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Nuclear moments of the antimony isotopes 113−133Sb are measured by collinear laser spectroscopy and used to benchmark phenomenological shell-model and ab initio calculations in the valence-space in-medium similarity renormalization group (VS-IMSRG). The shell-model calculations reproduce the electromagnetic moments over all Sb isotopes when suitable effective g-factors and charges are employed. Good agreement is achieved by VS-IMSRG for magnetic moments on the neutron-deficient side for both odd-even and odd-odd Sb isotopes while its results deviate from experiment on the neutron-rich side. When the same effective g-factors are used, VS-IMSRG agrees with experiment nearly as well as the shell model. Hence, the wave functions are very similar in both approaches and missing contributions to the M1 operator are identified as the cause of the discrepancy of VS-IMSRG with experiment. Electric quadrupole moments remain more challenging for VS-IMSRG.

Situated in the so-called “island of inversion,” the nucleus 32Mg is considered as an archetypal example of the disappearance of magicity at N=20. We report on high statistics in-beam spectroscopy of 32Mg with a unique approach, in that two direct reaction probes with different sensitivities to the underlying nuclear structure are employed at the same time. More specifically, states in 32Mg were populated by knockout reactions starting from 33Mg and 34Si, lying inside and outside the island of inversion, respectively. The momentum distributions of the reaction residues and the cross sections leading to the individual final states were confronted with eikonal-based reaction calculations, yielding a significantly updated level scheme for 32Mg and spin-parity assignments. By fully exploiting observables obtained in this measurement, a variety of structures coexisting in 32Mg was unraveled. Comparisons with theoretical predictions based on shell-model overlaps allowed for clear discrimination between different structural models, revealing that the complete theoretical description of this key nucleus is yet to be achieved.

A thick neutron skin emerges from the first determination of root mean square radii of the proton distributions for 17−22N from charge changing cross section measurements around 900A MeV at GSI. Neutron halo effects are signalled for 22N from an increase in the proton and matter radii. The radii suggest an unconventional shell gap at N = 14 arising from the attractive proton–neutron tensor interaction, in good agreement with shell model calculations. Ab initio, in-medium similarity re-normalization group, calculations with a state-of-the-art chiral nucleon–nucleon and three-nucleon interaction reproduce well the data approaching the neutron drip-line isotopes but are challenged in explaining the complete isotopic trend of the radii. Keywords: Proton and matter radii, Neutron skin, Magic number, Shell model, Ab initio theory, Radioactive beams

Self-conjugate nuclei in the A≈70–80 region have attracted a great deal of attention due to phenomena such as shape coexistence and increasing collectivity along the N=Z line. We investigate the structure of nuclei in this region through lifetime measurements using the GRETINA array. The first implementation of the Differential Recoil Distance Doppler Shift technique with fast radioactive beams is demonstrated and verified through a measurement of the well-known B(E2;21+→01+) transition strength in 74Kr. The method is then applied to determine the B(E2;21+→01+) transition strength in 74Rb, the heaviest odd–odd N=Z nucleus for which this quantity has been determined. This result and extended systematics along N=Z suggest the dominance of the isoscalar part of the quadrupole transition strengths in self-conjugate nuclei, as well as the possible presence of shape coexistence in 74Rb. Keywords: Lifetimes, Nuclear transition probabilities, Isospin

Excited states in the N=40 isotone 62Ti were populated via the 63V(p,2p)62Ti reaction at ∼200 MeV/nucleon at the Radioactive Isotope Beam Factory and studied using γ-ray spectroscopy. The energies of the 21+→0gs+ and 41+→21+ transitions, observed here for the first time, indicate a deformed 62Ti ground state. These energies are increased compared to the neighboring 64Cr and 66Fe isotones, suggesting a small decrease of quadrupole collectivity. The present measurement is well reproduced by large-scale shell-model calculations based on effective interactions, while ab initio and beyond mean-field calculations do not yet reproduce our findings. The shell-model calculations for 62Ti show a dominant configuration with four neutrons excited across the N=40 gap. Likewise, they indicate that the N=40 island of inversion extends down to Z=20, disfavoring a possible doubly magic character of the elusive 60Ca. Keywords: Shell evolution, Radioactive beams, Gamma-ray spectroscopy

Many-body nuclear theory utilizing microscopic or chiral potentials has developed to the point that collectivity might be studied within a microscopic or ab initio framework without the use of effective charges; for example with the proper evolution of the E2 operator, or alternatively, through the use of an appropriate and manageable subset of particle–hole excitations. We present a precise determination of E2 strength in 22Mg and its mirror 22Ne by Coulomb excitation, allowing for rigorous comparisons with theory. No-core symplectic shell-model calculations were performed and agree with the new B(E2) values while in-medium similarity-renormalization-group calculations consistently underpredict the absolute strength, with the missing strength found to have both isoscalar and isovector components. The discrepancy between two microscopic models demonstrates the sensitivity of E2 strength to the choice of many-body approximation employed. Keywords: 22Mg, 22Ne, Ab initio, Collectivity, Coulomb excitation

The E0 transition strength in the 22+→21+ transitions of 58,60,62Ni have been determined for the first time following a series of measurements at the Australian National University (ANU) and the University of Kentucky (UK). The CAESAR Compton-suppressed HPGe array and the Super-e solenoid at ANU were used to measure the δ(E2/M1) mixing ratio and internal conversion coefficient of each transition following inelastic proton scattering. Level half-lives, δ(E2/M1) mixing ratios and γ-ray branching ratios were measured at UK following inelastic neutron scattering. The new spectroscopic information was used to determine the E0 strengths. These are the first 2+→2+ E0 transition strengths measured in nuclei with spherical ground states and the E0 component is found to be unexpectedly large; in fact, these are amongst the largest E0 transition strengths in medium and heavy nuclei reported to date. Keywords: Electric monopole (E0) transitions, Internal conversion, Mixing ratios, Nuclear structure