Shape coexistence in the very neutron-rich odd-oddRb96

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 \ensuremath{\gamma} 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 $\ensuremath{\pi}[431\phantom{\rule{0.3em}{0ex}}3/2]\ifmmode\times\else\texttimes\fi{}\ensuremath{\nu}[541\phantom{\rule{0.3em}{0ex}}3/2]K={3}^{\ensuremath{-}}$ Nilsson assignment and a deformation ${\ensuremath{\beta}}_{2}g0.28$. It is fed by a ${I}^{\ensuremath{\pi}}={10}^{\ensuremath{-}}$ microsecond isomer consistent with a $\ensuremath{\pi}({g}_{9/2})\ensuremath{\nu}({h}_{11/2})$ spherical configuration. It is interesting to note that the same unique-parity states $\ensuremath{\pi}({g}_{9/2})$ and $\ensuremath{\nu}({h}_{11/2})$ 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.