Excited states in ${}^{95}\mathrm{Y}$, populated following the spontaneous fission of ${}^{248}\mathrm{Cm}$ and ${}^{252}\mathrm{Cf}$ and following fission of ${}^{235}\mathrm{U}$ induced by thermal neutrons, were studied by means of $\gamma$ 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 ${}^{95}\mathrm{Y}$ at 3142.2 keV with a half-life of $T_{1/2}=14.9(5)$ ns. Another isomer was identified in ${}^{95}\mathrm{Y}$ at 5022.1 keV and it was assigned a spin-parity ($27/2^{-}$). For this isomer a half-life of $T_{1/2}=65(4)$ 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 ${}^{95}\mathrm{Y}$, for which we measured a half-life of 51.2(9) μs. The $B(E3)$ and $B(E1)$ transition rates, of 2.0 and $3.8\times {10}^{-7}$ W.u., respectively, observed in ${}^{95}\mathrm{Y}$ are significantly lower than in the neighboring ${}^{96}\mathrm{Zr}$ core, suggesting that octupole correlations in this region are mainly due to the coupling of proton $\Delta j=3$ orbitals. Shell-model calculations indicate that the ($27/2^{-}$) isomer in ${}^{95}\mathrm{Y}$ corresponds to the $\pi g_{9/2}\nu (g_{7/2}{h}_{11/2})$ maximally aligned configuration and that all three isomers in ${}^{95}\mathrm{Y}$ decay, primarily, by $M2$ transitions between proton $g_{9/2}$ and $f_{5/2}$ orbitals.

• Received 20 December 2008

DOI:https://doi.org/10.1103/PhysRevC.79.044304