Editing Enrico Fermi (section)

== Manhattan Project ==
{{Main|Manhattan Project}}
[[File:Stagg Field reactor.jpg|thumb|upright=1.2|Illustration of [[Chicago Pile-1]], the first nuclear reactor to achieve a self-sustaining chain reaction. Designed by Fermi, it consisted of uranium and uranium oxide in a cubic lattice embedded in graphite.]]
[[File:Enrico Fermi Los Alamos.png|thumb|Fermi's ID photo from [[Los Alamos National Laboratory|Los Alamos]]]]
[[File:Atomic physicists Ernest O. Lawrence, Enrico Fermi, and Isidor Rabi - NARA - 558595.jpg|thumb|upright=1.1|[[Ernest O. Lawrence]], Fermi, and [[Isidor Isaac Rabi]] |alt=Three men talking. The one on the left is wearing a tie and leans against a wall. He stands with his head and shoulders visibly above the other two's heads. The one in the center is smiling, and wearing an open-necked shirt. The one on the right wears a shirt and lab coat. All three have photo ID passes.]]
[[File:Fermiac.jpg|thumb|right|upright=0.85|The [[FERMIAC]], an [[analog computer]] invented by Fermi to study neutron transport]]

Fermi arrived in New York City on 2 January 1939.{{sfn|Cooper|1999|p=52}} He was immediately offered positions at five universities, and accepted one at [[Columbia University]],{{sfn|Persico|2001|p=40}} where he had already given summer lectures in 1936.{{sfn|Bonolis|2001|p=352}} He received the news that in December 1938, the German chemists [[Otto Hahn]] and [[Fritz Strassmann]] had detected the element [[barium]] after bombarding uranium with neutrons,<ref>{{cite journal
 |last1=Hahn |first1=O.
 | author-link = Otto Hahn
 |last2=Strassmann |first2=F.
 | author-link2 = Fritz Strassmann
 |year=1939
 |language=de
 |title=Über den Nachweis und das Verhalten der bei der Bestrahlung des Urans mittels Neutronen entstehenden Erdalkalimetalle
 |trans-title=On the detection and characteristics of the alkaline earth metals formed by irradiation of uranium with neutrons
 |journal=[[Naturwissenschaften]]
 |volume=27 |issue=1 |pages=11–15
 |doi=10.1007/BF01488241
 |bibcode = 1939NW.....27...11H|s2cid=5920336
 }}</ref> which [[Lise Meitner]] and her nephew [[Otto Frisch]] correctly interpreted as the result of [[nuclear fission]]. Frisch confirmed this experimentally on 13 January 1939.<ref name="Frisch1939">{{cite journal|last1=Frisch |first1=O. R. |title=Physical Evidence for the Division of Heavy Nuclei under Neutron Bombardment |journal=Nature |volume=143 |issue=3616 |year=1939 |pages=276 |doi=10.1038/143276a0 |bibcode=1939Natur.143..276F |s2cid=4076376 |doi-access=free }}</ref><ref>{{cite journal
 |last1=Meitner
 |first1=L.
 |author-link=Lise Meitner
 |last2=Frisch
 |first2=O.R.
 |author-link2=Otto Robert Frisch
 |year=1939
 |title=Disintegration of Uranium by Neutrons: a New Type of Nuclear Reaction
 |url=http://www.nature.com/physics/looking-back/meitner/index.html
 |journal=[[Nature (journal)|Nature]]
 |volume=143
 |issue=3615
 |pages=239–240
 |doi=10.1038/143239a0
 |bibcode=1939Natur.143..239M
 |s2cid=4113262
 |access-date=17 March 2008
|archive-date=28 April 2019
|archive-url=https://web.archive.org/web/20190428141914/http://www.nature.com/physics/looking-back/meitner/index.html
 |url-status=live
 |url-access=subscription
 }}</ref> The news of Meitner and Frisch's interpretation of Hahn and Strassmann's discovery crossed the Atlantic with [[Niels Bohr]], who was to lecture at [[Princeton University]]. [[Isidor Isaac Rabi]] and [[Willis Lamb]], two Columbia University physicists working at Princeton, found out about it and carried it back to Columbia. Rabi said he told Enrico Fermi, but Fermi later gave the credit to Lamb:{{sfn|Rhodes|1986|p=267}}
{{Blockquote|I remember very vividly the first month, January, 1939, that I started working at the Pupin Laboratories because things began happening very fast. In that period, Niels Bohr was on a lecture engagement at the Princeton University and I remember one afternoon Willis Lamb came back very excited and said that Bohr had leaked out great news. The great news that had leaked out was the discovery of fission and at least the outline of its interpretation. Then, somewhat later that same month, there was a meeting in Washington where the possible importance of the newly discovered phenomenon of fission was first discussed in semi-jocular earnest as a possible source of [[nuclear power]].{{sfn|Segrè|1970|pp=222–223}}}}

Noddack was proven right after all. Fermi had dismissed the possibility of fission on the basis of his calculations, but he had not taken into account the [[binding energy]] that would appear when a [[nuclide]] with an odd number of neutrons absorbed an extra neutron.{{sfn|Amaldi|2001a|pp=161–162}} For Fermi, the news came as a profound embarrassment, as the [[transuranic elements]] that he had partly been awarded the Nobel Prize for discovering had not been transuranic elements at all, but [[fission products]]. He added a footnote to this effect to his Nobel Prize acceptance speech.{{sfn|Rhodes|1986|p=267}}<ref name="Nobel" />

The scientists at Columbia decided that they should try to detect the energy released in the nuclear fission of uranium when bombarded by neutrons. On 25 January 1939, in the basement of [[Pupin Hall]] at Columbia, an experimental team including Fermi conducted the first nuclear fission experiment in the United States. The other members of the team were [[Herbert L. Anderson]], [[Eugene T. Booth]], [[John R. Dunning]], [[G. Norris Glasoe]], and [[Francis G. Slack]].<ref>{{cite journal|last1=Anderson|first1=H.L.|last2=Booth|first2=E. |last3=Dunning|first3=J.|last4=Fermi |first4=E.|last5=Glasoe |first5=G. |last6=Slack|first6=F.|title=The Fission of Uranium|journal=[[Physical Review]]|volume=55|issue=5|date=16 February 1939|pages=511–512 |doi=10.1103/PhysRev.55.511.2|bibcode = 1939PhRv...55..511A }}</ref> The next day, the fifth [[Washington Conference on Theoretical Physics]] began in Washington, D.C. under the joint auspices of [[George Washington University]] and the [[Carnegie Institution of Washington]]. There, the news on nuclear fission was spread even further, fostering many more experimental demonstrations.{{sfn|Rhodes|1986|pp=269–270}}

French scientists [[Hans von Halban]], [[Lew Kowarski]], and Frédéric Joliot-Curie had demonstrated that uranium bombarded by neutrons emitted more neutrons than it absorbed, suggesting the possibility of a chain reaction.<ref name="Von HalbanJoliot1939">{{cite journal|last1=Von Halban |first1=H.|last2=Joliot |first2=F.|last3=Kowarski |first3=L. |title=Number of Neutrons Liberated in the Nuclear Fission of Uranium|journal=Nature|volume=143|issue=3625|date=22 April 1939|pages=680 |doi=10.1038/143680a0|bibcode = 1939Natur.143..680V |s2cid=4089039|doi-access=free}}</ref> Fermi and Anderson did so too a few weeks later.<ref name="AndersonFermi1939">{{cite journal|last1=Anderson|first1=H.|last2=Fermi|first2=E.|last3=Hanstein|first3=H.|title=Production of Neutrons in Uranium Bombarded by Neutrons|journal=Physical Review|volume=55|issue=8|date=16 March 1939|pages=797–798|doi=10.1103/PhysRev.55.797.2|bibcode = 1939PhRv...55..797A }}</ref><ref>{{cite journal|last=Anderson|first=H.L.|title=Early Days of Chain Reaction|url=https://books.google.com/books?id=IgwAAAAAMBAJ&pg=PA10|date=April 1973|journal=Bulletin of the Atomic Scientists|volume=29|issue=4|pages=8–12|bibcode=1973BuAtS..29d...8A|doi=10.1080/00963402.1973.11455466|access-date=20 November 2015|archive-date=8 June 2020|archive-url=https://web.archive.org/web/20200608222703/https://books.google.com/books?id=IgwAAAAAMBAJ&pg=PA10|url-status=live|url-access=subscription}}</ref> [[Leó Szilárd]] obtained {{convert|200|kg}} of [[uranium oxide]] from Canadian [[radium]] producer [[Eldorado Mining and Refining Limited|Eldorado Gold Mines Limited]], allowing Fermi and Anderson to conduct experiments with fission on a much larger scale.<ref name=Anderson1939 /> Fermi and Szilárd collaborated on the design of a device to achieve a self-sustaining nuclear reaction—a [[nuclear reactor]]. Owing to the rate of absorption of neutrons by the hydrogen in water, it was unlikely that a self-sustaining reaction could be achieved with natural uranium and water as a [[neutron moderator]]. Fermi suggested, based on his work with neutrons, that the reaction could be achieved with uranium oxide blocks and [[graphite]] as a moderator instead of water. This would reduce the neutron capture rate, and in theory make a self-sustaining chain reaction possible. Szilárd came up with a workable design: a pile of uranium oxide blocks interspersed with graphite bricks.{{sfn|Salvetti|2001|pp=186–188}} Szilárd, Anderson, and Fermi published a paper on "Neutron Production in Uranium".<ref name=Anderson1939>{{cite journal|last1=Anderson|first1=H.|last2=Fermi|first2=E.|last3=Szilárd|first3=L.|title=Neutron Production and Absorption in Uranium|journal=[[Physical Review]]|volume=56|issue=3|date=1 August 1939|pages=284–286|doi=10.1103/PhysRev.56.284|url=http://docs.fdrlibrary.marist.edu/psf/box5/a64g01.html|bibcode=1939PhRv...56..284A|access-date=19 October 2013|archive-date=25 February 2021|archive-url=https://web.archive.org/web/20210225023106/http://docs.fdrlibrary.marist.edu/psf/box5/a64g01.html|url-status=live|url-access=subscription}}</ref> But their work habits and personalities were different, and Fermi had trouble working with Szilárd.{{sfn|Bonolis|2001|pp=356–357}}

Fermi was among the first to warn military leaders about the potential impact of nuclear energy, giving a lecture on the subject at the [[United States Department of the Navy|Navy Department]] on 18&nbsp;March 1939. The response fell short of what he had hoped for, although the Navy agreed to provide $1,500 towards further research at Columbia.{{sfn|Salvetti|2001|p=185}} Later that year, Szilárd, [[Eugene Wigner]], and [[Edward Teller]] sent [[Einstein–Szilárd letter|the letter signed by Einstein]] to US president [[Franklin D. Roosevelt]], warning that [[Nazi Germany]] was likely to build an [[atomic bomb]]. In response, Roosevelt formed the [[Advisory Committee on Uranium]] to investigate the matter.{{sfn|Salvetti|2001|pp=188–189}}

The Advisory Committee on Uranium provided money for Fermi to buy graphite,{{sfn|Rhodes|1986|pp=314–317}} and he built a pile of graphite bricks on the seventh floor of the Pupin Hall laboratory.{{sfn|Salvetti|2001|p=190}} By August 1941, he had six tons of uranium oxide and thirty tons of graphite, which he used to build a still larger pile in Schermerhorn Hall at Columbia.{{sfn|Salvetti|2001|p=195}}

The S-1 Section of the [[Office of Scientific Research and Development]], as the Advisory Committee on Uranium was now known, met on 18 December 1941, with the US now engaged in [[World War II]], making its work urgent. Most of the effort sponsored by the committee had been directed at producing [[enriched uranium]], but Committee member [[Arthur Compton]] determined that a feasible alternative was [[plutonium]], which could be mass-produced in nuclear reactors by the end of 1944.{{sfn|Salvetti|2001|pp=194–196}} He decided to concentrate the plutonium work at the [[University of Chicago]]. Fermi reluctantly moved, and his team became part of the new [[Metallurgical Laboratory]] there.{{sfn|Rhodes|1986|pp=399–400}}

The possible results of a self-sustaining nuclear reaction were unknown, so it seemed inadvisable to build the first nuclear reactor on the University of Chicago campus in the middle of the city. Compton found a location in the Argonne Woods Forest Preserve, about {{convert|20|miles}} from Chicago. [[Stone & Webster]] was contracted to develop the site, but the work was halted by an industrial dispute. Fermi then persuaded Compton that he could build the reactor in the [[squash (sport)|squash]] court under the stands of the University of Chicago's [[Stagg Field]]. Construction of the pile began on 6 November 1942, and [[Chicago Pile-1]] went [[Nuclear reactor physics#Criticality|critical]] on 2 December.{{sfn|Salvetti|2001|pp=198–202}} The shape of the pile was intended to be roughly spherical, but as work proceeded Fermi calculated that criticality could be achieved without finishing the entire pile as planned.<ref>{{cite journal | last=Fermi |first=E. | title=The Development of the First Chain Reaction Pile | journal=[[Proc. Am. Philos. Soc.]] | year=1946 | volume=90 |issue=1 | pages=20–24 | jstor=3301034}}</ref>

This experiment was a landmark in the quest for energy, and it was typical of Fermi's approach. Every step was carefully planned, and every calculation was meticulously done.{{sfn|Salvetti|2001|pp=198–202}} When the first self-sustained nuclear chain reaction was achieved, Compton made a coded phone call to [[James B. Conant]], the chairman of the [[National Defense Research Committee]].{{quote|
I picked up the phone and called Conant. He was reached at the President's office at [[Harvard University]].
"Jim," I said, "you'll be interested to know that the Italian navigator has just landed in the new world." Then, half apologetically, because I had led the S-l Committee to believe that it would be another week or more before the pile could be completed, I added, "the earth was not as large as he had estimated, and he arrived at the new world sooner than he had expected."

"Is that so," was Conant's excited response. "Were the natives friendly?"
"Everyone landed safe and happy."{{sfn|Compton|1956|p=144}} }}

To continue the research where it would not pose a public health hazard, the reactor was disassembled and moved to the Argonne Woods site. There Fermi directed experiments on nuclear reactions, reveling in the opportunities provided by the reactor's abundant production of free neutrons.{{sfn|Bonolis|2001|p=366}} The laboratory soon branched out from physics and engineering into using the reactor for biological and medical research. Initially, Argonne was run by Fermi as part of the University of Chicago, but it became a separate entity with Fermi as its director in May 1944.{{sfn|Hewlett|Anderson|1962|p=207}}

When the air-cooled [[X-10 Graphite Reactor]] at [[Oak Ridge National Laboratory|Oak Ridge]] went critical on 4 November 1943, Fermi was on hand just in case something went wrong. The technicians woke him early so that he could see it happen.{{sfn|Hewlett|Anderson|1962|pp=208–211}} Getting X-10 operational was another milestone in the plutonium project. It provided data on reactor design, training for [[DuPont]] staff in reactor operation, and produced the first small quantities of reactor-bred plutonium.{{sfn|Jones|1985|p=205}} Fermi became an American citizen in July 1944, the earliest date the law allowed.{{sfn|Segrè|1970|p=104}}

In September 1944, Fermi inserted the first uranium fuel slug into the [[B Reactor]] at the [[Hanford Site]], the production reactor designed to breed plutonium in large quantities. Like X-10, it had been designed by Fermi's team at the Metallurgical Laboratory and built by DuPont, but it was much larger and was water-cooled. Over the next few days, 838 tubes were loaded, and the reactor went critical. Shortly after midnight on 27 September, the operators began to withdraw the [[control rod]]s to initiate production. At first, all appeared to be well, but around 03:00, the power level started to drop and by 06:30 the reactor had shut down completely. The Army and DuPont turned to Fermi's team for answers. The cooling water was investigated to see if there was a leak or contamination. The next day the reactor suddenly started up again, only to shut down once more a few hours later. The problem was traced to [[neutron poison]]ing from [[xenon-135]] or Xe-135, a fission product with a half-life of 9.1 to 9.4 hours. Fermi and [[John Archibald Wheeler|John Wheeler]] both deduced that Xe-135 was responsible for absorbing neutrons in the reactor, thereby sabotaging the fission process. Fermi was recommended by colleague Emilio Segrè to ask [[Chien-Shiung Wu]], as she prepared a printed draft on this topic to be published by the [[Physical Review]].<ref>{{Cite web|last=Dicke|first=William|title=Chien-Shiung Wu, 84, Top Experimental Physicist|url=http://cwp.library.ucla.edu/articles/wuobit.html|date=18 February 1997|access-date=12 March 2021|archive-date=14 July 2010|archive-url=https://web.archive.org/web/20100714030031/http://cwp.library.ucla.edu/articles/wuobit.html|url-status=live}}</ref> Upon reading the draft, Fermi and the scientists confirmed their suspicions: Xe-135 indeed absorbed neutrons, in fact it had a huge neutron cross-section.<ref>{{Cite web|last=Benczer-Koller|first=Noemie|title=Chien-shiungwu 1912–1997|url=http://www.nasonline.org/publications/biographical-memoirs/memoir-pdfs/wu-chien-shiung.pdf|date=January 2009|access-date=12 March 2021|archive-date=26 March 2015|archive-url=https://web.archive.org/web/20150326081624/http://www.nasonline.org/publications/biographical-memoirs/memoir-pdfs/wu-chien-shiung.pdf|url-status=live}}</ref><ref>{{Cite book|last=Lykknes|first=Annette|title=Women In Their Element: Selected Women's Contributions To The Periodic System|url=https://books.google.com/books?id=2ZmxDwAAQBAJ&q=chien+shiung+wu+work+showed+xe+135+neutron+absorption+b+reactor&pg=PA387|year=2019|publisher=World Scientific |isbn=9789811206306|access-date=3 May 2021|archive-date=30 May 2021|archive-url=https://web.archive.org/web/20210530222342/https://books.google.com/books?id=2ZmxDwAAQBAJ&q=chien+shiung+wu+work+showed+xe+135+neutron+absorption+b+reactor&pg=PA387|url-status=live}}</ref><ref name="chiang">{{cite web
 |last=Chiang
 |first=T.-C.
 |date=27 November 2012
|title=Inside Story: C S Wu&nbsp;– First Lady of physics research
 |url=http://cerncourier.com/cws/article/cern/51556
 |work=[[CERN Courier]]
 |access-date=5 April 2014
|archive-date=12 June 2018
|archive-url=https://web.archive.org/web/20180612144506/http://cerncourier.com/cws/article/cern/51556
 |url-status=live
 }}</ref> DuPont had deviated from the Metallurgical Laboratory's original design in which the reactor had 1,500 tubes arranged in a circle, and had added 504 tubes to fill in the corners. The scientists had originally considered this over-engineering a waste of time and money, but Fermi realized that if all 2,004 tubes were loaded, the reactor could reach the required power level and efficiently produce plutonium.{{sfn|Hewlett|Anderson|1962|pp=304–307}}{{sfn|Jones|1985|pp=220–223}}
[[File:ChicagoPileTeam.png|thumb|upright=1.2|Some of the [[University of Chicago]] team that worked on the production of the world's first human-caused self-sustaining nuclear reaction, including Enrico Fermi in the front row and [[Leó Szilárd]] in the second.]]
In April 1943, Fermi raised with [[Robert Oppenheimer]] the possibility of using the radioactive byproducts from enrichment to contaminate the German food supply. The background was fear that the German atomic bomb project was already at an advanced stage, and Fermi was also sceptical at the time that an atomic bomb could be developed quickly enough. Oppenheimer discussed the "promising" proposal with Edward Teller, who suggested the use of [[strontium-90]]. James B. Conant and [[Leslie Groves]] were also briefed, but Oppenheimer wanted to proceed with the plan only if enough food could be contaminated with the weapon to kill half a million people.{{sfn|Rhodes|1986||pp=510–511}}

In mid-1944, Oppenheimer persuaded Fermi to join his [[Project Y]] at [[Los Alamos, New Mexico]].{{sfn|Bonolis|2001|pp=368–369}} Arriving in September, Fermi was appointed an associate director of the laboratory, with broad responsibility for nuclear and theoretical physics, and was placed in charge of F Division, which was named after him. F Division had four branches: F-1 Super and General Theory under Teller, which investigated the [[History of the Teller–Ulam design|"Super" (thermonuclear) bomb]]; F-2 Water Boiler under L. D. P. King, which looked after the "water boiler" [[Aqueous homogeneous reactor|aqueous homogeneous]] [[research reactor]]; F-3 Super Experimentation under [[Egon Bretscher]]; and F-4 Fission Studies under Anderson.{{sfn|Hawkins|1961|p=213}} Fermi observed the [[Trinity test]] on 16 July 1945 and conducted an experiment to estimate the bomb's yield by dropping strips of paper into the blast wave. He paced off the distance they were blown by the explosion, and calculated the yield as ten kilotons of TNT; the actual yield was about 18.6 kilotons.{{sfn|Rhodes|1986|pp=674–677}}

Along with Oppenheimer, Compton, and [[Ernest Lawrence]], Fermi was part of the scientific panel that advised the [[Interim Committee]] on target selection. The panel agreed with the committee that atomic bombs would be used without warning against an industrial target.{{sfn|Jones|1985|pp=531–532}} Like others at the Los Alamos Laboratory, Fermi found out about the [[atomic bombings of Hiroshima and Nagasaki]] from the [[public address system]] in the technical area. Fermi did not believe that atomic bombs would deter nations from starting wars, nor did he think that the time was ripe for [[world government]]. He therefore did not join the [[Association of Los Alamos Scientists]].{{sfn|Fermi|1954|pp=244–245}}