Editing Nuclear chain reaction (section)

==History==

Chemical [[chain reaction]]s were first proposed by German chemist [[Max Bodenstein]] in 1913, and were reasonably well understood before nuclear chain reactions were proposed.<ref>{{cite web| url = http://nobelprize.org/nobel_prizes/chemistry/laureates/1956/press.html| title = See this 1956 Nobel lecture for history of the chain reaction in chemistry}}</ref> It was understood that chemical chain reactions were responsible for exponentially increasing rates in reactions, such as produced in chemical explosions.

The concept of a nuclear chain reaction was reportedly first hypothesized by Hungarian scientist [[Leó Szilárd]] on September 12, 1933.<ref>{{cite web |last1=Jogalekar |first1=Ashutosh |title= Leo Szil&nbsp;rd, a traffic light and a slice of nuclear history |url= http://blogs.scientificamerican.com/the-curious-wavefunction/leo-szilard-a-traffic-light-and-a-slice-of-nuclear-history/ |website= Scientific American |access-date= 4 January 2016}}</ref> Szilárd that morning had been reading in a London paper of an experiment in which [[Proton|protons]] from an [[Accelerator mass spectrometry|accelerator]] had been used to split [[Isotopes of lithium|lithium-7]] into [[Alpha particle|alpha particles]], and the fact that much greater amounts of energy were produced by the reaction than the proton supplied. [[Ernest Rutherford]] commented in the article that inefficiencies in the process precluded use of it for power generation. However, the [[neutron]] had been discovered by [[James Chadwick]] in 1932, shortly before, as the product of a [[nuclear reaction]]. Szilárd, who had been trained as an engineer and physicist, put the two nuclear experimental results together in his mind and realized that if a nuclear reaction produced neutrons, which then caused further similar nuclear reactions, the process might be a self-perpetuating nuclear chain reaction, spontaneously producing new [[Isotope|isotopes]] and power without the need for protons or an accelerator. Szilárd, however, did not propose [[Nuclear fission|fission]] as the mechanism for his chain reaction since the fission reaction was not yet discovered, or even suspected. Instead, Szilárd proposed using mixtures of lighter known isotopes which produced neutrons in copious amounts. He filed a patent for his idea of a simple nuclear reactor the following year.<ref>L. Szilárd, "Improvements in or relating to the transmutation of chemical elements," British patent number: GB630726 (filed: 28 June 1934; published: 30 March 1936). [http://v3.espacenet.com/textdoc?DB=EPODOC&IDX=GB630726 esp@cenet document view<!-- Bot generated title -->]</ref>

In 1936, Szilárd attempted to create a chain reaction using [[beryllium]] and [[indium]] but was unsuccessful. Nuclear fission was discovered by [[Otto Hahn]] and [[Fritz Strassmann]] in December 1938<ref>Lise Meitner: ''Otto Hahn - the discoverer of nuclear fission.'' In: Forscher und Wissenschaftler im heutigen Europa. Stalling Verlag, Oldenburg/Hamburg 1955.</ref> and [[discovery of nuclear fission|explained theoretically]] in January 1939 by [[Lise Meitner]] and her nephew [[Otto Robert Frisch]].<ref>[[Lise Meitner]] & [[Otto Robert Frisch|O. R. Frisch]], "[http://www.nature.com/articles/143239a0 Disintegration of Uranium by Neutrons: A New Type of Nuclear Reaction]," ''Nature'' '''143''', 3615 (1939-02-11): 239, {{Bibcode|1939Natur.143..239M}}, {{doi|10.1038/143239a0}}; [[Otto Robert Frisch|O. R. Frisch]], "[https://www.nature.com/articles/143276a0 Physical Evidence of Division of Heavy Nuclei under Neutron Bombardment]," ''Nature'' '''143''', 3616 (1939-02-18): 276, {{doi|10.1038/143276a0}}. The paper is dated 16 January 1939. Meitner is identified as being at the Physical Institute, Academy of Sciences, Stockholm. Frisch is identified as being at the Institute of Theoretical Physics, University of Copenhagen.</ref> In their second publication on nuclear fission in February 1939, Hahn and Strassmann used the term ''uranspaltung'' ([[uranium]] fission) for the first time and predicted the existence and liberation of additional neutrons during the fission process, opening up the possibility of a nuclear chain reaction.<ref>{{cite journal |last1=Hahn |first1=O. |last2=Strassmann |first2=F. |author-link2=Fritz Strassmann |title=Nachweis der Entstehung aktiver Bariumisotope aus Uran und Thorium durch Neutronenbestrahlung; Nachweis weiterer aktiver Bruchstücke bei der Uranspaltung |journal=Naturwissenschaften |volume=27 |issue=6 |pages=89–95 |date=February 1939 |doi=10.1007/BF01488988 |bibcode=1939NW.....27...89H |s2cid=33512939 }}</ref>

A few months later, [[Frédéric Joliot-Curie]], [[Hans von Halban|H. Von Halban]] and [[Lew Kowarski|L. Kowarski]] in Paris<ref>H. von Halban, F. Joliot and L. Kowarski, ''Nature'' 143 (1939) 470 and 680.</ref> {{Secondary source needed|date=January 2025}}searched for, and discovered, neutron multiplication in uranium, proving that a nuclear chain reaction by this mechanism was indeed possible. On May 4, 1939, Joliot-Curie, Halban, and Kowarski filed three patents. The first two described power production from a nuclear chain reaction, the last one called ''Perfectionnement aux charges explosives'' was the first patent for the [[Nuclear weapon|atomic bomb]] and is filed as patent No. 445686 by the [[Centre national de la recherche scientifique|Caisse nationale de Recherche Scientifique]].<ref>{{Cite book |title=Histoire secrète de la bombe atomique française |location=Paris|publisher=Cherche Midi|language=fr|year=2000|isbn=978-2-862-74794-1|oclc=45842105|last1=Bendjebbar|first1=André}}</ref>{{Additional citation needed|date=January 2025}} In parallel, Szilárd and [[Enrico Fermi]] in New York made the same analysis.<ref>{{cite journal|author1-link=Herbert L. Anderson|first1= H. L. |last1 = Anderson|first2= E.|last2= Fermi|first3= Leo|last3= Szilárd|title =Neutron production and absorption in uranium|journal =Physical Review|volume = 56 | pages= 284–286 |date =1 August 1939|issue= 3 |doi= 10.1103/PhysRev.56.284 |bibcode= 1939PhRv...56..284A |url = https://library.ucsd.edu/dc/object/bb01380563/_1.pdf}}</ref> This discovery prompted [[Einstein–Szilárd letter|the letter]] from Szilárd and signed by [[Albert Einstein]] to President [[Franklin D. Roosevelt]], warning of the possibility that [[Nazi Germany]] might be attempting to build an atomic bomb.<ref>{{cite book|last1=Lanouette|first1=William|url=https://archive.org/details/geniusinshadowsa00lano |title=Genius in the Shadows: A Biography of Leo Szilárd: The Man Behind The Bomb|last2=Silard|first2=Bela|publisher=Charles Scribner's Sons|year=1992|isbn=978-0-684-19011-2|location=New York|pages=199, 202|url-access=registration}}</ref>

On December 2, 1942, a team led by Fermi (and including Szilárd) produced the first artificial self-sustaining nuclear chain reaction with the [[Chicago Pile-1]] experimental reactor in a [[racquets (sport)|racquets]] court below the bleachers of [[Stagg Field]] at the [[University of Chicago]]. Fermi's experiments at the University of Chicago were part of [[Arthur H. Compton]]'s [[Metallurgical Laboratory]] of the [[Manhattan Project]]; the lab was renamed [[Argonne National Laboratory]] and tasked with conducting research in harnessing fission for nuclear energy.<ref name="Holl">
{{cite book
 |last=Holl |first=Jack
 |year=1997
 |title=Argonne National Laboratory, 1946-96
 |publisher=[[University of Illinois Press]]
 |isbn=978-0-252-02341-5
}}</ref>

In 1956, [[Paul Kuroda]] of the [[University of Arkansas]] postulated that a natural fission reactor may have once existed. Since nuclear chain reactions may only require natural materials (such as water and uranium, if the uranium has sufficient amounts of [[Uranium-235|<sup>235</sup>U]]), it was possible to have these chain reactions occur in the distant past when uranium-235 concentrations were higher than today, and where there was the right combination of materials within the [[Earth's crust]]. Uranium-235 made up a larger share of uranium on Earth in the geological past because of the different [[Half-life|half-lives]] of the isotopes {{chem|235|U}} and {{chem|238|U}}, the former decaying almost an [[order of magnitude]] faster than the latter. Kuroda's prediction was verified with the discovery of evidence of [[Natural nuclear fission reactor|natural self-sustaining nuclear chain reactions]] in the past at [[Oklo]] in [[Gabon]] in September 1972.<ref>[http://www.ocrwm.doe.gov/factsheets/doeymp0010.shtml Oklo: Natural Nuclear Reactors—Fact Sheet] {{webarchive|url=https://web.archive.org/web/20081020201724/http://www.ocrwm.doe.gov/factsheets/doeymp0010.shtml |date=2008-10-20 }}</ref> To sustain a nuclear fission chain reaction at present isotope ratios in natural uranium on Earth would require the presence of a [[neutron moderator]] like [[heavy water]] or high purity carbon (e.g. graphite) in the absence of [[neutron poison]]s, which is even more unlikely to arise by natural geological processes than the conditions at Oklo some two billion years ago.