Isotopic anomalies in the galactic cosmic-ray source

High-resolution (${\ensuremath{\sigma}}_{M}l0.25$ amu) observations have been made of the isotopic composition of oxygen, neon, and magnesium in the galactic cosmic rays (\ensuremath{\sim} 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 ${4.1}_{\ensuremath{-}0.2}^{+0.3}$, ${1.6}_{\ensuremath{-}0.2}^{+0.3}$ and ${1.6}_{\ensuremath{-}0.2}^{+0.3}$, 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.