Sir George Paget Thomson

Sir George Paget Thomson

The English atomic physicist Sir George Paget Thomson (born 1892) shared the Nobel Prize in physics for the discovery of electron waves.

George Paget Thomson, son of Sir J. J. Thomson, the discoverer of electrons, was born at Cambridge on May 3, 1892. He studied mathematics and physics at Trinity College, Cambridge, and graduated in 1913. He was then elected a Fellow and lecturer of Corpus Christi College. Early in World War I he served as an infantry officer in France, but from 1915 he worked on aerodynamical problems at Farnborough. From 1917 to 1918 he was in the United States as a member of the British War Mission.

After the war Thomson continued his research and teaching at Cambridge. In 1922 he became professor of natural philosophy in the University of Aberdeen, where he did his fundamental work on electron waves. In 1930 he was appointed professor of physics at the Imperial College, University of London.

During the first quarter of the 20th century, it was learned that the electron not only had an electric charge but also mass and spin. However, the theoretical concepts did not fully agree with the results of experiments. In 1924, Louis de Brogile postulated theoretically that any particle of matter must possess not only mass but also a wave structure.

In 1927 Thomson began working on this problem, using the effect of a diffraction grating on a beam of electrons—cathode rays—and photography of the results. But cathode rays have little penetrative power, and a crystal could not be used as a diffraction grating. It was decided to use extremely thin sheets of the precious metals as diffraction gratings, since their atom structure was known and in their natural state they were crystalline. When a beam of electrons was passed through such a sheet of gold foil, the photograph showed a central dark spot formed by the undiffracted beams, surrounded by concentric rings formed by the diffracted beams.

The results agreed with the hypothesis that electrons exhibited wave characters. From the experimental data, combined with the distances between the rings, the wavelengths of the electronic waves could be calculated by the De Broglie formula. It was also found that the beam was deflected by a magnetic field in agreement with the De Broglie formula. One application of the method in engineering is the examination of the atomic structure of solid surfaces by reflection technique.

Unknown to Thomson, the American physicist C. J. Davisson had been studying this problem by a different method, and their results were published almost simultaneously. For the discovery of the electronic waves Thomson shared the Nobel Prize for Physics with Davisson in 1937.

In the late 1930s Thomson became interested in atomic fission, and he persuaded the British Air Ministry to begin extensive experiments. After the outbreak of World War II he became chairman of the British Committee on Atomic Energy, and in 1941 he went to the United States to deliver to American scientists the committee's report that established the feasibility of the atomic bomb. After the war he was active in research on controlled thermonuclear reactions, and he was consultant to the British Atomic Energy Authority. In 1952 Thomson was elected Master of Corpus Christi College, Cambridge, from which post he retired in 1962. After retirement, he remained in Cambridge, where he stayed active academically and socially. Thomson died on September 10, 1975, at age 83.

Thomson received many honors. Elected a Fellow of the Royal Society in 1929, he was awarded its Hughes Medal in 1939 and its Royal Medal in 1949. He was knighted in 1943 and received honorary degrees from many universities. Among his important books are Wave Mechanics of the Free Electron (1930) and, with W. Cochrane, The Theory and Practice of Electron Diffraction (1939). His more elementary work, The Atom (1930), passed through many editions. For further reading, see Biographical Memoirs of Fellows of the Royal Society, Volume 23 (1977). Other good sources include Barbara Cline's Men Who Made a New Physics: Physicists and the Quantum Theory (1987), Modern Men of Science Volume I (1968), and Robert Weber's Pioneers of Science: Nobel Prize Winners in Physics (1980).

Further Reading

There is a biography of Thomson in Nobel Lectures, Physics, 1922-1941 (1965), which also includes his Nobel Lecture. For a discussion of his work see N. H. de V. Heathcote, Nobel Prize Winners, Physics, 1901-1950 (1953). For the background of Thomson's work see his The Atom (1930; 5th ed. 1956); also B. Hoffmann, The Strange Story of the Quantum (1959), and A. d'Abro, The Rise of the New Physics (1951). □