GALACTIC EVOLUTION OF THE LIGHT-ELEMENT ISOTOPES REVISITED

We have studied the evolution of the light element abundances by means of a relatively simple model of galactic chemical evolution. It is sh own that it is possible to reasonably account for the element abundanc es and abundance ratios recently determined in stars on the grounds of the standard galactic cosmic ray nucleosynthesis and the stellar prod uction of Li-7 in low mass AGE stars. The apparent constancy of the Li -7/Li-6 ratio from the epoch of the Solar System formation (12.5) unti l now can be naturally explained with this stellar source of Li. Howev er, if the overabundances of Be (and perhaps B) found in very metal de ficient stars are confirmed by further observations, another origin be sides cosmic ray nucleosynthesis must be considered to explain the ear ly evolution of the Be (B?) abundances. A primordial production of Be is suggested.