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Published May 1, 1976 | Published
Journal Article Open

Isotopic and elemental composition of the anomalous low-energy cosmic-ray fluxes


Recent observations of cosmic rays below ~30 MeV nucleon^(-1) have revealed anomalous enhancements in the energy spectra of oxygen, nitrogen, and helium relative to those of other nuclei such as boron and carbon. We have measured the quiet-time fluxes of the elements hydrogen through oxygen in the ~4-30 MeV nucleon^(-1) energy interval during the period 1972 October through 1974 October. We find that the low-energy fluxes of Li, Be, B, and Care consistent with those expected from adiabatic deceleration and show no significant evidence for secondary fragmentation products arising from the enhanced nitrogen and oxygen fluxes. In the ~6-12 MeV nucleon^(-1) interval, the observed nitrogen and oxygen nuclei are predominantly ^(14)N and ^(16)O, with upper limits (84% confidence level) of ^(15)N/N ≤ 0.26, ^(17)O/O ≤ 0.13, and ^(18)O/O ≤ 0.12 for the other stable nitrogen and oxygen isotopes. These isotopic measurements are consistent with the presumed isotopic composition of the neutral interstellar medium, as would be the case if the anomalous component is locally accelerated. If, on the other hand, the enhanced low-energy cosmic rays result from unusual nucleosynthesis processes which enhance nitrogen and oxygen but not carbon, then these processes are constrained to producing predominantly ^(14)N and ^(16)O.

Additional Information

© 1976 American Astronomical Society. Received 1975 August 20. Mr. W. E. Althouse, Dr. G. J. Hurford, and Dr. J. E. Lupton made significant contributions to the design and development of the Electron/Isotope Spectrometer. In addition, Dr. Hurford was responsible for many of the data analysis programs. This work was supported in part by the National Aeronautics and Space Administration under contract NAS5-11066 and grant NGR 05-002-160.

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Published - 1976ApJ___205__931M.pdf


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