The diffusion model of cosmic-ray propagation

Abstract

We set up diffusion equations for the nuclear component of cosmic rays and solve these to find the ratio of light to medium nuclei in the cosmic rays as well as the gamma-ray distribution in our Galaxy. From a comparison of our calculated quantities with observational data we determine the values of various parameters appearing in the model. We find that best agreement between theory and observations is obtained if the cosmic-ray confinement region consists of a narrow disk of total height 160 pc and radius 16 kpc, where the cosmic-ray sources are located, and an extensive halo of height 20 kpc. The diffusion coefficient near the Sun must be between 1026 and 1027 cm2 s−1 while it equals 1028 to 1029 cm2 s−1 in the halo. Finally, we find that the diffusion coefficient in the Galaxy must depend on the gas density as a power law with an index of the order of −1.