XV. Nuclear transmutations produced by cosmic-ray particles of great energy

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Abstract
A new method of measuring the scattering of charged particles in their passage through, photographic emulsions has been developed. It has been employed to determine the mass of charged particles emerging from nuclear “explosions” produced by cosmic radiation. Of the mesons among the “shower” particles, produced in these explosions with momentum less than about 180 MeV./c, it is shown that at least 90 per cent are π-particles; and that less than 5 per cent, and possibly none, are μ-particles, electrons or other particles of small mass. If mesons of greater mass are sometimes created in nuclear interactions with an energy less than 300 MeV., they must be produced with a frequency less than 1 per cent of the protons and less than 5 per cent of the μ-particles. The observations therefore prove that the great majority of the charged particles created in nuclear interactions are π-particles. The greatly increased rate of measurement with the new method and the fact that it allows the determination of the scattering of particles of much greater energy than has been possible hitherto will enable a detailed study of the nuclear transmutations produced by protons and α-particles with energies in the interval from 109 to 1010 eV. to be made.