Klein-Nishina formula

Etymology
Named after and  who derived the equation in 1928.

Proper noun

 * 1)  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).