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Published March 10, 1993 | Published
Journal Article Open

The Elemental and Isotopic Composition of Galactic Cosmic-Ray Nuclei from Scandium through Nickel


Measurements of the relative elemental and isotopic abundances of iron-group Galactic cosmic rays at energies of ~ 325 Me V per nucleon have been made using data collected from 1978 to 1981 by the high-energy cosmic ray detector aboard the /SEE 3 spacecraft. Assuming a standard leaky box model of cosmic-ray propagation, it is found that the source abundance ratio of ^(60)Ni/^(58)Ni is 1.07 ± 0.39, which is a factor of 2.8 ± 1.0 larger than the solar system value. Our measurements imply the presence of ^(59)Co at the source, which can be reconciled with the predictions of conventional nucleosynthesis models if there exists a time delay of ≥10^5 yr between nucleosynthesis and acceleration. Most of the 54Mn produced by spallation during cosmic-ray propagation in the Galaxy is found to have decayed to ^(54)Fe, indicating a confinement time of greater than 2 Myr. The source ratio of ^(54)Fe/^(56)Fe corrected for the ^(54)Mn decay is 0.046 ± 0.020, which is consistent with the solar system value of 0.063. The source ratio ^(55)Mn/^(56)Fe = 0.025 ± 0.010 is a factor of 2.1 ± 0.8 greater than solar. Also, the value of the Cr/Fe elemental ratio is found to be marginally enhanced. The isotope ^(52)Cr appears to be present in the cosmic-ray source at almost the 95% confidence level. The limits obtained on the abundances of the lighter iron-group elements at the source are Sc/Fe < 0.005, Ti/Fe < 0.007, and V /Fe < 0.005.

Additional Information

© 1993 The American Astronomical Society. The author wishes to thank his faculty advisor, Professor Mark Wiedenbeck, for his continual guidance and encouragement throughout this work. We also thank the Heckman/ Greiner group at the Lawrence Berkeley Laboratory who designed, constructed, and calibrated the instrument used for this study. We gratefully acknowledge the contributions of Professor William Webber who provided the computer code used for calculating the fragmentation cross sections, and of Professor James Truran for enlightening discussions of recent ideas and results in the field of iron-group nucleosynthesis. This work was supported, in part, by NASA under grants NAG5-308 and NAGW-1982, and by NASA's Graduate Student Researchers Program under grant NGT 14-020-802.

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August 20, 2023
October 26, 2023