Electron Scattering in Helium

Abstract

An electron scattering apparatus has been used to investigate the scattering of 100 volt incident electrons in helium gas. The angular distribution curves for total scattering and for elastic scattering are compared with the theory as given by Morse and by Mott and Massey and are found to give greater relative scattering at angles near both 0° and 180° than is predicted by the theory. In absolute magnitude the experimental curves generally fall somewhat below the theoretical curves. The angular distributions of electrons scattered with various energy losses equal to or greater than the ionization loss were determined. The curves show that in general, the greater the energy loss the more uniform is the distribution in angle of the scattered electrons. There is a pronounced preference for forward scattering when the energy loss over that required for ionization is small. Integration over the entire solid angle gives the probability for scattering with different energy losses. Curves so obtained for this probability as a function of the energy loss are in qualitative agreement with Wetzel's theoretical calculations except for electrons which have lost nearly all their energy or just slightly more than the ionization energy.