The lifetimes of low-lying excited states below the 8+ seniority isomer were directly measured using fast timing detectors in the neutron-deficient isotopes 98,100Cd. This experiment was conducted with the DEcay SPECtroscopy (DESPEC) setup at GSI, where the ions of interest were produced via a fragmentation reaction and identified using the FRagment Separator (FRS) before being implanted in the AIDA active stopper system, and the γ rays emitted during the de-excitation of isomeric states were detected by the LaBr3 FATIMA Array. The newly deduced values for the reduced transition probabilities were compared with shell-model calculations using different interactions and effective charges. The results indicate that, while 98Cd aligns well with a seniority scheme description, in 100Cd the transition strengths among low-lying states are not fully reproduced, and the nature of these states remains an open problem within the present theoretical description. Ultimately, a key element in the description of this region, crucial for nuclear physics and astrophysics, appears to be the proton-neutron term of the nuclear effective interaction.

Data on the structure of sulphur isotopes close to the neutron drip-line are rather scarce. The excited states of the very neutron-rich 46S and 47S nuclei have been investigated by in-beam gamma-ray spectroscopy at the Radioactive Isotope Beam Factory at the RIKEN Nishina Center. After multi-nucleon knockout reactions on the liquid-hydrogen MINOS target, the 2(1)(+) -> 0(1)(+) gamma transition of S-46, already reported in literature, has been confirmed. Additionally, two new gamma rays have been assigned to this isotope and one gamma line has been observed in S-47.

Excited states ranging from low to high spin in Nd135 have been investigated using the Mo100(Ar40, 5n) heavy ion fusion evaporation reaction with the JUROGAM II γ-ray spectrometer. In the present work we report a new 17/23- state and a new band composed of E2 transitions at high spin. The configuration assigned to the 17/23- state is obtained by coupling one neutron in the 1/2+[400] orbital to the 8- isomer in Nd134 based on the ν7/2+[404] - 9/2-[514] configuration. The deduced ratio of reduced transition probabilities of 2.0(5) from the new 17/23- state to the 13/22- and 13/21- states supports the tilted precession interpretation of the band built on the 13/22- state, in which, instead of the rotation around the intermediate axis present in the yrast band, the rotation is around the long axis of the intrinsic reference frame. The configuration of the newly observed high-spin band is discussed in the framework of the cranked Nilsson-Strutinsky model. The calculated results provide evidence for large triaxiality of the discussed bands.

Lifetime measurements of low-lying excited states in the semimagic (N=50) nucleus Rh95 have been performed by means of the fast-timing technique. The experiment was carried out using γ-ray detector arrays consisting of LaBr3(Ce) scintillators and germanium detectors integrated into the DESPEC experimental setup commissioned for the Facility for Antiproton and Ion Research (fair) Phase-0, Darmstadt, Germany. The excited states in Rh95 were populated primarily via the β decays of Pd95 nuclei, produced in the projectile fragmentation of a 850 MeV/nucleon Xe124 beam impinging on a 4g/cm2Be9 target. The deduced electromagnetic E2 transition strengths for the γ-ray cascade within the multiplet structure depopulating from the isomeric Iπ=21/2+ state are found to exhibit strong deviations from predictions of standard shell model calculations which feature approximately conserved seniority symmetry. In particular, the observation of a strongly suppressed E2 strength for the 13/2+→9/2+ ground state transition cannot be explained by calculations employing standard interactions. This remarkable result may require revision of the nucleon-nucleon interactions employed in state-of-the-art theoretical model calculations, and might also point to the need for including three-body forces in the Hamiltonian.

The neutron-rich rare isotope 190W is discussed as a candidate for a prolate-oblate transitional nucleus with maximum γ-softness. The collectivity of this isotope is assessed for the first time by the measurement of the reduced E2 transition probability of its first 2+ state to the ground state. The experiment employed the FAst TIming Array (FATIMA), comprised of 36 LaBr3(Ce) scintillators, which was part of the DESPEC setup at GSI, Darmstadt. The 41+ and 21+ states of 190W were populated subsequently to the decay of its 127(12) μs isomeric Jπ=10− state. The mean lifetime of the 21+ state was determined to be τ=274(28) ps, which corresponds to a B(E2;21+→01+) value of 95(10) W.u. The results motivated a revision of previous calculations within an energy-density functional-based interacting boson model-2 approach, yielding E2 transition properties and spectroscopic quadrupole moments for tungsten isotopes. From comparison to theory, the new data suggest that 190W is at the transition from prolate to oblate structure along the W isotopic chain, which had previously been discussed as a nuclear shape-phase transition.

The shell closure at N = 32 has been investigated by a first spectroscopy of the N = 31 nucleus 49Ar at the Radioactive Isotope Beam Factory. Using the 50Ar(p, pn) reaction channel in inverse kinematics, 50Ar projectiles at 217 MeV/nucleon impinged on a 150 mm long liquid hydrogen target, part of the MINOS device. Prompt deexcitation gamma rays were measured with the NaI(Tl) array DALI2+. Reaction products were analyzed with the SAMURAI spectrometer, which allowed the measurement of the momentum distributions and angular momentum transfer. Data were compared to state-of-the-art theoretical predictions, including shell -model, energy -density functional, and ab initio calculations. An onset of collectivity is suggested besides the spherical configuration typical of a closed shell nucleus, such as for 52Ca.

The calcium isotopes are an ideal system to investigate the evolution of shell structure and magic numbers. Although the properties of surface nucleons in calcium have been well studied, probing the structure of deeply bound nucleons remains a challenge. Here, we report on the first measurement of unbound states in Ca-53 and (55) Ca, populated from (54,56) Ca( p, pn) reactions at a beam energy of around 216 MeV/nucleon at the RIKEN Radioactive Isotopes Beam Factory. The resonance properties, partial cross sections, and momentum distributions of these unbound states were analyzed. Orbital angular momentum I assignments were extracted from momentum distributions based on calculations using the distorted wave impulse approximation (DWIA) reaction model. The resonances at excitation energies of 5516(41) keV in (53) Ca and 6000(250) keV in (55) Ca indicate a significant l = 3 component, providing the first experimental evidence for the v(0) f (7/2) single-particle strength of unbound hole states in the neutron-rich Ca isotopes. The observed excitation energies and cross-sections point towards extremely localized and well separated strength distributions, with some fragmentation for the v(0) f (7/2) orbital in (55) Ca. These results are in good agreement with predictions from shell-model calculations using the effective GXPF1Bs interaction and ab initio calculations and diverge markedly from the experimental distributions in the nickel isotones at Z = 28.

The first spectroscopy of K52 was investigated via in-beam γ-ray spectroscopy at the RIKEN Radioactive Isotope Beam Factory after one-proton and one-neutron knockout from Ca53 and K53 beams impinging on a 15-cm liquid hydrogen target at ≈230 MeV/nucleon. The energy level scheme of K52 was built using single γ and γ-γ coincidence spectra. The spins and parities of the excited states were established based on momentum distributions of the fragment after the knockout reaction and based on exclusive cross sections. The results were compared to state-of-the-art shell model calculations with the SDPF-Umod interaction and ab initio in-medium similarity renormalization group calculations with chiral effective field theory nucleon-nucleon and three-nucleon forces.

Reduced transition probabilities have been extracted between excited, yrast states in the N=Z+2 nucleus 94Pd. The transitions of interest were observed following decays of the Iπ=14+, Ex=2129-keV isomeric state, which was populated following the projectile fragmentation of a 124Xe primary beam at the GSI Helmholtzzentrum für Schwerionenforschung accelerator facility as part of FAIR Phase-0. Experimental information regarding the reduced E2 transition strengths for the decays of the yrast 8+ and 6+ states was determined following isomer-delayed Eγ1−Eγ2−△T2,1 coincidence method, using the LaBr3(Ce)-based FATIMA fast-timing coincidence gamma-ray array, which allowed direct determination of lifetimes of states in 94Pd using the Generalized Centroid Difference (GCD) method. The experimental value for the half-life of the yrast 8+ state of 755(106) ps results in a reduced transition probability of B(E2:8→+6+) = 205−25+34 e2 fm4, which enables a precise verification of shell-model calculations for this unique system, lying directly between the N=Z line and the N=50 neutron shell closure. The determined B(E2) value provides an insight into the purity of (g9/2)n configurations in competition with admixtures from excitations between the (lower) N=3pf and (higher) N=4gds orbitals for the first time. The results indicate weak collectivity expected for near-zero quadrupole deformation and an increasing importance of the T=0 proton-neutron interaction at N=48.

We report on a study of the alpha-decay fine structure and the associated E alpha-E gamma correlations in the decays of 171,172Os and 171,172,174Ir. In total, 13 new alpha-decay energy lines have been resolved, and three new gamma-ray transitions have been observed following the new decay branches to 168Re and 167W. The weak alpha-decay branch from the bandhead of the nu i13/2 band in 171Os observed in this work highlights an unusual competition between alpha, beta, and electromagnetic decays from this isomeric state. The nucleus 171Os is therefore one of few nuclei observed to exhibit three different decay modes from the same excited state. The nuclei of interest were produced in 92Mo(83Kr, xpyn) fusion-evaporation reactions at the Accelerator Laboratory of the University of Jyvaskyla, Finland. The fusion products were selected using the gas-filled ion separator RITU and their decays were characterized using an array of detectors for charged particles and electromagnetic radiation known as GREAT. Prompt gamma-ray transitions were detected and correlated with the decays using the JUROGAM II germanium detector array surrounding the target position. Results obtained from total Routhian surface (TRS) calculations suggest that alpha-decay fine structure and the associated hindrance factors may be a sensitive probe of even relatively small shape changes between the final states in the daughter nucleus.