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Session 72 - Cosmic Rays and Abundances.
Oral session, Thursday, June 11

[72.02] Cosmic-Ray Isotopes in the Iron--Nickel Group

M. E. Wiedenbeck, B. L. Dougherty, N. E. Yanasak (JPL), A. C. Cummings, R. A. Leske, R. A. Mewaldt, E. C. Stone, M. R. Thayer (Caltech), E. R. Christian, T. T. von Rosenvinge (NASA/GSFC), W. R. Binns, P. L. Hink, J. Klarmann, M. Lijowski (Washington U.)

New, isotopically-resolved, statistically-accurate measurements of the abundances of galactic cosmic rays in the iron-nickel peak have been made with the Cosmic Ray Isotope Spectrometer (CRIS) on the Advanced Composition Explorer (ACE). Nuclides in this group can be used to address a number of important problems in cosmic-ray astrophysics. Stable primary species such as ^54,56,58Fe and ^58,60,62Ni carry information about the nucleosynthetic processes which formed the material. Species with large secondary components such as ^53,55Mn can be used to determine the amount of matter that iron-group cosmic rays traverse in the Galaxy and to derive accurate corrections for the secondary contributions to the observed abundances of predominantly-primary nuclides. Radioactive primaries which can decay only by electron capture such as ^59Ni and ^57Co can be used to constrain the time delay between nucleosynthesis and particle acceleration, as can the daughters produced by those decays (^59Co and ^57Fe). The radioactive secondary nuclide ^54Mn, which beta-decays with a halflife estimated to be \sim0.8 Myr at cosmic ray energies, is useful for the study of the confinement time of iron-group cosmic rays in the Galaxy. We will present CRIS measurements of iron-group isotopic abundances, compare them with previous observations, and discuss their implications for the origin and transport of galactic cosmic rays.

This research was supported by the National Aeronautics and Space Administration at the California Institute of Technology (under grant NAG5-6912), the Jet Propulsion Laboratory, the Goddard Space Flight Center, and Washington University.

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