The Specific Probable Ionization of Electrons Observed with a Wilson Cloud Chamber

Abstract

The specific probable ionization of electrons has been measured for the energy range in which it is a rapidly varying function of velocity by counting the droplets along cloud-chamber tracks. The electron momenta have been determined by the use of a magnetic field perpendicular to the direction of photography, permitting counting along appreciable lengths of the helical tracks of slow electrons. The dependence of the measured specific ionization upon velocity agrees within the experimental uncertainty with that predicted by the Bethe-Bloch theory.