GALACTIC EVOLUTION OF D AND HE-3

The primordial (i.e., pre-Galactic) abundances of deuterium and of He-3 provide a valuable probe of cosmology and a crucial test of the consistency of big bang nucleosynthesis (BBN). To utilize current observational data on the D and He-3 abundances in the solar system and the interstellar medium to infer the primordial values, it is necessary to adopt some--necessarily model-dependent-assumptions about the evolution of D and He-3 during the course of Galactic evolution. Here, we follow the D and He-3 evolution using several models for the chemical evolution of the disk of the Galaxy. Comparing our model predictions with the solar system and interstellar medium data, we infer upper and lower bounds to the primordial mass fractions: 3.9 less than or similar to 10(5)X2P less than or similar to 9.0, 1.9 less than or similar to 10(5)X3P less than or similar to 4.0, 6.3 less than or similar to 10(5)X23P less than or similar to 11. Using these bounds we reinvestigatethe the the consistency of BBN and derive new, stringent bounds to the nucleon-to-photon ratio (3.7 less than or similar to eta10 less than or similar to 4.2) and to the number of new, light elementary particles (DELTAN(nu) less than or similar to 0.25).