CHADWICK, JAMES

James Chadwick, who won the Nobel Prize in Physics in 1935 for his discovery of the neutron, was born in Bollington, south of Manchester, England, on October 20, 1891. He was the first of four children whose parents were so poor that they had to send him to live in nearby Macclesfield with his grandmother, who saw to his primary education. Thereafter he attended the Manchester Municipal Secondary School, where he excelled in his studies and gained a scholarship to enter the University of Manchester in 1908, all the while living at home and skipping lunch because he could not afford it. He intended to study mathematics, but prior to his matriculation he was interviewed by mistake as a potential physics student and was too immature and shy to correct the error. That turned out to be fortunate, however, because during his first year his physics lecturer had to go to London for a few weeks and his place was taken by the new professor

at Manchester, Ernest Rutherford, whose infectious enthusiasm for physics captivated the young student. Later, in his third and final year as an undergraduate, Chadwick began to carry out some research under Rutherford's direction. He received his B.A. degree with First Class Honors in Physics in 1911, embarked on further research, received his M.Sc. degree in 1912, and gained fellowship support for the academic year 1912–1913 to continue his research under Rutherford's direction.

In the fall of 1913, on Rutherford's recommendation, Chadwick was awarded an 1851 Exhibition Senior Research Studentship to pursue research under Hans Geiger, who in 1908 had invented the particle counter named after him while working as Rutherford's research assistant in Manchester, and who in 1912 had returned to Germany to become the director of his own laboratory in the Physikalisch-Technische Reichsanstalt (Imperial Physical-Technical Institute) in Charlottenburg, a suburb of Berlin. There Chadwick mastered the German language and came into contact with Albert Einstein, Otto Hahn, Lise Meitner, Walther Bothe, and other prominent physicists and chemists. In the spring of 1914, he made an important and perplexing discovery, that of the continuous spectrum of beta rays emitted by certain radioactive elements, whose correct explanation would have to wait until the end of 1930 when Wolfgang Pauli postulated the existence of the neutrino to preserve the laws of conservation of energy and momentum in the beta-decay process.

Soon after Chadwick made that discovery, on August 4, 1914, war was declared. As a British subject, he was interned in Ruhleben, near Spandau on the western outskirts of Berlin, where he and around four thousand other foreigners were billeted in unused racehorse stables for the duration of the Great War. Conditions were harsh, especially during the winter famine of 1916–1917, but even then he managed to carry out some research with other interned scientists using primitive equipment. After the Armistice on November 11, 1918, he returned to Manchester, his digestion permanently impaired by his wartime ordeal. Around six months later, when Rutherford moved from Manchester to Cambridge to succeed J. J. Thomson as Cavendish Professor of Experimental Physics, he was able to take Chadwick along with him because Gonville and Caius College awarded him a Wollaston Studentship and a small supplement for teaching, just enough to sustain his meager needs. In 1921 he was elected as a Fellow of Gonville and Caius College, which gave him an assured higher income plus college rooms and meals. In 1924 he was formally appointed as Assistant Director of Research of the Cavendish Laboratory. In 1925 he married Aileen Stewart-Brown, the daughter of a prominent Liverpool stockbroker; two years later they became the parents of twin daughters, Joanna and Judy. In 1927 Chadwick was elected as a Fellow of the Royal Society of London, the highest distinction apart from the Nobel Prize that a British scientist can receive.

At the Cavendish Laboratory, Chadwick introduced and taught each year his "Attic Course," an introductory six-week course on radioactivity, glass blowing, the production of high vacua, and the like, from which generation after generation of entering research students learned basic experimental skills. His own research throughout the 1920s, most of which he carried out with Rutherford, focused on following up Rutherford's 1918 discovery of artificial disintegration, that alpha particles from radioactive elements can disintegrate light nuclei with the emission of protons. Chadwick, like Rutherford, was a brilliant experimentalist, and the two worked together closely, elucidating new phenomena and defending their work successfully when it was challenged, especially by researchers working in Vienna. Rutherford and Chadwick gave a full account of their work in their book, Radiations from Radioactive Substances, which they published jointly with Charles D. Ellis in 1930, and which became the standard work from which numerous others learned about the emerging field of experimental nuclear physics. Chadwick's experiments and discussions with Rutherford during their long and close association in the Cavendish Laboratory laid the groundwork for his discovery of the neutron in February 1932.

Chadwick left Cambridge in 1935 to accept the Lyon Jones Chair of Physics at the University of Liverpool, knowing that he would never be able to overcome Rutherford's opposition to building a cyclotron in the Cavendish Laboratory, and being firmly convinced that future advances in nuclear physics would require the use of one. He realized that dream in Liverpool, where he and his coworkers constructed and brought a 36-inch cyclotron into operation in July 1939, just before the outbreak of war in Europe, which would end his career as a research scientist and open up a new one as a scientific administrator and statesman.

Thus, following the death of Rutherford in October 1937, Chadwick was the most prominent nuclear physicist in Britain, and as such he became deeply involved with the development of nuclear energy for military purposes during the second world war. He became a member of the so-called MAUD committee, which was established to look into the possible military use of uranium, and he coordinated the work on nuclear fission at British universities until the British decided to abandon that work and join the American atomic bomb project. In 1943 he moved to the United States to take charge of the British effort on the bomb project, becoming the only British scientist who was granted complete access to all aspects of the Manhattan Project. His scientific acumen and diplomatic skills earned him the full respect and confidence of its military head, General Leslie R. Groves, as well as the head of the Los Alamos laboratory, J. Robert Oppenheimer, and other leading scientists. In 1945 he was knighted, becoming Sir James Chadwick. Many other honors also were bestowed upon him.

After the war Chadwick returned first to Liverpool and then, in 1948, he left to become Master of Gonville and Caius College in Cambridge. A shy and reserved man, nervous and anxious in front of any audience, he had little taste for controversy, and when one developed that promised to sap his limited energy, he suddenly resigned the Mastership in 1958 and retired to a cottage in North Wales. In 1969 he and his wife, Lady Chadwick, returned to Cambridge to be near their two daughters. He died there on July 24, 1974, at the age of 82.

See also:Neutron, Discovery of

Bibliography

Brown, A. The Neutron and the Bomb: A Biography of Sir James Chadwick (Oxford University Press, Oxford, UK, 1997).

Massey, Sir H., and Feather, N. "James Chadwick 20 October 1891–24 July 1974." Biographical Memoirs of Fellows of the Royal Society22 , 11–70 (1976).

Stuewer, R. H. "Artificial Disintegration and the Cambridge-Vienna Controversy" in Observation, Experiment, and Hypothesis in Modern Physical Science , edited by P. Achinstein and O. Hannaway (MIT Press, Cambridge, MA, 1985).

Roger H. Stuewer