Isotopic Composition of Cosmic Rays: Results from the Cosmic Ray Isotope Spectrometer on the ACE Spacecraft

The Cosmic Ray Isotope Spectrometer on the ACE spacecraft measures the isotopic composition of cosmic-ray elements from Li through Zn with an unprecedented combination of excellent mass resolution and high statistics. The results indicate a cosmic-ray source whose composition is remarkably similar to that of the solar system, but which is enriched in material that may have originated in Wolf-Rayet stars. The lack of 59Ni is strong indication that the cosmic rays are accelerated at least 105 years after nucleosynthesis. We examine these results in the context of the superbubble model of cosmic-ray origin that has been described by Higdon and Lingenfelter.