The Compton effect

The challenge of showing that the photon has momentum was answered in 1923, when Arthur H. Compton (1892-1962) made a discovery which was to earn him the Nobel Prize in 1927. He set out to demonstrate that a photon behaves exactly like a particle when it makes a collision with an electron, and both energy and momentum are conserved in the process.

In order to penetrate a carbon target, and interact with atoms and their orbital electrons, Compton needed more energetic photons than those of visible light. Accordingly he bombarded graphite with X-rays of sharply defined wavelength X. Some X-rays could be expected to scatter from electrons in orbit around the carbon atoms, and others from the much heavier carbon nucleus.

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