Who's Behind This?

  On December 12, 2005, APS President-elect John Hopfield presented a plaque in honor of Arthur H. Compton at Washington University in St. Louis. Compton was a professor at Washington University, studying the scattering of X-rays when he discovered the effect that is named after him in 1922.

A graduate of the University of Wooster and Princeton University, Compton developed a theory of the intensity of X-ray reflection from crystals as a means of studying the arrangement of electrons and atoms. In 1918 he started a study of X-ray scattering.

In 1919 Compton was awarded one of the first National Research Council fellowships. He took his fellowship to the Cavendish Laboratory in Cambridge, England, and then to Washington University, St. Louis when the equipment in England turned out to be inadequate for his needs. Working with X-rays, he perfected his apparatus to measure the shift of wavelength with a scattering angle that is now known as the Compton effect.

Compton observed the scattering of X-rays from electrons in a carbon target and found that the scattered X-rays had a longer wavelength than those incidents upon the target. The shift of the wavelength increased with the scattering angle. Compton explained and modeled the data by assuming a particle (photon) nature for light and applying conservation of energy and conservation of momentum to the collision between the photon and the electron. The scattered photon has lower energy and therefore a longer wavelength according to the relationship between energy and wavelength discovered in 1900 by German physicist Max Planck.

Compton submitted his theory of the scattering of X-rays by electrons to the Physical Review in December 1922, and the paper was published in May 1923. In the paper, he compares the predictions of his theory with as-yet-unpublished experimental data, and concludes “This remarkable agreement between our formulas and the experiments can leave but little doubt that the scattering of X-rays is a quantum phenomenon.” The analysis of the Compton effect presented in his paper requires special relativity and quantum mechanics, both used in ways that were novel at the time. 

The explanation and measurement of the Compton effect earned Compton a share of the Nobel Prize in physics in 1927.