Study of the hydrogen, helium, and heavy nuclei in the November 12, 1960 solar cosmic-ray event

Abstract

A study of the composition and energy spectra of solar cosmic rays from the Nov. 12, 1960 solar flare has been made using rocket-borne nuclear emulsions. The abundances of hydrogen, helium, carbon, nitrogen, oxygen, neon, and larger nuclei have been determined, and upper limits were set for light nuclei (3≤Z≤5) and fluorine nuclei. The relative numbers of helium, light, medium (6≤Z≤9), and large (Z≥10) nuclei in the solar beam were found to be 680±110, <0.1, 10, and 1.0±0.3, respectively. The composition was seen to be similar to that of the solar atmosphere as determined by spectroscopic means, for those elements where a comparison could be made, but markedly different from that of galactic cosmic rays. The differential energy per nucleon spectra of hydrogen, helium, and medium nuclei could be represented by an equation of the form dJdW=K(WW₀)^-γ for kinetic energies greater than 35 MeV per nucleon. The values of γ for He nuclei and medium nuclei were the same within uncertainties, but were larger than that for hydrogen nuclei by a factor of more than two in the energy interval from 40 to 130 MeV/nucleon. In spite of the different energy/nucleon spectra, the ratio of protons to heavier nuclei in the same energy/nucleon interval was the same at different times in the event and also the same as that observed in two other events. The measurements are shown to be consistent with a diffusion process which has a predominantly velocity dependent diffusion coefficient at low energies, as suggested by Parker, and therefore the different energy/nucleon spectra mentioned earlier are most probably due to differences generated by the acceleration process. Present ideas concerning the acceleration mechanism for solar cosmic rays are discussed in relation to the experimental results.