Cloud Chamber Photographs of Counter Selected Cosmic-Ray Showers

Abstract

A detailed discussion is given of the appearance of cosmic-ray showers from a lead plate 1.3 cm thick in a large cloud chamber controlled by three G---M counters, one above and two below the chamber. Showers of photons were responsible for about half the triple coincident counts, but sprays of electrons from the lead accounted for the tripping of the lower counters in most of the other cases. Three-quarters of the single-centered electron shower sprays were due to electrons which traversed the upper counter and struck the lead from above. The remainder were due to nonionizing rays, presumably photons. Twenty-three photographs out of a total of a hundred seventy-four showed complex phenomena. The distributions of the showers according to size and the shower electrons according to angular spread are given.