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Published October 2001 | public
Journal Article

The Origin of Primary Cosmic Rays: Constraints from ACE Elemental and Isotopic Composition Observations


Cosmic-ray isotope observations from NASA's Advanced Composition Explorer (ACE) mission have been used to investigate the composition of cosmic-ray source material. Source abundances relative to ^(56)Fe are reported for eleven isotopes of Ca, Fe, Co, and Ni, including the very rare isotopes ^(48)Ca and ^(64)Ni. Although the source abundances range over a factor ∼10^4, most of the ratios to ^(56)Fe are consistent with solar-system values to within ∼20%. However, there are some notable differences, the most significant being an excess of ∼(70±30)% relative to the solar system for the cosmic-ray source ratio ^(58)Fe/^(56)Fe. The possible association of such an excess with a contribution to the cosmic-ray source from Wolf–Rayet star ejecta is discussed.

Additional Information

© 2001 Kluwer Academic Publishers. Received 29 September 2000; Accepted in final form: 15 January 2001. We are grateful to the large group of dedicated individuals that participated in the development of the CRIS instrument (listed in Stone et al., 1998). We also thank J. Klarmann for contributions to the CRIS data analysis. 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.

Additional details

August 19, 2023
October 17, 2023