Decay properties of exoticN≃28 S and Cl nuclei and theCa48/46Ca abundance ratio

Abstract

Beta-decay half-lives and β-delayed neutron-emission probabilities of the very neutron-rich nuclei ${}_{}{}^{44}{}_{}{}^{}\mathrm{S}$ and ${}_{}{}^{45–47}{}_{}{}^{}\mathrm{Cl}$ 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 ${}_{}{}^{48}{}_{}{}^{}\mathrm{Ca}$ beam from GANIL (Grand Accélérateur National d’Ions Lourds) with a ${}_{}{}^{64}{}_{}{}^{}\mathrm{Ni}$ target, and were separated by the doubly achromatic spectrometer LISE (Ligne d’Ions Super Epluchés). Their decay was studied by a β-n time correlation measurement. The results are compared to recent model predictions and indicate a rapid weakening of the N=28 shell effect below ${}_{20}{}^{48}{}_{}{}^{}\mathrm{Ca}_{28}^{}{}_{}{}^{}$. 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 ${}_{}{}^{48}{}_{}{}^{}\mathrm{Ca}$ ${/}^{46}$Ca abundance ratio measured in the solar system as well as the Ca-Ti-Cr anomalies observed in E. King inclusions of the Allende meteorite.