On the Nature of Cosmic-Ray Particles

Abstract

Various authors1 have taken the view that cosmic-ray particles consist of two or more kinds of corpuscles. According to Compton and Bethe, and Auger1, the soft component near sea level is thus composed of electrons and the penetrating one of protons. Assuming the theory of showers by Bhabha and Heitler2 and by Oppenheimer and Carlson3 to be correct, we ought to be able to distinguish cosmic-ray electrons from protons, if they exist at all, by observing whether or not the particles suffer a large loss of energy and often produce showers on colliding with a lead plate of a suitable thickness. We carried out such experiments with a lead bar 1.5 cm thick mounted in the middle of a Wilson chamber 40 cm in diameter, which is placed in a magnetic field of about 17,000 oersteds. The operation of the chamber is actuated by the coincidence of two Geiger-Muller tube counters mounted above the chamber, the distance between the counters being about 50 cm. The results showed that at sea level near Tokyo (geomag. lat. 25.4◦N) about 10 to 20 percent of cosmic-ray particles of energies, high enough to produce coincidence in the strong magnetic field and pass through the Wilson chamber, consist of electrons and positrons, the rest being heavy particles, since they do not produce showers nor suffer much loss of energy in passing through the lead bar. Among the latter, however, we were eurprised to find that there are some particles of both signs, which have much greater penetrating power for lead than protons of the same momentum (Hρ) would have. The specific