The isotopic composition of the elements carbon, oxygen, neon, magnesium and silicon in the galactic cosmic rays

High resolution observations of the isotopic composition of C, O, Ne, Mg, and Si in the galactic cosmic rays (GCR) are used to derive the isotopic compositions of these elements in the GCR source. It is found that the source is enhanced in the neutron-rich isotopes of Ne, Mg, and Si (relative to solar system composition). The significance and possible interpretations of these enhancements are discussed.