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[28.03] Observational Constraints on Models of Cosmic Ray Origin: ACE-CRIS measurements of the Time Delay between Nucleosynthesis and Cosmic-Ray Acceleration

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

Isotopic abundance measurements of galactic cosmic-ray Ni-59 and Co-59 will be reported from the Cosmic Ray Isotope Spectrometer (CRIS) on the NASA Advanced Composition Explorer (ACE). These nuclides form a parent-daughter pair in a radioactive decay which can occur only by electron capture, and is no longer possible once the nuclei are accelerated to high energies and stripped of their electrons. The CRIS results show that, within the accuracy of the measurements, the decay of Ni-59 to Co-59 has gone to completion. This leads to the conclusion that a time longer than the 7.5 x 10⁴ yr halflife of Ni-59 has elapsed between nucleosynthesis and acceleration to cosmic ray energies. Such long delays rule out models of cosmic ray origin which assume prompt acceleration to cosmic ray energies of freshly synthesized individual nuclei. It suggests the acceleration of old, stellar or interstellar material, but is not inconsistent with a recent model of acceleration of cosmic rays in superbubbles (Higdon et al.).

Supported by NASA at Caltech (Grant NAG5-6912), JPL, GSFC, and Washington U.

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