Compton Effect

The Compton effect is the name given to the increase in wavelength which occurs when photons with energies, of around 0.5MeV to 3.5MeV, interact with electrons in a material. Because the photons have such high energy, the interaction results in the electron being given enough energy to be completely ejected from its atom and a photon containing the remaining energy, being emitted in a different direction from the original, so that the overall momentum of the system is conserved. If the photon still has enough energy, the process may be repeated. Because of the overall reduction in energy of the photon, there is a corresponding reduction in its wavelength. Thus overall there is a slight 'reddening' and scattering of the photons as they pass through the material. This scattering is known as Compton Scattering. In a material where there are free electrons, this effect will occur at all photon energies and hence all wavelengths.

The effect is important in scientific terms because it demonstrates that light cannot be explained purely as a wave phenomenon. Light must behave as if it consists of particles in order to explain the Compton effect.