The composition of Galactic cosmic rays and solar energetic particles

The progress made by U.S. researchers during 1983-1986 in studies on the composition of the Galactic cosmic-ray source (GCRS) and solar energetic particles (SEP) is reviewed. New information concerning element abundances in GCRS (obtained from HEAO-3 data) and SEP composition in large flares and (He-3)-rich events (from data obtained by the Voyager and ISEE spacecraft) was used to obtain direct correlation between the GCRS and SEP compositions. For elements heavier than He, the linear correlation coefficient beween the points was 0.96, and the slope of the least-squares fit line was found to be 1.01 + or - 0.01. Hydrogen and helium are more abundant in the SEP than in the GCRS. The close resemblance between the SEP composition and the GCRS composition means that the ratio of SEP abundances to solar-system abundances shows a correlation with the first ionization potential.