The decay of a new $3.2\text{−}\mu \mathrm{s}$, $(4^{-})$ isomeric state at 1298.0 keV has been observed using $\gamma$-ray spectroscopy at the Lohengrin mass spectrometer of the Institut Laue-Langevin. By comparison with theoretical calculations this state was assigned a $\nu 5/2[642]\otimes \nu 3/2[521]$ dominant configuration. Prompt $\gamma$-ray data from a spontaneous fission experiment have also been analyzed allowing the observation of a collective band on top of this isomeric state, the identification of a new band on top of the previously reported ($5^{-}$) isomer of ${}^{156}\mathrm{Nd}$ and the extension of collective bands on top of ($5^{-}$) isomers of the neighboring ${}^{156,158}\mathrm{Sm}$ nuclei. Quasiparticle rotor model calculations reported in this work correctly predict the energies and decay patterns of these bands. A new ($5^{-}$) isomer in ${}^{160}\mathrm{Sm}$ has also been observed. The calculations predict $\nu 5/2[642]\otimes \nu 5/2[523]$ dominant configurations for all these ($5^{-}$) isomers.

• Received 2 April 2009

DOI:https://doi.org/10.1103/PhysRevC.80.024304