Light isotopes, extinct radioisotopes, and gamma-ray lines from low-energy cosmic-ray interactions

We have carried out detailed calculations of gamma-ray line, light isotope, and extinct radioactive isotope production by low-energy cosmic rays for a broad range of accelerated particle abundances and energy spectra. We first apply these calculations to the gamma-ray line emission observed from the Orion molecular cloud complex. These gamma rays have provided the most direct evidence for the presence of large fluxes of low-energy cosmic rays in the Galaxy. Next we show that the bulk of the Galactic boron, beryllium, and 6Li could have been produced over the age of the Galaxy by interactions of low-energy cosmic rays having typical particle energies around 30 MeV nucleon(-1). Such cosmic-ray interactions can account for the observed meteoritic B-11/B-10 which is higher than the isotopic ratio predicted by relativistic cosmic-ray interactions. Low-energy cosmic rays of similar energies could have also made a significant contribution to the production of Ca-41 in meteoritic calcium-aluminum inclusions (CAIs) formed in the early solar system, provided that the cosmic-ray irradiation and CAI formation periods were essentially cotemporal. However, the production of significant amounts of Al-26 by low-energy cosmic rays in the early solar system is unlikely because it would overproduce Be-9 and Li-6.