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Chadwick, Sir James

atomic neutron rutherford war

(1891–1974) British physicist: discoverer of the neutron.

Chadwick graduated in physics in Manchester in 1911 and stayed there to do research under . He won an award in 1913 to allow him to work with in Berlin, and when the First World War began in 1914 he was interned. Although held in poor conditions in a racecourse stable for 4 years, he was able to do some useful research as a result of help from and others.

In 1919 he rejoined Rutherford, who had moved to Cambridge, and for 16 years was to be his principal researcher. Chadwick’s research with him was mainly with alpha particles (helium nuclei ); from the way these were scattered by heavier nuclei he could work out the positive charge of the scattering nucleus and show it to be the same as the atomic number. They also used alpha particles to bombard light elements and induce artificial disintegration. Then, in 1932, he was able to reinterpret an experiment reported by the , which he saw as evidence for the existence of the neutron (charge 0, mass 1), which Rutherford had foreseen in 1920. Chadwick quickly did his own experiments to confirm his deduction; the neutron allowed a massive advance in knowledge of atomic nuclei and was one of a series of major discoveries in atomic physics made in the ‘marvellous year’ of 1932, largely in Rutherford’s laboratory.

In 1935 Chadwick won the Nobel Prize for his discovery of the neutron, but soon afterwards friction with Rutherford arose because Chadwick wanted to build a cyclotron and Rutherford opposed this. Chadwick went to Liverpool as professor and soon had his cyclotron (the first in the UK) and made the department there a leading centre for atomic physics. When the Second World War came, he was the natural leader of the UK’s effort to secure an atomic bomb before the enemy succeeded in this. Clearly the work had to be done in the USA, as the UK was exposed to German bombing. Chadwick made a masterly job of first propelling the work there into effectiveness, and then ensuring that collaboration proceeded smoothly.

Back in the UK after the war, advising government on nuclear matters and increasingly doubtful of the wisdom of its policies, he had an unsatisfying last phase in his career as Master of his old Cambridge college.


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