Cosmic-ray propagation in the Galaxy and in the heliosphere - The path-length distribution at low energy

• Published in: The Astrophysical journal. Supplement series 1987-05, Vol.64 (1), p.269-304
• Main Authors: Garcia-Munoz, M., Simpson, J. A., Guzik, T. G., Wefel, J. P., Margolis, S. H.
• Format: Article
• Language: English
• Subjects: Astronomy; Cosmic rays; Earth, ocean, space; Exact sciences and technology; Solar system; Space Radiation
• ISSN: 0067-0049; 1538-4365
• DOI: 10.1086/191197

The energy dependence of the path-length distribution of cosmic rays at low energies, below relativistic velocities, is studied, and its implications for models of cosmic-ray confinement and propagation in the Galaxy and Galactic halo, including the effects of a possible Galactic wind, are studied. It is found that the mean free path in Galactic propagation must be fully energy-dependent, with the mean of an exponential path-length distribution increasing with increasing energy below 1 GeV per nucleon and decreasing with increasing energy above 1 GeV per nucleon. This indicates that, at low energies, diffusion is not the controlling process. The path-length distribution is not purely exponential but is depleted in short path lengths at low energies. This depletion is energy-dependent, being largest at low energies and decreasing with increasing energy.