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The nucleus $^{212}$Po has been produced through the fragmentation of a $^{238}$U primary beam at 1 GeV/nucleon at GSI, separated with the FRagment Separator, FRS, and studied via isomer γ-decay spectroscopy with the RISING setup. Two delayed previously unknown γ rays have been observed. One has been attributed to the E3 decay of a 21$^{−}$ isomeric state feeding the α-emitting 45-s (18$^{+}$) high-spin isomer. The other γ-ray line has been assigned to the decay of a higher-lying 23$^{+}$ metastable state. These are the first observations of high-spin states above the $^{212}$Po (18$^{+}$) isomer, by virtue of the selectivity obtained via ion-by-ion identification of $^{238}$U fragmentation products. Comparison with shell-model calculations points to shortfalls in the nuclear interactions involving high-j proton and neutron orbitals, to which the region around Z∼100 is sensitive.

The DEcay SPECtroscopy (DESPEC) setup for nuclear structure investigations was developed and commissioned at GSI, Germany in preparation for a full campaign of experiments at the FRS and Super-FRS. In this paper, we report on the first employment of the setup in the hybrid configuration with the AIDA implanter coupled to the FATIMA LaBr3(Ce) fast-timing array, and high-purity germanium detectors. Initial results are shown from the first experiments carried out with the setup. An overview of the setup and function is discussed, including technical advancements along the path. © 2022 Elsevier B.V.

International audience; The structure of As83, As85, and As87 have been studied in fusion-fission reaction U238+Be9. Fission fragments were identified in mass and atomic number using the VAMOS++ spectrometer and the coincident γ rays were detected in the γ-ray tracking array AGATA. New transitions in As83 and As85 are reported and placed in the level schemes. A level scheme of the excited states in As87 is proposed for the first time. The data are interpreted in frame of large-scale shell-model calculations, SU3 symmetries, and beyond mean-field frameworks. A spherical regime at magic number N=50 is predicted and the location of the proton g9/2 orbital is proposed for the first time. Development of collectivity in a prolate deformed, γ-soft regime in the open shell cases As85 and As87, most neutron-rich isotopes beyond N=50, is concluded. Data and theoretical calculations give confidence to a relatively high extrapolated excitation energy about 4 MeV of the 9/2+ state in Cu79, one proton above Ni78.

Excited states in $^{56}$Zn were populated following one-neutron removal from a $^{57}$Zn beam impinging on a Be target at intermediate energies in an experiment conducted at the Radioactive Isotope Beam Factory at RIKEN. Three γ rays were observed and tentatively assigned to the 6+→4+→2+→0+ yrast sequence. This turns $^{56}$Zn into the heaviest Tz=−2 nucleus in which excited states are known. The excitation-energy differences between these levels and the isobaric analogue states in the Tz=+2 mirror partner, $^{56}$Fe, are compared with large-scale shell-model calculations considering the full pf valence space and various isospin-breaking contributions. This comparison, together with an analysis of the mirror energy differences in the A=58, Tz=±1 pair $^{58}$Zn and $^{58}$Ni, provides valuable information with respect to the size of the monopole radial and the isovector multipole isospin-breaking terms in the region above doubly-magic $^{56}$Ni.

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.

The low-lying excited states in the neutron-deficient $N = Z + 1$ nucleus $^{87}_{43}$Tc$_{44}$ have been studied via the fusion-evaporation reaction $^{54}$Fe $(^{36}Ar, 2n1p)$ $^{87}$Tc at the Grand Accélérateur National d'Ions Lourds (GANIL), France. The AGATA spectrometer was used in conjunction with the auxiliary NEDA, Neutron Wall, and DIAMANT detector arrays to measure coincident prompt γ rays, neutrons, and charged particles emitted in the reaction. A level scheme of $^{87}$Tc from the $(9/2^+_{g.s})$ state to the $( 33 / 2^+_1$) state was established based on six mutually coincident γ -ray transitions. The constructed level structure exhibits a rotational behavior with a sharp backbending at $ℏω ≈ 0.50$ MeV. A decrease in alignment frequency and increase in alignment sharpness in the odd-mass isotonic chains around $N=44$ is proposed as an effect of the enhanced isoscalar neutron-proton interactions in odd-mass nuclei when approaching the $N=Z$ line. The low-lying excited states in the neutron-deficient $N=Z+1$ nucleus $^{87}_{43}$Tc$^{\ }_{44}$ have been studied via the fusion-evaporation reaction $^{54}$Fe($^{36}$Ar, $2n1p$)$^{87}$Tc at the Grand Accélérateur National d'Ions Lourds (GANIL), France. The AGATA spectrometer was used in conjunction with the auxiliary NEDA, Neutron Wall, and DIAMANT detector arrays to measure coincident prompt $\gamma$-rays, neutrons, and charged particles emitted in the reaction. A level scheme of $^{87}$Tc from the (9/2$^{+}_{g.s.}$) state to the (33/2$^{+}_{1}$) state was established based on 6 mutually coincident $\gamma$-ray transitions. The constructed level structure exhibits a rotational behavior with a sharp backbending at $\hbar\omega\approx 0.50$ MeV. A decrease in alignment frequency and increase in alignment sharpness in the odd-mass isotonic chains around $N=44$ is proposed as an effect of the enhanced isoscalar neutron-proton interactions in odd-mass nuclei when approaching the $N=Z$ line.

Excited states in the mirror nuclei $^{31}$P and $^{31}$S were populated in the 1p and 1n exit channels of the reaction $^{20}$Ne + $^{12}$C, at a beam energy of 33 MeV. The $^{20}$Ne beam was delivered for the first time by the Piave-Alpi accelerator of the Laboratori Nazionali di Legnaro. Angular correlations of coincident γ-rays and Doppler-shift attenuation lifetime measurements were performed using the multi-detector array GASP in conjunction with the EUCLIDES charged particle detector. In the observed B(E1) strengths, the isoscalar component, amounting to 24% of the isovector one, provides strong evidence for breaking of the isospin symmetry in the A=31 mass region. Self-consistent beyond mean field calculations using Equation of Motion method based on a chiral potential and including two- and three-body forces reproduce well the experimental B(E1) strengths, reinforcing our conclusion. Coherent mixing from higher-lying states involving the Giant Isovector Monopole Resonance accounts well for the effect observed. The breaking of the isospin symmetry originates from the violation of the charge symmetry of the two- and three-body parts of the potential, only related to the Coulomb interaction.

The neutron-rich $^{213}$Pb isotope was produced in the fragmentation of a primary 1 GeV A $^{238}$U beam, separated in FRS in mass and atomic number, and then implanted for isomer decay γ-ray spectroscopy with the RISING setup at GSI. A newly observed isomer and its measured decay properties indicate that states in $^{213}$Pb are characterized by the seniority quantum number that counts the nucleons not in pairs coupled to angular momentum J=0. The conservation of seniority is a consequence of a geometric phase associated with particle-hole conjugation, which becomes observable in semi-magic nuclei where nucleons half-fill the valence shell. The γ-ray spectroscopic observables in $^{213}$Pb are thus found to be driven by two mechanisms, particle-hole conjugation and seniority conservation, which are intertwined through a Berry phase.

International audience; Excited states in Ba131 and Ce133 were studied using in-beam γ-ray spectroscopy through the Sn122(C13,4n)Ba131 and Te125(C12,4n)Ce133 reactions, respectively. A strongly coupled band, associated with the νg7/2[404]7/2+ configuration, was identified in Ba131 and Ce133. It is the first time to observe the νg7/2[404]7/2+ bands in the N=75 isotones. The signature partners exhibit considerable energy splitting in comparison with those in the πg7/2[404]7/2+ bands in the odd-A Ta and Re isotopes. Extensive cranked shell model and quasiparticle-plus-triaxial-rotor model calculations reveal the origin of the signature splitting, which depends not only on the triaxiality, but also on the configuration mixing with nearby low-j orbitals.

International audience; A $\gamma$ -ray spectroscopic study of $^{212}$Po was performed at the Grand Accélérateur National d’Ions Lourds, using the inverse kinematics α-transfer reaction $^{12}$C($^{208}$Pb, $^{212}$Po) $^8$Be and the AGATA spectrometer. A careful analysis based on $\gamma \gamma$ coincidence relations allowed us to establish 14 new excited states in the energy range between 1.9 and 3.3 MeV. None of these states, however, can be considered as candidates for the levels with spins and parities of $1^-$ and $2^-$ and excitation energies below 2.1 MeV, which have been predicted by recent αcluster model calculations. A systematic comparison of the experimentally established excitation scheme of $^{212}$Po with shell-model calculations was performed. This comparison suggests that the six states with excitation energies (spins and parities) of 1744 (4$^-$), 1751 (8$^-$), 1787 (6$^-$), 1946 (4$^-$), 1986 (8$^-$), and 2016 (6$^-$) keV, which previously were interpreted as α-cluster states, may in fact be of positive parity and belong to low-lying shell-model multiplets. This reinterpretation of the structure of $^{212}$Po is supported by experimental information with respect to the linear polarization of $\gamma$ rays, which suggests a magnetic character of the 432-keV $\gamma$ ray decaying from the state at an excitation energy of 1787 keV to the $6^+_1$ yrast state, and exclusive reaction cross sections.

5 pags., 4 figs., 1 tab., Neutron-rich nuclei in the vicinity of the $N=40$ island of inversion are characterized by shell evolution and exhibit deformed ground states. In several nuclei isomeric states have been observed and attributed to excitations to the intruder neutron $1g_{9/2}$ orbital. In the present study we searched for isomeric states in nuclei around $N=40$, $Z=22$ produced by projectile fragmentation at RIBF. Delayed $\gamma$ rays were detected by the EURICA germanium detector array. High statistics data allowed for an updated decay scheme of $^{60}$V. The lifetime of an isomeric state in $^{64}$V was measured for the first time in the present experiment. A previously unobserved isomeric state was discovered in $^{58}$Sc. The measured lifetime suggests a parity changing transition, originating from an odd number of neutrons in the $1g_{9/2}$ orbital. The nature of the isomeric state in $^{58}$Sc is thus different from isomers in the less exotic V and Sc nuclei., This experiment was carried out at the RIBF operated by RIKEN Nishina Center, RIKEN, and CNS, University of Tokyo. We would like to thank the RIKEN accelerator and BigRIPS teams for providing the high intensity beams. This work has been supported by JSPS KAKENHI (Grants No. 25247045 and No. 19H00679), by the German BMBF (Grants No. 05P15RDFN1 and No. 05P19RDFN1), by the German DFG (Project No. 279384907-SFB 1245), by the STFC (U.K.), by the Korean National Research Foundation (Grants No. NRF-21A20131111123 and No. NRF2015H1A2A1030275), by NKFIH (Grant No. NN128072), and by the UNKP-20-5-DE-2 New National Excellence Program of the Ministry of Human Capacities of Hungary. K.W. acknowledges support from the Spanish Ministerio de Economía y Competitividad Grant No. RYC-2017-22007. G.K. acknowledges support from the Janos Bolyai Research Fellowship of the Hungarian Academy of Sciences.

Background: The heaviest Tz=0 doubly-magic nucleus, 100Sn, and the neighboring nuclei offer unique opportunities to investigate the properties of nuclear interaction. For instance, the structure of light-Sn nuclei has been shown to be affected by the delicate balance between nuclear-interaction components, such as pairing and quadrupole correlations. From Cd to Te, many common features and phenomena have been observed experimentally along the isotopic chains, leading to theoretical studies devoted to a more general and comprehensive study of the region. In this context, having only two proton holes in the Z=50 shell, the Cd isotopes are expected to present properties similar to those found in the Sn isotopic chain. Purpose: The aim of this work was to measure lifetimes of excited states in neutron-deficient nuclei in the vicinity of 100Sn. Methods: The neutron-deficient nuclei in the N≈Z≈50 region were populated using a multinucleon transfer reaction with a 106Cd beam and a 92Mo target. The beamlike products were identified by the VAMOS++ spectrometer, while the γ rays were detected using the AGATA array. Lifetimes of excited states were determined using the recoil distance Doppler-shift method, employing the Cologne differential plunger. Results: Lifetimes of low-lying states were measured in the even-mass 102–108Cd isotopes. In particular, multiple states with excitation energy up to ≈3 MeV, belonging to various bands, were populated in 106Cd via inelastic scattering. The transition strengths corresponding to the measured lifetimes were compared with those resulting from state-of-the-art beyond-mean-field calculations using the symmetry-conserving configuration-mixing approach. Conclusions: Despite the similarities in the electromagnetic properties of the low-lying states, there is a fundamental structural difference between the ground-state bands in the Z=48 and Z=50 isotopes. The comparison between experimental and theoretical results revealed a rotational character of the Cd nuclei, which have prolate-deformed ground states with β2≈0.2. At this deformation Z=48 becomes a closed-shell configuration, which is favored with respect to the spherical one.

19 pags., 14 figs., 3 tabs., A γ-ray spectroscopic study of Po212 was performed at the Grand Accélérateur National d'Ions Lourds, using the inverse kinematics α-transfer reaction C12(Pb208,Po212)Be8 and the AGATA spectrometer. A careful analysis based on γγ coincidence relations allowed us to establish 14 new excited states in the energy range between 1.9 and 3.3 MeV. None of these states, however, can be considered as candidates for the levels with spins and parities of 1- and 2- and excitation energies below 2.1 MeV, which have been predicted by recent α-cluster model calculations. A systematic comparison of the experimentally established excitation scheme of Po212 with shell-model calculations was performed. This comparison suggests that the six states with excitation energies (spins and parities) of 1744 (4-), 1751 (8-), 1787 (6-), 1946 (4-), 1986 (8-), and 2016 (6-) keV, which previously were interpreted as α-cluster states, may in fact be of positive parity and belong to low-lying shell-model multiplets. This reinterpretation of the structure of Po212 is supported by experimental information with respect to the linear polarization of γ rays, which suggests a magnetic character of the 432-keV γ ray decaying from the state at an excitation energy of 1787 keV to the 61+ yrast state, and exclusive reaction cross sections., This project has received funding from the European Union’s Horizon 2020 research and innovation programme under Grant Agreement No. 654002 and FEDER funds. We furthermore acknowledge support from the Spanish Ministerio de Ciencia, Inovación y Universidades under contracts FPA2014-57196-C5, FPA2017-84756-C4, and SEV-2014-0398, the Generalitat Valenciana under Grant No. PROMETEO/2019/005, the Swedish Research Council (Vetenskapsrådet, VR 2016-3969), and the German BMBF under Contracts No. 05P18PKFN9 and No. 05P19PKFNA.

International audience; Background: The evolution of shell structure around doubly magic exotic nuclei is of great interest in nuclear physics and astrophysics. In the ‘southwest’ region of Ni78, the development of deformation might trigger a major shift in our understanding of explosive nucleosynthesis. To this end, new spectroscopic information on key close-lying nuclei is very valuable.Purpose: We intend to measure the isomeric and β decay of Co75, with one-proton and two-neutron holes relative to Ni78, to access new nuclear structure information in Co75 and its β-decay daughters Ni75 and Ni74.Methods: The nucleus Co75 is produced in relativistic in-flight fission reactions of U238 at the Radioactive Ion Beam Factory in the RIKEN Nishina Center. Its isomeric and β decay are studied exploiting the BigRIPS and EURICA setups.Results: We obtain partial β-decay spectra for Ni75 and Ni74, and report a new isomeric transition in Co75. The energy [Eγ=1914(2)keV] and half-life [t1/2=13(6)μs] of the delayed γ ray lend support for the existence of a Jπ=(1/2−) isomeric state at 1914(2) keV. A comparison with PFSDG-U shell-model calculations provides a good account for the observed states in Ni75, but the first calculated 1/2− level in Co75, a prolate K=1/2 state, is predicted about 1 MeV below the observed (1/2−) level.Conclusions: The spherical-like structure of the lowest-lying excited states in Ni75 is proved. In the case of Co75, the results suggest that the dominance of the spherical configurations over the deformed ones might be stronger than expected below Ni78. Further experimental efforts to discern the nature of the Jπ=(1/2−) isomer are necessary.

The heaviest N=Z doubly-magic nucleus, $^{100}$Sn, and the neighboring nuclei offer unique opportunities to investigate the properties of nuclear interaction in extreme conditions. In particular, the Cd isotopes are expected to present features similar to those found in the Sn isotopic chain, since they have only two proton holes in the Z=50 shell. In this manuscript, the lifetime measurements of low-lying states in the even-mass $^{102-108}$Cd is presented. Thanks to the powerful detection capabilities of AGATA array and VAMOS++ spectrometer, the unusual employment of multi-nucleon transfer reactions permitted to investigate the first 2$^+$ and 4$^+$ states in all these nuclei, together with various deformed bands in $^{106}$Cd. The results were interpreted in the context of new state-of-the-art beyond-mean-field calculations, using the symmetry-conserving configuration-mixing approach. Despite the similarities in the electromagnetic properties of the low-lying states, there is a fundamental structural difference between the ground-state bands in the Z=48 and Z=50 isotopes. The comparison between experimental and theoretical results revealed a rotational character of the Cd nuclei, which have prolate-deformed ground states with $\beta_2 \approx 0.2$. At this deformation Z=48 becomes a closed-shell configuration, which is favored with respect to the spherical one., Comment: V1 : 14 pages, 12 figures. V2 : 16 pages, 11 figures. V3 : 16 pages, 11 figures (figure 11 corrected); triaxiality evaluated with "quadrupole sum rule". submitted to Phys.Rev.C

International audience; Mirror energy differences (MED) between excited states in the A=31, T=1/2 mirror pair S31 and P31 have been measured up to high spin yrast states of positive and negative parity. The mirror nuclei were populated in the Mg24(C12, αn) and Mg24(C12, αp) reactions, respectively. For the first time the MED are described in the framework of the shell model in a valence space that includes three main shells. The theoretical MED values as a function of angular momentum indicate that the main contribution arises from the Coulomb interaction, however, the isospin symmetry breaking term is not at all negligible and needs to be considered to reproduce the experimental findings.

5 pags., 4 figs., The low-lying excited states in the neutron-deficient N=Z+1 nucleus Tc444387 have been studied via the fusion-evaporation reaction Fe54(Ar36, 2n1p)Tc87 at the Grand Accélérateur National d'Ions Lourds (GANIL), France. The AGATA spectrometer was used in conjunction with the auxiliary NEDA, Neutron Wall, and DIAMANT detector arrays to measure coincident prompt γ rays, neutrons, and charged particles emitted in the reaction. A level scheme of Tc87 from the (9/2g.s.+) state to the (33/21+) state was established based on six mutually coincident γ-ray transitions. The constructed level structure exhibits a rotational behavior with a sharp backbending at ω≈0.50 MeV. A decrease in alignment frequency and increase in alignment sharpness in the odd-mass isotonic chains around N=44 is proposed as an effect of the enhanced isoscalar neutron-proton interactions in odd-mass nuclei when approaching the N=Z line., This work was supported by the Swedish Research Council under Grants No. 621-2014-5558 and No. 2019-04880, the EU 7th Framework Programme, Integrating Activities Transnational Access, Project No. 262010 ENSAR, the UK STFC under Grants No. ST/L005727/1 and No. ST/P003885/1, the Polish National Science Centre, Grants No. 2017/25/B/ST2/01569, No. COPIN-INFN, No. COPIN-IN2P3, and No. COPIGAL projects, the National Research, Development and Innovation Fund of Hungary (Project No. K128947), the European Regional Development Fund (Contract No. GINOP-2.3.3-15-2016-00034), the Hungarian National Research, Development and Innovation Office - NKFIH, Contract No. PD124717, the Ministerio de Ciencia e Innovación and Generalitat Valenciana, Spanish, under Grants No. SEV-2014-0398, No. FPA2017-84756-C4, and No. PROMETEO/2019/005 and by the EU FEDER funds. X.L. gratefully acknowledges support from the China Scholarship Council, Grant No. 201700260183 for his stay in Sweden.