The isotopic composition of galactic cosmic-ray iron nuclei

Creators: Mewaldt, R. A.; Spalding, J. D.; Stone, E. C.; Vogt, R. E.

Abstract

We report high-resolution observations made in interplanetary space of 83-284 MeV per nucleon galactic cosmic-ray iron isotopes and directly establish that ^(56)Fe is the dominant cosmic-ray Fe isotope. We find the following percentage abundances for Fe at the cosmic-ray source: ^(54)Fe = 9(+8, -5)%, ^(55)Fe ≤ 7%, ^(56)Fe = 91(+5, -11)%, ^(57)Fe ≤ 8%, and ^(58)Fe ≤ 6%. When compared to calculated nucleosynthesis yields and other observations, these results place significant constraints on the neutron excess of the environment where cosmic-ray Fe originates.

Additional Information

© 1980 American Astronomical Society. Received 1979 October 9; accepted 1979 November 28. W. E. Althouse, A. C. Cummings, and T. L. Garrard made significant contributions to the design and development of HIST. We are grateful to the Heckman/Greiner group, including Hank Crawford, and the Bevalac staff at Lawrence Berkeley Laboratory for making the heavy-ion calibrations possible. This work was supported in part by NASA under contract NASS-20721 and grant NGR 05-002-160.

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