Cosmic-ray sources and source composition

Present data on cosmic-ray elemental and isotopic relative abundances are s hown to be unable to distinguish between various models of cosmic-ray sourc es and their composition. For example, the model of freshly nucleosynthesiz ed material from supernova explosions as the cosmic-ray source is unable to account for some measured, key cosmic-ray elemental abundances. This and t wo other models are evaluated here in light of recent isotopic and elementa l measurements. It is shown that model-dependent preferential injection, ac celeration, and reacceleration do not allow a clear distinction of one mode l against the others. Future measurements of critical elements and isotopes are suggested, which should afford us the ability to do that. We base our suggestions on measurements and a quantitative comparison between the predi ctions of the standard leaky-box model for the Galactic propagation of cosm ic rays and one in which reacceleration is taken into account.