Isotopes in Galactic Cosmic Rays

Abstract

The data on isotopic ratios of elements in Galactic Cosmic Rays (GCR) is steadily improving and has recently reached the point where some information can be extracted, which has bearing on the problem of the origin of the cosmic rays. By and large, these data have generally confirmed the similarity between solar-type matter and GCR source, when spallation effects and selective acceleration are taken into account. The silicon and iron isotopic ratios, for instance, are consistent with meteoritic ratios. For iron, this is particularly important since two or perhaps even three different nucleosynthesis mechanisms are required to account for the species 54Fe, 56Fe, 58Fe. For carbon, nitrogen and oxygen the problem is that the spallation corrections are large compared to the solar system ratios but nevertheless the present upper limits are not in contradiction with the solar system ratios.