Solar gamma-ray spectrum between 4 and 8 MeV

We evaluate in detail the properties of nuclear gamma-ray emission in the 4--8 MeV range. This emission consists of broad (ΔE/Eapprox. =20%) and narrow (ΔE/Eapprox. =1%) lines resulting from nuclear reactions of energetic H, He, C, and O nuclei with ambient matter. From the comparison of the calculations with observations of the 1972 August 4 flare, we conclude: (1) that essentially all the observed radiation in the 4 to 8 MeV region is due to the superposition of broad and narrow lines of nuclear origin with almost no contribution from other mechanisms; (2) that the accelerated particles in the energy region from about 10 to 100 MeV amu-1 have a relatively flat energy spectrum (for a power law, E-, sapproximately-less-than2.5); (3) that the calculated γ-ray spectrum obtained from an isotropic distribution of accelerated particles fits the observed spectrum better than the spectrum derived from an anisotropic distribution for which the velocity vectors of the particles point toward the photosphere; and (4) that it is possible to set a stringent upper limit on the ratio of relativistic electrons to protons in flares, consistent with the small, but finite, electron-to-proton ratio in galactic cosmic rays