  Gamma ray emission lines resulting from accelerated particle bombardment of
ambient gas can serve as an important spectroscopic tool for abundance
determinations. The method is illustrated by considering the gamma ray line
emission observed from solar flares. The observation of similar gamma ray lines
from Orion suggests the existence of large fluxes of low energy Galactic cosmic
rays. The role of these cosmic rays in the nucleosynthesis of the light
isotopes is discussed.
