Decay Properties Of Exotic N-Similar-Or-Equal-To-28-S And Cl Nuclei And The Ca-48/Ca-46 Abundance Ratio

Beta-decay half-lives and beta-delayed neutron-emission probabilities of the very neutron-rich nuclei 44S and Cl-45-47 have been measured. These isotopes, which lie at or close to the N = 28 magic shell, were produced in interactions of a 60 MeV/U 48Ca beam from GANIL (Grand Accelerateur National d'Ions Lourds) with a 64Ni target, and were separated by the doubly achromatic spectrometer LISE (Ligne d'Ions Super Epluches). Their decay was studied by a beta-n time correlation measurement. The results are compared to recent model predictions and indicate a rapid weakening of the N = 28 shell effect below Ca-48(20)28. The nuclear structure effects reflected in the decay properties of the exotic S and Cl isotopes may be the clue for the astrophysical understanding of the unusual 48Ca/46Ca abundance ratio measured in the solar system as well as the Ca-Ti-Cr anomalies observed in E. King inclusions of the Al-lende meteorite.