The Increase of Ionization with Momentum for Energetic Cosmic-Ray Particles

An experiment is described in which the momentum and specific ionization of cosmic-ray mesons were simultaneously measured, the momentum by means of a cloud chamber in a magnetic field, and the specific ionization by rectangular proportional counters. The difficulties inherent in the use of proportional counters for such measurements are discussed The experimental results are in satisfactory agreement with theoretical predictions of an increase of specific ionization for very energetic μ-mesons.