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Published 1973 | Published
Book Section - Chapter Open

The Elemental Abundance Ratios of Interstellar Secondary and Primary Cosmic Rays


The rigidity dependence of the ratios. of abundances of interstellar secondary and primary cosmic rays contains important information on their confinement and propagation in the Galaxy. Recent results suggest that high energy cosmic rays (> 20 GeV/nucleon) have propagated through much less interstellar matter than lower energy nuclei (< 1 GeV/nucleon). We report new observations of abundances in the charge range 2 ≤ Z ≤ 10, which were obtained with a dE/dx-Cerenkov detector launched into a polar orbit on OGO-6 as part of the Caltech Solar and Galactic Cosmic Ray Experiment. Integral rigidity spectra of all the elements observed have shapes similar to that of the helium spectrum in the rigidity range ~ 2 to ~ 14 GV, approaching a power law with exponent -1.6 above 8 GV. Calculations of interstellar propagation assuming a steady-state model and including the presence of interstellar helium and the effects of solar modulation predict a variation with rigidity of ratios such as Be/O and B/O, which is not observed. The data can be explained by assuming a rigidity-dependent confinement of cosmic rays within the Galaxy.

Additional Information

© 1973 University of Colorado. Provided by the NASA Astrophysics Data System. Dr. S. S. Murray made significant contributions to the OGO-6 program. Dr. J. Audouze kindly provided us with a copy of the computer program for the propagation calculation and provided us with cross section data. Dr. M. Shea kindly supplied us with detailed geomagnetic cutoff data, and Dr. T. L. Garrard supplied the solar modulation program. We appreciate discussions with Dr. C. Cesarsky. One of us (Brown) received support from the National Science Foundation, while another (Stone) was an Alfred P. Sloan research fellow. This work was supported in part by NASA contract NAS5-9312 and grant NGR 05-002-160. Space Radiation Laboratory SRL ID #: 1973-07.

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August 19, 2023
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