Propagation of Cosmic‐Ray Nucleons in the Galaxy

We describe a method for the numerical computation of the propagation ofprimary and secondary nucleons, primary electrons, and secondary positrons andelectrons. Fragmentation and energy losses are computed using realisticdistributions for the interstellar gas and radiation fields, and diffusivereacceleration is also incorporated. The models are adjusted to agree with theobserved cosmic-ray B/C and 10Be/9Be ratios. Models with diffusion andconvection do not account well for the observed energy dependence of B/C, whilemodels with reacceleration reproduce this easily. The height of the halopropagation region is determined, using recent 10Be/9Be measurements, as >4 kpcfor diffusion/convection models and 4-12 kpc for reacceleration models. Forconvection models we set an upper limit on the velocity gradient of dV/dz < 7km/s/kpc. The radial distribution of cosmic-ray sources required is broaderthan current estimates of the SNR distribution for all halo sizes. Full detailsof the numerical method used to solve the cosmic-ray propagation equation aregiven.