Directionality of Solar Flare–accelerated Protons and α‐Particles from γ‐Ray Line Measurements

The energies and widths of gamma-ray lines emitted by ambient nuclei excitedby flare-accelerated protons and alpha particles provide information on theions directionality and spectra, and on the characteristics of the interactionregion. We have measured the energies and widths of strong lines fromde-excitations of 12C, 16O, and 20Ne in solar flares as a function ofheliocentric angle. The line energies from all three nuclei exhibit ~1%redshifts for flares at small heliocentric angles, but are not shifted near thelimb. The lines have widths of ~3% FWHM. We compare the 12C line measurementsfor flares at five different heliocentric angles with calculations fordifferent interacting-particle distributions. A downward isotropic distribution(or one with a small upward component) provides a good fit to the linemeasurements. An angular distribution derived for particles that undergosignificant pitch angle scattering by MHD turbulence in coronal magnetic loopsprovides comparably good fits