Proton Degrees Of Freedom Research Articles

Description of the critical point symmetry in 124Te by IBM-2 * * Supported by the National Natural Science Foundation of China (11475062, 11147148, 11747312)

Based on the neutron and proton degrees of freedom, low-lying energy levels, , , and transition strengths of nucleus 124Te have been calculated by the neutron-proton interacting boson model. The calculated results are reasonably consistent with the experimental data. By comparing the key observables of the states at the critical point of - transition with the experimental data and calculated results, we show that the 124Te is a possible nucleus at the critical point of the second-order phase transition from vibration to unstable rotation, and such a critical point exhibits slight triaxial rotation. The 0 state of 124Te can be interpreted as the lowest state of the first-excited family of the intrinsic levels in the critical point symmetry.

Single Particle Levels and ββ-Decay Matrix Elements in The Interacting Boson Model

Recently a new method to calculate the occupancies of single particle levels in atomic nuclei was developed in the context of the microscopic interacting boson model, in which neutron and proton degrees of freedom are treated explicitly (IBM-2). The energies of the single particle levels constitute a very important input for the calculation of the occupancies in this method, and further they play important role in the calculation of double beta decay nuclear matrix elements. Here we discuss how the 0νββ, 0νhββ, and 2νββ-decay nuclear matrix elements (NMEs) are affected when the energies of single particle levels are changed.

Quantum-disordered state of magnetic and electric dipoles in an organic Mott system

Strongly enhanced quantum fluctuations often lead to a rich variety of quantum-disordered states. Developing approaches to enhance quantum fluctuations may open paths to realize even more fascinating quantum states. Here, we demonstrate that a coupling of localized spins with the zero-point motion of hydrogen atoms, that is, proton fluctuations in a hydrogen-bonded organic Mott insulator provides a different class of quantum spin liquids (QSLs). We find that divergent dielectric behavior associated with the approach to hydrogen-bond order is suppressed by the quantum proton fluctuations, resulting in a quantum paraelectric (QPE) state. Furthermore, our thermal-transport measurements reveal that a QSL state with gapless spin excitations rapidly emerges upon entering the QPE state. These findings indicate that the quantum proton fluctuations give rise to a QSL—a quantum-disordered state of magnetic and electric dipoles—through the coupling between the electron and proton degrees of freedom.

Occupation probabilities of single particle levels using the microscopic interacting boson model: Application to some nuclei of interest in neutrinoless double-βdecay

We have developed a new method to calculate the occupancies of single particle levels in atomic nuclei. This method has been developed in the context of the microscopic interacting boson model, in which neutron and proton degrees of freedom are treated explicitly. The energies of the single particle levels constitute a very important input for the calculation of the occupancies in this method. In principle these energies can be considered as input parameters that can be fitted to reproduce the experimental occupancies. Instead of fitting, in this study we have extracted the single particle energies from experimental data on nuclei with a particle more or one particle less than a shell closure. We provide the sets of these single particle energies suitable for several major shells and apply our method to calculate the occupancies of several nuclei of interest in neutrinoless double-$\ensuremath{\beta}$ decay using these sets. Our results are compared with other theoretical calculations and experimental occupancies, when available.

Artificial reaction coordinate "tunneling" in free-energy calculations: the catalytic reaction of RNase H.

We describe a method for the systematic improvement of reaction coordinates in quantum mechanical/molecular mechanical (QM/MM) calculations of reaction free-energy profiles. In umbrella-sampling free-energy calculations, a biasing potential acting on a chosen reaction coordinate is used to sample the system in reactant, product, and transition states. Sharp, nearly discontinuous changes along the resulting reaction path are used to identify coordinates that are relevant for the reaction but not properly sampled. These degrees of freedom are then included in an extended reaction coordinate. The general formalism is illustrated for the catalytic cleavage of the RNA backbone of an RNA/DNA hybrid duplex by the RNase H enzyme of Bacillus halodurans. We find that in the initial attack of the phosphate diester by water, the oxygen-phosphorus distances alone are not sufficient as reaction coordinates, resulting in substantial hysteresis in the proton degrees of freedom and a barrier that is too low (approximately 10 kcal/mol). If the proton degrees of freedom are included in an extended reaction coordinate, we obtain a barrier of 21.6 kcal/mol consistent with the experimental rates. As the barrier is approached, the attacking water molecule transfers one of its protons to the O1P oxygen of the phosphate group. At the barrier top, the resulting hydroxide ion forms a penta-coordinated phosphate intermediate. The method used to identify important degrees of freedom, and the procedure to optimize the reaction coordinate are general and should be useful both in classical and in QM/MM free-energy calculations.

A Correspondence Between IBA-I and IBA-II Model and Electromagnetic Transitions of Some Erbium Isotopes

Since the lowest levels are symmetric under the interchange of neutrons and protons from calculations in the interacting boson approximation IBA-2 model, IBA-1 model space, in which neutron and proton degrees of freedom are not distinguished can be considered as a subspace of the IBA-2 model space. Using the microscopic background of the IBA-2 model, a correspondence can be established between IBA-1 and IBA-2 model space. Since the space of the IBA-1 model can be regarded as a subspace of the IBA-2 model there is a unique way to “Project” the operators of the IBA-2 model onto those of IBA-1. This projection can be carried out by using the Fspin formalism. In the IBA-2, the lowest states are indeed fully symmetric, the calculations with the help of this projection, we explore the energy levels and the electric quadrupole transition probabilities B(E2;Ii If) and -ray E2/M1 mixing ratios for selected transitions of 166-168Er .Owing to admixtures of non-fully-symmetric states in IBA-2, we renormalized the parameters (ε) and (κ).This is the first time we show that this projection can be applied to some heavier isotopes and the results obtained for 166-168Er isotopes are reasonably in good agreement with the previous experimental values.

A correspondence between IBA-1 and IBA-2 models and electromagnetic transitions in the decay of some erbium isotopes

The interacting boson approximation IBA-1 model space, in which neutron and proton degrees of freedom are not distinguished, can be considered as a subspace of the IBA-2 model space. Using the microscopic background of the IBA-2 model, a correspondence can be established between IBA-1 and IBA-2 model space. Since the space of the IBA-1 model can be regarded as a subspace of the IBA-2 model there is a unique way to ‘Project’ the operators of the IBA-2 model onto those of IBA-1. This projection can be carried out using theF-spin formalism. In the IBA-2 model, the lowest states are indeed fully symmetric, and using the calculations with the help of this projection, we explore the energy levels and the electric quadrupole transition probabilitiesB(E2; {ie393-01}) and γ-ray E2/M1 mixing ratios for selected transitions of162, 164, 166, 168, 170Er. Owing to admixtures of non-fully-symmetric states in IBA-2, we renormalized the parameters (e) and (κ). This is the first time we show that this projection can be applied to some heavier isotopes and the results obtained for162, 164, 166, 168, 170Er isotopes are reasonably in good agreement with the previous experimental values.

Attractive and repulsive contributions of medium fluctuations to nuclear superfluidity

Oscillations of mainly surface character ($S=0$ modes) give rise, in atomic nuclei, to an attractive (induced) pairing interaction, while spin ($S=1$) modes of mainly volume character generate a repulsive interaction, the net effect being an attraction which accounts for a sizeable fraction of the experimental pairing gap. Suppressing the particle-vibration coupling mediated by the proton degrees of freedom, i.e., mimicking neutron matter, the total surface plus spin-induced pairing interaction becomes repulsive.

Effective triaxial deformations of even-even Ru isotopes in the neutron-proton interacting boson model

We analyze recent experimental data on energy spectra and electromagnetic transition intensities of neutron-rich even Ru isotopes within the framework of the interacting boson model, taking into account both neutron and proton degrees of freedom. Signatures supporting an effective $\ensuremath{\gamma}$ deformation different from zero in the mass region around $A=110$ are pointed out.

Collective and quasiparticle structures in 192Pb

The structure of 192Pb has been investigated using the 173Yb( 24Mg, 5n) reaction at E b = 132 MeV. The level scheme has been extended up to an excitation energy of 7 MeV and a spin of 23 ħ. Two collective bands of levels linked by M1 transitions and four groups of states of non-collective character have been observed. Based on comparison with experimental data on odd- A Tl isotopes and with cranked shell-model calculations assuming an oblate shape, the collective Ml bands are interpreted as having an underlying proton 2-quasiparticle configuration coupled to a pair of rotation-aligned i 13 2 neutrons. The four groups of non-collective level-sequences are understood as 4-quasiparticle excitations associated with aligned neutron 2-quasiparticle states that involve a mixture of neutron and proton degrees of freedom.

Interacting Boson-Fermion Model description of Ru and Rh isotopes

We present a detailed analysis of nuclear structure properties concerning99,101Ru and101,103Rh, within the framework of the Interacting Boson-Fermion Model (IBFM) version 2, where both neutron and proton degrees of freedom are taken into account. Calculated energy spectra, electromagnetic moments, transition probabilities and spectroscopic factors for one-nucleon transfer reactions are compared with the corresponding experimental data.

Orbital magnetic dipole strength in 148,150,152,154Sm and nuclear deformation.

Nuclear-resonance-fluorescence spectra have been measured in the chain of $^{148,150,152,154}\mathrm{Sm}$ isotopes. Together with supplementary information from inelastic electron scattering and other reaction studies, orbital M1 transition strengths have been deduced for a number of ${1}^{+}$ states located around an excitation energy of 3 MeV. The systematic study, carried out for the first time, for nuclei within a large range of the deformation parameter \ensuremath{\delta} shows that the orbital M1 strength varies quadratically with \ensuremath{\delta}. This result is interpreted in terms of models containing explicitly neutron and proton degrees of freedom.

Medium energy proton scattering from 154Gd and the interacting boson model of nuclei.

The interacting boson model of nuclei is used to study 650 MeV proton scattering to the ${\mathit{J}}_{\mathit{i}}^{\mathrm{\ensuremath{\pi}}}$=${0}_{1}^{+}$,${2}_{1,3}^{+}$ state in $^{154}\mathrm{Gd}$. All coupled channels within the interacting boson model space are included. The hadronic boson quadrupole operator is determined. Comparison with the electromagnetic boson quadrupole operator suggests that the ${2}_{3}^{+}$ state is not completely symmetric in the neutron and proton degrees of freedom.

Ground state of solid hydrogen at high pressures.

Quantum Monte Carlo calculations of the properties of bulk hydrogen at zero temperature have been performed. The only approximations involved in these calculations are the restriction to finite systems (64 to 432 atoms), the use of the fixed-node approximation to treat Fermi statistics, and the finite length of the Monte Carlo runs. The Born-Oppenheimer approximation was avoided by solving the quantum many-body problem simultaneously both for the electron and proton degrees of freedom. Using different trial functions and several different crystal structures the transition between the explored molecular and atomic phases was determined to occur at 3.0\ifmmode\pm\else\textpm\fi{}0.4 Mbar. The transition to a rotationally ordered molecular phase occurred at about 1.0 Mbar. A lower bound to the static dielectric constant, given in terms of the static structure factor, was found to lie close to experimental values and became large for pressures greater than 500 kbar.

Microscopic calculations for the interacting boson model

The parameters of the interacting boson model are calculated in a shell model framework, using a generalized seniority basis. The effect of the neutron-proton interaction on the $s$- and $d$-boson structure is explicitly considered. The renormalization due to the truncation of the full fermion space to the $S\ensuremath{-}D$ subspace is considered by taking the effects of the $G$-pair state into account using perturbation theory. It is found that this effects mainly the single boson energies and introduces a Majorana force that favors states symmetric in neutron and proton degrees of freedom over antisymmetric ones.NUCLEAR STRUCTURE Microscopic calculation of interacting boson approximation parameters. Shell model calculations in the generalized seniority basis.