Pioneer 10 measurements of the charge and energy spectrum of solar cosmic rays during 1972 August

Abstract

We have measured the energy spectrum and charge composition of solar cosmic rays integrated over the giant events of 1972 August on the Pioneer 10 spacecraft located at 2.2 AU. Within the energy range 8-50 MeV nucleon -1, the individual nuclei from He to Si appear to have average differential spectra of the form dN/dE E -2.7, except for carbon, which exhibits a slightly steeper spectrum with = 3.1. The average charge composition in this energy range is similar in most respects to that measured in other recent flare events using counters, emulsions, and plastic detectors, although it differs significantly, for Z = 10-14 nuclei, from some earlier emulsion abundances. These data provide further evidence that the He abundance relative to C and N and 0 nuclei is variable from event to event, and also that this ratio is energy-dependent. The abundance of Na and Al nuclei was determined for the first time in solar cosmic rays. In the light of these data, the question of th- relative abundances of solar cosmic rays and solar atmospheric abundances in the Z = 10-14 range is reexamined. Results are also presented for the 8He flux. Subject headings: abundances, cosmic-ray - abundances, solar - cosmic rays