High Altitude Cosmic Radiation

Abstract

VERY great advances have been made during the last year in the understanding of the complicated phenomena of cosmic radiation. One of the most important steps has been the experimental verification of the validity of the predictions of the quantum theory of radiation up to very high energies. The application by Heitler of the quantum theory to the collisions of energetic electrons with atoms, and also the semi-classical treatment of the same problem by Williams and by Weizsacker, show that energetic electrons are rapidly absorbed in matter by the emission of energetic photons, and further that the photons are equally rapidly absorbed by the production of pairs of positive and negative electrons. The combination of these two processes leads to the cascade theory of showers, which was developed independently by Bhabha and Heitler, and by Carlson and Oppenheimer. When an energetic electron traverses an absorber, it gives rise, by successive acts of photon emission and pair production to a large number, and for very energetic electrons, to a very large number of positive and negative electrons and photons. Eventually the loss of energy by ionization brings this process to an end, leading after the first building up of a shower to its eventual absorption.