Compton, Arthur H(olly) (1892–1962)

US physicist who in 1923 found that X-rays scattered by such light elements as carbon increased in wavelength. He concluded from this unexpected result that the X-rays were displaying both wavelike and particlelike properties, a phenomenon later named the Compton effect. He was awarded the Nobel Prize for Physics in 1927 for his study of the transfer of energy from electromagnetic radiation to a particle. He shared the award with Scottish physicist Charles Wilson. Compton was also a principal contributor to the development of the atomic bomb.

The behaviour of the X-ray, previously considered only as a wave, is explained best by considering that it acts as a corpuscle or particle of electromagnetic radiation – as a photon (Compton's term). Quantum mechanics benefited greatly from this interpretation. Further confirmation came from experiments using a cloud chamber in which collisions between X-rays and electrons were photographed and analysed.

Compton was born in Wooster, Ohio, studied at Princeton, and worked 1919–20 in the UK with nuclear physicist Ernest Rutherford at Cambridge. His academic career in the USA was spent at Washington University, St Louis, 1920–23 and 1945–61, and at the University of Chicago 1923–45. Compton became chancellor of Washington University, St Louis, Missouri (1945–54), and remained there until 1961. To determine whether cosmic rays consist of particles or electromagnetic radiation, Compton made measurements at various latitudes of comparative cosmic-ray intensities, using ionization chambers. By 1938 he had collated the results and demonstrated that the rays are deflected into curved paths by the Earth's magnetic field, proving that at least some components of cosmic rays consist of charged particles. During World War II, Chicago University was the prime location of the Manhattan Project, the effort to produce the first atomic bomb, and in 1942 Compton became one of its leaders. He organized research into methods of isolating fissionable plutonium and worked with Italian physicist Enrico Fermi on producing a self-sustaining nuclear chain reaction.