James Chadwick

[b. Manchester, England, October 20, 1891, d. Cambridge, England, July 24, 1974]

Chadwick's early experiments established that atomic number is determined by the number of protons in an atom (now the definition). In 1932 he discovered the fourth known subatomic particle, the neutron (following the electron, photon, and proton); its existence had been suspected since 1924. Chadwick's later experiments with particle accelerators contributed to the invention of the nuclear fission bomb.

The English physicist Sir James Chadwick (1891-1974) made his most outstanding contribution to modern physics by demonstrating the existence of the neutron.

James Chadwick was born in Manchester on Oct. 20, 1891, the eldest son of John Joseph and Anne Mary Knowles Chadwick. In 1908 he enrolled at Victoria University in Manchester. Although his intention was to study mathematics, Chadwick was admitted to the physics programs and was too shy to correct the error. He graduated from the Honours School of Physics in 1911. During the next 2 years his education was continued in Ernest Rutherford's laboratory at the same university. It was there that Rutherford outlined his planetary theory of the atom. Chadwick's acquaintances in the physics department included Hans Geiger and Niels Bohr… After Chadwick received his master's degree in 1913, he was awarded the 1851 Exhibition Scholarship, which he used to finance his studies under Geiger in the foremost German research institute, the Physikalisch-Technische Reichsanstalt in Charlottenburg near Berlin. An early result of his work there was the establishment of the first energy spectrum of beta particles. Years later, subsequent developments along these lines prompted Wolfgang Pauli to postulate the existence of the neutrino.

Discovered the Neutron

After spending the years of World War I in a civilian internment camp in Ruhleben, Chadwick returned to England and used his fellowship at Gonville and Caius College to work with Rutherford at Cambridge University's Cavendish Laboratory. In 1920 he became the first to use a direct method in determining the electric charge on the nucleus. In 1922, he became assistant director of research under Rutherford. Together they spent much of their time experimenting with the transmutation of elements, attempting to break up the nucleus of one element so that different elements could be formed.

Throughout the years of work, Chadwick and Rutherford struggled with an inconsistency. They saw that almost every element had an atomic number that was less than its atomic mass. Rutherford suggested this might be due to the existence of a particle with the mass of a proton but with a neutral charge. However, their attempts to find such a particle were in vain. But in 1932 Chadwick found the answer in the work of the Joliot-Curies, who observed that beryllium had become radioactive after being exposed to alpha particles. Chadwick showed, by using a cloud chamber filled with nitrogen, that the radiation caused the nitrogen atoms to recoil with such energy as could be imparted only by collisions with uncharged particles having approximately the mass of protons. Chadwick had proven the existence of the neutron and received the Nobel Prize in physics in 1935.

From 1935 until 1948 Chadwick held the Lyon Jones chair of physics at the University of Liverpool. From 1943-1946, he also served as head of the British mission to the Manhattan Project and was present at the first atomic test in the New Mexico desert. He was knighted in 1945 and in 1948 was elected master of Gonville and Caius College, a post from which he retired in 1959. Three years later he retired also from the United Kingdom Atomic Energy Authority, on which he had served as part-time member from 1957. Sir James Chadwick died in Cambridge, England, on July 24, 1974.

Further Reading

Pais, Abraham, Inward Bound, Oxford University Press, 1986.

Rhodes, Richard, The Making of the Bomb Simon & Schuster, 1986.

For the bishop, see James Chadwick (bishop).

James Chadwick
Born	20 October 1891(1891-10-20) Bollington, Cheshire, England
Died	24 July 1974 (aged 82) Cambridge, England
Citizenship	United Kingdom
Fields	Physics
Institutions	Technical University of Berlin Liverpool University Gonville and Caius College Cambridge University Manhattan Project
Alma mater	University of Manchester University of Cambridge.
Academic advisors	Ernest Rutherford Hans Geiger
Doctoral students	Maurice Goldhaber Ernest C. Pollard Charles Drummond Ellis Dai Chuanzeng
Known for	Discovery of the neutron
Notable awards	Nobel Prize in Physics (1935)

Sir James Chadwick, CH, FRS (20 October 1891 – 24 July 1974) was an English Nobel laureate in physics awarded for his discovery of the neutron.

Contents 1 Biography 2 Career 2.1 Research at Cambridge 2.2 Liverpool 3 References 4 Further reading 5 External links

Biography

Chadwick was born in Bollington, Cheshire to John Joseph Chadwick and Annie Mary née Knowles. He went to Bollington Cross C of E Primary School, attended the Central Grammar School for Boys in Manchester,^[1] and then studied at the Universities of Manchester and Cambridge.

In 1913 Chadwick went and worked with Hans Geiger at the Technical University of Berlin. He also worked with Ernest Rutherford. He was in Germany at the start of World War I and was interned in Ruhleben P.O.W. Camp just outside Berlin. While he was interned, he had the freedom to set up a laboratory in the stables. With the help of Charles Ellis he worked on the ionization of phosphorus and also on the photo-chemical reaction of carbon monoxide and chlorine.^[2] He spent most of the war years in Ruhleben until Geiger's laboratory interceded for his release.

Career

Research at Cambridge

In 1932, Chadwick discovered a previously unknown particle in the atomic nucleus.^[3] This particle became known as the neutron because of its lack of electric charge. Chadwick's discovery was crucial for the fission of uranium 235. Unlike positively charged alpha particles, 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 split the nuclei of even the heaviest elements. For this discovery he was awarded the Hughes Medal of the Royal Society in 1932 and the Nobel Prize for Physics in 1935.^[4]

Chadwick’s discovery made it possible to create elements heavier than uranium in the laboratory. His discovery particularly inspired Enrico Fermi, Italian physicist and Nobel laureate, to discover nuclear reactions brought by slowed neutrons, and led Otto Hahn and Fritz Strassmann, German radiochemists in Berlin, to the revolutionary discovery of “nuclear fission”.

Liverpool

Chadwick became professor of physics at Liverpool University in 1935. As a result of the Frisch-Peierls memorandum in 1940 on the feasibility of an atomic bomb, he was appointed to the MAUD Committee that investigated the matter further. He visited North America as part of the Tizard Mission in 1940 to collaborate with the Americans and Canadians on nuclear research. Returning to England in November 1940, he concluded that nothing would emerge from this research until after the war. In December 1940 Franz Simon, who had been commissioned by MAUD, reported that it was possible to separate the isotope uranium-235. Simon's report included cost estimates and technical specifications for a large uranium enrichment plant. James Chadwick later wrote that it was at that time that he "realised that a nuclear bomb was not only possible, it was inevitable. I had to then take sleeping pills. It was the only remedy."

He shortly afterward joined the Manhattan Project in the United States, which developed the atomic bombs dropped on Hiroshima and Nagasaki. Chadwick was knighted in 1945.

In 1940, Chadwick forwarded to the Royal Society the work of two French scientists, Hans Von Halban and Lew Kowarski, who worked in Cambridge. He asked that the papers be held as they were not appropriate for publication during the war. In 2007, the Society discovered the documents during an audit of their archives.^[5]

References

1. ^ Falconer, Isobel. ‘Chadwick, Sir James (1891–1974)’, Oxford Dictionary of National Biography, Oxford University Press, Sept 2004; online edn, Jan 2009 accessed 26 June 2009
2. ^ Obituary: "Sir James Chadwick," The Times (of London, England), 25 July 1974, page 20, column F. (Available in part on-line at: http://ruhleben.tripod.com/id5.html .) See also: Obituary: "Sir Charles Ellis," The Times (of London, England), 15 January 1980, page 14, column F. (Available in part on-line at: http://ruhleben.tripod.com/id6.html .)
3. ^ Chadwick announced his initial findings in: James Chadwick (27 Feb. 1932) "Letters to the editor: Possible existence of a neutron," Nature, vol. 129, page 312. (Available on-line at: http://web.mit.edu/22.54/resources/Chadwick.pdf .) Subsequently he communicated his findings in more detail in: (1) Chadwick, J. (1932) "The existence of a neutron," Proceedings of the Royal Society, Series A, vol. 136, pages 692-708 (Available on-line at: http://www.chemteam.info/Chem-History/Chadwick-1932/Chadwick-neutron.html .); and (2) Chadwick, J. (1933) "The Bakerian Lecture: The neutron," Proceedings of the Royal Society, Series A, vol. 142, pages 1-25.
4. ^ James Chadwick - Biography
5. ^ Staff writers (1 June 2007). "Nuclear Reactor Secrets Revealed". BBC News. http://news.bbc.co.uk/2/hi/science/nature/6709855.stm. Retrieved 2009-02-12. 

Further reading

• Brown, Andrew (1997). The Neutron and the Bomb: A Biography of Sir James Chadwick. Oxford ; New York: Oxford University Press. ISBN 0-19-853992-4. 

External links

• Chadwick's article in Nature (10 May 1932: "The Existence of a Neutron")
• Another letter (3 months earlier) from Chadwick to Nature
• Annotated bibliography for James Chadwick from the Alsos Digital Library for Nuclear Issues
• Nobel prize Website entry
• The Papers of Sir James Chadwick are held at the Churchill Archives Centre in Cambridge and are accessible to the public.

v • d • e Nobel Laureates in Physics Jean Perrin (1926) · Arthur Compton / Charles Wilson (1927) · Owen Richardson (1928) · Louis de Broglie (1929) · C. V. Raman (1930) · Werner Heisenberg (1932) · Erwin Schrödinger / Paul Dirac (1933) · James Chadwick (1935) · Victor Hess / Carl Anderson (1936) · Clinton Davisson / George Thomson (1937) · Enrico Fermi (1938) · Ernest Lawrence (1939) · Otto Stern (1943) · Isidor Rabi (1944) · Wolfgang Pauli (1945) · Percy Bridgman (1946) · Edward Appleton (1947) · Patrick Blackett (1948) · Hideki Yukawa (1949) · Cecil Powell (1950) Complete roster | (1901–1925) | (1926–1950) | (1951–1975) | (1976–2000) | (2001–present)

v • d • e Masters of Gonville and Caius College, Cambridge John Rickinghall (1421) John Caius (1559) · Thomas Legge (1573) · William Branthwaite (1607) · John Gostlin (1619) · William Dell (1649) · Robert Brady (1660) · James Halman (1700) · John Ellys  · Thomas Gooch (1716) · James Burrough (1754) · Benedict Chapman (1839) · Edwin Guest (1852) · Norman Macleod Ferrers (1880) · Ernest Stewart Roberts (1903) · John Forbes Cameron  · Hugh Kerr Anderson (1912) · James Chadwick (1948) · Nevill Francis Mott (1959) · Joseph Needham (1966) · Henry William Rawson Wade (1976) · Peter Gray (1988) · Neil McKendrick · Christopher Hum (2006)

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