Background: Shape coexistence in the $Z\approx 82$ region has been established in mercury, lead, and polonium isotopes. For even-even mercury isotopes with $100\le N\le 106$ multiple fingerprints of this phenomenon are observed, which seems to be no longer present for $N\ge 110$. According to a number of theoretical calculations, shape coexistence is predicted in the ${}^{188}\mathrm{Hg}$ isotope.

The electromagnetic structure of ${}^{66}\mathrm{Zn}$ at low excitation energy was investigated via low-energy Coulomb excitation at INFN Legnaro National Laboratories, using the Gamma Array of Legnaro Infn Laboratories for nuclEar spectrOscopy (GALILEO) $\gamma$-ray spectrometer coupled to the SPIDER (Silicon PIe DEtectoR). A set of reduced $E2, E3$, and $M1$ matrix elements was extracted from the collected data using the gosia code, yielding 12 reduced transition probabilities between the low-spin states and the spectroscopic quadrupole moment of the ${2_1}^{+}$ state. The $B\left(E2\right)$ values for transitions depopulating the ${0_2}^{+}$ state have been determined for the first time, allowing for the lifetime of this state to be deduced and, consequently, the ${\rho }^2(E0;{0_2}^{+}\to {0_1}^{+})$ monopole transition strength to be extracted. In addition, the $B(E3;{3_1}^{-}\to {0_1}^{+})$ value has been determined for the first time in a Coulomb excitation experiment. The obtained results resolve the existing discrepancies between literature lifetimes and demonstrate that ${}^{66}\mathrm{Zn}$ cannot be described by using simple collective models. Therefore, new state-of-the-art beyond-mean-field and large-scale shell-model calculations were performed in order to interpret the structure of this nucleus. Both the experimental and theoretical results suggest that the triaxial degree of freedom has an important impact on electromagnetic properties of ${}^{66}\mathrm{Zn}$, while the unique features of the ${0_2}^{+}$ state indicate its distinct and rather isolated structure.

Lead-208 is the heaviest known doubly magic nucleus and its structure is therefore of special interest. Despite this magicity, which acts to provide a strong restorative force toward sphericity, it is known to exhibit both strong octupole correlations and some of the strongest quadrupole collectivity observed in doubly magic systems. In this Letter, we employ state-of-the-art experimental equipment to conclusively demonstrate, through four Coulomb-excitation measurements, the presence of a large, negative, spectroscopic quadrupole moment for both the vibrational octupole 3 1 − and quadrupole 2 1 + state, indicative of a preference for prolate deformation of the states. The observed quadrupole moment is discussed in the context of the expected splitting of the 3 − ⊗ 3 − two-phonon states, due to the coupling of the quadrupole and octupole motion. These results are compared with theoretical values from three different methods, which are unable to reproduce both the sign and magnitude of this deformation. Thus, in spite of its well-studied nature, Pb 208 remains a puzzle for our understanding of nuclear structure.

The excited states of $N=44$ ${}^{74}\mathrm{Zn}$ were investigated via $\gamma$-ray spectroscopy following ${}^{74}\mathrm{Cu}$ $\beta$ decay. By exploiting $\gamma \text{−}\gamma$ angular correlation analysis, the $2_2^{+}$, $3_1^{+}$, $0_2^{+}$, and $2_3^{+}$ states in ${}^{74}\mathrm{Zn}$ were firmly established. The $\gamma$-ray branching and $E2/M1$ mixing ratios for transitions deexciting the $2_2^{+}$, $3_1^{+}$, and $2_3^{+}$ states were measured, allowing for the extraction of relative $B(E2)$ values. In particular, the $2_3^{+}\to 0_2^{+}$ and $2_3^{+}\to 4_1^{+}$ transitions were observed for the first time. The results show excellent agreement with new microscopic large-scale shell-model calculations, and are discussed in terms of underlying shapes, as well as the role of neutron excitations across the $N=40$ gap. Enhanced axial shape asymmetry (triaxiality) is suggested to characterize ${}^{74}\mathrm{Zn}$ in its ground state. Furthermore, an excited $K=0$ band with a significantly larger softness in its shape is identified. A shore of the $N=40$ “island of inversion” appears to manifest above $Z=26$, previously thought as its northern limit in the chart of the nuclides.