Composition of Cosmic Rays. III. Nature of cosmic-ray particles

Abstract

The first section of this report contains a brief summary of those experiments which have made substantial contributions to our knowledge of the nature and mode of absorption of cosmic-ray particles. Included is a discussion of the difficulties which inhere in the attempts to interpret the observed cosmic-ray phenomena in terms of the assumption that the cosmic-ray particles are practically all protons and positive and negative electrons. These difficulties are resolved by demonstrating that in the same momentum range there exist two types of particles, one of which is highly absorbed in a heavy material, mostly through radiation, while the other is relatively penetrating. Behavior of the first kind is typical of shower particles in general, and of all single negatron secondaries, which are presumably produced in elastic collisions with atomic electrons. This group is therefore to be identified with electrons. As it can be shown that particles of the penetrating group cannot be of protonic mass, it follows that they must be neither electrons nor protons. The simplest assumption is that their distinguishing property is a mass intermediate between the electron and proton. Confirmation of this view is found in the observation by other writers and by ourselves of particles whose range, ionization and curvature relations are such that they demand a mass in this region. The best range and ionization data seem to give mass determinations in the neighborhood of 200 electron masses. A discussion is given of certain difficulties which exist in the interpretation of cosmic-ray particles as electrons and mesotrons of a unique mass.

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