Compton scattering

Compton scattering is an inelastic collision in which a photon transfers energy and momentum to a charged particle, usually an electron, changing the photon’s wavelength and direction.

Compton wavelength shift: The increase in a scattered photon’s wavelength determined by its scattering angle and the electron’s Compton wavelength. It is the characteristic measurable change produced by the collision.
Arthur Compton: American physicist who discovered the wavelength shift of X-rays scattered by electrons. His experiments and interpretation gave the effect its name.
Compton camera: A gamma-ray imaging instrument that reconstructs photon directions from measured Compton interactions. It uses the scatter angle and energy deposit to locate incoming gamma rays.
Rayleigh scattering: Elastic scattering of light by particles much smaller than its wavelength. It changes photon direction without the Compton energy transfer.
Klein–Nishina formula: A relativistic formula for the differential cross section of photon scattering by free electrons. It predicts how scattering probability varies with photon energy and angle.
Compton's 1923 experiment: Arthur Compton’s measurement of the wavelength distribution of X-rays scattered by graphite. It directly revealed the angle-dependent shift predicted for photon collisions.
Compton telescope: A gamma-ray telescope that infers source directions from photons scattered inside its detector. Its event reconstruction relies on Compton kinematics.
Photoelectric effect: The emission or excitation of a bound electron after it absorbs a photon. It absorbs the photon rather than scattering it with reduced energy.
Four-momentum: A relativistic vector combining an object's energy and three-momentum. Conservation of four-momentum yields the photon’s wavelength shift.
X-ray diffraction: The scattering of X-rays by the regularly spaced atoms in a material, producing interference patterns. Compton distinguished the shifted radiation from diffraction by the graphite crystal.

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