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G.H. Share, R.J. Murphy (NRL)
The energies and widths of \gamma-ray lines emitted by ambient nuclei excited by flare-accelerated protons and \alpha-particles provide information on their directionality, spectra, and on the uniformity of the interaction region. For example, the \gamma-rays observed from a downward beam of particles impacting at 0\circ heliocentric angle would exhibit a clear Doppler red-shift and some broadening, dependent on the spectrum of the particles. In contrast, \gamma-rays observed from the same beam of particles impacting at 90\circ would be neither observably shifted nor broadened. We have studied the energies and widths of strong lines from de-excitations of 20Ne, 12C, and 16O in solar flares as a function of heliocentric angle. We use spectra from 21 flares observed with NASA's {\em Solar Maximum Mission}/GRS and {\em Compton Observatory}/OSSE experiments. The line energies of all three nuclei exhibit ~0.9% red-shifts from their laboratory values for flares observed at heliocentric angles <40\circ. In contrast, the energies are not significantly shifted for flares observed at angles >80\circ. The lines at all heliocentric angles are broadened between ~2.5% to 4%. These results are suggestive of a broad downward distribution of accelerated particles in flares or an isotropic distribution in a medium that has a significant density gradient. Detailed comparisons of these data with results from the gamma-ray production code (Ramaty, {\em et al.} 1979, ApJS, 40, 487; Murphy, {\em et al.} 1991, ApJ, 371, 793) are required in order to place constraints on the angular distributions of particles.
This research has been supported by NASA grant W-18995.
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The author(s) of this abstract have provided an email address for comments about the abstract: share@gamma.nrl.navy.mil