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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 Jπ=41+ states of the Kr isotopes and, in particular, on the hexadecapole degree of freedom. By performing coupled-channels calculations, hexadecapole deformation parameters β4 were determined for the Jπ=41+ 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 β4 solutions. These β4 values are unambiguously linked to the well deformed prolate configuration. Given the β2−β4 trend, established in this work, it appears that β4 values could provide a sensitive measure of the nuclear shell structure.

The heavy-ion inelastic scattering of the neutron-rich nucleus $^{29}$Ne to its excited states was studied using a 100.1 MeV/u $^{29}$Ne rare isotope beam on $^{181}$Ta and $^{9}$Be targets. The combined setup consisting of the GRETINA array, the TRIPLEX device and the S800 Spectrograph facilitates the simultaneous measurements of the two inelastic reactions, providing the first measurement of the transition strengths for this isotope. A sizable E2 strength B(E2↑) which amounts to 163(30) e$^{2}$fm$^{4}$ was determined in the excitation to the 931-keV state, demonstrating a large degree of collectivity. The present results of B(E2↑) are compared to various shell-model calculations, confirming the role of intruder configurations in $^{29}$Ne at the boundary of the island of inversion.

The neutron-deficient Ca isotopes continue to attract attention due to their importance for testing isospin symmetry and their relevance in capture reactions of interest for nova nucleosynthesis and the shape of light curves in Type I X-ray bursts. To date, spectroscopic information on 38,39 Ca is largely limited to data on lower-spin excited states. Here, we report in-beam {\gamma}-ray spectroscopy of complementary higher-spin, complex-structure states in 39 Ca populated in fast-beam-induced, momentum-dissipative processes leading to neutron pickup onto excited configurations of the projectile, 9 Be(38 Ca , 39 Ca + {\gamma})X. Such a dissipative reaction was recently characterized for the case of inelastic scattering of 38 Ca off 9 Be, 9 Be(38 Ca, 38 Ca + {\gamma})X. Additional data and discussion on the nuclear structure of 38 Ca is also presented. An explanation for the more-complex-structure states, populated with small cross sections in one-nucleon knockout reactions, and observed in the tails of their longitudinal momentum distributions, is also offered., Comment: Submitted to Phys. Rev. C

The $^{25}$F($5/2^+) (-1p) ^{24}$O reaction was studied at the NSCL using the S800 spectrometer. The experimental spectroscopic factor for the ground-state to ground-state transition indicates a substantial depletion of the proton $d_{5/2}$ strength compared to shell-model expectations. Our result supports the findings reported by Tang \textit{et al.}, from their study of the $(p,2p)$ reaction at RIBF. The overlap between the $^{25}$F and $^{24}$O ground-states is considerably less than anticipated if $^{24}$O acted as a robust and rigid doubly-magic core in $^{25}$F. We interpret the results within the framework of the Particle-Vibration Coupling (PVC) of a $d_{5/2}$ proton coupled to a quadrupole phonon of an effective core. This approach provides a good description of the experimental data by requiring an effective $^{24}$O* core with a phonon energy of $\hbar\omega_2$= 3.2 MeV, and a $B(E2) ~ 2.7$ W.u., softer and more collective than a bare $^{24}$O. Both the Nilsson deformed mean field and the PVC models appear to capture the properties of the effective core of $^{25}$F, suggesting that the additional proton tends to polarize the free, doubly magic $^{24}$O in such a way that it becomes either slightly deformed or a quadrupole vibrator., Comment: 6 pages, 2 figures

Background: The nucleus $^{32}$Mg ($N=20$ 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 $^{32}$Mg, 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 $^{32}$Mg was performed using two direct-reaction probes, one-neutron (two-proton) knockout reactions on $^{33}$Mg ($^{34}$Si). 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 $^{32}$Mg, 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 $^{32}$Mg 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.

A sequence of excited states has been established for the first time in the proton-rich nucleus 48Fe (Z=26, N=22). The technique of mirrored (i.e. analogue) one-nucleon knockout reactions was applied, in which the Tz= ±2 mirror pair, 48Fe/48Ti were populated via one-neutron/one-proton knockout from the secondary beams 49Fe/49V, respectively. The analogue properties of the reactions were used to help establish the new level scheme of 48Fe. The inclusive and exclusive cross sections were determined for the populated states. Large differences between the cross sections for the two mirrored reactions were observed and have been interpreted in terms of different degrees of binding of the mirror nuclei and in the context of the recent observations of suppression of spectroscopic strength as a function of nuclear binding, for knockout reactions on light solid targets. Mirror energy differences (MED) have been determined between the analogue T=2 states and compared with the shell model predictions. MED for this mirror pair, due to their location in the shell, are especially sensitive to excitations out of the f7/2 shell, and present a stringent test of the shell-model prescription.

Situated in the so-called “island of inversion,” the nucleus $^{32}$Mg is considered as an archetypal example of the disappearance of magicity at N=20. We report on high statistics in-beam spectroscopy of $^{32}$Mg 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 $^{32}$Mg were populated by knockout reactions starting from $^{33}$Mg and $^{34}$Si, 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 $^{32}$Mg and spin-parity assignments. By fully exploiting observables obtained in this measurement, a variety of structures coexisting in $^{32}$Mg 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.

Mortality among patients hospitalized for COVID-19 has declined over the course of the pandemic. Mortality trends specifically in solid organ transplant recipients (SOTR) are unknown. Using data from a multicenter registry of SOTR hospitalized for COVID-19, we compared 28-day mortality between early 2020 (March 1, 2020-June 19, 2020) and late 2020 (June 20, 2020-December 31, 2020). Multivariable logistic regression was used to assess comorbidity-adjusted mortality. Time period of diagnosis was available for 1435/1616 (88.8%) SOTR and 971/1435 (67.7%) were hospitalized: 571/753 (75.8%) in early 2020 and 402/682 (58.9%) in late 2020 (p&nbsp

International audience; Excited states in the neutron-rich nucleus Fe68 were populated using a Be9(Co68, 68Fe+γ)X charge-exchange reaction at 95 MeV/u. The new γ-ray transitions reported here for the first time complement data from β-decay studies and nucleon knockout reactions. In comparison to shell-model calculations with the LNPS effective interaction, two candidate states for the 61+ level emerge. The distinct population pattern of excited states and the magnitude of the cross section, σinc=0.51(6) mb, make this reaction a promising one for future in-beam γ-ray spectroscopy. Reaction calculations with nuclear structure input from a new, locally optimized Hamiltonian, f7j4a, together with general considerations for heavy-ion-induced charge-exchange reactions appear consistent with most of the observations, although challenges remain.

The region of neutron-rich Cr isotopes has garnered much attention in recent years due to a rapid onset of collectivity near neutron number N=40. We report here on the first γ-ray spectroscopy beyond the (41+) state in Cr62,64, using nucleon removal reactions from several projectiles within a rare-isotope beam cocktail. A candidate for the 6+ state in Cr64 is presented as well as one for, possibly, the second excited 0+ state in Cr62. The results are discussed in comparison to the LNPS shell-model predictions that allow for neutron excitations across the N=40 harmonic oscillator gap into the g9/2 and d5/2 orbitals. The calculated level schemes for Cr62,64 reveal intriguing collective structures. From the predicted neutron particle-hole character of the low-lying states in these Cr isotopes, Cr62 emerges as a transitional system on the path to the center of the N=40 island of inversion.

Discovering unexplored high-spin states in neutron-rich nuclei can open up a new direction to study band structure and the associated shell structure in isospin-asymmetric many-body systems. However, experimental reach has so far been limited to neutron-deficient or stable nuclei which are preferentially produced in fusion reactions used in such studies. Here, we report the first γ-ray spectroscopy with fusion reactions using a reaccelerated rare-isotope beam of 45K performed at the ReA3 facility of the National Superconducting Cyclotron Laboratory. Using particle and γ-ray coincidence techniques, three new higher-lying states around 6 MeV and five new γ-ray transitions were identified for 46Ca, suggesting three independent band structures formed from different particle-hole configurations. The rotational-like band built on the 0+2 state is established up to the tentatively assigned 6+2 state. New results are compared to large-scale shell model calculations, confirming the validity of the effective interaction describing particle-hole excitations across the Z=20 and N=28 shell gaps in the vicinity of doubly magic 48Ca.

The shape and collectivity of 106Cd was investigated via a sub-barrier-energy Coulomb excitation experiment performed at the National Superconducting Cyclotron Laboratory Re-accelerator facility using the JANUS setup. Transition matrix elements between low-lying states were found to agree with adopted values, and information on the shape and collectivity of higher-lying states was extracted for the first time. Locally optimized large-scale shell-model calculations were found to describe well the B(E2) transition strengths but failed to reproduce the spectroscopic quadrupole moments Qs. An analysis of the E2 rotational invariants and the normalized quadrupole moment qs indicates that this may be due to a significant degree of triaxiality in 106Cd which is not captured by the present shell-model calculations. Analogous calculations for the Fe isotopes (two protons below the Z=28 magic number) reveal the critical role of high-j neutron configurations for the description of quadrupole moments in the heavy Fe and Cd isotopes (two protons below magic Z=50), but this effect is insufficient to explain the shape of 106Cd, posing a puzzle for the understanding of nuclear structure towards N=50.

International audience; The region of neutron-rich Cr isotopes has garnered much attention in recent years due to a rapid onset of collectivity near neutron number N = 40. We report here on the first γ-ray spectroscopy beyond the (4 + 1) state in 62,64 Cr, using nucleon removal reactions from several projectiles within a rare-isotope beam cocktail. A candidate for the 6 + state in 64 Cr is presented as well as one for, possibly, the second excited 0 + state in 62 Cr. The results are discussed in comparison to the LNPS shell-model predictions that allow for neutron excitations across the N = 40 harmonic oscillator gap into the g 9/2 and d 5/2 orbitals. The calculated level schemes for 62,64 Cr reveal intriguing collective structures. From the predicted neutron particle-hole character of the low-lying states in these Cr isotopes, 62 Cr emerges as a transitional system on the path to the center of the N = 40 island of inversion.

Energy differences between isobaric analogue states have been extracted for the A=79, $^{79}$Zr/$^{79}$Y mirror pair following their population via nucleon-knockout reactions from intermediate-energy rare-isotope beams. These are the heaviest nuclei where such measurements have been made to date. The deduced mirror energy differences (MED) are compared with predictions from a new density-functional based approach, incorporating isospin-breaking effects of both Coulomb and nuclear charge-symmetry breaking and configuration mixing.

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.

We report on the first in-beam γ-ray spectroscopy of the proton-dripline nucleus $^{40}$Sc using two-nucleon pickup onto an intermediate-energy rare-isotope beam of $^{38}$Ca. The $^{9}$Be($^{38}$Ca,$^{40}$Sc+γ)X reaction at 60.9 MeV/nucleon mid-target energy selectively populates states in $^{40}$Sc 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 $^{39}$Ca, such states in $^{40}$Sc 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 $^{40}$Ca as well as $^{40}$Ti 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.

The single-particle structure of the N = 27 isotones provides insights into the shell evolution of neutron-rich nuclei from the doubly-magic 48Ca toward the drip line. 43S was studied employing the one-neutron knockout reaction from a radioactive 44S beam. Using a combination of prompt and delayed γ-ray spectroscopy the level structure of 43S was clarified. Momentum distributions were analyzed and allowed for spin and parity assignments. The deduced spectroscopic factors show that the 44S ground-state configuration has a strong intruder component. The results were confronted with shell model calculations using two effective interactions. General agreement was found between the calculations, but strong population of states originating from the removal of neutrons from the 2p3/2 orbital in the experiment indicates that the breakdown of the N = 28 magic number is more rapid than the theoretical calculations suggest.

The single-particle structure of the $N=27$ isotones provides insights into the shell evolution of neutron-rich nuclei from the doubly-magic $^{48}$Ca toward the drip line. $^{43}$S was studied employing the one-neutron knockout reaction from a radioactive $^{44}$S beam. Using a combination of prompt and delayed $\gamma$-ray spectroscopy the level structure of $^{43}$S was clarified. Momentum distributions were analyzed and allowed for spin and parity assignments. The deduced spectroscopic factors show that the $^{44}$S ground-state configuration has a strong intruder component. The results were confronted with shell model calculations using two effective interactions. General agreement was found between the calculations, but strong population of states originating from the removal of neutrons from the $2p_{3/2}$ orbital in the experiment indicates that the breakdown of the $N=28$ magic number is more rapid than the theoretical calculations suggest., Comment: accepted for publication, Physical Review C

The structure of ³³Si was studied by a one-neutron knockout reaction from a ³⁴Si beam at 98.5 MeV/u incident on a 9 Be target. The prompt γ rays following the de-excitation of ³³Si were detected using the GRETINA γ -ray tracking array while the reaction residues were identified on an event-by-event basis in the focal plane of the S800 spectrometer at the National Superconducting Cyclotron Laboratory. The presently derived spectroscopic factor values, C 2 S , for the 3 / 2 + and 1 / 2 + states, corresponding to a neutron removal from the 0 d 3 / 2 and 1 s 1 / 2 orbitals, agree with shell model calculations and point to a strong N = 20 shell closure. Three states arising from the more bound 0 d 5 / 2 orbital are proposed, one of which is unbound by about 930 keV. The sensitivity of this experiment has also confirmed a weak population of 9 / 2 − and 11 / 2 − 1 , 2 final states, which originate from a higher-order process. This mechanism may also have populated, to some fraction, the 3 / 2 − and 7 / 2 − negative-parity states, which hinders a determination of the C 2 S values for knockout from the normally unoccupied 1 p 3 / 2 and 0 f 7 / 2 orbits.

The structure of exotic nuclei provides valuable tests for state-of-the-art nuclear theory. In particular electromagnetic transition rates are more sensitive to aspects of nuclear forces and many-body physics than excitation energies alone. We report the first lifetime measurement of excited states in $^{21}$O, finding τ1/2+=420−32+35(stat)−12+34(sys) ps. This result together with the deduced level scheme and branching ratio of several γ-ray decays are compared to both phenomenological shell-model and ab initio calculations based on two- and three-nucleon forces derived from chiral effective field theory. We find that the electric quadrupole reduced transition probability of B(E2;1/2+→5/2g.s.+)=0.71−0.06−0.06+0.07+0.02 e$^{2}$fm$^{4}$, derived from the lifetime of the 1/2+ state, is smaller than the phenomenological result where standard effective charges are employed, suggesting the need for modifications of the latter in neutron-rich oxygen isotopes. We compare this result to both large-space and valence-space ab initio calculations, and by using multiple input interactions we explore the sensitivity of this observable to underlying details of nuclear forces.

New experimental data obtained from $\gamma$-ray tagged one-neutron and one-proton knockout from $^{55}$Co is presented. A candidate for the sought-after $T=1, T_z = 0, J^{\pi} = 6^+$ state in $^{54}$Co is proposed based on a comparison to the new data on $^{54}$Fe, the corresponding observables predicted by large-scale-shell-model (LSSM) calculations in the full $fp$-model space employing charge-dependent contributions, and isospin-symmetry arguments. Furthermore, possible isospin-symmetry breaking in the $A=54$, $T=1$ triplet is studied by calculating the experimental $c$ coefficients of the isobaric mass multiplet equation (IMME) up to the maximum possible spin $J=6$ expected for the $(1f_{7/2})^{-2}$ two-hole configuration relative to the doubly-magic nucleus $^{56}$Ni. The experimental quantities are compared to the theoretically predicted $c$ coefficients from LSSM calculations using two-body matrix elements obtained from a realistic chiral effective field theory potential at next-to-next-to-next-to-leading order (N$^3$LO)., Comment: 6 pages, 5 figures. Work has been published

Simpson and Tostevin proposed that the width and shape of exclusive parallel momentum distributions of the A-2 residue in direct two-nucleon knockout reactions carry a measurable sensitivity to the nucleon single-particle configurations and their couplings within the wave functions of exotic nuclei. We report here on the first benchmarks and use of this new spectroscopic tool. Exclusive parallel momentum distributions for states in the neutron-deficient nuclei $^{22}$Mg, $^{23}$Al, and $^{24}$Si populated in such direct two-neutron removal reactions were extracted and compared to predictions combining eikonal reaction theory and shell-model calculations. For the well-known $^{22}$Mg and $^{23}$Al nuclei, measurements and calculations were found to agree, supporting the dependence of the parallel momentum distribution width on the angular momentum composition of the shell-model two-neutron amplitudes. In $^{24}$Si, a level at 3439(9) keV, of relevance for the important $^{23}$Al(p,$\gamma$)$^{24}$Si astrophysical reaction rate, was confirmed to be the $2^+_2$ state, while the $4^+_1$ state, expected to be strongly populated in two-neutron knockout, was not observed. This puzzle is resolved by theoretical considerations of the Thomas-Ehrman shift, which also suggest that a previously reported 3471-keV state in $^{24}$Si is in fact the ($0^+_2$) level with one of the largest experimental mirror-energy shifts ever observed., Comment: Accepted for publication in Phys. Rev. C as a Rapid Communication

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