Francesco Recchia

Background: The neutron-deficient Hg isotopes provide one of the most prominent examples of nuclear shape coexistence. While the even-even nuclei have been extensively investigated, much less is known about how an unpaired neutron influences the evolution of collectivity in the odd-mass isotopes.Purpose: To determine lifetimes of low-spin states in $^{189}\mathrm{Hg}$ and investigate the evolution of collectivity in the rotational band built on the $13/{2}^{+}$ isomer through comparison with neighboring shape-coexisting Hg isotopes.Methods: Excited states in $^{189}\mathrm{Hg}$ were populated in the $^{160}\mathrm{Gd}(^{34}\mathrm{S},5n)^{189}\mathrm{Hg}$ fusion-evaporation reaction at a beam energy of 185 MeV. The reaction channel of interest was selected by requiring coincidence with at least one neutron detected in the neutron wall array, while prompt $\ensuremath{\gamma}$ rays were measured with the GALILEO spectrometer. Lifetimes of low-lying states above the $13/{2}^{+}$ isomer were measured with the recoil-distance Doppler-shift method using the GALILEO plunger device. The experimental results were compared with total Routhian surface calculations.Results: Lifetimes of the $17/{2}^{+}, 21/{2}^{+}$, and $25/{2}^{+}$ states were measured for the first time and the corresponding $B$($E2$) strengths were extracted. The excitation energies and transition strengths closely follow the systematics observed in neighboring odd- and even-mass Hg isotopes, supporting the interpretation of the rotational sequence as the coupling of an ${i}_{13/2}$ neutron to the weakly oblate structures of the neighboring even-even cores. The extracted ${B}_{4/2}$-type ratio is significantly below unity, extending the occurrence of anomalous transition-strength ratios to this odd-mass nucleus. Total Routhian surface calculations reproduce the weakly oblate equilibrium deformation but not the observed evolution of the transition strengths.Conclusions: The present results indicate that the ${i}_{13/2}$-based rotational band largely inherits the structural complexity of the neighboring shape-coexisting even-even Hg nuclei. They further demonstrate that electromagnetic transition strengths provide stringent constraints on the evolution of the underlying wave functions beyond those accessible from excitation energies or static mean-field descriptions alone.

The structure of light nuclei approaching the \(N = 20\) Island of Inversion was investigated in two multi-nucleon transfer experiments performed at Legnaro National Laboratories using the AGATA-PRISMA setup. This paper presents preliminary results on the decay level schemes of \(^{23,25}\)Ne. The analysis presented here focuses on the study of negative-parity states to probe the evolution of shell structure along the \(Z = 10\) isotopic chain, and provide stringent constraints for state-of-the-art theoretical models. Published by the Jagiellonian University 2026 authors