Background: The nucleus 32Mg (N = 20 and Z = 12) plays a central role in the so-called "island of inversion," where in the ground states sd-shell neutrons are promoted to the fp-shell orbitals across the shell gap, resulting in the disappearance of the canonical neutron magic number N = 20. Purpose: The primary goals of this work are to extend the level scheme of 32Mg, provide spin-parity assignments to excited states, and discuss the microscopic structure of each state through comparisons with theoretical calculations. Method: In-beam gamma -ray spectroscopy of 32Mg was performed using two direct-reaction probes: one-neutron (two-proton) knockout reactions on 33Mg (34Si). Final-state exclusive cross sections and parallel momentum distributions were extracted from the experimental data and compared with eikonal-based reaction model calculations combined with shell-model overlap functions. Results: Owing to the remarkable selectivity of the one-neutron and two-proton knockout reactions, a significantly updated level scheme for 32Mg, which exhibits negative-parity intruder and positive-parity normal states, was constructed. The experimental results were confronted with four different nuclear structure models. Conclusions: In some of these models, different aspects of 32Mg and the transition into the island of inversion are well described. However, unexplained discrepancies remain, and, even with the help of these state-of-the-art theoretical approaches, the structure of this key nucleus is not yet fully captured.

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.

Background: In the "island of inversion", ground states of neutron-rich $sd$-shell nuclei exhibit strong admixtures of intruder configurations from the $fp$ shell. The nucleus $^{30}$Mg, located at the boundary of the island of inversion, serves as a cornerstone to track the structural evolution as one approaches this region. Purpose: Spin-parity assignments for excited states in $^{30}$Mg, especially negative-parity levels, have yet to be established. In the present work, the nuclear structure of $^{30}$Mg was investigated by in-beam $\gamma$-ray spectroscopy mainly focusing on firm spin-parity determinations. Method: High-intensity rare-isotope beams of $^{31}$Mg, $^{32}$Mg, $^{34}$Si, and $^{35}$P bombarded a Be target to induce nucleon removal reactions populating states in $^{30}$Mg. $\gamma$ rays were detected by the state-of-the-art $\gamma$-ray tracking array GRETINA. For the direct one-neutron removal reaction, final-state exclusive cross sections and parallel momentum distributions were deduced. Multi-nucleon removal reactions from different projectiles were exploited to gain complementary information. Results: With the aid of the parallel momentum distributions, an updated level scheme with revised spin-parity assignments was constructed. Spectroscopic factors associated with each state were also deduced. Conclusions: Results were confronted with large-scale shell-model calculations using two different effective interactions, showing excellent agreement with the present level scheme. However, a marked difference in the spectroscopic factors indicates that the full delineation of the transition into the island of inversion remains a challenge for theoretical models.

Excited states in 28 Na have been studied using the β -decay of implanted 28 Ne ions at GANIL/LISE as well as the in-beam γ -ray spectroscopy at the NSCL/S800 facility. New states of positive (J π =3,4 + ) and negative (J π =1-5 − ) parity are proposed. The former arise from the coupling between 0d 5 / 2 protons and a 0d 3 / 2 neutron, while the latter are due to couplings with 1p 3 / 2 or 0f 7 / 2 neutrons. While the relative energies between the J π =1-4 + states are well reproduced with the USDA interaction in the N=17 isotones, a progressive shift in the ground state binding energy (by about 500 keV) is observed between 26 F and 30 Al. This points to a possible change in the proton-neutron 0d 5 / 2 -0d 3 / 2 effective interaction when moving from stability to the drip line. The presence of J π =1-4 − negative parity states around 1.5 MeV as well as of a candidate for a J π =5 − state around 2.5 MeV give further support to the collapse of the N=20 gap and to the inversion between the 0f 7 / 2 and 1p 3 / 2 levels below Z=12. These features are discussed in the framework of Shell Model and EDF calculations, leading to predicted negative parity states in the low energy spectra of the 26 F and 25 O nuclei.