Speaker
Description
Quadrupole deformation of low-lying excited states in zirconium nuclei has attracted considerable attention in the last years. An enhanced $B(E2; 2^+_2 \rightarrow 0^+_2$) value was observed in $^{96}$Zr [1], suggesting that an excited deformed configuration coexists with a nearly spherical ground state. This observation has been linked to the type-II shell-evolution mechanism [2], i.e. reorganization of nuclear shells due to specific proton and neutron occupations. The Monte-Carlo shell-model calculations [2] that reproduced well the measured $B(E2)$ strengths in $^{96}$Zr, were particularly successful in describing the rapid ground-state shape transition occurring between $^{98}$Zr and $^{100}$Zr, at the same time predicting a variety of deformed configurations -- prolate, oblate and triaxial ones -- to appear throughout the Zr isotopic chain. A large set of experimental spectroscopic data related to the shape transition in the Zr isotopes was also satisfactorily reproduced in the framework of configuration mixing within the interacting boson model (IBM-CM), invoking an 'intertwined quantum phase transition' [3].
We pursue a broad experimental programme addressing quadrupole and octupole collectivity in even-even Zr nuclei ranging from $A$=90 to 100. To this aim, we combine the powerful Coulomb-excitation technique with high-statistics $\beta$ decay. The measurements were performed with the GALILEO and AGATA $\gamma$-ray spectrometers at LNL (Italy), the GRIFFIN $\gamma$-ray spectrometer at TRIUMF (Canada) and Q3D magnetic spectrograph at MLL (Munich, Germany). I will present our recent results firmly establishing coexisting shapes in $^{94}$Zr [4] and reevaluating quadrupole in $^{96}$Zr [5].
[1] C. Kremer et al., Phys. Rev. Lett. 117, 172503 (2016)
[2] T. Togashi et al., Phys. Rev. Lett. 117, 172502 (2016)
[3] N. Gavrielov, A. Leviatan, and F. Iachello, Phys. Rev. C 105, 014305 (2022)
[4] N. Marchini, M. Rocchini, M. Zielinska et al., Phys. Lett. B 879, 140668 (2026)
[5] M. Zielinska, P. Garrett, M. Rocchini et al., Phys. Lett. B 877, 140481 (2026)