The Average ‘Forward’ Momentum of Photoelectrons

Abstract

IT is well known that the emission of photoelectrons by X-rays is not symmetrically distributed about the plane normal to the rays, the photoelectrons possessing an average momentum in the ‘forward’ direction. I showed about a year ago (NATURE, Jan. 28, 1928, p. 134) that, contrary to general supposition, the average forward momentum, µ, of a photoelectron is, according to experiment, not equal to the momentum hv/c of an incident quantum, but is appreciably greater. Sommerfeld in his recently published book, “Atombau und Spektrallinien, Wellenmechanischer Ergänzungsband” (1929), has treated the problem theoretically by the wave mechanics, and the purpose of the present note is to show the remarkable agreement of Sommerfeld's result with experiment.