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The collective structure of $^{106}$Cd is elucidated by multi-step Coulomb excitation of a 3.849 MeV/A beam of $^{106}$Cd on a 1.1 mg/cm$^{2}$ $^{208}$Pb target using GRETINA-CHICO2 at ATLAS. Fourteen E2 matrix elements were obtained. The nucleus $^{106}$Cd is a prime example of emergent collectivity that possesses a simple structure: it is free of complexity caused by shape coexistence and has a small, but collectively active number of valence nucleons. This work follows in a long and currently active quest to answer the fundamental question of the origin of nuclear collectivity and deformation, notably in the cadmium isotopes. The results are discussed in terms of phenomenological models, the shell model, and Kumar-Cline sums of E2 matrix elements. The 〈02+||E2||21+〉 matrix element is determined for the first time, providing a total, converged measure of the electric quadrupole strength, 〈Q2〉, of the first-excited 21+ level relative to the 01+ ground state, which does not show an increase as expected of harmonic and anharmonic vibrations. Strong evidence for triaxial shapes in weakly collective nuclei is indicated; collective vibrations are excluded. This is contrary to the only other cadmium result of this kind in $^{114}$Cd by C. Fahlander et al. (1988) [38], which is complicated by low-lying shape coexistence near midshell.

International audience; The collective structure of 106Cd is elucidated by multi-step Coulomb excitation of a 3.849 MeV/A beam of 106Cd on a 1.1 mg/cm2208Pb target using GRETINA-CHICO2 at ATLAS. Fourteen E2 matrix elements were obtained. The nucleus 106Cd is a prime example of emergent collectivity that possesses a simple structure: it is free of complexity caused by shape coexistence and has a small, but collectively active number of valence nucleons. This work follows in a long and currently active quest to answer the fundamental question of the origin of nuclear collectivity and deformation, notably in the cadmium isotopes. The results are discussed in terms of phenomenological models, the shell model, and Kumar-Cline sums of E2 matrix elements. The 〈02+||E2||21+〉 matrix element is determined for the first time, providing a total, converged measure of the electric quadrupole strength, 〈Q2〉, of the first-excited 21+ level relative to the 01+ ground state, which does not show an increase as expected of harmonic and anharmonic vibrations. Strong evidence for triaxial shapes in weakly collective nuclei is indicated; collective vibrations are excluded. This is contrary to the only other cadmium result of this kind in 114Cd by C. Fahlander et al. (1988) [38], which is complicated by low-lying shape coexistence near midshell.

Radioactive $^{129}$Sb, which can be treated as a proton plus semi-magic $^{128}$Sn core within the particle-core coupling scheme, was studied by Coulomb excitation. Reduced electric quadrupole transition probabilities, $B(E2)$, for the $2^+$ $\times$ $\pi g_{{7/2}}$ multiplet members and candidate $\pi d_{{5/2}}$ state were measured. The results indicate that the total electric quadrupole strength of $^{129}$Sb is a factor of 1.39(11) larger than the $^{128}$Sn core, which is in stark contrast to the expectations of the empirically successful particle-core coupling scheme. Shell-model calculations performed with two different sets of nucleon-nucleon interactions suggest that this enhanced collectivity is due to constructive quadrupole coherence in the wavefunctions stemming from the proton-neutron residual interactions, where adding one nucleon to a core near a double-shell closure can have a pronounced effect. The enhanced electric quadrupole strength is an early signal of the emerging nuclear collectivity that becomes dominant away from the shell closure., Comment: Accepted, Physical Review Letters

13 pags., 9 figs., 2 tabs., Excited states of In129 populated following the β decay of Cd129 were experimentally studied with the GRIFFIN spectrometer at the ISAC facility of TRIUMF, Canada. A 480-MeV proton beam was impinged on a uranium carbide target and Cd129 was extracted using the Ion Guide Laser Ion Source (IG-LIS). β and γ rays following the decay of Cd129 were detected with the GRIFFIN spectrometer comprising the plastic scintillator SCEPTAR and 16 high-purity germanium (HPGe) clover-type detectors. From the β-γ-γ coincidence analysis, 32 new transitions and seven new excited states were established, expanding the previously known level scheme of In129. The logft values deduced from the β-feeding intensities suggest that some of the high-lying states were populated by the ν0g7/2→π0g9/2 allowed Gamow-Teller (GT) transition, which indicates that the allowed GT transition is more dominant in the Cd129 decay than previously reported. Observation of fragmented Gamow-Teller strengths is consistent with theoretical calculations., The authors would like to thank the operators at the TRIUMF-ISAC facility for providing the radioactive beam. This work was partially supported by the Natural Sciences and Engineering Research Council of Canada (NSERC), the Canada Research Chairs Program, NSERC Discovery Grants No. SAPIN-2014-00028 and No. RGPAS 462257-2014, the NSERC CREATE Program IsoSiM (Isotopes for Science and Medicine), the Spanish Ministerio de Economía y Competitividad under Contract No. FPA2017-84756-C4-2-P, the US National Science Foundation (NSF) under Contract No. NSF14-01574, and the Mexican DGAPA-UNAM program under Contract No. PAPIIT-IN110418. The GRIFFIN spectrometer was funded by the Canada Foundation for Innovation (CFI), TRIUMF, and the University of Guelph. TRIUMF receives federal funding via a contribution agreement with the National Research Council of Canada (NRC). Y.S. would like to thank Jorge Agramunt (IFIC Valencia, Spain) for providing a program for fitting the time distribution of β particles.The authors would like to thank the operators at the TRIUMF-ISAC facility for providing the radioactive beam. This work was partially supported by the Natural Sciences and Engineering Research Council of Canada (NSERC), the Canada Research Chairs Program, NSERC Discovery Grants No. SAPIN-2014-00028 and No. RGPAS 462257-2014, the NSERC CREATE Program IsoSiM (Isotopes for Science and Medicine), the Spanish Ministerio de Economía y Competitividad under Contract No. FPA2017-84756-C4-2-P, the US National Science Foundation (NSF) under Contract No. NSF14-01574, and the Mexican DGAPA-UNAM program under Contract No. PAPIIT-IN110418. The GRIFFIN spectrometer was funded by the Canada Foundation for Innovation (CFI), TRIUMF, and the University of Guelph. TRIUMF receives federal funding via a contribution agreement with the National Research Council of Canada (NRC). Y.S. would like to thank Jorge Agramunt (IFIC Valencia, Spain) for providing a program for fitting the time distribution of β particles.

Spectroscopic data, such as precise γ-ray branching and E2/M1 multipole-mixing ratios, provide vital constraints when performing multi-dimensional Coulomb-excitation analyses. Consequently, as part of our new Coulomb-excitation campaign aimed at investigating the role of exotic non-axial (triaxial) deformations in the unstable refractory Ru-Mo isotopes, additional beta-decay data was obtained. These measurements make use of ANL's CARIBU facility, which provides intense beams of radioactive refractory isotopes along with the excellent efficiency and angular resolution of the GRETINA γ-ray tracking array. In this article, we report on the analysis of the A = 110 decay chain, focussing on the identification of previously unreported states in 110Ru following the decay of 110Tc.

The island of inversion for neutron-rich nuclei in the vicinity of N=20 has become the testing ground par excellence for our understanding and modeling of shell evolution with isospin. In this context, the structure of the transitional nucleus Mg29 is critical. The first quantitative measurements of the single-particle structure of Mg29 are reported, using data from the d(Mg28, p γ)Mg29 reaction. Two key states carrying significant 3 (f-wave) strength were identified at 2.40±0.10 (Jπ=5/2-) and 4.28±0.04 MeV (7/2-). New state-of-the-art shell-model calculations have been performed and the predictions are compared in detail with the experimental results. While the two lowest 7/2- levels are well described, the sharing of single-particle strength disagrees with experiment for both the 3/2- and 5/2- levels and there appear to be general problems with configurations involving the p3/2 neutron orbital and core-excited components. These conclusions are supported by an analysis of the neutron occupancies in the shell-model calculations.

The island of inversion for neutron-rich nuclei in the vicinity of N=20 has become the testing ground par excellence for our understanding and modeling of shell evolution with isospin. In this context, the structure of the transitional nucleus ²⁹Mg is critical. The first quantitative measurements of the single-particle structure of ²⁹Mg are reported, using data from the d(²⁸Mg, p γ)²⁹Mg reaction. Two key states carrying significant ℓ=3 (f-wave) strength were identified at 2.40±0.10 (Jπ=5/2¯) and 4.28±0.04 MeV (7/2¯). New state-of-the-art shell-model calculations have been performed and the predictions are compared in detail with the experimental results. While the two lowest 7/2¯ levels are well described, the sharing of single-particle strength disagrees with experiment for both the 3/2¯ and 5/2¯ levels and there appear to be general problems with configurations involving the p3/2 neutron orbital and core-excited components. These conclusions are supported by an analysis of the neutron occupancies in the shell-model calculations.

Excited states in Cs137 have been studied by using the near-barrier, single-proton transfer reaction B10(Xe136,Be9γ)Cs137 in inverse kinematics and performing particle-γ and particle-γγ coincidence measurements. The low-spin level scheme of Cs137 has been augmented: (i) The expected set of single-proton, seniority υ=1 states has been delineated in its entirety; (ii) Another member of the υ=3 proton 0g7/2 multiplet, a low-lying 9/2+ level, has been identified and this set of states now approaches completion; (iii) A second 9/2+ and a candidate 13/2+ level have been observed. The results are discussed in the framework of shell-model calculations in the proton 2s1d0g0h shell.

The "Island of Inversion" for neutron-rich nuclei in the vicinity of N=20 has become the testing ground par excellence for our understanding and modelling of shell evolution with isospin. In this context, the structure of the transitional nucleus 29Mg is critical. The first quantitative measurements of the single particle structure of 29Mg are reported, using data from the d(28Mg,p gamma)29Mg reaction. Two key states carrying significant ell=3 (f-wave) strength were identified at 2.40 +/- 0.10 (Jpi = 5/2-) and 4.28 +/- 0.04 MeV (7/2-). New state-of-the-art shell model calculations have been performed and the predictions are compared in detail with the experimental results. Whilst the two lowest 7/2- levels are well described, the sharing of single-particle strength disagrees with experiment for both the 3/2- and 5/2- levels and there appear to be general problems with configurations involving the p3/2 neutron orbital and core-excited components. These conclusions are supported by an analysis of the neutron occupancies in the shell model calculations., Comment: 15 pages, 10 figures, 4 tables

The neutron-shell structure of $^{25}$F was studied using quasi-free (p,2p) knockout reaction at 270A MeV in inverse kinematics. The sum of spectroscopic factors of $\pi$0d$_{5/2}$ orbital is found to be $1.0 \pm 0.3$. However, the spectroscopic factor for the ground-state to ground-state transition ($^{25}$F, $^{24}$O$_{g.s.}$) is only $0.36\pm 0.13$, and $^{24}$O excited states are produced from the 0d$_{5/2}$ proton knockout. The result shows that the $^{24}$O core of $^{25}$F nucleus significantly differs from a free $^{24}$O nucleus, and the core consists of 35% $^{24}$O$_{g.s}$. and 65% excited $^{24}$O.

Excited states in Xe-137 have been studied by using the near-barrier single-neutron transfer reactions C-13(Xe-136, C-12 gamma) Xe-137 and Be-9(Xe-136, Be-8 gamma) Xe-137 in inverse kinematics. Particle-gamma and particle-gamma gamma coincidence measurements have been performed with the Phoswich Wall and Digital Gammasphere detector arrays. Evidence is found for a 13/2(2)(+) level (E = 3137 keV) and for additional high-lying 3/2(-) and 5/2(-) states. The results are discussed in the framework of realistic shell-model calculations. These calculations are also extended to the 13/2(1)(+) and 13/2(2)(+) levels in the N = 83 isotonic chain. They indicate that there is a need for a value of the neutron 0i(13/2) single-particle energy (E-SPE = 2366 keV) lower than the one proposed in the literature. It is also demonstrated that the population patterns of the j = l +/- 1/2 single-particle states in Xe-137 are different for the two targets used in these measurements and the implications of this effect are addressed.

Excited states in Xe137 have been studied by using the near-barrier single-neutron transfer reactions C13(Xe136,C12γ)Xe137 and Be9(Xe136,Be8γ)Xe137 in inverse kinematics. Particle-γ and particle-γγ coincidence measurements have been performed with the Phoswich Wall and Digital Gammasphere detector arrays. Evidence is found for a 13/22+ level (E=3137keV) and for additional high-lying 3/2- and 5/2- states. The results are discussed in the framework of realistic shell-model calculations. These calculations are also extended to the 13/21+ and 13/22+ levels in the N=83 isotonic chain. They indicate that there is a need for a value of the neutron 0i13/2 single-particle energy (ESPE=2366keV) lower than the one proposed in the literature. It is also demonstrated that the population patterns of the j=±1/2 single-particle states in Xe137 are different for the two targets used in these measurements and the implications of this effect are addressed.