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A Re-Examination of the Cosmic Ray Helium Spectrum and the ^3He/^4He Ratio at High Energies

Webber, W. R. and Golden, R. L. and Mewaldt, R. A. (1987) A Re-Examination of the Cosmic Ray Helium Spectrum and the ^3He/^4He Ratio at High Energies. Astrophysical Journal, 312 . pp. 178-182. ISSN 0004-637X. doi:10.1086/164858.

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We have reexamined the implications of a recent measurement of cosmic-ray ^3He at ~6 GeV per nucleon which reported an unexpected high abundance of this rare isotope. The implied ^3He/^4He ratio from this high-energy measurement depends critically on the assumed rigidity spectrum of helium nuclei between ~10 and 20 GV. A careful analysis of published measurements of the helium spectrum, along with new data obtained using a magnetic spectrometer, show that the appropriate spectral index (γ) to be used to interpret this measurement has a value of less than 2.55, for a differential rigidity spectrum dJ/dR α R^(-γ). Since this index is lower than originally used, the ^3He/^4He ratio of less than 0.17 that we derive (evaluated at constant energy per nucleon), is significantly lower than the original quoted value of 0.24 ± 0.05. The cosmic-ray escape pathlength in g cm^(-2) of interstellar material deduced from this revised ratio and from the ^3He/^4He measurements at low energies is now found to be consistent with that deduced from studies of heavier nuclei. The body of ^3He/^4He measurements now available thus severely restricts the types of models that might be invoked to explain the high intensity of cosmic-ray antiprotons that has been reported.

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Mewaldt, R. A.0000-0003-2178-9111
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Additional Information:© 1987. The American Astronomical Society. Received 1986 March 18; accepted 1986 June 10. This work was supported by the National Aeronautics and Space Administration under grant NGR 30-002-052 at the University of New Hampshire, NAGW-110 at New Mexico State University, and grants NGR 05-002-160, NAG-722, and NAG5-727 at Caltech.
Group:Space Radiation Laboratory
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NASANGR 30-002-052
NASANGR 05-002-160
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Space Radiation Laboratory1986-04
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ID Code:45319
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Deposited On:29 Apr 2014 23:15
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