Lifetime measurements in Rb96 via fast-timing techniques: Investigating shape coexistence at A≃100

Le résumé fourni par la source

Lifetime measurements of the (${3}^{\ensuremath{-}}$), (${4}^{\ensuremath{-}}$), and (${6}^{\ensuremath{-}}$) intraband states in the neutron-rich, odd-odd $^{96}\mathrm{Rb}$ nucleus were performed at the LOHENGRIN spectrometer of Institut Laue-Langevin, using thermal-neutron-induced fission of $^{235}\mathrm{U}$ and fast-timing techniques with ${\mathrm{LaBr}}_{3}:\mathrm{Ce}$ scintillator detectors. The nanosecond isomeric nature of the (${3}^{\ensuremath{-}}$) bandhead was established as well as the ${\ensuremath{\beta}}_{2}=0.39(3)$ deformation parameter of the band, pointing to a robust deformation in $^{96}\mathrm{Rb}$. Moreover, a hindered $B(E2)$ value of $3.{9}_{\ensuremath{-}13}^{+19}\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}2}$ W.u. was found for the $\ensuremath{\gamma}$ decay of the deformed (${4}^{\ensuremath{-}}$) state to the spherical ${2}^{\ensuremath{-}}$ ground state. A retardation was also found for the (${3}^{\ensuremath{-}}$) $\ensuremath{\rightarrow} {2}^{\ensuremath{-}}$ 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 $^{98}\mathrm{Y}$ isotone are discussed.

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