Implications of the Galactic Cosmic Ray Neon Isotopic Abundances Measured by the Cosmic Ray Isotope Spectrometer (CRIS) on ACE.
W.R. Binns1, M.E. Wiedenbeck3, E.R. Christian4, A.C. Cummings2, J.S. George2, P.L. Hink1, J. Klarmann1, R.A. Leske2, M. Lijowski1, S.M. Niebur1, R. A. Mewaldt2, E.C. Stone2, T.T. von Rosenvinge4, and N.E. Yanasak3
1. Washington University, St. Louis, MO 63130 USA
2. California Institute of Technology, Pasadena, CA 91125 USA
3. Jet Propulsion Laboratory, Pasadena, CA 91109
4. NASA/Goddard Space Flight Center, Greenbelt, MD 20771 USA
We have obtained new measurements of the Neon isotopic abundances in the galactic cosmic rays (GCR) with the Cosmic Ray Isotope Spectrometer (CRIS) on ACE for the energy range ~80-260 MeV/nuc. These abundance measurements as a function of energy, and the source abundances obtained from them using a leaky box propagation model will be presented. Recent GCR measurements of the 59Ni and 59Co abundances, combined with measurements of the chemical fractionation pattern of elements, suggest the acceleration of cosmic rays out of interstellar matter (dust and gas). Isotopic composition has been well determined in the very local interstellar medium (VLISM) for Neon by the ACE-SIS experiment from analysis of the anomalous cosmic rays (ACR). It is of interest to examine to what extent the GCRs and ACRs are accelerated from the same seed population. The 22Ne/20Ne ratio for these two samples of galactic matter are in disagreement, indicating that either the GCR 22Ne may be coming from a different source than the bulk of GCRs (e.g WR stars as has been previously proposed) or that there is a distinct difference between the composition of the VLISM sampled by the ACR and the much larger interstellar volume from which GCRs are accelerated. Other samples of interstellar matter for which detailed isotopic abundance measurements have been made are interstellar grains included in primitive meteorites. We will compare the ACE Ne results with those grain abundances.