Solar gamma rays above 8 MeV

Processes which lead to the production of γ-rays with energy greater than 8 MeV in solar flares are reviewed and evaluated. Excited states which can be produced by inelastic scattering, charge exchange, and spallation reactions in the abundant nuclear species are considered in order to identify nuclear lines which may contribute to the γ-rays spectrum of solar flares. The flux of 15.11 MeV γ-rays relative to the flux of 4.44 MeV γ-rays from the de-excitation of the corresponding states in 12C is calculated for a number of assumed distributions of exciting particles. This flux ratio is shown to be a sensitive diagnostic of accelerated particle spectra. Other high-energy nuclear levels are not so isolated as the 15.11 MeV state and are not expected to be so strong. The spectrum of γ-rays from the decay of π0 is shown to be sensitive to the energy distribution of particles accelerated to energies greater than 100 MeV