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Published September 20, 1999 | Published
Journal Article Open

Constraints on the Time Delay between Nucleosynthesis and Cosmic-Ray Acceleration from Observations of ^(59)Ni and ^(59)Co


Measurements of the abundances of cosmic-ray ^(59)Ni and ^(59)Co are reported from the Cosmic-Ray Isotope Spectrometer (CRIS) on the Advanced Composition Explorer. These nuclides form a parent-daughter pair in a radioactive decay which can occur only by electron capture. This decay cannot occur once the nuclei are accelerated to high energies and stripped of their electrons. The CRIS data indicate that the decay of ^(59)Ni to ^(59)Co has occurred, leading to the conclusion that a time longer than the 7.6 × 10^4 yr half-life of ^(59)Ni elapsed before the particles were accelerated. Such long delays indicate the acceleration of old, stellar or interstellar material rather than fresh supernova ejecta. For cosmic-ray source material to have the composition of supernova ejecta would require that these ejecta not undergo significant mixing with normal interstellar gas before ~10^5 yr has elapsed.

Additional Information

© 1999 American Astronomical Society. Received 1999 February 26; accepted 1999 July 15; published 1999 August 18. We are grateful to the large group of dedicated individuals that contributed to the development of the CRIS instrument (listed in Stone et al. 1998). We thank W. R. Webber for providing new cross section estimates prior to publication. 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 and by the McDonnell Center for the Space Sciences at Washington University.

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