Cosmic-ray elemental abundances

Abstract

The elemental composition of the cosmic radiation as function of particle energy is one of the major sources of information concerning the origin and life history of cosmic rays. The Danish-French spectrometer on the HEAO-3 satellite /1/ has recently provided new and detailed data on the composition and energy spectra of the cosmic rays for the elements between beryllium and germanium in the energy range between 0.7 and 25 GeV/nucleon. The analysis of these data appear to be consistent with the following assumptions: 1) a source composition similar to that of the Solar System, 2) an injection process favouring elements with low values of the first ionization potential, 3) a rapid acceleration proces yielding identical energy spectra for all species, and 4) a diffusive propagation in the Galaxy with the average amount of matter traversed before escape from the confinement volume being a decreasing function of the particle rigidity. Despite the consistency of the HEAO-data with this set of assumptions it is unfortunately too early to regard these as well established facts of general validity. Observations of the hydrogen-helium component of the cosmic radiation have yielded constraints on the source composition, the injection and acceleration processes, and the propagation history which seems to be at variance with the picture described above.