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Compton, Arthur Holly

photons rays quantum cosmic

(1892–1962) US physicist: discovered the Compton effect concerning the wavelength of scattered photons.

Compton was the son of a Presbyterian minister who was also a professor of philosophy, and inherited a deep religious faith from him. He obtained his doctorate at Princeton, and spent two years with Westinghouse Corporation. On travelling to Britain he spent a year doing research under at Cambridge before returning to America as head of the Physics Department at Washington University, St Louis, MO (1920). A professorship at Chicago followed in 1923. In 1945 he returned to Washington as chancellor.

In 1923 Compton observed that X-rays scattered by passing through paraffin wax had their wavelength increased by this scattering. Compton and explained this in detail, stating that photons (electromagnetic waves) behave as particles as well as waves; they lose energy E and momentum on making elastic collisions and as where c is the speed of light, their wavelength ? increases. Here h is constant. Compton found tracks in photographs taken in a Wilson cloud chamber, showing electrons recoiling from collisions with the invisible (because uncharged) photons of an X-ray beam. This work established belief that photons had energy and momentum, and also assertion (1925) that in quantum mechanics objects display both wave and particle properties. Compton and received the 1927 Nobel Prize for physics for their work, which is now part of the foundation of the new quantum theory (as opposed to old quantum theory).

Compton developed an ionization chamber for detecting cosmic rays and in the 1930s used a worldwide survey to demonstrate that cosmic rays are deflected by the Earth’s magnetic field and some are therefore charged particles (and not radiation). Variation of ray intensity with time of day, year and the Sun’s rotation also indicated that the cosmic rays probably originate outside our Galaxy (1938).

In 1941 Compton was asked to take part in feasibility studies and the development of plutonium production for the atomic bomb. His religious faith made him question what was happening, but he felt that only such a weapon would quickly end the massive slaughter of the war. He became director of a major part of the Manhattan Project at Chicago and built the first reactor with (1942), publishing an account in his book Atomic Quest (1958).

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