Microsecond isomers of neutron-rich nuclei in masses $A=96$ and 98 were reinvestigated at the Institut Laue-Langevin reactor (Grenoble). These nuclei were produced by thermal-neutron induced fission of ${}^{241}\mathrm{Pu}$. The detection is based on the time correlation between fission fragments selected by the Lohengrin mass spectrometer and the γ rays and conversion electrons from the isomers. A new level scheme of ${}^{96}\mathrm{Rb}$ is proposed. We have found that the ground state and low-lying levels of this nucleus are rather spherical, and a rotational band develops at 461-keV energy. This band has properties consistent with a $\pi [4313/2]\times \nu [5413/2]K=3^{-}$ Nilsson assignment and a deformation ${\beta }_2>0.28$. It is fed by a $I^{\pi }={10}^{-}$ microsecond isomer consistent with a $\pi (g_{9/2})\nu (h_{11/2})$ spherical configuration. It is interesting to note that the same unique-parity states $\pi (g_{9/2})$ and $\nu (h_{11/2})$ are present in the same nucleus in a deformed and in a spherical configuration. The neighboring odd-odd nucleus ${}^{98}\mathrm{Y}$ presents a strong analogy with ${}^{96}\mathrm{Rb}$ and is also discussed.

• Received 6 April 2005

DOI:https://doi.org/10.1103/PhysRevC.71.064327