PROPAGATION OF COSMIC-RAY NUCLEI IN A DIFFUSING GALAXY WITH CONVECTIVE HALO AND THIN MATTER DISK

We have utilized a diffusion model for cosmic-ray propagation in the galaxy that includes the effects of convection in the halo. This model has several novel features. The matter is assumed to be distributed within an infinitely thin disk within which the sources are also found. Calculations are made for 13 primary and secondary nuclei with rigidities between 1 and 10(3)GV. These calculations are made using interaction loss rates, secondary production rates, and radioactive decay, based on recent new cross section measurements. We find that in order to fit the rather weak radial dependence of cosmic-ray protons derived from gamma-ray data, the radial profile of the cosmic-ray sources must also have a weak radial dependence. Large halos that could redistribute the cosmic rays into flatter radial profiles are ruled out from a study of cosmic-ray primary to primary, secondary to primary, and radioactive decay isotope abundance ratios. The most sensitive of these ratios using current data are the secondary to primary ratios, B/C and Z = 21-23/Fe. These ratios set limits on the halo thickness of less than 4 kpc and a galactic wind convection velocity less than 20 km s-1 within this distance from the plane. These limits are interrelated, however, so that as L --> 4 kpc, V(c) --> 0. The data on radioactive secondaries set similar limits although because of the accuracy of the data and the lack of high-energy measurements these limits are not as stringent as they could be. These results suggest that convection perpendicular to the disk of our galaxy may not be important even at rigidities less than a few GV. These limits on halo thicknesses are consistent with what can be determined for the distribution of cosmic-ray electrons in the halo based on the distribution of radio synchrotron emission in our galaxy and other galaxies.