Shape coexistence in the very neutron-rich odd-odd {sup 96}Rb

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 {sup 241}Pu. The detection is based on the time correlation between fission fragments selected by the Lohengrin mass spectrometer and the {gamma} rays and conversion electrons from the isomers. A new level scheme of {sup 96}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}[431 3/2]x{nu}[541 3/2]K=3{sup -} Nilsson assignment and a deformation {beta}{sub 2}>0.28. It is fed by a I{sup {pi}}=10{sup -} microsecond isomer consistent with a {pi}(g{sub 9/2}){nu}(h{sub 11/2}) spherical configuration. It is interesting to note that the same unique-parity states {pi}(g{sub 9/2}) and {nu}(h{sub 11/2}) are present in the same nucleus in a deformed and in a spherical configuration. The neighboring odd-odd nucleus {sup 98}Y presents a strong analogy with {sup 96}Rb and is also discussed.