The abundances in the cosmic radiation (the elements lighter than Ge)

Abstract

Regarded as a sample of cosmic material the cosmic ray nuclei arriving at the Earth have a composition, which is noticeably different from that of other matter samples available to us. Moveover, the composition of the arriving nuclei varies significantly over the energy range where precise measurements are available. However, most of these peculiarities can be understood in terms of the transformations, induced in the cosmic ray beam during the propagation of the relativistic particles in the Galaxy. I therefore believe, that we are, afterall, entitled to speak about a definite composition of the cosmic ray source, and except for a few elements, the inferred source composition is remarkably solar like. But the low abundances of hydrogen and helium in the cosmic radiation remains a major puzzle, and the question of the mechanism and the energy source for the cosmic ray acceleration remains as open as it was forty years ago.