Isotopic Anomalies in the Galactic Cosmic-Ray Source

High-resolution (σM<0.25 amu) observations have been made of the isotopic composition of oxygen, neon, and magnesium in the galactic cosmic rays ({~} 100-300 MeV/amu). Derived source abundances shown enhancements of ²²Ne/²⁰Ne, ²⁵Mg/²⁴Mg, and ²⁶Mg/²⁴Mg over solar-system values by factors of 4.1_-0.2+0.3, 1.6_-0.2+0.3 and 1.6_-0.2+0.3, respectively. These data demonstrate that the cosmic-ray source is compositionally distinct from the solar system and constrain nucleosynthesis models, several of which are considered.