Isotopic Anomalies in the Galactic Cosmic-Ray Source

High-resolution (${\sigma }_M<0.25\mathrm{}$ 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 ${}_{}{}^{22}{}_{}{}^{}\mathrm{Ne}$/${}_{}{}^{20}{}_{}{}^{}\mathrm{Ne}$, ${}_{}{}^{25}{}_{}{}^{}\mathrm{Mg}$/${}_{}{}^{24}{}_{}{}^{}\mathrm{Mg}$, and ${}_{}{}^{26}{}_{}{}^{}\mathrm{Mg}$/${}_{}{}^{24}{}_{}{}^{}\mathrm{Mg}$ over solar-system values by factors of ${4.1}_{-0.2\mathrm{}}^{+0.3\mathrm{}}$, ${1.6}_{-0.2\mathrm{}}^{+0.3\mathrm{}}$ and ${1.6}_{-0.2\mathrm{}}^{+0.3\mathrm{}}$, 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.