A cosmochemical view of cosmic rays and solar particles

Abstract

The composition of cosmic rays and solar particles is reviewed with emphasis on the question of whether they are representative samples of Galactic and solar matter. The composition of solar particles changes with energy and from flare to flare. A strong excess of heavy elements at energies below a few MeV/nuc decreases with energy, and at energies above ~ 15 MeV/nuc the composition of solar particles resembles that of galactic cosmic rays somewhat better than that of the solar atmosphere. The elements Ne through Pb have remarkably similar abundances in cosmic ray sources and in the matter of the solar system. The lighter elements are depleted in cosmic rays, whereas U and Th may be enriched or not, depending on whether the meteoritic or solar abundance of Th is used. Two prototype sources of cosmic rays are considered: gas with solar system composition but enriched in elements with Z>8 during acceleration and emission (by analogy with solar particle emission), and highly evolved matter enriched in r-process elements such as U, Th and transuranic elements. The energy-dependence of cosmic ray composition suggests that both sources may contribute at different energies.

The acceleration of heavy nuclei in solar flares

“…However it is also known that, for solar cosmic rays of energy > 10 Mev/nucleon, their nuclear abundances are very similar to those of the solar atmosphere (e.g., Biswas and Fichtel, 1964and Fichtel, , 1965Bertsch et al, 1969Bertsch et al, , 1972Bertsch et al, , 1973Price, 1973). This difference mentioned above may be related to the acceleration processes of solar cosmic rays in or near the flare region (Mogro-Capero and Simpson, 1972a,b;Mogro-Capero, 1972, 1973).…”