On the Creation of Pairs or Positrons by Fast Electrons

Abstract

By means of the cloud chamber a search was made for the creation of pairs or positrons by electrons of energies between one and 12 Mev, in air, mica, lead and platinum. A total of 2588 traversals of electrons through solid materials, and a total track length of 628 meters in air were examined. The abnormally large cross section for the process, as reported in numerous papers by other workers, was not confirmed. The data found point toward agreement with the theoretical calculations. A test for an anomaly at the threshold (one Mev) was not attempted, because of the difficulty of making a decisive experiment in a cloud chamber under conditions in which the pairs formed would have very small energy. A resumé of the literature on the subject of pair and positron formation by electrons, and a rather full discussion of the possibilities for error in the experimental method are given.