Klein-Nishina formula

English[edit]

Named after Oskar Klein and Yoshio Nishina who derived the equation in 1928.

(particle physics) A formula for the differential cross section of photons scattered from a single free electron, calculated in the lowest order of quantum electrodynamics: ${\frac {d\sigma }{d\Omega }}={\frac {1}{2}}r_{e}^{2}\left({\frac {\lambda }{\lambda '}}\right)^{2}\left[{\frac {\lambda }{\lambda '}}+{\frac {\lambda '}{\lambda }}-\sin ^{2}(\theta )\right],$ where $r_{e}$ is the classical electron radius, $\lambda /\lambda '$ is the ratio of the wavelengths of the incident and scattered photons, and $\theta$ is the scattering angle (0 for an undeflected photon).