Matter Traversed by Low-Energy Cosmic-Ray Nuclei in Space

The amount of matter traversed in space by the primary cosmic-ray nuclei of energy 50-150, 200-500, 500-1000, and >1500 MeV/nucleon are obtained as 5.5±1.4, 9.1±0.9, 5.3±0.5, and 3.1±0.4 g ${\mathrm{cm}}^{-2\mathrm{}}$ of hydrogen, respectively, using recent measurements of spallation cross sections with proton beams from accelerators and $\frac{\mathrm{Li}}{M}$ ratios of cosmic-ray nuclei (where $M$ denotes nuclei with $6<~Z<~9$). These results and other evidence seem to suggest the hypothesis of two distinct sources (or propagation paths) of cosmicray nuclei, one responsible for nuclei of energy roughly 50-150 MeV/nucleon and the other of energies greater than this.