High-resolution in-beam gamma-ray spectroscopy was used to study excited states of the neutron-deficient nucleus 32Ar populated in fast-beam induced four-and six-nucleon removal reactions from 36,38Ca. One new gamma-ray transition and indications for an additional two were found, allowing for a glimpse at the level scheme beyond the 2+1 state. The nature of the new 1900(4)-keV transition is discussed in the context of the known energy spectrum of the mirror nucleus 32Si and shell-model calculations using the FSU and SDPF-M cross-shell effective interactions. Its resulting parent state at 3767(5) keV, more than 1.3 MeV above the proton separation energy, is tentatively assigned to have mixed sd-shell and 2p-2h character. It might either be the mirror of the J pi = 2+2 state of 32Si at 4230.8(8) keV, but with a decay branch favoring a transition to the 2+1 over the ground state, or the mirror of the 4983.9(11)-keV state with quantum numbers 0+. The resulting mirror-energy differences of -473(5) and -1218(5) keV are both sizable when compared to systematics; in the latter case the result would, in fact, be among the largest reported to date in the nuclear chart or suggest the potential existence of an additional, hitherto unidentified, low-lying 0+ state of 32Si.

A fast secondary beam of Ca-37 impinged on a Be-9 target resulting in a set of reactions populating proton-rich nuclei including Ca-35 and the first observations of Sc-37,Sc-38 and K-34. Invariant-mass spectroscopy, used to reconstruct proton decays for these nuclei, yielded three new ground-state masses and information on their low-lying structures. The newly measured mass excesses are: Delta M(Sc-37) = 3500(410)keV, Delta M(Sc-38) = -4656(14)keV, and Delta M(K-34)=-1487(17)keV. These nuclei straddle the well-known Z = 20 shell closure as well as the N = 16 subshell closure. Trends in separation energies help elucidate how nuclear structure evolves showing a fading of the Z = 20 shell gap for N <= 18 and indications of a N = 16 subshell gap.

We report experimental data for excited states of 72,74Se obtained from proton removal from 73,75Br secondary beams on a proton target. The experiments were performed with the Ursinus-NSCL liquid hydrogen target and the combined GRETINA+S800 setup at the Coupled Cyclotron Facility of the National Superconducting Cyclotron Laboratory at Michigan State University. Within uncertainties, the inclusive cross sections for proton removal from 73,75Br on a proton target are identical suggesting that the same single -particle orbitals contribute to the proton -removal reaction. In addition, details of the partial cross section fragmentation are discussed. The data might suggest that l = 1, 2, 3, and 4 angular momentum transfers are important to understand the population of excited states of 72,74Se in proton removal. Available data for excited states of 74Ge populated through the 75As(d, 3He)74Ge proton -removal reaction in normal kinematics suggest indeed that the fp and sd shell as well as the 1g9/2 orbital contribute. A comparison to data available for odd -A nuclei supports that the bulk of the spectroscopic strengths could be found at lower energies in the even -even Se isotopes than in, for instance, the even -even Ge isotopes. In addition, the population of high -J states seems to indicate that multistep processes contribute to proton -removal reactions at intermediate energies in these collective nuclei.

In -beam gamma -ray spectroscopy was used to study excited states of the neutron -deficient nucleus 37 K populated in fast -beam inelastic -scattering and proton -removal reactions at high -momentum loss. New gamma -ray transitions and gamma gamma coincidence relationships were established using the gamma -ray tracking array GRETINA. The extension of the level scheme up to the first (13 / 2 - ) state highlights the potential of this recently demonstrated population pathway for studies of isospin symmetry involving mirror -energy differences. The nature of the newly identified states is discussed in comparison to shell -model calculations with the FSU cross -shell effective interaction. The calculated occupation numbers of individual orbitals are shown to offer a consistent explanation of the measured mirror -energy differences between 37 K and 37 Ar.

Bound states of the neutron -deficient, near-dripline nucleus 36Ca were populated in two -neutron removal from the ground state of 38Ca, a direct reaction sensitive to the single -particle configurations and couplings of the removed neutrons in the projectile wave function. Final -state exclusive cross sections for the formation of 36Ca and the corresponding longitudinal momentum distributions, both determined through the combination of particle and gamma -ray spectroscopy, are compared to predictions combining eikonal reaction theory and shellmodel two -nucleon amplitudes from the USDB, USDC, and ZBM2 effective interactions. The final -state crosssection ratio sigma (2+1 )/sigma (0+) shows particular sensitivity and is approximately reproduced only with the twonucleon amplitudes from the ZBM2 effective interaction that includes proton cross -shell excitations into the pf shell. Characterizing the proton pf-shell occupancy locally and schematically, an increase of the sd-pf shell gap by 250 keV yields an improved description of this cross-section ratio and simultaneously enables a reproduction of the B(E2; 0+1 -> 2+1 ) excitation strength of 36Ca. This highlights an important aspect if a new shell -model effective interaction for the region was to be developed on the quest to model the neutron -deficient Ca isotopes and surrounding nuclei whose structure is impacted by proton cross -shell excitations.

In the Ge-Sr mass region, isotopes with neutron number N <= 40 are known to feature rapid shape changes with both nucleon number and angular momentum. To gain new insights into their structure, inelastic proton scattering experiments in inverse kinematics were performed on the rare isotopes 74,76Kr. This work focuses on observables related to the J pi = 4+1 states of the Kr isotopes and, in particular, on the hexadecapole degree of freedom. By performing coupled-channels calculations, hexadecapole deformation parameters /34 were determined for the J pi = 4+1 states of 74,76Kr from inelastic proton scattering cross sections. Two possible coupled-channels solutions were found. A comparison to predictions from nuclear energy density functional theory, employing both non-relativistic and relativistic functionals, clearly favors the large, positive /34 solutions. These /34 values are unambiguously linked to the well deformed prolate configuration. Given the /32 - /34 trend, established in this work, it appears that /34 values could provide a sensitive measure of the nuclear shell structure.(c) 2023 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons .org /licenses /by /4 .0/). Funded by SCOAP3.

The B(E2, 0+1 -> 2+1 ) strengths of 36Ca and 38Ca are measured to be 131(20) e2fm4 and 101(11) e2fm4, respectively. The B(E2) value for 36Ca required a measurement of the p/gamma branching ratio because the 2+ state is proton unbound. This branching ratio is Bp = 0.087(8). These B(E2) and branching-ratio values can be reproduced in the shell-model with the ZMB2 interaction, an interaction that predicts the Z = 20 sd-shell closure is incomplete with large proton pf-shell occupancies in the ground state. These occupancies are at odds with other shell-model and energy-density-functional calculations of 36Ca. New data are used to provide an update on constraints of the density dependence of the symmetry energy through mirror charge-radii differences as well as to help reduce uncertainties of the astrophysical important 35K(p, gamma ) reaction.

Enhanced octupole collectivity is expected in the neutron-deficient Ge, Se and Kr isotopes with neutron number $N \approx 40$ and has indeed been observed for $^{70,72}$Ge. Shape coexistence and configuration mixing are, however, a notorious challenge for theoretical models trying to reliably predict octupole collectivity in this mass region, which is known to feature rapid shape changes with changing nucleon number and spin of the system. To further investigate the microscopic configurations causing the prolate-oblate-triaxial shape transition at $A \approx 72$ and their influence on octupole collectivity, the rare isotopes $^{72}$Se and $^{74,76}$Kr were studied via inelastic proton scattering in inverse kinematics. While significantly enhanced octupole strength of $\sim 32$ Weisskopf units (W.u.) was observed for $^{72}$Se, only strengths of $\sim 15$ W.u. were observed for $^{74,76}$Kr. In combination with existing data, the new data clearly question a simple origin of enhanced octupole strengths around $N = 40$. The present work establishes two regions of distinct octupole strengths with a sudden strength increase around the $A=72$ shape transitional point.

We report on the first in-beam γ-ray spectroscopy of the proton-dripline nucleus 40Sc using two-nucleon pickup onto an intermediate-energy rare-isotope beam of 38Ca. The 9Be(38Ca,40Sc+γ)X reaction at 60.9 MeV/nucleon mid-target energy selectively populates states in 40Sc for which the transferred proton and neutron couple to high orbital angular momentum. In turn, due to angular-momentum selection rules in proton emission and the nuclear structure and energetics of 39Ca, such states in 40Sc then exhibit γ-decay branches although they are well above the proton separation energy. This work uniquely complements results from particle spectroscopy following charge-exchange reactions on 40Ca as well as 40Ti EC/β+ decay which both display very different selectivities. The population and γ-ray decay of the previously known first (5−) state at 892 keV and the observation of a new level at 2744 keV are discussed in comparison to the mirror nucleus and shell-model calculations. On the experimental side, this work shows that high-resolution in-beam γ-ray spectroscopy is possible with new generation Ge arrays for reactions induced by rare-isotope beams on the level of a few μb of cross section.