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{{Short description|British physicist (1891–1974)}}
{{About||the bishop|James Chadwick (bishop)|the American gynaecologist|James Read Chadwick}}
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{{Use British English|date=April 2013}}
{{Use dmy dates|date=July 2024}}
{{Infobox scientist
| honorific_prefix  = [[Sir]]
| name              = James Chadwick
| honorific_suffix  = {{post-nominals|country=GBR|size=100%|CH|FRS}}
| image             = James Chadwick.jpg
| image_size        = 
| caption           = Chadwick {{c.|1945}}
| birth_date        = {{Birth date|df=yes|1891|10|20}}
| birth_place       = [[Bollington]], Cheshire, United Kingdom
| death_date        = {{death date and age|df=yes|1974|7|24|1891|10|20}}
| death_place       = [[Cambridge]], United Kingdom
| field             = [[Physics]]
| work_institution  = {{plainlist|
* [[Physikalisch-Technische Reichsanstalt]]
* [[University of Liverpool]]
* [[University of Cambridge]]
* [[Manhattan Project]]
}}
| education         = {{plainlist|
* [[University of Manchester]] ([[Bachelor of Science|BSc]])
* [[Gonville and Caius College, Cambridge]] ([[Master of Science|MSc]], [[Doctor of Philosophy|PhD]])
}}
| doctoral_advisor  = [[Ernest Rutherford]]
| academic_advisors = 
| doctoral_students = {{plainlist|
* [[Étienne Biéler]]<ref name=AcademicTree>{{cite web
 |title=James Chadwick
 |url=http://academictree.org/physics/peopleinfo.php?pid=49582
 |website=academictree.org
 |access-date=21 July 2014
}}</ref>
* [[Charles Drummond Ellis]]<ref name=AcademicTree />
* [[Ernest C. Pollard]]<ref name=AcademicTree />
* [[Maurice Goldhaber]]<ref name=AcademicTree />
* [[Louis Harold Gray]]
* [[Joseph Rotblat]]
}}
| known_for         = {{plainlist|
* [[Discovery of the neutron]]
* [[MAUD Committee]] Report
* [[Manhattan Project]]
}}
| prizes            = {{plainlist|
* [[Fellow of the Royal Society]] (1927)
* [[Hughes Medal]] (1932)
* [[Nobel Prize in Physics]] (1935)
* [[Knight Bachelor]] (1945)
* [[Melchett Medal]] (1946)
* [[Copley Medal]] (1950)
* [[Faraday Medal]] (1950)
* [[Franklin Medal]] (1951)
* [[Guthrie Medal and Prize]] (1967)
* [[Member of the Order of the Companions of Honour]] (1970)
}}
| signature         = Solvay1933Signature Chadwick.jpg
}}

'''Sir James Chadwick''', {{post-nominals|country=GBR|size=100%|sep=,|CH|FRS}} (20 October 1891&nbsp;– 24 July 1974) was an English [[physicist]] who was awarded the 1935 [[Nobel Prize in Physics]] for his [[discovery of the neutron]] in 1932. In 1941, he wrote the final draft of the [[MAUD Committee|MAUD Report]], which inspired the U.S. government to begin serious [[atom bomb]] research efforts. He was the head of the British team that worked on the [[Manhattan Project]] during [[World War&nbsp;II]]. He was [[Knight Bachelor|knighted]] in Britain in 1945 for his achievements in physics.

Chadwick graduated from the [[Victoria University of Manchester]] in 1911, where he studied under [[Ernest Rutherford]] (known as the "father of nuclear physics").<ref>{{cite web |title=Ernest Rutherford |url=http://www.orcbs.msu.edu/radiation/resources_links/historical_figures/rutherford.htm |work=Figures in Radiation History |publisher=[[Michigan State University]] |access-date=3 June 2014 |url-status=dead |archive-url=https://web.archive.org/web/20150629192822/http://www.orcbs.msu.edu/radiation/resources_links/historical_figures/rutherford.htm |archive-date=29 June 2015 }}</ref> At Manchester, he continued to study under Rutherford until he was awarded his MSc in 1913. The same year, Chadwick was awarded an [[1851 Research Fellowship]] from the [[Royal Commission for the Exhibition of 1851]]. He elected to study [[beta radiation]] under [[Hans Geiger]] in Berlin. Using Geiger's recently developed [[Geiger counter]], Chadwick was able to demonstrate that beta radiation produced a [[Beta decay#Beta emission spectrum|continuous spectrum]], and not discrete lines as had been thought. Still in Germany when [[World War&nbsp;I]] broke out in Europe, he spent the next four years in the [[Ruhleben internment camp]].

After the war, Chadwick followed Rutherford to the [[Cavendish Laboratory]] at the [[University of Cambridge]], where Chadwick earned his [[Doctor of Philosophy]] degree under Rutherford's supervision from [[Gonville and Caius College, Cambridge]], in June 1921. He was Rutherford's assistant director of research at the Cavendish Laboratory for over a decade at a time when it was one of the world's foremost centres for the study of physics, attracting students like [[John Cockcroft]], [[Norman Feather]], and [[Mark Oliphant]]. Chadwick followed his discovery of the [[neutron]] by measuring its [[mass]]. He anticipated that neutrons would become a major weapon in the fight against cancer. Chadwick left the Cavendish Laboratory in 1935 to become a professor of physics at the [[University of Liverpool]], where he overhauled an antiquated laboratory and, by installing a [[cyclotron]], made it an important centre for the study of [[nuclear physics]].

During the Second World War, Chadwick carried out research as part of the [[Tube Alloys]] project to build an atom bomb, while his Manchester lab and environs were harassed by [[Luftwaffe]] bombing. When the [[Quebec Agreement]] merged his project with the American Manhattan Project, he became part of the British Mission, and worked at the [[Los Alamos Laboratory]] and in Washington, D.C. He surprised everyone by earning the almost-complete trust of project director [[Leslie R. Groves, Jr.]] For his efforts, Chadwick received a knighthood in the [[1945 New Year Honours|New Year Honours on 1 January 1945]]. In July 1945, he viewed the [[Trinity nuclear test]]. After this, he served as the British scientific advisor to the United Nations Atomic Energy Commission. Uncomfortable with the trend toward [[Big Science]], he became the [[Master (college)|Master]] of Gonville and Caius College in 1948. He retired in 1959.

== Education and early life ==
James Chadwick was born in [[Bollington]], [[Cheshire]], on 20 October 1891,{{sfn|Falconer|2004}}{{sfn|Oliphant|1974}} the first child of John Joseph Chadwick, a cotton spinner, and Anne Mary Knowles, a domestic servant. He was named James after his paternal grandfather. In 1895, his parents moved to [[Manchester]], leaving him in the care of his maternal grandparents. He went to Bollington Cross Primary School, and was offered a scholarship to [[Manchester Grammar School]], which his family had to turn down as they could not afford the small fees that still had to be paid. Instead he attended the [[Central Grammar School for Boys]] in Manchester, rejoining his parents there. He now had two younger brothers, Harry and Hubert; a sister had died in infancy. At the age of 16, he sat two examinations for university scholarships, and won both of them.{{sfn|Brown|1997|pp=3–5}}<ref name="Nobel" />

Chadwick chose to attend [[Victoria University of Manchester]], which he entered in 1908. He meant to study mathematics, but enrolled in [[physics]] by mistake. Like most students, he lived at home, walking the {{convert|4|miles}} to the university and back each day. At the end of his first year, he was awarded a Heginbottom Scholarship to study physics. The physics department was headed by [[Ernest Rutherford]], who assigned research projects to final-year students, and he instructed Chadwick to devise a means of comparing the amount of radioactive energy of two different sources. The idea was that they could be measured in terms of the activity of {{convert|1|g}} of [[radium]], a unit of measurement which would become known as the [[Curie (unit)|curie]]. Rutherford's suggested approach was unworkable—something Chadwick knew but was afraid to tell Rutherford—so Chadwick pressed on, and eventually devised the required method. The results became Chadwick's first paper, which, co-authored with Rutherford, was published in 1912.{{sfn|Rutherford|Chadwick|1912}} He graduated with [[first class honours]] in 1911.{{sfn|Brown|1997|pp=6–14}}

Having devised a means of measuring gamma radiation, Chadwick proceeded to measure the absorption of gamma rays by various gases and liquids. This time the resulting paper was published under his name alone. He was awarded his [[Master of Science]] (MSc) degree in 1912, and was appointed a Beyer Fellow. The following year he was awarded an [[1851 Exhibition Scholarship]], which allowed him to study and research at a university in continental Europe. He elected to go to the [[Physikalisch-Technische Reichsanstalt]] in Berlin in 1913, to study [[beta radiation]] under [[Hans Geiger]].{{sfn|Brown|1997|pp=16–21}} Using Geiger's recently developed [[Geiger counter]], which provided more accuracy than the earlier photographic techniques, he was able to demonstrate that beta radiation did not produce [[spectral lines|discrete lines]], as has been previously thought, but rather a [[Beta decay#Beta emission spectrum|continuous spectrum]] with peaks in certain regions.{{sfn|Chadwick|1914}}{{sfn|Chadwick|Ellis|1922}}{{sfn|Weiner|1969}}{{sfn|Jensen|2000|pp=88–90}} On a visit to Geiger's laboratory, [[Albert Einstein]] told Chadwick that: "I can explain either of these things, but I can't explain them both at the same time."{{sfn|Weiner|1969}} The continuous spectrum would remain an [[Beta decay#History|unexplained phenomenon for many years]].{{sfn|Brown|1997|pp=24–26}}

Chadwick was still in Germany at the start of the [[First World War]], and was interned in the [[Ruhleben internment camp]] near Berlin, where he was allowed to set up a laboratory in the stables and conduct scientific experiments using improvised materials such as [[radioactive quackery|radioactive toothpaste]].<ref name=APSNews>{{cite journal |year=2007 |title= This Month in Physics History: May 1932: Chadwick reports the discovery of the neutron |url=http://www.aps.org/publications/apsnews/200705/physicshistory.cfm |journal=[[APS News]] |volume=16 |issue=5 |page=2}}</ref> With the help of [[Charles Drummond Ellis]], he worked on the [[ionisation]] of [[phosphorus]], and the [[mechanistic organic photochemistry|photochemical reaction]] of [[carbon monoxide]] and [[chlorine]].<ref>{{cite news |title=Obituary: Sir James Chadwick |newspaper=[[The Times]] |date=25 July 1974 |page=20, column F}}</ref><ref>{{cite news |title=Obituary: Sir Charles Ellis |newspaper=[[The Times]] |date=15 January 1980 |page=14, column F}}</ref> He was released after the [[Armistice with Germany]] came into effect in November 1918, and returned to his parents' home in Manchester, where he wrote up his findings over the previous four years for the 1851 Exhibition commissioners.{{sfn|Brown|1997|p=39}}

Rutherford gave Chadwick a part-time teaching position at Manchester, allowing him to continue research.{{sfn|Brown|1997|p=39}} He looked at the [[nuclear charge]] of [[platinum]], [[silver]], and [[copper]], and experimentally found that this was the same as the [[atomic number]] within an error of less than 1.5 per cent.{{sfn|Brown|1997|pp=43}} In April 1919, Rutherford became director of the [[Cavendish Laboratory]] at the [[University of Cambridge]], and Chadwick joined him there a few months later. Chadwick was awarded a Clerk-Maxwell studentship in 1920, and enrolled as a [[Doctor of Philosophy]] (PhD) student at [[Gonville and Caius College, Cambridge]]. The first half of his thesis was his work with atomic numbers. In the second, he looked at the [[nuclear force|forces]] inside the [[atomic nucleus|nucleus]]. His degree was awarded in June 1921.{{sfn|Brown|1997|pp=43–50}} In November, he became a Fellow of Gonville and Caius College.{{sfn|Brown|1997|p=58}}

== Researcher ==
=== Cambridge ===
Chadwick's Clerk-Maxwell studentship expired in 1923, and he was succeeded by the Russian physicist [[Pyotr Kapitza]]. The Chairman of the Advisory Council of the [[Department of Scientific and Industrial Research (United Kingdom)|Department of Scientific and Industrial Research]], Sir [[William Symington McCormick|William McCormick]] arranged for Chadwick to become Rutherford's assistant director of research. In this role, Chadwick helped Rutherford select PhD students. Over the next few years these would include [[John Cockcroft]], [[Norman Feather]] and [[Mark Oliphant]], who would become firm friends with Chadwick. As many students had no idea what they wanted to research, Rutherford and Chadwick would suggest topics. Chadwick edited all the papers produced by the laboratory.{{sfn|Brown|1997|pp=73–76}}

[[File:The Cavendish Laboratory - geograph.org.uk - 631839.jpg|thumb|upright=1.35|left|The original building of the  [[Cavendish Laboratory]] was the home of some of the great discoveries in physics. It was founded in 1874 by the [[William Cavendish, 7th Duke of Devonshire|Duke of Devonshire]] (whose family name was Cavendish), and its first professor was [[James Clerk Maxwell]]. The Laboratory has since moved to [[West Cambridge]].<ref>{{cite web |url=http://www.phy.cam.ac.uk/history |title=The History of the Cavendish |date=13 August 2013 |publisher=University of Cambridge |access-date=15 August 2014 }}</ref> ]]
In 1925, Chadwick met Aileen Stewart-Brown, the daughter of a Liverpool stockbroker. The two were married in August 1925,{{sfn|Brown|1997|pp=73–76}} with Kapitza as Best Man. The couple had twin daughters, Joanna and Judith, who were born in February 1927.{{sfn|Brown|1997|p=85}}

In his research, Chadwick continued to probe the nucleus. In 1925, the concept of [[Spin (physics)|spin]] had allowed physicists to explain the [[Zeeman effect]], but it also created unexplained anomalies. At the time it was believed that the nucleus consisted of [[proton]]s and electrons, so [[nitrogen]]'s nucleus, for example, with a [[mass number]] of 14, was assumed to contain 14 protons and 7 electrons. This gave it the right [[mass]] and charge, but the wrong spin.{{sfn|Brown|1997|pp=92–93}}

At a conference at Cambridge on beta particles and gamma rays in 1928, Chadwick met Geiger again. Geiger had brought with him a new model of his Geiger counter, which had been improved by his post-doctoral student [[Walther Müller]]. Chadwick had not used one since the war, and the new [[Geiger counter|Geiger–Müller counter]] was potentially a major improvement over the [[Scintillation (physics)|scintillation]] techniques then in use at Cambridge, which relied on the human eye for observation. The major drawback with it was that it detected [[Alpha decay|alpha]], [[Beta particle|beta]] and [[Gamma ray|gamma]] radiation, and radium, which the Cavendish laboratory normally used in its experiments, emitted all three, and was therefore unsuitable for what Chadwick had in mind. However, [[polonium]] is an alpha emitter, and [[Lise Meitner]] sent Chadwick about 2 millicuries (about {{val|0.5|u=ug}}) from [[Germany]].{{sfn|Brown|1997|pp=95–97}}{{sfn|Sublette|2006}}

In Germany, [[Walther Bothe]] and his student [[Herbert Becker (physicist)|Herbert Becker]] had used polonium to bombard [[beryllium]] with alpha particles, producing an unusual form of radiation. Chadwick had his Australian 1851 Exhibition scholar, Hugh Webster, duplicate their results. To Chadwick, this was evidence of something that he and Rutherford had been hypothesising for years: the [[neutron]], a theoretical nuclear particle with no electric charge.{{sfn|Brown|1997|pp=95–97}} Then in January 1932, Feather drew Chadwick's attention to another surprising result. [[Frédéric Joliot-Curie|Frédéric]] and [[Irène Joliot-Curie]] had succeeded in knocking protons from [[paraffin wax]] using polonium and beryllium as a source for what they thought was gamma radiation. Rutherford and Chadwick disagreed; protons were too heavy for that. But neutrons would need only a small amount of energy to achieve the same effect. In Rome, [[Ettore Majorana]] came to the same conclusion: the Joliot-Curies had discovered the neutron but did not know it.{{sfn|Brown|1997|pp=103–104}}

[[File:Sir Ernest Rutherfords laboratory, early 20th century. (9660575343).jpg|thumb|right|Sir Ernest Rutherford's laboratory]]

Chadwick dropped all his other responsibilities to concentrate on proving the existence of the neutron, assisted by Feather<ref name="sessI">{{Cite web | title=Oral History interview transcript with Norman Feather, Session I | date= 25 February 1971 | publisher=American Institute of Physics, Niels Bohr Library and Archives | author=<!--Staff writer(s); no by-line.--> | url=https://www.aip.org/history-programs/niels-bohr-library/oral-histories/4559-1}}</ref> and frequently working late at night. He devised a simple apparatus that consisted of a cylinder containing a polonium source and beryllium target. The resulting radiation could then be directed at a material such as paraffin wax.  The displaced particles, which were protons, would go into a small ionisation chamber where they could be detected with an [[oscilloscope]].{{sfn|Brown|1997|pp=103–104}}
In February 1932, after only about two weeks of experimentation with neutrons,<ref name=APSNews /> Chadwick sent a letter to ''[[Nature (journal)|Nature]]'' titled "Possible Existence of a Neutron".{{sfn|Chadwick|1932a}} He communicated his findings in detail in an article sent to ''[[Proceedings of the Royal Society A]]'' titled "The Existence of a Neutron" in May.{{sfn|Chadwick|1932b}}{{sfn|Chadwick|1933}} His [[discovery of the neutron]] was a milestone in understanding the nucleus. Reading Chadwick's paper, [[Robert Bacher]] and [[Edward Condon]] realised that anomalies in the then-current theory, like the spin of nitrogen, would be resolved if the neutron has a [[spin-½|spin of 1/2]] and that a nitrogen nucleus consisted of seven protons and seven neutrons.{{sfn|Whaling|2009|pp=8–9}}{{sfn|Bacher|Condon|1932}}

The theoretical physicists [[Niels Bohr]] and [[Werner Heisenberg]] considered whether the neutron could be a fundamental [[nucleon|nuclear particle]] like the proton and electron, rather than a proton–electron pair.{{sfn|Heisenberg|1932a}}{{sfn|Heisenberg|1932b}}{{sfn|Heisenberg|1933}}{{sfn|Bromberg|1971}}  Heisenberg showed that the neutron was best described as a new nuclear particle,{{sfn|Heisenberg|1933}}{{sfn|Bromberg|1971}} but its exact nature remained unclear.  In his 1933 [[Royal Society Bakerian Medal|Bakerian Lecture]], Chadwick estimated that a neutron had a mass of about {{val|1.0067|ul=u}}. Since a proton and an electron had a combined mass of {{val|1.0078|u=u}}, this implied the neutron as a proton–electron composite had a binding energy of about {{val|2|ul=MeV}}, which sounded reasonable,{{sfn|Brown|1997|pp=115–116}} although it was hard to understand how a particle with so little binding energy could be stable.{{sfn|Bromberg|1971}}  Estimating such a small mass difference required challenging precise measurements, however, and several conflicting results were obtained in 1933–4.  By bombarding [[boron]] with alpha particles, Frédéric and Irène Joliot-Curie obtained a large value for the mass of a neutron, but [[Ernest Lawrence]]'s team at the [[University of California]] produced a small one.{{sfn|Heilbron|Seidel|1989|pp=153–157}}  Then [[Maurice Goldhaber]], a refugee from [[Nazi Germany]] and a graduate student at the Cavendish Laboratory, suggested to Chadwick that [[deuteron]]s could be [[Photodisintegration|photodisintegrated]] by the 2.6 MeV gamma rays of <sup>208</sup>Tl (then known as [[Decay chain#Thorium series|thorium C"]]):
:{| border="0"
|- style="height:2em;"
|{{nuclide|link=yes|deuterium|2}}&nbsp;||+&nbsp;||{{Subatomic particle|link=yes|gamma}}&nbsp;||→&nbsp;||{{nuclide|link=yes|hydrogen|1}}&nbsp;||+&nbsp;||{{Subatomic particle|link=yes|neutron}}
|}
An accurate value for the mass of the neutron could be determined from this process. Chadwick and Goldhaber tried this and found that it worked.{{sfn|Goldhaber|1934}}{{sfn|Chadwick|Goldhaber|1934}}{{sfn|Chadwick|Goldhaber|1935}}  They measured the kinetic energy of the proton produced as 1.05 MeV, leaving the mass of the neutron as the unknown in the equation. Chadwick and Goldhaber calculated that it was either 1.0084 or 1.0090 atomic units, depending on the values used for the masses of the proton and deuteron.{{sfn|Brown|1997|pp=122–125}}{{sfn|Chadwick|Goldhaber|1935}}  (The modern accepted value for the mass of the neutron is {{val|1.00866|ul=u}}.) The mass of the neutron was too large to be a proton–electron pair.{{sfn|Brown|1997|pp=122–125}}

For his discovery of the neutron, Chadwick was awarded the [[Hughes Medal]] by the [[Royal Society]] in 1932, the [[Nobel Prize in Physics]] in 1935, the [[Copley Medal]] in 1950 and the [[Franklin Medal]] in 1951.<ref name="Nobel">{{cite web |url=http://nobelprize.org/nobel_prizes/physics/laureates/1935/chadwick-bio.html |title=James Chadwick – Biography |publisher=[[The Nobel Foundation]] |access-date=21 April 2013}}</ref> His discovery of the neutron made it possible to produce elements heavier than [[uranium]] in the laboratory by the capture of slow neutrons followed by [[beta decay]]. Unlike the positively charged [[alpha particle]]s, which are repelled by the electrical forces present in the nuclei of other atoms, neutrons do not need to overcome any [[Coulomb barrier]], and can therefore penetrate and enter the nuclei of even the heaviest elements such as uranium. This inspired [[Enrico Fermi]] to investigate the nuclear reactions brought about by collisions of nuclei with slow neutrons, work for which Fermi would receive the Nobel Prize in 1938.{{sfn|Brown|1997|pp=125}}

[[Wolfgang Pauli]] proposed another kind of particle on 4 December 1930 to explain the continuous spectrum of beta radiation that Chadwick had reported in 1914. Since not all of the energy of beta radiation could be accounted for, the law of [[conservation of energy]] appeared to be violated, but Pauli argued that this could be redressed if another, undiscovered, particle was involved.{{sfn|Brown|1997|pp=119–120}} Pauli also called this particle a neutron, but it was clearly not the same particle as Chadwick's neutron. Fermi renamed it the [[neutrino]], Italian for "little neutron".{{sfn|Close|2012|pp=15–18}} In 1934, Fermi proposed his [[Fermi's interaction|theory of beta decay]] which explained that the electrons emitted from the nucleus were created by the decay of a neutron into a proton, an electron, and a neutrino.{{sfn|Fermi|1968}}{{sfn|Close|2012|pp=22–25}}  The neutrino could account for the missing energy, but a particle with little mass and no electric charge was difficult to observe. [[Rudolf Peierls]] and [[Hans Bethe]] calculated that neutrinos could easily pass through the Earth, so the chances of detecting them were slim.{{sfn|Close|2012|pp=26–28}}<ref>{{cite journal |title=The Neutrino |journal=[[Nature (journal)|Nature]] |issn=0028-0836 |volume=133 |issue=3362 |pages=532 |date=7 April 1934 |doi=10.1038/133532a0 |bibcode = 1934Natur.133..532B |last1=Bethe |first1=H |last2=Peierls |first2=R |s2cid=4001646 |doi-access=free }}</ref> [[Frederick Reines]] and [[Clyde Cowan]] would [[neutrino experiment|confirm the neutrino]] on 14 June 1956 by placing a detector within a large antineutrino flux from a nearby nuclear reactor.{{sfn|Close|2012|pp=37–41}}

=== Liverpool ===
With the onset of the [[Great Depression in the United Kingdom]], the government became more parsimonious with funding for science. At the same time, Lawrence's recent invention, the [[cyclotron]], promised to revolutionise experimental nuclear physics, and Chadwick felt that the Cavendish laboratory would fall behind unless it also acquired one. He therefore chafed under Rutherford, who clung to the belief that good nuclear physics could still be done without large, expensive equipment, and turned down the request for a cyclotron.{{sfn|Brown|1997|pp=129–132}}

[[File:Victoria Clock Tower, Liverpool University - geograph.org.uk - 374422.jpg|thumb|left|upright|"[[Red brick university|Red brick]]" [[Victoria Building, University of Liverpool|Victoria Building]] at the [[University of Liverpool]] ]]
Chadwick was himself a critic of [[Big Science]] in general, and Lawrence in particular, whose approach he considered careless and focused on technology at the expense of science. When Lawrence postulated the existence of a new and hitherto unknown particle that he claimed was a possible source of limitless energy at the [[Solvay Conference]] in 1933, Chadwick responded that the results were more likely attributable to contamination of the equipment.{{sfn|Herken|2002|p=10}} While Lawrence rechecked his results at Berkeley only to find that Chadwick was correct, Rutherford and Oliphant conducted an investigation at the Cavendish that found that deuterium [[Nuclear fusion|fuses]] to form [[helium-3]], thereby causing the effect that Lawrence had observed. This was another major discovery, but the Oliphant-Rutherford [[particle accelerator]] was an expensive state-of-the-art piece of equipment.{{sfn|Heilbron|Seidel|1989|pp=165–167}}{{sfn|Oliphant|Rutherford|1933}}{{sfn|Oliphant|Kinsey|Rutherford|1933}}{{sfn|Oliphant|Harteck|Rutherford|1934}}

In March 1935, Chadwick received an offer of the Lyon Jones Chair of physics at the [[University of Liverpool]], in his wife's home town, to succeed [[Lionel Wilberforce]]. The laboratory was so antiquated that it still ran on [[direct current]] electricity, but Chadwick seized the opportunity, assuming the chair on 1 October 1935. The university's prestige was soon bolstered by Chadwick's Nobel Prize, which was announced in November 1935.{{sfn|Brown|1997|pp=134–139}} His medal was sold at auction in 2014 for $329,000.<ref>{{cite news |newspaper=Yahoo News |title=Sold! Nobel Prize for Neutron Discovery Auctioned for $329,000 |first=Megan |last=Gannon |date=4 June 2014 |url=https://news.yahoo.com/sold-nobel-prize-neutron-discovery-auctioned-329-000-161620108.html |access-date=16 September 2014 }}</ref>

Chadwick set about acquiring a cyclotron for Liverpool. He started by spending £700 to refurbish the antiquated laboratories at Liverpool, so some components could be made in-house.{{sfn|Brown|1997|p=142}} He was able to persuade the university to provide £2,000 and obtained a grant for another £2,000 from the Royal Society.{{sfn|Brown|1997|pp=149–151}} To build his cyclotron, Chadwick brought in two young experts, Bernard Kinsey and Harold Walke, who had worked with Lawrence at the University of California. A local cable manufacturer donated the copper conductor for the coils. The cyclotron's 50-ton magnet was manufactured in [[Trafford Park]] by [[Metropolitan-Vickers]], which also made the vacuum chamber.{{sfn|Holt|1994}} The cyclotron was completely installed and running in July 1939. The total cost of £5,184 was more than Chadwick had received from the university and the Royal Society, so Chadwick paid the rest from his {{SEK|159,917|link=yes}} (£8,243) Nobel Prize money.{{sfn|Brown|1997|pp=173–174}}

At Liverpool the Medicine and Science faculties worked together closely. Chadwick was automatically a committee member of both faculties, and in 1938 he was appointed to a commission headed by [[Edward Stanley, 17th Earl of Derby|Lord Derby]] to investigate the arrangements for cancer treatment in Liverpool. Chadwick anticipated that neutrons and radioactive isotopes produced with the 37-inch cyclotron could be used to study biochemical processes, and might become a weapon in the fight against cancer.{{sfn|King|1997}}{{sfn|Brown|1997|p=150}}

== Second World War ==
=== Tube Alloys and the MAUD Report ===
In Germany, [[Otto Hahn]] and [[Fritz Strassmann]] bombarded uranium with neutrons, and noted that [[barium]], a lighter element, was among the products produced. Hitherto, only the same or heavier elements had been produced by the process. In January 1939, Meitner and her nephew [[Otto Frisch]] astounded the physics community with a paper that [[discovery of nuclear fission|explained this result]].{{sfn|Brown|1997|p=170}} They theorised that uranium atoms bombarded with neutrons can break into two roughly equal fragments, a process they called [[nuclear fission|fission]]. They calculated that this would result in the release of about 200 [[Electronvolt|MeV]], implying an energy release orders of magnitude greater than chemical reactions,{{sfn|Meitner|Frisch|1939}} and Frisch confirmed their theory experimentally.{{sfn|Frisch|1939}} It was soon noted by Hahn that if neutrons were released during fission, then a chain reaction was possible.{{sfn|Hahn|Strassmann|1939}} French scientists, [[Pierre Joliot]], [[Hans von Halban]] and [[Lew Kowarski]], soon verified that more than one neutron was indeed emitted per fission.{{sfn|von Halban|Joliot|Kowarski|1939}} In a paper co-authored with the American physicist [[John Archibald Wheeler|John Wheeler]], Bohr theorised that fission was more likely to occur in the [[uranium-235]] [[isotope]], which made up only 0.7 per cent of natural uranium.{{sfn|Gowing|1964|pp=24–27}}{{sfn|Bohr|Wheeler|1939}}

[[File:William Penney, Otto Frisch, Rudolf Peierls and John Cockroft.jpg|thumb|upright=1.3|right|Key British physicists. Left to right: [[William Penney, Baron Penney|William Penney]], [[Otto Robert Frisch]], [[Rudolf Peierls]] and [[John Cockcroft]]. They are wearing the American [[Medal of Freedom (1945)|Medal of Freedom]].]]
Chadwick did not believe that there was any likelihood of another war with Germany in 1939, and took his family for a holiday on a remote lake in northern Sweden. The news of the outbreak of the [[Second World War]] therefore came as a shock. Determined not to spend another war in an internment camp, Chadwick made his way to [[Stockholm]] as fast as he could, but when he arrived there with his family, he found that all air traffic between Stockholm and London had been suspended. They made their way back to England on a [[tramp steamer]]. When he reached Liverpool, Chadwick found [[Joseph Rotblat]], a Polish post-doctoral fellow who had come to work with the cyclotron, was now destitute, as he was cut off from funds from Poland. Chadwick promptly hired Rotblat as a lecturer, despite his poor grasp of English.{{sfn|Brown|1997|pp=174–178}}

In October 1939, Chadwick received a letter from Sir [[Edward Victor Appleton|Edward Appleton]], the Secretary of the Department of Scientific and Industrial Research, asking for his opinion on the feasibility of an [[atom bomb]]. Chadwick responded cautiously. He did not dismiss the possibility, but carefully went over the many theoretical and practical difficulties involved. Chadwick decided to investigate the properties of [[uranium oxide]] further with Rotblat.{{sfn|Gowing|1964|pp=38–39}} In March 1940, Otto Frisch and [[Rudolf Peierls]] at the [[University of Birmingham]] re-examined the theoretical issues involved in a paper that became known as the [[Frisch–Peierls memorandum]]. Instead of looking at unenriched uranium oxide, they considered what would happen to a sphere of pure uranium-235, and found that not only could a chain reaction occur, but that it might require as little as {{convert|1|kg}} of uranium-235, and unleash the energy of tons of dynamite.{{sfn|Gowing|1964|pp=39–41}}

[[File:Liverpool Blitz D 5984.jpg|thumb|left|400px|Part of [[Liverpool]] devastated by the [[The Blitz|Blitz]]]]
A special subcommittee of the Committee for the Scientific Survey of Air Warfare (CSSAW), known as the [[MAUD Committee]], was created to investigate the matter further. It was chaired by Sir [[George Paget Thomson|George Thomson]] and its original membership included Chadwick, along with Mark Oliphant, John Cockcroft and [[Philip Moon]].{{sfn|Gowing|1964|p=45}} While other teams investigated [[uranium enrichment]] techniques, Chadwick's team at Liverpool concentrated on determining the [[nuclear cross section]] of uranium-235.{{sfn|Gowing|1964|p=63}} By April 1941, it had been experimentally confirmed that the [[critical mass]] of uranium-235 might be {{convert|8|kg}} or less.{{sfn|Brown|1997|p=206}} His research into such matters was complicated by all-but-incessant [[Luftwaffe]] bombings of the environs of his Liverpool lab; the windows were blown out so often that they were replaced by cardboard.{{sfn|Brown|1997|p=204}}

In July 1941, Chadwick was chosen to write the final draft of the MAUD Report, which, when presented by [[Vannevar Bush]] to [[President of the United States|President]] [[Franklin D. Roosevelt]] in October 1941, inspired the U.S. government to pour millions of dollars into the pursuit of an atom bomb.{{sfn|Bundy|1988|pp=48–49}} When [[George B. Pegram]] and [[Harold Urey]] visited Britain to see how the project,{{sfn|Gowing|1964|p=85}} now known as [[Tube Alloys]],{{sfn|Gowing|1964|p=109}} was going, Chadwick was able to tell them: "I wish I could tell you that the bomb is not going to work, but I am 90 per cent sure that it will."{{sfn|Gowing|1964|p=85}}

In a recent book about the Bomb project, [[Graham Farmelo]] wrote that "Chadwick did more than any other scientist to give Churchill the Bomb.&nbsp;... Chadwick was tested almost to the breaking point."{{sfn|Farmelo|2013|p=119}} So worried that he could not sleep, Chadwick resorted to sleeping pills, which he continued to take for most of his remaining years. Chadwick later said that he realised that "a nuclear bomb was not only possible—it was inevitable. Sooner or later these ideas could not be peculiar to us. Everybody would think about them before long, and some country would put them into action".{{sfn|Brown|1997|p=205}} Sir [[Hermann Bondi]] suggested that it was fortunate that Chadwick, not Rutherford, was the doyen of UK physics at the time, as the latter's prestige might otherwise have overpowered Chadwick's interest in "looking forward" to the Bomb's prospects.{{sfn|Bondi|1997}}

=== Manhattan Project ===
[[File:Quebec conference 1943.png|thumb|right|[[Mackenzie King]], [[Franklin D. Roosevelt]] and [[Winston Churchill]] at the [[Quebec Conference, 1943|first Quebec Conference]] in 1943]]
Owing to the danger from aerial bombardment, the Chadwicks sent their twins to Canada as part of a [[Evacuations of civilians in Britain during World War II|government evacuation scheme]].{{sfn|Brown|1997|pp=197–198}} Chadwick was reluctant to move Tube Alloys there, believing that the United Kingdom was a better location for the isotope separation plant.{{sfn|Brown|1997|pp=218–219}} The enormous scope of the effort became more apparent in 1942: even a pilot separation plant would cost over £1 million and strain Britain's resources, to say nothing of a full-scale plant, which was estimated to cost somewhere in the vicinity of £25 million. It would have to be built in America.{{sfn|Gowing|1964|pp=141–142}} At the same time that the British became convinced that a joint project was necessary, the progress of the American [[Manhattan Project]] was such that British cooperation seemed less essential, although the Americans were still eager to use Chadwick's talents.{{sfn|Gowing|1964|p=152}}

The matter of cooperation had to be taken up at the highest level. In September 1943, the [[Prime Minister of the United Kingdom|Prime Minister]], [[Winston Churchill]], and President Roosevelt negotiated the [[Quebec Agreement]], which reinstated cooperation between Britain, the United States and Canada. Chadwick, Oliphant, Peierls and [[Francis Simon|Simon]] were summoned to the United States by the director of Tube Alloys, Sir [[Wallace Akers]], to work with the Manhattan Project. The Quebec Agreement established a new [[Combined Policy Committee]] to direct the joint project. The Americans disliked Akers, so Chadwick was appointed technical advisor to the Combined Policy Committee, and the head of the British Mission.{{sfn|Gowing|1964|pp=166–171}}

Leaving Rotblat in charge in Liverpool, Chadwick began a tour of the Manhattan Project facilities in November 1943, except for the [[Hanford Site]] where plutonium was produced, which he was not allowed to see. He became the only man, apart from Groves and his second in command, to have access to all the American research and production facilities for the uranium bomb. Observing the work on the [[K-25]] [[gaseous diffusion]] facility at [[Oak Ridge, Tennessee]], Chadwick realised how wrong he had been about building the plant in wartime Britain. The enormous structure could never have been concealed from the Luftwaffe.{{sfn|Brown|1997|p=253}} In early 1944, he moved to [[Los Alamos, New Mexico]], with his wife and their twins, who now spoke with Canadian accents.{{sfn|Brown|1997|pp=250–261}} For security reasons, he was given the cover name of James Chaffee.{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|p=95}}

[[File:Groves and Chadwick 830308.jpg|thumb|left|Chadwick (left) with [[Major General (United States)|Major General]] [[Leslie R. Groves, Jr.]], the director of the [[Manhattan Project]]]]
Chadwick accepted that the Americans did not need British help, but that it could still be useful in bringing the project to an early and successful conclusion. Working closely with the director of the Manhattan Project, [[Major General (United States)|Major General]] [[Leslie R. Groves, Jr.]], he attempted to do everything he could to support the effort.{{sfn|Brown|1997|pp=247–51}} He also endeavoured to place British scientists in as many parts of the project as possible to facilitate a post-war British nuclear weapons project to which Chadwick was committed. Requests from Groves via Chadwick for particular scientists tended to be met with an immediate rejection by the company, ministry or university currently employing them, only to be overcome by the overriding priority accorded to Tube Alloys.{{sfn|Gowing|1964|pp=241–244}} As a result, the British team was critical to the Project's success.{{sfn|Szasz|1992|p=xvi}}

Although he had more knowledge of the project than anyone else from Britain,{{sfn|Gowing|1964|p=329}} Chadwick had no access to the Hanford site. [[Charles Portal, 1st Viscount Portal of Hungerford|Lord Portal]] was offered a tour of Hanford in 1946. "This was the only plant to which Chadwick had been denied access in wartime, and now he asked Groves if he could accompany Portal. Groves replied that he could, but if he did then 'Portal will not see very much'."{{sfn|Brown|1997|p=317}} For his efforts, Chadwick received a [[knighthood]] in the [[1945 New Year Honours|New Year Honours on 1 January 1945]].<ref name="Kt">{{London Gazette|issue=36866 |supp=y|page=1|date=29 December 1944}} ''Knight Bachelor''</ref> He considered this to be a recognition of the work of the whole Tube Alloys project.{{sfn|Brown|1997|p=279}}

By early 1945, Chadwick was spending most of his time in Washington, D.C., and his family relocated from Los Alamos to a house on Washington's [[Dupont Circle]] in April 1945.{{sfn|Brown|1997|p=279}} He was present at the meeting of the Combined Policy Committee on 4 July when [[Field Marshal (United Kingdom)|Field Marshal]] Sir [[Henry Maitland Wilson]] gave Britain's agreement to use the atom bomb against Japan,{{sfn|Brown|1997|p=290}} and at the [[Trinity nuclear test]] on 16 July, when the first atom bomb was detonated.{{sfn|Brown|1997|p=292}} Inside its [[Pit (nuclear weapon)|pit]] was a polonium-beryllium [[modulated neutron initiator]], a development of the technique that Chadwick had used to discover the neutron over a decade before.{{sfn|Brown|1997|p=287}} [[William L. Laurence]], ''[[The New York Times]]'' reporter attached to the Manhattan Project, wrote that "never before in history had any man lived to see his own discovery materialize itself with such telling effect on the destiny of man."{{sfn|Laurence|1946|p=26}}

== Later life ==
Shortly after the war ended, Chadwick was appointed to the Advisory Committee on Atomic Energy (ACAE). He was also appointed as the British scientific advisor to the [[United Nations Atomic Energy Commission]]. He clashed with fellow ACAE member [[Patrick Blackett]], who disagreed with Chadwick's conviction that Britain needed to acquire its own nuclear weapons; but it was Chadwick's position that was ultimately adopted. He returned to Britain in 1946, to find a country still beset by wartime rationing and shortages.{{sfn|Brown|1997|pp=306, 316}}

At this time, Sir James Mountford, the Vice Chancellor of the University of Liverpool, wrote in his diary "he had never seen a man 'so physically, mentally and spiritually tired" as Chadwick, for he "had plumbed such depths of moral decision as more fortunate men are never called upon even to peer into&nbsp;... [and suffered]&nbsp;... almost insupportable agonies of responsibility arising from his scientific work'."{{sfn|Brown|1997|p=323}}

In 1948, Chadwick accepted an offer to become the [[Master (college)|Master]] of Gonville and Caius College. The job was prestigious but ill-defined; the Master was the titular head of the college, but authority actually resided in a council of 13 fellows, of whom one was the Master. As Master, Chadwick strove to improve the academic reputation of the college. He increased the number of research fellowships from 31 to 49, and sought to bring talent into the college.{{sfn|Brown|1997|pp=340–353}} This involved controversial decisions, such as hiring in 1951 the Chinese biochemist [[Tien-chin Tsao]]{{sfn|Zhang|2010}} and the Hungarian-born economist [[Peter Thomas Bauer|Peter Bauer]]. In what became known as the Peasants' Revolt, fellows led by [[Patrick Hadley]] voted an old friend of Chadwick's off the council and replaced him with Bauer. More friends of Chadwick's were removed over the following years, and he retired in November 1958. It was during his mastership that [[Francis Crick]], a PhD student at Gonville and Caius College, and [[James Watson]] discovered the structure of [[DNA]].{{sfn|Brown|1997|pp=340–353}}

By the 1970s Chadwick became more frail, and seldom left his flat, although he travelled to Liverpool for celebrations of his eightieth birthday. A lifelong atheist, he saw no reason to adopt religious faith in later life. He died in his sleep on 24 July 1974.{{sfn|Brown|1997|pp=360–363}}

==Honours==
* Elected a [[Fellow of the Royal Society]] in 1927.{{sfn|Massey|Feather|1976|p=11}}
* ''[[Medal for Merit]]'' from the United States,
* ''[[Pour le Mérite]]'' from Germany.{{sfn|Brown|1997|pp=360–363}}
* Foreign member of the [[Royal Netherlands Academy of Arts and Sciences]] in 1946
* International member of the [[American Philosophical Society]] in 1948.<ref>{{cite web|url=http://www.dwc.knaw.nl/biografie/pmknaw/?pagetype=authorDetail&aId=PE00004579 |title=J. Chadwick (1891–1974) |publisher=Royal Netherlands Academy of Arts and Sciences |access-date=21 July 2015}}</ref>
* [[Member of the Order of the Companions of Honour]] in the New Year Honours on 1 January 1970 for "services to science",<ref name="CH">{{London Gazette|issue=44999 |supp=y|page=23|date=30 December 1969}} ''Companion of Honour''</ref> and went to [[Buckingham Palace]] for the investiture ceremony.

==Legacy==
* Chadwick's papers are held at the [[Churchill Archives Centre]] in Cambridge, and are accessible to the public.<ref>{{cite web|title=The Papers of Sir James Chadwick|url=https://archivesearch.lib.cam.ac.uk/repositories/9/resources/1474|access-date=30 September 2021|publisher=Churchill Archives Centre, ArchiveSearch}}</ref>
* The Chadwick Laboratory at the University of Liverpool.<ref>{{cite web |url=http://www.scienceplaces.org/liverpool/liverpool_list.html |title=Liverpool Science Places |publisher=Scienceplaces.org |access-date=6 August 2014 |archive-url=https://web.archive.org/web/20140815041701/http://www.scienceplaces.org/liverpool/liverpool_list.html |archive-date=15 August 2014 |url-status=live  }}</ref>
* Sir James Chadwick Chair of Experimental Physics, also at the University of Liverpool. Named in 1991 as part of celebrations of the centenary of his birth.<ref>{{cite web |url=http://www.liv.ac.uk/commsec/calendar/University%20Chairs%20and%20their%20Holders%20Past%20and%20Present.pdf |title=University Chairs and their Holders Past and Present |publisher=[[University of Liverpool]] |access-date=1 August 2014 }}{{dead link|date=September 2017 |bot=InternetArchiveBot |fix-attempted=yes }}</ref>
* James Chadwick Building, which houses part of the [[School of Chemical Engineering and Analytical Sciences, University of Manchester]], as well as the Industrial Hub for Sustainable Engineering.<ref>{{cite web |url=http://www.ceas.manchester.ac.uk/about-us/maps-and-travel/james-chadwick-building-directions/ |title=James Chadwick Building – directions |publisher=The University of Manchester |access-date=18 May 2016 }}</ref>
* Chadwick was described by the [[United Kingdom Atomic Energy Authority]] official historian [[Lorna Arnold]] as "a physicist, a scientist-diplomat, and a good, wise, and humane man."{{sfn|Arnold|1998}}
* [[Chadwick (crater)]], on the Moon<ref>{{cite web |url=http://planetarynames.wr.usgs.gov/Feature/1118?__fsk=1722400487 |title=Planetary Names: Crater, craters: Chadwick on Moon |publisher=[[United States Geological Survey]] |access-date=12 August 2012 |archive-url=https://web.archive.org/web/20171122063758/https://planetarynames.wr.usgs.gov/Feature/1118?__fsk=1722400487 |archive-date=22 November 2017 |url-status=dead  }}</ref>

== Notes ==
{{reflist|30em}}

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* {{cite book
 |last1=Herken |first1=Gregg
 |year=2002
 |title=Brotherhood of the Bomb: The Tangled Lives and Loyalties of Robert Oppenheimer, Ernest Lawrence, and Edward Teller
 |publisher=[[Holt Paperbacks]]
 |isbn=978-0-8050-6589-3
}}
* {{cite book |last1=Hoddeson |first1=Lillian |author-link=Lillian Hoddeson |first2=Paul W. |last2=Henriksen |first3=Roger A. |last3=Meade |first4=Catherine L. |last4=Westfall |author4-link=Catherine Westfall |year=1993 |title=Critical Assembly: A Technical History of Los Alamos During the Oppenheimer Years, 1943–1945 |publisher=[[Cambridge University Press]] |isbn=978-0-521-44132-2 |url-access=registration |url=https://archive.org/details/criticalassembly0000unse }}
* {{cite journal
 |last=Holt |first=John R. |author-link=John Riley Holt
 |year=1994
 |title=James Chadwick at Liverpool
 |journal=[[Notes and Records of the Royal Society of London]]
 |volume=48 |issue=2 |pages=299–308
 |doi=10.1098/rsnr.1994.0030
 |jstor=532169
|doi-access=free
 }}
* {{cite book
 |last=Jensen
 |first=Carsten
 |year=2000
 |title=Controversy and Consensus: Nuclear Beta Decay 1911–1934
 |url=https://books.google.com/books?id=wcYlmDm3wJEC&pg=PA88
 |publisher=[[Birkhäuser]]
 |isbn=978-3-7643-5313-1
 }}
* {{cite journal
 |last=King
 |first=Charles D.
 |year=1997
 |title=Sir James Chadwick and his Medical Plans for the Liverpool 37-inch Cyclotron
 |url=http://www.evolve360.co.uk/Data/10/Docs/09/09King.pdf
 |journal=Medical Historian
 |volume=9
 |pages=43–55
 |access-date=7 August 2014
|archive-url=https://web.archive.org/web/20141215050544/http://www.evolve360.co.uk/Data/10/Docs/09/09King.pdf
 |archive-date=15 December 2014
|url-status=dead
 }}
* {{cite book |last=Laurence |first=William L. |author-link=William L. Laurence |year=1946 |title=Dawn Over Zero: The Story of the Atomic Bomb |url=https://archive.org/details/dawnoverzerostor0000laur |url-access=registration |oclc=4354887 |publisher=[[Alfred A. Knopf]] }}
* {{cite journal
 |last1=Massey |first1=Harrie |author-link1=Harrie Massey
 |last2=Feather |first2=Norman |author-link2=Norman Feather
 |year=1976
 |title=James Chadwick. 20 October 1891&nbsp;– 24 July 1974
 |journal=[[Biographical Memoirs of Fellows of the Royal Society]]
 |volume=22 |pages=10–70
 |doi=10.1098/rsbm.1976.0002
 |jstor=769732
|doi-access=free
 }}
* {{cite journal
 |last1=Meitner |first1=Lise |author-link1=Lise Meitner
 |last2=Frisch |first2=Otto R. |author-link2=Otto Robert Frisch
 |year=1939
 |title=Disintegration of Uranium by Neutrons: A New Type of Nuclear Reaction
 |journal=[[Nature (journal)|Nature]]
 |volume=143 |issue=3615 |pages=239–240
 |bibcode=1939Natur.143..239M
 |doi=10.1038/143239a0
 |s2cid=4113262}}
* {{cite journal
 |last1=Oliphant |first1=M. L. E. |author-link=Mark Oliphant
 |last2=Rutherford |first2=Lord |author-link2=Ernest Rutherford
 |year=1933
 |title=Experiments on the Transmutation of Elements by Protons
 |volume=141 |issue=843 |pages=259–281
 |journal=[[Proceedings of the Royal Society A]]
 |bibcode=1933RSPSA.141..259O
 |doi=10.1098/rspa.1933.0117
 |jstor=96218
|doi-access=free
 }}
* {{cite journal
 |last1=Oliphant |first1=M. L. E. |author-mask=1
 |last2=Kinsey |first2=B. B.
 |last3=Rutherford |first3=Lord |author-link3=Ernest Rutherford
 |year=1933
 |title=The Transmutation of Lithium by Protons and by Ions of the Heavy Isotope of Hydrogen
 |journal=[[Proceedings of the Royal Society A]]
 |volume=141 |issue=845 |pages=722–733
 |bibcode=1933RSPSA.141..722O
 |doi=10.1098/rspa.1933.0150
 |jstor=96179
|doi-access=free
 }}
* {{cite journal
 |last1=Oliphant |first1=M. L. E. |author-mask=1
 |last2=Harteck |first2=P. |author-link2=Paul Harteck
 |last3=Rutherford |first3=Lord |author-link3=Lord Rutherford
 |year=1934
 |journal=[[Proceedings of the Royal Society A]]
 |title=Transmutation Effects Observed with Heavy Hydrogen
 |volume=144 |issue=853 |pages=692–703
 |bibcode=1934RSPSA.144..692O
 |doi=10.1098/rspa.1934.0077
 |jstor=2935553
|doi-access=free
 }}
* {{cite journal
 |last=Oliphant |first=Mark |author-mask=1
 |year=1974
 |title=James Chadwick
 |journal=[[Physics Today]]
 |volume=27 |issue=10 |pages=87–89
 |bibcode=1974PhT....27j..87O
 |doi=10.1063/1.3128956
}}
* {{cite journal
 |last1=Rutherford
 |first1=Ernest
 |author-link=Ernest Rutherford
 |last2=Chadwick
 |first2=James
 |year=1912
 |title=A Balance Method for Comparison of Quantities of Radium and Some of its Applications
 |journal=[[Proceedings of the Physical Society]]
 |volume=24
 |issue=1
 |pages=141–151
 |bibcode=1911PPSL...24..141R
 |doi=10.1088/1478-7814/24/1/320
 |url=https://zenodo.org/record/1431497
 }}
* {{cite web
 |last=Sublette
 |first=Carey
 |title=Polonium Poisoning
 |date=14 December 2006
|url=http://nuclearweaponarchive.org/News/PoloniumPoison.html
 |publisher=Nuclear Weapon Archive
 |access-date=1 August 2014
}}
* {{cite book
 |last=Szasz |first=Ferenc
 |year=1992
 |title=British Scientists and the Manhattan Project: The Los Alamos Years
 |publisher=[[St. Martin's Press]]
 |isbn=978-0-312-06167-8
}}
* {{cite web
 |last=Weiner
 |first=Charles
 |date=20 April 1969
|title=Interview with Sir James Chadwick
 |url=http://www.aip.org/history/ohilist/3974_1.html
 |publisher=[[American Institute of Physics]]
 |access-date=5 August 2014
|archive-date=16 July 2014
|archive-url=https://web.archive.org/web/20140716020131/http://www.aip.org/history/ohilist/3974_1.html
 |url-status=dead
 }}
* {{cite book
 |last         = Whaling
 |first        = Ward
 |year         = 2009
 |title        = Robert F. Bacher 1905–2004
 |url          = http://www.nasonline.org/publications/biographical-memoirs/memoir-pdfs/bacher-robert-f.pdf
 |series       = [[Biographical Memoirs of the National Academy of Sciences]]
 |publisher    = [[National Academy of Sciences]]
 |access-date  = 22 March 2013
|url-status   = dead
 |archive-url  = https://web.archive.org/web/20140531133917/http://www.nasonline.org/publications/biographical-memoirs/memoir-pdfs/bacher-robert-f.pdf
 |archive-date = 31 May 2014
|df           = dmy-all
}}
* {{cite journal
 |last         = Zhang
 |first        = Youshang
 |year         = 2010
 |title        = In memory of Professor Tianqin Cao (Tien-chin Tsao)
 |url          = http://journal.hep.com.cn/pac/EN/article/downloadArticleFile.do?attachType=PDF&id=10366
 |journal      = [[Protein & Cell]]
 |volume       = 1
 |issue        = 6
 |pages        = 507–509
 |doi          = 10.1007/s13238-010-0074-2
 |pmid         = 21246905
 |pmc          = 4875321
 |url-status   = dead
 |archive-url  = https://web.archive.org/web/20140810185715/http://journal.hep.com.cn/pac/EN/article/downloadArticleFile.do?attachType=PDF&id=10366
 |archive-date = 10 August 2014
|df           = dmy-all
}}
{{refend}}

== Further reading ==
{{Commons category}}
* {{cite journal
 |year=1948
 |title=Sir James Chadwick, F.R.S.
 |journal=[[Nature (journal)|Nature]]
 |volume=161 |issue=4103 |pages=964
 |bibcode=1948Natur.161Q.964.
 |doi=10.1038/161964a0
|doi-access=free
 }}
* {{cite journal
 |year=1972
 |title=Sir James Chadwick, C.H., LL.D., F.R.S.: 80th birthday
 |journal=[[Contemporary Physics]]
 |volume=13 |issue=3 |pages=310
 |bibcode=1972ConPh..13..310.
 |doi=10.1080/00107517208205684
}}
* {{cite book
 |last1=Rutherford |first1=Ernest |author-link1=Ernest Rutherford
 |last2=Chadwick |first2=James
 |last3=Ellis |first3=Charles D. |author-link3=Charles Drummond Ellis
 |year=2010
 |title=Radiation from Radioactive Substances
 |edition=Reprint of 2nd
 |publisher=[[Cambridge University Press]]
 |isbn=978-1-108-00901-0
 |ref=none
}}

==External links==
* [https://www.aip.org/history-programs/niels-bohr-library/oral-histories/3974-1 Oral history interview transcript with James Chadwick on 15 April 1969, American Institute of Physics, Niels Bohr Library & Archives] – Session I
* [https://www.aip.org/history-programs/niels-bohr-library/oral-histories/3974-2 Oral history interview transcript with James Chadwick on 16 April 1969, American Institute of Physics, Niels Bohr Library & Archives] – Session II
* [https://www.aip.org/history-programs/niels-bohr-library/oral-histories/3974-3 Oral history interview transcript with James Chadwick on 17 April 1969, American Institute of Physics, Niels Bohr Library & Archives] – Session III
* [https://www.aip.org/history-programs/niels-bohr-library/oral-histories/3974-4 Oral history interview transcript with James Chadwick on 20 April 1969, American Institute of Physics, Niels Bohr Library & Archives] – Session IV
* {{Nobelprize}}

{{s-start}}
{{s-aca}}
{{s-bef|before=[[John Forbes Cameron]]}}
{{s-ttl|title=Master of [[Gonville and Caius College, Cambridge|Gonville and Caius College]]|years=1948–1959}}
{{s-aft|after=[[Nevill Francis Mott|Sir Nevill Francis Mott]]}}
{{s-end}}

{{Copley Medallists 1901–1950}}
{{Nobel Prize in Physics Laureates 1926–1950}}
{{1935 Nobel Prize winners}}
{{Gonville and Caius Masters}}
{{Manhattan Project}}
{{Portal bar|Biography|Physics|History of science|Nuclear technology}}
{{Authority control}}

{{DEFAULTSORT:Chadwick, James}}
[[Category:1891 births]]
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