Spectroscopy of Si-34,Si-35 by beta decay: sd-fp shell gap and single-particle states - art. no. 044316

The Al-34,Al-35 beta decays have been studied at the CERN online mass separ ator ISOLDE by beta-gamma, beta-gamma-gamma, and beta -n-gamma measurements in order to corroborate the low-level description of Si-34 and to obtain t he first information on the level structure of the N = 21 isotope Si-35. Ea rlier observed gamma lines in Al-34 decay were confirmed and new gamma tran sitions following both beta decay and beta -delayed neutron emission have b een established. The first level scheme of Si-35 includes three excited sta tes at 910, 974, and 2168 keV. Indication is found for J(pi) = (3/2)(-) and (312)(+) for the first two excited states, respectively. Beta-decay half-l ife of T-1/2 = 38.6(4) ms and beta -delayed neutron branching value P-n = 4 1(13)% were measured unambiguously. The significance of the single-particle energy determination at N = 21, Z = 14 for assessing the effective interac tion in sd-fp shell-model calculations is discussed and illustrated by pred ictions for different neutron-rich isotopes.