On Electron Scattering in Helium

Abstract

Velocity and angular distribution of electrons scattered by single collisions in helium.—An apparatus is described in which both the velocity and the angular distribution of electrons which have suffered single collisions in a gas are examined. It is found in helium that, for initial velocities of 100 volts and over, the principal energy loss is due to the excitation of the $2{}_{}{}^1{}_{}{}^{}S$ state, corresponding to 20.5 volts. No loss corresponding to 19.7 volts is found for these velocities. For still higher velocities it seems probable that the energy interchange ceases to be quantized, and that the atom is capable of absorbing temporarily more energy than is required for excitation. The angular distribution of electrons which have lost 20.5 volts energy in colliding shows very marked maxima, the predominant one being in the forward direction. The bearing of the Schrödinger wave mechanics on this point is discussed.