Giovanna Benzoni

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.

High-spin states in $^{123}\mathrm{Te}$ were populated in the $^{82}\mathrm{Se}(^{48}\mathrm{Ca},\ensuremath{\alpha}3n)^{123}\mathrm{Te}$ reaction at a beam energy of 205 MeV, and $\ensuremath{\gamma}$-ray coincidence events were measured with the Gammasphere array. The level scheme has been extended to spin $I\ensuremath{\approx}50$ through the identification of several new $\ensuremath{\gamma}$-ray transitions, and a rotational band feeding states above $I\ensuremath{\approx}20$. Cranked Nilsson-Strutinsky calculations are consistent with the observed low-spin yrast structure and support an interpretation of the high-spin band as a smooth terminating configuration involving two ${g}_{9/2}$ proton holes and no neutron excitations across the $N=82$ shell gap. A transition from near-prolate to triaxial rotation about the intermediate axis is suggested for the band near $I\ensuremath{\approx}40$.

This letter reports on the identification of a new isomeric state of $$^{164}$$ 164 Tb ( $$Z=65$$ Z = 65 , $$N=99$$ N = 99 ), which was measured with the DESPEC setup at the GSI Helmholtzzentrum für Schwerionenforschung GmbH following the first relativistic fragmentation of an $$^{170}$$ 170 Er primary beam. From the time distribution and coincidences of the emitted $$\gamma $$ γ rays, the isomer is tentatively assigned to a state with spin-parity $$(7^{-})$$ ( 7 - ) at an excitation energy of $$283.3(2)~\textrm{keV}$$ 283.3 ( 2 ) keV with a half-life of $$159(11)~\textrm{ns}$$ 159 ( 11 ) ns . The isomer is interpreted as the $$\pi 7/2^{-}[523]\otimes \nu 7/2^{+}[633]$$ π 7 / 2 - [ 523 ] ⊗ ν 7 / 2 + [ 633 ] configuration from the Nilsson orbital systematics. These results represent the first report of $$\gamma $$ γ -ray spectroscopy of $$^{164}$$ 164 Tb, providing insight into the ground-state and low-lying level structure.