A gamma ray interaction in which the gamma ray collides with an electron, transferring part of its energy to the electron, while itself being scattered at a reduced energy. Compton scattering occurs w [..]

If a photon encounters a charged particle it may transfer some of its momentum to the electron and is then scattered away with reduced energy, i.e. a longer wavelength. The inverse process may happen if a photon encounters a very fast electron. It may then gain energy and can be boosted to shorter wavelengths.

(physics) The increase in the wavelength, and corresponding decrease in the energy, of photons (especially of X-rays and gamma rays) when scattered by interaction with matter