Libby accepted an offer from the [[University of Chicago]] of a professorship in the chemistry department at the new [[Institute for Nuclear Studies]].<ref name="Nobelprize.org"/> He returned to his pre-war studies of radioactivity.{{sfn|Carey|2006|pp=231–232}} In 1939, [[Serge Korff]] had discovered that [[cosmic rays]] generated [[neutron]]s in the upper atmosphere. These interact with [[nitrogen-14]] in the air to produce [[carbon-14]]:<ref>{{cite journal |last1=Korff |first1=S. A. |title=On the contribution to the ionization at sea-level produced by the neutrons in the cosmic radiation |journal=Journal of the Franklin Institute |date=December 1, 1940 |volume=230 |issue=6 |pages=777–779 |doi=10.1016/S0016-0032(40)90838-9 }}</ref><ref name="Nobel lecture">{{Nobelprize|access-date=May 1, 2020 }} including the Nobel Lecture, December 12, 1960 ''Radiocarbon Dating''</ref>
:<sup>1</sup>n + <sup>14</sup>N → <sup>14</sup>C + <sup>1</sup>p
The [[half-life]] of carbon-14 is 5,730±40 years.<ref>{{cite journal|last=Godwin|first=H|year=1962|title=Half-life of radiocarbon|journal=Nature|volume=195|issue=4845|page=984|doi=10.1038/195984a0|bibcode = 1962Natur.195..984G |s2cid=27534222|doi-access=free}}</ref> Libby realized that when plants and animals die they cease to ingest fresh carbon-14, thereby giving any organic compound a built-in nuclear clock.<ref name="Nobel lecture" /> He published his theory in 1946,<ref>{{cite journal | title=Atmospheric Helium Three and Radiocarbon from Cosmic Radiation | author=W.F. Libby | journal=Physical Review | volume=69 | issue=11–12 | pages=671–672 | year=1946 | doi=10.1103/PhysRev.69.671.2| bibcode=1946PhRv...69..671L }}</ref><ref name="Anderson">{{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.|title=Radiocarbon From Cosmic Radiation|journal=Science|date=May 30, 1947 |volume=105 |issue=2735 |pages=576–577 |doi=10.1126/science.105.2735.576|bibcode=1947Sci...105..576A |pmid=17746224}}</ref> and expanded on it in his monograph ''Radiocarbon Dating'' in 1955. He also developed sensitive radiation detectors that could make the measurements required by the technique. Tests against [[Sequoia (genus)|sequoia]] with known dates from their tree rings showed [[radiocarbon dating]] to be reliable and accurate. The technique revolutionised [[archaeology]], [[palaeontology]] and other disciplines that dealt with ancient artefacts.{{sfn|Carey|2006|pp=231–232}} In 1960, he was awarded the [[Nobel Prize in Chemistry]] "for his method to use carbon-14 for age determination in archaeology, geology, geophysics, and other branches of science".<ref>{{cite web |url=https://www.nobelprize.org/nobel_prizes/chemistry/laureates/1960/ |title=The Nobel Prize in Chemistry 1960 |publisher=Nobel Foundation |access-date = July 27, 2015 }}</ref> He also discovered that [[tritium]] similarly could be used for dating water, and therefore wine.<ref name="Nobel lecture" />