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Background: One-phonon mixed-symmetry quadrupole excitations are a well-known feature of near-spherical, vibrational nuclei. Their interpretation as a fundamental building block of vibrational structures is supported by the identification of multiphonon states resulting from a coupling of fully-symmetric and mixed-symmetric quadrupole phonons. In addition, the observation of strong M1 transitions between low-lying 3- and 4+ states has been interpreted as an evidence for one-phonon mixed-symmetry excitations of octupole and hexadecapole character. Purpose: The aim of the present study is to identify collective one- and two-phonon excitations in the heaviest stable N = 52 isotone 96Ru based on a measurement of absolute Ail, E1, and E2 transition strengths. Methods: Inelastic proton-scattering experiments have been performed at the Wright Nuclear Structure Laboratory (WNSL), Yale University, and the Institute for Nuclear Physics (IKP), University of Cologne. From the acquired proton-γ and γγ coincidence data we deduced spins of excited states, y-decay branching ratios, and multipole mixing ratios, as well as lifetimes of excited states via the Doppler-shift attenuation method (DSAM). Results: Based on the new experimental data on absolute transition strengths, we identified the 2+ and 3+ members of the two-phonon mixed-symmetry quintuplet (21ms+⊙21ms+).Furthermore, we observed strong M1 transitions between low-lying 3- and 4+ states suggesting one-phonon symmetric and mixed-symmetric octupole and hexadecapole components in their wave functions, respectively. The experimental results are compared to sdg-IBM-2 and shell-model calculations. Conclusions: Both the sdg-IBM-2 and the shell-model calculations are able to describe key features of mixed-symmetry excitations of 96Ru. Moreover, they support the one-phonon mixed-symmetry hexadecapole assignment of the experimental 42+ state. [ABSTRACT FROM AUTHOR]

A metastable phase of body-centered-tetragonal ruthenium (bet Ru) is identified to exhibit a large perpendicular magnetocrystalline anisotropy (PMCA), whose energy EMCA is as large as 150 μeV/atom, which is two orders of magnitude greater than those of 3d magnetic metals. Further investigation over the range of tetragonal distortion suggests that the appearance of magnetism in the bet Ru is governed by the Jahn-Teller spit eg orbitals. Moreover, from band analysis, MCA is mainly determined by an interplay between two eg states, dx2-y2 and dz2 states, as a result of level reversal associated with tetragonal distortion. [ABSTRACT FROM AUTHOR]

New positive-parity states, having a bandlike structure, were observed in 105Ru. The nucleus was produced in an induced fission reaction, and the prompt γ-rays, emitted from the fragments, were detected by the EUROBALL III multidetector array. The partial scheme of excited 105Ru levels is analyzed within the triaxial-rotor-plus-particle approach. [ABSTRACT FROM AUTHOR]

Linear polarization and angular correlations of γ-rays depopulating excited states in the neutron-deficient nucleus 9444Ru50 have been measured, enabling firm spin-parity assignments for several excited states in this nucleus. The deduced multipolarities of strong transitions in the yrast structure were found to be mostly of stretched M1, E1, and E2 types and, in most cases, in agreement with previous tentative assignments. The deduced multipolarity of the 1869 keV and the connecting 257 and 1641 keV transitions indicates that the state at 6358 keV excitation energy has spin parity 12-1 rather than 12+3 as proposed in previous works. The presence of a 12-1 state is interpreted within the framework of large-scale shell-model calculations as a pure proton-hole state dominated by the π(p-11/2⊗g-59/2) and π(p-13/2⊗g-59/2) configurations. A new positive-parity state is observed at 6103 keV and is tentatively assigned as 12+2. The 14-1 state proposed earlier is reassigned as 13-4 and is interpreted as being dominated by neutron particle-hole core excitations. The strengths of several E1 transitions have been measured and are found to provide a signature of core-excited configurations. [ABSTRACT FROM AUTHOR]

116Ru and 118Ru have been studied via β-delayed y-ray spectroscopy of nuclei produced in fragmentation reactions at the Radioactive Ion-Beam Factory (RIBF) facility. Level schemes with positive-parity states up to spin 7=6 have been constructed. The results have been discussed in terms of the interacting boson model, the algebraic collective model, and total Routhian surfaces. We conclude that the very neutron-rich nuclei still show many features associated with triaxial y-soft nuclei, represented by the 0(6) symmetry, but are approaching a spherical structure, the U(5) symmetry, with increasing neutron number towards the N = 82 shell closure. In 118Ru, hints of a shape transition in the ground state have been observed. [ABSTRACT FROM AUTHOR]

The nature of the second-order phase transition that occurs in URu2Si2 at 17.5 K remains puzzling despite intensive research. A key question emerging in the field is whether a hybridization gap between the renormalized bands can be identified as the "hidden" order parameter. We report on the measurement of a hybridization gap in URU2SÍ2 employing a spectroscopic technique based on quasiparticle scattering. The differential conductance exhibits an asymmetric double-peak structure, a clear signature for a Fano resonance in a Kondo lattice. The hybridization gap opens well above 17.5 K, indicating that it is not the hidden order parameter. Our results put stringent constraints on the origin of the hidden order transition in URu2Si2 and demonstrate that quasiparticle scattering spectroscopy can probe the band renormalizations in a Kondo lattice via detection of a novel type of Fano resonance. [ABSTRACT FROM AUTHOR]

High-resolution scanning tunneling microscopy (STM) reveals that the first layer of water on Ru(0001) and also on Pd(l 11) consists of hexagonal molecular domains of two types, rotated by 30° relative to one another. Pentagon and heptagon clusters bridge the two types of hexagons. One of the orientations is in registry with the substrate. Its molecules lie flat and their O atoms form strong bonds to the metal atoms lying directly below. In the other domain the molecules have dangling H bonds. They are weakly bound to the substrate and lie correspondingly higher. This bonding motif, though nonperiodic, is of similar nature to the periodic wetting structure recently reported on Pt( 111 ), and very different from the conventional "ice-like" bilayer. First-principles density functional theory (DFT) simulations of the STM images support these conclusions. [ABSTRACT FROM AUTHOR]

Background: The experimental study of g(I > 2) factors of nuclear states can provide information about the evolution of collectivity in certain regions of the nuclear chart, and assist in obtaining a microscopic description of the nuclear wave functions. The measurements and explanations of g{I > 2) factors are still a challenge for experiments and theory. Purpose: Measurement of the g(2+1) and g(41) factors, the latter for the first time, in the 9644Ru nucleus. Comparison of the experimental results with calculations using the shell model and collective models. Methods: The experiments made use of the transient field technique, using a Coulomb-excitation reaction in inverse kinematics. Large scale shell model calculations were performed; comparisons with previous theoretical predictions, using the tidal-wave model and the hydrodynamical model, were carried out. Results: The values of g(2+1) = +0.46(2) and g(4+-) = +0.58(8) were experimentally obtained. While the g(2+1) value agrees with the hydrodynamical model prediction of g = Z/A = +0.46. the g(4+1 ) is in agreement with the shell model predictions. The trend of the experimental g factors, as a function of nuclear spin, is not reproduced by the theoretical models discussed. Conclusions: Measurements of g(2+1 ) and g(4+1 ) in 96Ru were performed. Further theoretical efforts are necessary to explain the trend of the g factors as a function of nuclear spin for the 96Ru nucleus. Future measurements of g(4+1) should reduce the uncertainty of the result. [ABSTRACT FROM AUTHOR]

The nucleus 102Ru was studied with the GRID lifetime technique and an upper limit on the Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed. of 21.6 W.u. was obtained. This nucleus is pivotal in the A ~ 100 region as it marks the boundary, in Z, between nuclei that do, and do not, become deformed with increasing neutron number, and, in N, between those that exhibit characteristics of a phase transition mediated by changes in subshell structure and those that do not. The measurements are discussed primarily in terms of vibrational structure. [ABSTRACT FROM AUTHOR]

The effective field theory (EFT) for triaxially deformed even-even nuclei is generalized to include the vibrational degrees of freedom. The pertinent Hamiltonian is constructed up to next-to-leading order (NLO). The leading-order part describes the vibrational motion, and the NLO part couples rotations to vibrations. The applicability of the EFT Hamiltonian is examined through the description of the energy spectra of the ground state bands, γ bands, and K=4 bands in the 108,110,112Ru isotopes. It is found that, by taking into account the vibrational degrees of freedom, the deviations for high-spin states in the γ band observed in the EFT with only rotational degrees of freedom disappear. This supports the importance of including vibrational degrees of freedom in the EFT formulation for the collective motion of triaxially deformed nuclei. [ABSTRACT FROM AUTHOR]

Background: Triaxiality in nuclear low-lying states has attracted great interest for many years. Recently, reduced transition probabilities for levels near the ground state in 110Ru have been measured and provided strong evidence of a triaxial shape of this nucleus. Purpose: The aim of this work is to provide a microscopic study of low-lying states for Ru isotopes with A≈100 and to examine in detail the role of triaxiality and the evolution of quadrupole shapes with the isospin and spin degrees of freedom. Method: Low-lying excitation spectra and transition probabilities of even-even Ru isotopes are described at the beyond-mean-field level by solving a five-dimensional collective Hamiltonian with parameters determined by constrained self-consistent mean-field calculations based on the relativistic energy density functional PC-PK1. Results: The calculated energy surfaces, low-energy spectra, and intraband and interband transition rates, as well as some characteristic collective observables, such as E(4+g.s.)/E(2+g.s.),E(2+γ)/E(4+g.s.), and B(E2;2+g.s.→0+g.s.) and γ-band staggerings, are in good agreement with the available experimental data. Conclusions: The main features of the experimental low-lying excitation spectra and electric transition rates are well reproduced and, thus, strongly support the onset of triaxiality in the low-lying excited states of Ru isotopes around 110Ru. [ABSTRACT FROM AUTHOR]

The 98Ru nucleus, populated via the 97Mo(³He,2n) reaction, has been investigated by means of K-internal conversion coefficient, γ-ray angular distribution, γ-γ coincidence, and γ-γ angular correlation measurements. The results have led to an improved knowledge of the excitation energy pattern via the identification of new levels and transitions. New information on spin and parities of many levels as well as on mixing ratios of several transitions has been obtained. The presence of large M1 components in many transitions definitely excludes the possibility of considering 98 as a nucleus having a structure very close to the vibrational one and points to the need of an enlarged framework for a successful description. [ABSTRACT FROM AUTHOR]

Low-lying states of even-even and odd-mass ruthenium isotopes with mass numbers from 95 to 102, including level schemes, electric quadrupole and magnetic dipole moments, and E2 transition rates, are studied within the framework of the nucleon pair approximation (NPA) of the shell model, by using the phenomenological pairing plus quadrupole interactions. Good agreement is obtained between the calculated results and experimental data. The interesting behaviors of g(J1+) factors versus nuclear spin J (and mass number A) in even-even 96-102Ru nuclei are analyzed. The dominant configurations of yrast low-lying states in odd-mass 95-101Ru isotopes are discussed in the collective nucleon-pair subspace. The calculated electric quadrupole moments and magnetic moments of low-lying states, many of which have not yet been measured for these nuclei, are useful for future studies. [ABSTRACT FROM AUTHOR]

The structure of the low-lying states in the odd- and even-mass A≈100 Ru isotopes is studied in the framework of two algebraic models. The even-mass Ru nuclei are first described within the interacting boson model 1 (IBM-1). The output of these calculations was then used to calculate the odd-A isotopes within the interacting boson-fermion model 1 (IBFM-1), where a coupling of the odd neutron to the even-even core is considered. The level energies and transition probabilities calculated in the present work are tested against the experimental data. One-nucleon transfer spectroscopic factors as well as electromagnetic moments were also calculated for the odd-A Ru and compared to the experimental values. The transitional character of the isotopes is studied. Most of the low-lying positive-parity states in the odd-A Ru nuclei below 2 MeV are interpreted on the basis of νd5/2 and νg7/2 configurations. The role of the νs1/2 orbital in the nuclear structure of the odd-mass Ru nuclei at low energies is also studied. The negative-parity states are interpreted as νh11/2 excitations coupled to the core. The evolution of the IBM-1 and IBFM-1 parameters is discussed. [ABSTRACT FROM AUTHOR]