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Gamma ray line emission from nuclear deexcitation following ener getic particle reactions is evaluated. The compiled nuclear data and the calculated gamma ray spectra and intensities can be used for the study of astrophysical sites which contain large fluxes of energetic protons and nuclei. A detailed evaluation of gamma ray line production in the interstellar medium is made in the present paper.

Observations of Be and B in low-metallicity halo stars formed during the Ðrst 109 yr of Galactic evolution show that cosmic-ray acceleration must have taken place in the early Galaxy. The observed abundances of these elements relative to Fe, which, in the early Galaxy, is almost exclusively produced in Type II supernovae, strongly suggest that the cosmic-ray acceleration is also related to such supernovae with the particles being accelerated out of freshly nucleosynthesized matter before it mixes into the ambient, essentially nonmetallic interstellar medium. The observed abundances require that about 3 ] 1049 to 2 ] 1050 ergs per Type II supernova be imparted to these metallic cosmic rays, depending on whether or not H and He are accelerated along with the metals. The current data, however, are not sufficient to decide whether these cosmic rays are predominantly low energy or high energy. But, in any case, arguments of energetics imply a hard-energy spectrum extending up in energy to at least 50 MeV nucleon~1. This rules out Be and B production by supernova ejecta without further acceleration. In addition to production by cosmic rays, there must also be signiÐcant 11B production by neutrinos. This argument is driven by the observed 11B/10B ratio in meteorites that is very difficult to reproduce by cosmic-ray interactions. Observations of 6Li and Li in the early Galaxy provide information on the acceleration of nonmetallic cosmic rays out of the interstellar medium.

Total cross sections for the production of gamma-ray lines from nuclear deexcitation as a function of the projectile energy are evaluated and presented. Included are proton and α reactions with He, C, N, O, Ne, Mg, Al, Si, S, Ca and Fe. Such functions are essential for interpretation of gamma-ray line observations of astrophysical sites which contain large fluxes of energetic particles such as solar flares, the Earth's atmosphere, planetary atmospheres and surfaces, the interstellar medium and galactic nebulae.

Using cosmic-ray energetics as a discriminator, we investigate the viability of evolutionary models for the light elements, Li, Be and B (LiBeB). We employ a Monte Carlo code which incorporates hitherto ignored effects, the delayed mixing into the ISM both of the synthesized Fe, due to its incorporation into high velocity dust grains, and of the cosmic-ray produced LiBeB, due to the transport of the cosmic rays. We use supernova O and Fe ejecta based on calculations and observations, and we normalize the LiBeB production to the integral energy imparted to cosmic rays per supernova. We find that models in which the cosmic rays are accelerated mainly out of the average ISM which is increasingly metal poor at early times, significantly under predict the measured Be abundance of the early Galaxy, the increase in [O/Fe] with decreasing [Fe/H] indicated by recent data notwithstanding. We suggest that this increase could be due to the delayed mixing of the Fe. On the other hand, if the cosmic-ray metals are accelerated primarily out of supernova ejecta