Nuclear-Charge Spectra and Energy Spectra in the September 2, 1966, Solar-Particle Event

Heavy nuclei (Z »= 3) were detected in the September 2, 1966, solar-particle event. This brings to five the number of events in which these particles have been detected. The proton energy spectrum was measured down to energies as low as 3 MeV and up to energies as high as 100 MeV, with measurements on the helium and heavier nuclei covering a more restricted range. The relative abundances of helium, light (3 «= Z «= 5), medium (6 «= Z «= 9), and heavier nuclei obtained in this experiment in the energy range from about 14 to 35 MeV nucleon' agree with those measured in previous solar-particle events at higher energies and hence with those of the solar photosphere. This result strengthens the concept of a multicharged nuclear composition, which is a characteristic of solar-particle events. Use of the recent solar spectroscopic data and the ratio of helium to medium nuclei observed in the solar cosmic rays results in a hydrogen-to-helium ratio of 16 ± 2. An examination of the relative abundances of protons and medium nuclei shows that the propagation of solar particles in this event cannot be described by a simple diffusion model with a diffusion coefficient proportional to j3 or 13R