Lifetime measurements in Rb 96 via fast-timing techniques: Investigating shape coexistence at A≃100 [Lifetime measurements in ⁹⁶Rb via fast-timing techniques: Investigating shape coexistence at A≃100]

Lifetime measurements of the (3-), (4-), and (6-) intraband states in the neutron-rich, odd-odd Rb96 nucleus were performed at the LOHENGRIN spectrometer of Institut Laue-Langevin, using thermal-neutron-induced fission of U235 and fast-timing techniques with LaBr3:Ce scintillator detectors. The nanosecond isomeric nature of the (3-) bandhead was established as well as the β2=0.39(3) deformation parameter of the band, pointing to a robust deformation in Rb96. Moreover, a hindered B(E2) value of 3.9-13+19×10-2 W.u. was found for the γ decay of the deformed (4-) state to the spherical 2- ground state. A retardation was also found for the (3-) → 2- transition, possibly due to the shape change and giving strong support to a shape coexistence scenario in this nucleus, at the borders of the island of deformation at N=60. Analogies with the structure of the Y98 isotone are discussed.