CERN Accelerating science

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
 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
 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 𝜋⁢[4313/2]×𝜈⁢[5413/2]⁢𝐾=3− Nilsson assignment and a deformation 𝛽2>0.28. It is fed by a I𝜋=10− microsecond isomer consistent with a 𝜋⁡(𝑔9/2)⁢𝜈⁡(ℎ11/2) spherical configuration. It is interesting to note that the same unique-parity states 𝜋⁡(𝑔9/2) and 𝜈⁡(ℎ11/2) are present in the same nucleus in a deformed and in a spherical configuration. The neighboring odd-odd nucleus  
98
 Y 
  presents a strong analogy with  
96
 Rb 
  and is also discussed.