PU-244 DATING .10. INITIAL ABUNDANCE OF I-129 IN CARBONACEOUS CHONDRITES

Excess radiogenic Xe-129, which should have been produced by the beta- decay of the extinct radionuclide I-129, is conspicuously missing in t he acid residues isolated from various carbonaceous chondrites, in whi ch Pu-244 fission xenon is highly enriched. Results from recent studie s indicate that either a) the last supernova exploded more than 150 to 200 million years prior to the time the carbonaceous chondrites began to retain their Pu-244 fission xenon or b) fine-grained interstellar diamond crystals in the carboaceous chondrites played the role of a fi ssion product catcher for a quantitative retention of Pu-244 fission x enon, while allowing excess Xe-129 from the weak beta-decay of I-129 t o escape from the meteorites.