New isomers and medium-spin structure of the 95Y nucleus
Résumé
Excited states in 95Y, populated following the spontaneous fission of 248Cm and 252Cf and following fission of 235U induced by thermal neutrons, were studied by means of γ spectroscopy using the EUROGAM2 and GAMMASPHERE multidetector Ge arrays and the LOHENGRIN fission-fragment separator, respectively. We have found a new (17/2−) isomer in 95Y at 3142.2 keV with a half-life of T1/2 = 14.9(5) ns. Another isomer was identified in 95Y at 5022.1 keV and it was assigned a spin-parity (27/2−). For this isomer a half-life of T1/2 = 65(4) ns was determined and four decay branches were found, including an E3 decay. A new E3 decay branch was also found for the known, 1087.5-keV isomer in 95Y, for which we measured a half-life of 51.2(9) μs. The B(E3) and B(E1) transition rates, of 2.0 and 3.8 × 10−7 W.u., respectively, observed in 95Y are significantly lower than in the neighboring 96Zr core, suggesting that octupole correlations in this region are mainly due to the coupling of proton deltaj = 3 orbitals. Shell-model calculations indicate that the (27/2−) isomer in 95Y corresponds to the πg9/2ν(g7/2h11/2) maximally aligned configuration and that all three isomers in 95Y decay, primarily, by M2 transitions between proton g9/2 and f5/2 orbitals.