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Published June 1, 1992 | Published
Journal Article Open

The Isotopic Composition of Cosmic Ray B, C, N, and O: Evidence for an Overabundance ^(18)O


New observations of galactic cosmic rays at higher energies (about 400-780 MeV nucleon^(-1)) than obtained in previous direct mass measurements have resulted in determinations of the isotopic composition of B, C, N, and O. The derived cosmic-ray source abundances provide evidence for an enhancement of ^(18)O/^(16)O by a factor of 5.6 ± 1.9 over the solar system value and give a ^(13)C/^(12)C ratio consistent with the solar system abundance ratio, but lower than some recent measurements of the local interstellar medium.

Additional Information

Copyright 1992, American Astronomical Society. Received 1992 January 13; accepted 1992 March 12. This work was supported in part by NASA under grant NAGW-1919. We thank A. Buffington, D. Burke, E. Christian, J. Grove, I. Rasmussen, J. Weger, and the Caltech Central Engineering Services for their contributions to HEIST and the National Scientific Balloon Facility and NASA Wallops Flight Facility for their excellent support.

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