A. J. Davis, R. A. Mewaldt and M. E. Wiedenbeck Caltech, Pasadena, CA 91125 USA
Galactic cosmic ray secondary/primary ratios such as B/C and (Sc+Ti+V)/Fe are commonly used to determine the mean free path for cosmic ray escape from the Galaxy (Lesc). These secondary/primary ratios are observed to be energy (or rigidity) dependent, with a relative maximum at ~1 GeV/nucleon. The decrease in Lesc at energies >1 GeV/nucleon is commonly taken to indicate that high-energy cosmic rays escape more easily from the Galaxy. The interpretation of the observed decrease in Lesc at energies <1 GeV/nucleon is much more controversial. The suggested possibilities include the effects of a galactic wind, or the effects of distributed acceleration (sometimes called re-acceleration) of cosmic rays during passage through the interstellar medium.
We suggest a new interpretation for the low-energy decrease in cosmic ray secondary/primary ratios - the presence of a second, low-energy component of cosmic rays that has passed through very little matter. We present the results of our attempt to fit the observed cosmic ray composition with this model, and discuss other possible observable consequences. This work was supported by NASA under grant NAG5-6912.