Nuclear structure of Si-37,Si-38 investigated by decay spectroscopy of Al-37,Al-38

We present a study on the beta decays of the neutron-rich isotopes Al-37 and Al-38, produced by projectile fragmentation of a Ca-48 beam with an energy E - 345 A MeV at the RIKEN Nishina Center. The half-lives of Al-37 and Al-38 have been measured to 11.5(4) ms and 9.0(7) ms, respectively, using the CAITEN implantation and decay detector setup. The level schemes for Si-37 and Si-38 were deduced by employing gamma-gamma coincidence spectroscopy following the event-by-event identification of the implanted nuclei. Comparison to large scale nuclear shell model calculations allowed for a tentative assignment of spin and parity of the populated states. The data indicate that the classical shell gap at magic neutron number N = 28 between the nu f(7/2) and nu p(3/2) orbits gets reduced by 0.3 MeV in this region leading to low-energy states with intruder configuration in Si-37.