UH cosmic rays and solar system material: The elements just beyond iron

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The origin of the elements from Cu to As in the UH (ultra-heavy) cosmic rays is investigated and related to current concepts of the nucleosynthesis of solar system material. The charge spectrum of the UH cosmic rays in the interval 29≤Z≤60 is studied via a fully developed propagation calculation for source abundances given by solar system material, the r-process, the massive-star core helium-burning s-process, and explosive carbon burning. None of these sources considered individually can explain the cosmic ray observations. However a combination of material produced in the r-process, the core helium-burning s-process and in explosive carbon burning provides a good representation of the experimental data. The cosmic-ray r-process is found to differ from solar system r-process events by an underproduction of the low-mass r-process peaks relative to the A∼195 peak. The large cosmicray abundance for Z=40-44 may be due to an r-process fission component, but this explanation is by no means certain. Improved cosmic-ray data, especially for Zn-Sr, can provide limits to the various source contributions. The model described here gives a consistent picture for the origin of both the cosmic rays and the solar system elements just beyond iron, and adds additional evidence for the importance of massive stars as a site of nucleosynthesis and the birthplace of the cosmic rays. © 1977 D. Reidel Publishing Company.

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Astrophysics and Space Science

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