Three ΔI=1 bands with the πg_{9/2}⊗νg_{9/2} configuration have been identified in _{35}^{74}Br_{39}. Angular distribution, linear polarization, and lifetime measurements were performed to determine the multipolarity, type, mixing ratio, and absolute transition probability of the transitions. By comparing these experimental observations with the corresponding fingerprints and the quantum particle rotor model calculations, the second and third lowest bands are, respectively, suggested as the chiral partner and one-phonon wobbling excitation built on the yrast band. The evidence indicates the first chiral wobbler in nuclei.

This work reports the first rotational bands observed in the neutron-deficient nucleus ^231 U. Excited states were populated in the ^232 Th( α ,5n) reaction at a beam energy of 52 MeV. Coincident decay γ -rays were measured with the high-purity germanium detectors of the afrodite spectrometer array, in conjunction with a recoil detector to discriminate against the fission background. The bands are interpreted as the ground-state band ν [633]5/2^+ , yrast band ν [752]5/2^- , and an excited band ν [631]3/2^+ . Configuration assignments are supported by Cranked Shell Model and B(M1)/B(E2) calculations. The excitation energy of the ν [752]5/2^- bandhead is suggested to be 113.0 keV.

The changes in the mean-squared charge radius of Tlg209 (N=128) and Tlm207 (N=126) relative to Tl205 have been measured for the first time using the in-source laser resonance-ionization spectroscopy technique with the Laser Ion Source and Trap (LIST) at ISOLDE (CERN). The application of the LIST suppresses the dominant background from isobaric francium isotopes and allows access to thallium nuclides with A⩾207. The characteristic kink in the charge radii at the N=126 neutron shell closure, as well as the odd-even effect similar to that in the adjacent bismuth, lead, and mercury isotopic chains, have been observed. The self-consistent theory of finite Fermi systems based on the energy density functional by Fayans reproduces the behavior of charge radii in these isotopic chains near N=126. The comparison with calculations in the framework of the relativistic mean field (RMF) approach is also presented. In the case of the Fayans functional it is a specific form of pairing interaction with the dependence on the density gradient that is essential to provide agreement with the experimental charge radii. In particular, the kink is reproduced without the inversion of g9/2 and i11/2 neutron single-particle states, which is a prerequisite to correctly describe the kink in the RMF models. Published by the American Physical Society 2024

The magnetic dipole moments (μ) of 209Tlg (N=128) and 207Tlm (N=126) have been measured for the first time using the in-source laser resonance-ionization spectroscopy technique with the Laser Ion Source and Trap (LIST) at ISOLDE (CERN). The application of the LIST suppresses the usually overwhelming background of the isobaric francium isotopes and allows access to heavy thallium isotopes with A⩾207. The self-consistent theory of finite Fermi systems based on the energy density functional by Fayans et al. well describes the N dependence of μ for 1/2+ thallium ground states, as well as μ for the 11/2− isomeric states in europium, gold and thallium isotopes. The inclusion of particle-vibration coupling leads to a better agreement between the theory and experiment for μ(Tlg, Iπ=1/2+). It is shown that beyond mean-field contributions to μ cannot be neglected at least for thallium isotopes with Iπ=1/2+.

The excited structure of A = 128 isobars populated in the beta decay of Cd-128 has been investigated by means of high-resolution gamma-spectroscopy and fast-timing measurements. The experiment was performed at the ISOLDE facility at CERN profiting from the production of intense and pure Cd beams by means of a temperature-controlled quartz transfer line, capable of suppressing surface-ionized species. The production yields and purity of Cd beams are presented. Results on sub-nanosecond lifetimes for excited states in In-128 and Te-128 are discussed.

The spectroscopic quadrupole moment of the first excited state, Q__S(2^+_1), at 1.634 MeV in ^20Ne was determined from sensitive reorientation-effect Coulomb-excitation measurements using a heavy target and safe energies well below the Coulomb barrier. Particle-γ coincidence measurements were collected at iThemba LABS with a digital data-acquisition system using the AFRODITE array coupled to an annular, doubled-sided silicon detector. A precise value of Q__S(2^+_1)=-0.22(2) eb was determined at backward angles in agreement with the only safe-energy measurement prior to this work, Q__S(2^+_1)=-0.23(8) eb. This result adopts 1ħω shell-model calculations of the nuclear dipole polarizability of the 2^+_1 state that contributes to the effective quadrupole interaction and determination of Q__S(2^+_1). It disagrees, however, with the ideal rotor model for axially-symmetric nuclei by almost 3σ. Larger discrepancies are computed by modern state-of-the-art calculations performed in this and prior work, including ab initio shell model with chiral effective interactions and the multi-reference relativistic energy density functional (MR-EDF) model. The intrinsic nucleon density of the 2^+_1 state in ^20Ne calculated with the MR-EDF model illustrates the presence of α clustering, which explains the largest discrepancy with the rotor model found in the nuclear chart and motivates the explicit inclusion of α clustering for full convergence of E2 collective properties.

High -spin states in 76As have been observed for the first time by using the 4He + 74Ge reaction at beam energies of 58.6 and 62.6 MeV. Two positive -parity and three negative -parity bands have been found in 76As. The two positive -parity bands with 7rg9/2 (R) vg9/2 configurations are tentatively interpreted as chiral doublet bands, which are supported by triaxial particle rotor model calculations. The electric dipole transitions linking the yrast positive- and negative -parity bands are also observed in this work, implying the possible presence of octupole correlations in 76As.

As part of a systematic study of the nuclear structure of the Ru isotopes, 98Ru was investigated via the β-decay of 98Rh at iThemba LABS, and the 100Ru(p, t) reaction at the Maier-Leibnitz Laboratory. The combined data results in significant revision of the previous spin assignments and clarification of the nature of levels in 98Ru, as well as providing insights into the evolution of the structures across the Ru isotopic chain.

Progress in the studies of chirality in atomic nuclei at iThemba LABS is reviewed. New regions of chirality, around mass 80 and 190 have been discovered using the AFRODITE array, specifically in the nuclei 74As, 78,80,82Br, 81Kr, and 193,194,198Tl. Many phenomena have been observed, including multiple chiral bands in the same nucleus, the coexistence of octupole correlations and nuclear chirality, and the coexistence of pseudo spin and nuclear chirality. The best example of chiral degeneracy to date was found in 194Tl. The level scheme of 106Ag has been revisited and interpreted in terms of two- and four-quasiparticle bands. Investigations using the particle-rotor model have shown that the fingerprints of chirality in the two-quasiparticle system only can occur in an idealised model description. For systems with a higher number of quasiparticles, the calculations showed that nuclear chirality can persist.

The Low Energy Radioactive Ion Beam (LERIB) facility [1] will be used to produce low-energy radioactive-ion beams (RIBs) with energies up to 60 keV. Radioactive reaction products will be created by a 66 MeV proton-beam impinging on a target made of carbide disks, such as SiC [2]. These reaction products will then be ionized in a target-ion-source (TIS) and extracted as beam. The TIS design allows three ion-sources: a surface ion-source [3], a forced electron-beam induced arc-discharge (FEBIAD) ion-source [4], and a resonance-ionization laser ion-source, or RILIS. The surface-ionization source was commissioned with stable beams in October 2021. The production of ions from Group-1 elements was accomplished with beams of 39 K + , 41 K + and 23 Na + where currents were measured in the μ A range. This source may be advantageous for producing stable pilot-beams for future radioactive-beam experiments. The FEBIAD is still in development at present.

High-spin states in As-74 were studied using the Ge-74(4He, 1p3n) reaction at beam energies of 58.6 and 62.6 MeV. Two positive-and one negative-parity bands have been identified in As-74. The two positive-parity bands are interpreted as chiral doublet bands, which is supported by the triaxial particle rotor model. Three electric dipole transitions linking the yrast positive-and negative-parity bands were also observed in this work, suggesting the existence of octupole correlations in As-74.

Neutron yields and cross-sections from the bombardment, by protons of energies 30, 42, 54 and 66 MeV, on thin O-18 water targets, and a 2.5 mm thick Li target, have been measured at 0 degrees and 16 degrees, in addition to that of a stopping length O-18 water target at 62 MeV. The results are compared with measured yields from beryllium targets and with FLUKA simulations.

Collective structures in 186Os have been investigated through the 186W(4He, 4n) 186Os reaction, at a beam energy of 48 MeV. The low-lying bands built on the excited 0+2 , 2+2 , and 4+3 states have been extended up to spins of 12+, 15+, and 8+, respectively, and a number of new linking transitions were identified. The features of the collective bands in 186Os, such as level energies, are presented in the context of a systematic study of the neighboring even-even 182-192Os isotopes. In addition, the validity of the K-selection rule, stemming from a description based on axial symmetry of the nuclear shape, is examined. The observed decays between the rotational bands support a description where K is conserved. However, some K-forbidden decays were also identified, suggesting that a model allowing for small K admixtures is probably required. The experimental data are further compared with calculations using a five-dimensional collective Hamiltonian based on covariant density functional theory. The calculations predict that the collective bands are associated with different nuclear shapes, varying in quadrupole deformation, triaxiality, and softness.

Two nearly degenerate positive-parity bands with the πg9/22⊗νg9/2−1 configuration and three nearly degenerate negative-parity bands with the πg9/2(p3/2,f5/2)⊗νg9/2−1 configuration have been identified in 81Kr. They are interpreted as chiral doublet bands and pseudospin-chiral triplet bands, which is supported by the constrained covariant density functional theory and the multiparticle plus rotor model calculations. The present work reports two new chiral configurations πg9/22⊗νg9/2−1 and πg9/2(p3/2,f5/2)⊗νg9/2−1, and the first example of pseudospin-chiral triplet bands involving the π(p3/2,f5/2) pseudospin doublet.

The spectroscopy of Ge-71 has been investigated via the fusion-evaporation reaction Ge-74(alpha, alpha 3n)Ge-71. Collective structures including a rotational band built on the 15/2(-) octupole state in Ge-71 have been established. The observation of strong E1 transitions and the well-behaved rotational sequence built on the 15/2(-) octupole state provide the first experimental evidence of an octupole rotational band in Ge isotopes, suggesting an enhanced octupole correlation around N = 40 in the A approximate to 70 region. A newly developed semimicroscopic cluster model provides a good description of the octupole characteristics of Ge-71.

The spectroscopy of 62Cu is studied via the 54Cr(12C, 1 p3n) 62Cu fusion-evaporation reaction. On the basis of the gamma -gamma coincidence analysis, angular distributions from oriented states, and linear polarization measurement, three positive-parity and three negative-parity level sequences in 62Cu are observed, including two new gamma -ray transitions and one new level. The collective structures are discussed in terms of the tilted axis cranking covariant density functional theory. Although not firmly confirmed in experiment, the properties of a magnetic rotational structure with the n(f7/2)-1(p3/2 f5/2)2 circle times v(g9/2)1(p3/2 f5/2)4 configuration have been discussed. Its angular momentum generation is probably due to the shears mechanism.

The level structure of I-124 (Z = 53, N = 71) has been studied via the Sn-122(Li-7, (5)n) I-124 reaction with a beam energy of 54 MeV. Through in-beam and out-of-beam gamma-ray spectroscopy, the sophisticated low-lying levels including isomeric states and numerous collective states have been established for the first time. A positive-parity collective band built on the 10(+) state at 1297 keV is interpreted as being associated with the combination of a proton and a neutron in the same intruder h(11/2) orbital, namely the pi h(11/2)nu h(11/2) configuration. This band shows a typical quadrupole vibrational character. In contrast, the negative parity bands based on the pi g(7/2)nu h(11/2) configuration show a soft triaxial rotation. An isomeric 8(-) state at 689 keV with a half-life of 14 ns can be explained as a K isomer due to a proton with an Omega(p) = 9/2 in the g(9/2) orbital coupled to a neutron with an Omega n = 7/2 in the h(11/2) orbital. The excited states based on this pi g(9/2)nu h(11/2) configuration show a coupled rotational structure. Another coupled rotational band built on the 6(+) state at 714 keV is thought to be based on the pg(9/2)nu d(3/2) configuration.

Excited states in Ba-131 and Ce-133 were studied using in-beam gamma-ray spectroscopy through the Sn-122(C-13, 4n) Ba-133 and Te-125(C-12, 4n) Ce-133 reactions, respectively. A strongly coupled band, associated with the nu g(7/2) [404]7/2(+) configuration, was identified in Ba-131 and Ce-133. It is the first time to observe the nu g(7/2) [404]7/2(+) bands in the N = 75 isotones. The signature partners exhibit considerable energy splitting in comparison with those in the pi g(7/2) [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.