How the Klein-Nishina formula was derived: Based on the Sangokan Nishina source materials

Abstract

In 1928, Klein and Nishina investigated Compton scattering based on the Dirac equation just proposed in the same year, and derived the Klein-Nishina formula for the scattering cross section of a photon. At that time the Dirac equation had the following unsettled conceptual questions: the negative energy states, its four-component wave functions, and the spin states of an electron. Hence, during their investigation struggles, they encountered various difficulties. In this article, we describe their struggles to derive the formula using the "Sangokan Nishina Source Materials" retained in the the Nishina Memorial Foundation.