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 ^(59)Ni is strong indication that the cosmic rays are accelerated at least 10^5 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.