Light Isotopes, Extinct Radioisotopes, and Gamma-Ray Lines from Low-Energy Cosmic-Ray Interactions

Abstract

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 <SUP>6</SUP>Li 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<SUP>-1</SUP> Such cosmic-ray interactions can account for the observed meteoritic <SUP>11</SUP>B/<SUP>10</SUP>B 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 <SUP>41</SUP>Ca in meteoritic calcium-aluminum inclusions (CAIs) formed in the early solar system, provided that the cosmic-ray irradiation and CAl formation periods were essentially cotemporal. However, the production of significant amounts of <SUP>26</SUP>Al by low-energy cosmic rays in the early solar system is unlikely because it would overproduce <SUP>9</SUP>Be and <SUP>6</SUP>Li.