Ba Nuclei Research Articles

Evolution of quadrupole-octupole collectivity in the even–even 54 ≤ Z ≤ 58 nuclei

We explore the quadrupole-octupole collectivity in the mass region of even–even 54 ≤ Z ≤ 58 (Xe, Ba and Ce) nuclei by analysing the fine structure of energy spectra. As a basic criterion for the presence of reflection-asymmetric degree of freedom we consider the formation of alternating-parity level-sequences. As a clear-cut criterion for the emergence of pronounced octupole deformation we consider the reduction of the parity-shift at certain angular momentum and the formation of a single energy sequence which can be interpreted as an octupole band. Applying these criteria we select out alternating-parity bands (APBs) in the region of Xe, Ba and Ce isotopes for which a manifestation of pronounced octupole collectivity can be considered. Their fine structure is probed in a collective quadrupole-octupole rotation model (QORM) providing a detailed analysis in terms of odd–even staggering diagrams. The obtained model descriptions of the energy levels and staggering patterns reveal the most characteristic features of the quadrupole-octupole deformations in this mass region and outline a clearly determined area of manifestation of nuclear reflection-asymmetric shapes.

Study of Octupole Transitions in Xe, Ba, Ce and Nd Nuclei within Interacting Boson Model

For nuclei with 54≤Z≤60 and 86≤N≤94, the results regarding the excitation spectra at low energies, both in positive and negative parity, as well as the transition probabilities for electric dipole (B(E1)), quadrupole (B(E2)), and octupole transitions (B(E(3)), indicate the emergence of significant octupole behavior. These observations have been made using the Interacting Boson Model-1 (IBM-1). The study examines the onset of octupole deformation and its impact on the spectroscopic characteristics in even-even neutron-rich lanthanide isotopes, specifically in the Ba and Nd nuclei. The investigation compares the results obtained from the Interacting Boson Model-1 (IBM-1) with the existing experimental data. The focus is on understanding how the addition of neutrons influences the development of octupole deformation and its manifestation in the observed spectroscopic features. The onset of strong octupolarity for Z≈ 56 and N ≈ 88 nuclei is indicated by the results obtained for the electric dipole, quadrupole, and octupole transition probabilities, as well as the low-energy positive and negative-parity excitation spectra. Conversely, discrepancies between the spectroscopic data and the IBM results suggest that the mapping quality needs to be evaluated in order to determine if the mapped boson Hamiltonian or the fermionic calculations are the source of the issues.

Structural evolution and shape transitions of even-even neutron rich $$^{140-150}$$Ba nuclei using triaxial projected shell model

Structural evolution and shape transitions of even-even neutron rich $$^{140-150}$$Ba nuclei using triaxial projected shell model

Quadrupole-octupole coupling and the evolution of collectivity in neutron-deficient Xe, Ba, Ce, and Nd isotopes

The evolution of quadrupole and octupole collectivity in neutron-deficient Xe, Ba, Ce, and Nd nuclei near the ``octupole magic'' neutron number $N=56$ is investigated within the mapped $sdf$-IBM framework. Microscopic input is obtained via quadrupole and octupole constrained Hartree-Fock-Bogoliubov calculations, based on the parametrization D1M of the Gogny energy density functional. Octupole-deformed mean-field ground states are predicted for Ba and Ce isotopes near $N=56$. Excitation energies of positive- and negative-parity states as well as electric transition rates are computed with wave functions resulting from the diagonalization of the mapped IBM Hamiltonian. The parameters of the Hamiltonian are determined via the mapping of the mean-field potential energy surfaces onto the expectation value of the Hamiltonian in the condensate state of the $s$, $d$, and $f$ bosons. Enhanced octupolarity is predicted for Xe, Ba, and Ce isotopes near $N=56$. The shape/phase transition from octupole-deformed to strongly quadrupole-deformed near $N=60$ is analyzed in detail.

Quantitative assessment of amygdala in Macaca fascicularis monkeys.

The amygdaloid complex (AC) is involved in very relevant cognitive and emotional pathways and exhibits changes in aging and in some neurological and psychiatric disorders. The quantitative estimators of AC could be useful to understand the impact of amygdaloid pathology in these processes, both globally and for each nucleus in particular, and their neurons. The present study analyzes morphometric and stereological estimators in the whole AC and its three main nuclei (lateral [La], basal [Ba], and accessory basal [AB]) in six Macaca fascicularis monkeys. All the brains were fixed and sectioned in the coronal plane; Nissl-stained sections were used for estimation of size and form parameters in both, the AC, and the La, Ba, and AB nuclei separately. The study includes stereological estimates of the volume and surface area of the AC; also, volume of the neurons in the amygdaloid nuclei was estimated using the point-sampled intercepts method. Our results show that the AB nucleus is smaller than both the La and Ba nuclei in both morphometric and stereological estimators. Brain hemispheric side had not significant influence on any of quantitative estimates. The neuron volume was higher in the AB nucleus relative to LA and Ba of the nuclei. These data describe some quantitative parameters of the amygdaloid complex and their main nuclei that could help us to detect small changes in neurodegenerative and other pathological processes.

β decay of odd- A nuclei with the interacting boson-fermion model based on the Gogny energy density functional

The low-energy excitations and $\beta$ decays of odd-A nuclei are studied within the interacting boson-fermion model (IBFM), based on the Gogny-D1M nuclear energy density functional (EDF). The constrained Hartree-Fock-Bogoliubov (HFB) approximation is employed to compute potential energy surfaces in terms of triaxial quadrupole degrees of freedom for even-even Xe and Ba nuclei in the mass $A\approx 130$ region. The mean field approximation also provides spherical single-particle energies and occupation probabilities for the neighboring odd-A nuclei. Those quantities represent a microscopic input for spectroscopic calculations in odd-A Xe and Ba, Cs and La isotopes. The Gamow-Teller (GT) and Fermi (F) transition matrix elements, needed to compute $\beta$-decay $\log{ft}$ values are obtained without any phenomenological fitting. It is shown that both the low-lying states and $\beta$ decays of the studied odd-A systems are described reasonably well within the employed theoretical framework.

Infinite nuclear matter characteristics of the finite nuclei within relativistic mean‐field formalism

We investigate the mass dependence of the nuclear structure and the effective symmetry energy for the Kr and Ba nuclei. The axially deformed self‐consistent relativistic mean field with the nonlinear NL3* parameter set is used in the analysis. The coherent density fluctuation model is adopted to formulate the nuclear matter observables such as symmetry energy, neutron pressure, and symmetry energy curvature of finite nuclei as a function of the radius. We found a notable signature of the shell/subshell closure at N = 50 and 82 for the isotopic chains of Kr and Ba nuclei, respectively.

Shape phase transitions and isotopic shift in barium isotopes within covariant density functional theory

A systematic search of the shape phase transitions and isotopic shift of the neutron-rich barium (Ba; [Formula: see text]) isotopes, as a candidate for transitional nuclei, is done within the covariant density functional theory (CDFT). The relativistic Hartree–Bogoliubov (RHB) formalism with separable pairing and relativistic mean-field (RMF) with BCS pairing are used. The constraint calculations assuming the axial symmetry as well as triaxial symmetry clearly manifest the shape coexistence and the transitional behavior in these nuclei. A strong shell closure is observed at [Formula: see text] and weaker shell/subshell closure is observed at [Formula: see text]. Shape transition below and above the shell closure location at [Formula: see text] (from prolate to spherical to prolate) is there. The candidates for [Formula: see text] and [Formula: see text] dynamical symmetries are found to be [Formula: see text]Ba, [Formula: see text]Ba and [Formula: see text]Ba, [Formula: see text]Ba nuclei, respectively. The calculated results are compared with the available experimental data and are in good agreement. We have investigated the model dependence as well as dependence on various model parameters. A comparison is made with other theoretical models: infinite nuclear matter (INM) model, macro–microscopic finite-range droplet model (FRDM) and the self-consistent Hartree–Fock–Bogoliubov (HFB) model. Overall good agreement is found within the different models used and between the calculated and experimental results.

β-decay properties in the Cs decay chain

The study of the decay of neutron-rich Cs isotopes has two main objectives: on one side β decay is a perfect tool to access the low-spin structures in the daughter Ba nuclei, where the evolution of octupole deformed shapes can be followed, while, on the other hand, the study of the gross properties of these decays, in terms of decay rates and branching to delayed-neutron emission, are fundamental inputs for the modelling of the r-process in the Rare-Earth Elements peak. Results obtained at CERN-ISOLDE are discussed within this framework and compared to existing data and predictions from state-of-the-art nuclear models.

Shape-phase transitions in odd-mass γ -soft nuclei with mass A≈130

Quantum phase transitions between competing equilibrium shapes of nuclei with an odd number of nucleons are explored using a microscopic framework of nuclear energy density functionals and a particle-boson core coupling model. The boson Hamiltonian for the even-even core nucleus, as well as the spherical single-particle energies and occupation probabilities of unpaired nucleons, are completely determined by a constrained self-consistent mean-field calculation for a specific choice of the energy density functional and pairing interaction. Only the strength parameters of the particle-core coupling have to be adjusted to reproduce a few empirical low-energy spectroscopic properties of the corresponding odd-mass system. The model is applied to the odd-A Ba, Xe, La and Cs isotopes with mass $A\approx 130$, for which the corresponding even-even Ba and Xe nuclei present a typical case of $\gamma$-soft nuclear potential. The theoretical results reproduce the experimental low-energy excitation spectra and electromagnetic properties, and confirm that a phase transition between nearly spherical and $\gamma$-soft nuclear shapes occurs also in the odd-A systems.

Unexpected5/2−spin of the ground state in147Ba: No octupole deformation in ground states of odd-ABa isotopes

The ${}^{147}$Ba nucleus has been studied in prompt $\ensuremath{\gamma}$-ray spectroscopy using the EUROGAM2 Ge array. Spin and parity of the ground state has been determined to be $5/{2}^{\ensuremath{-}}$. The unexpected, $5/{2}^{\ensuremath{-}}$ ground state results from interaction with other negative-parity configurations. A new ground-state band has been established in ${}^{147}$Ba and some previously reported levels have been arranged into a $3/{2}^{\ensuremath{-}}$ band, which may correspond to the $3/{2}^{\ensuremath{-}}$[532] configuration. The new spin assignments in ${}^{147}$Ba suggest that the theoretical predictions of static octupole deformation in the ground state of ${}^{147}$Ba may not be be valid. No candidates for parity doublets have been found in ${}^{147}$Ba. Instead, an octupole band built on the ground state has been proposed.

Neural substrates for the distinct effects of presynaptic group III metabotropic glutamate receptors on extinction of contextual fear conditioning in mice

The group III metabotropic glutamate (mGlu) receptors mGlu7 and mGlu8 are receiving increased attention as potential novel therapeutic targets for anxiety disorders. The effects mediated by these receptors appear to result from a complex interplay of facilitatory and inhibitory actions at different brain sites in the anxiety/fear circuits. To better understand the effect of mGlu7 and mGlu8 receptors on extinction of contextual fear and their critical sites of action in the fear networks, we focused on the amygdala. Direct injection into the basolateral complex of the amygdala of the mGlu7 receptor agonist AMN082 facilitated extinction, whereas the mGlu8 receptor agonist (S)-3,4-DCPG sustained freezing during the extinction acquisition trial. We also determined at the ultrastructural level the synaptic distribution of these receptors in the basal nucleus (BA) and intercalated cell clusters (ITCs) of the amygdala. Both areas are thought to exert key roles in fear extinction. We demonstrate that mGlu7 and mGlu8 receptors are located in different presynaptic terminals forming both asymmetric and symmetric synapses, and that they preferentially target neurons expressing mGlu1α receptors mostly located around ITCs. In addition we show that mGlu7 and mGlu8 receptors were segregated to different inputs to a significant extent. In particular, mGlu7a receptors were primarily onto glutamatergic afferents arising from the BA or midline thalamic nuclei, but not the medial prefrontal cortex (mPFC), as revealed by combined anterograde tracing and pre-embedding electron microscopy. On the other hand, mGlu8a showed a more restricted distribution in the BA and appeared absent from thalamic, mPFC and intrinsic inputs. This segregation of mGlu7 and mGlu8 receptors in different neuronal pathways of the fear circuit might explain the distinct effects on fear extinction training observed with mGlu7 and mGlu8 receptor agonists.This article is part of a Special Issue entitled ‘Metabotropic Glutamate Receptors’.

Effect of time-odd mean fields on inertial parameters of the quadrupole collective Hamiltonian

Most current implementations of the quadrupole collective Hamiltonian model do not include the contributions of time-odd mean fields to the moments of inertia and mass parameters (Thouless-Valatin dynamical rearrangement contributions). A hybrid model is introduced that allows a quantitative estimate of these contributions to the inertial functions of a five-dimensional collective Hamiltonian based on microscopic energy density functionals. Fully self-consistent constrained relativistic Hartree-Bogoliubov calculations of triaxial energy surfaces in the $\ensuremath{\beta}\ensuremath{-}\ensuremath{\gamma}$ plane are used to determine the parameters of an equivalent pairing-plus-quadrupole ($P+Q$) Hamiltonian. This Hamiltonian is employed in constrained Hartree-Fock-Bogoliubov (CHFB) plus local quasiparticle random-phase approximation (LQRPA) calculation of the deformation-dependent corrections to the Inglis-Belyaev moments of inertia and cranking mass parameters. This hybrid model is used to evaluate the influence of time-odd mean fields on vibrational and rotational collective masses and investigate their effect on the low-energy collective excitation spectra and transition rates of $\ensuremath{\gamma}$-soft Xe and Ba nuclei.

Nuclear structure of Xe-Pt nuclei in the framework of ARM and odd-even staggering

The asymmetric rotor model (ARM) of collective rotation is used to search for the correlation between the rotational energy with the asymmetric parameter \gamma_0 for Xe-Pt nuclei. The correspondence of the ratio ROTE/E(2_1^+) vs. R_{4/2}(=E(4_1^+)/E(2_1^+)) and \gamma_0 is used to distinguish between the axially symmetric and triaxial nuclei. The correlation between deformation parameter \beta and \gamma_0 is studied to understand the structure of the nuclei. The \gamma-band energy staggering in low-spin, low-energy spectra of even-even ^{122-124}Xe and ^{124-128}Ba nuclei is also discussed. We have compared our results with experimental data and other theoretical models.

Study and comparison of the decay modes of the systems formed in the reactions78Kr+40Ca and86Kr+48Ca at10AMeV

The first results of the ISODEC experiment, performed at the INFN Laboratori Nazionali del Sud (LNS) by using the CHIMERA detector, are presented. The principal aim of this experiment is to explore the isospin dependence of the decay modes of medium mass compound nuclei formed by fusion processes, by studying the competition between the various disintegration modes of 118,134 Ba nuclei produced in the reactions 78 Kr+ 40 Ca and 86 Kr+ 48 Ca at 10 AMeV. The studied systems allow in fact to produce compound nuclei with a large variation of N/Z, and such data will also provide new constraint on sophisticated models attempting to describe statistical and/or dynamical properties of excited nuclei. The experiment complements data already obtained at 5.5 AMeV for 78,82 Kr+ 40 Ca reactions, previously realized at GANIL by using the INDRA detector. First results show a strong staggering effects in the Z distributions, as well as different isotopic composition and enrichment for the reaction products in the two systems.

NUCLEAR SUB-STRUCTURE IN 112–122Ba NUCLEI WITHIN RELATIVISTIC MEAN FIELD THEORY

Working within the framework of relativistic mean field theory, we study for the first time the clustering structure (nuclear sub-structure) of 112–122 Ba nuclei in an axially deformed cylindrical coordinate. We calculate the individual neutrons and protons density distributions for Ba -isotopes. From the analysis of the clustering configurations in total (neutrons-plus-protons) density distributions for various shapes of both the ground and excited states, we find different sub-structures inside the Ba nuclei considered here. The important step, carried out here for the first time, is the counting of number of protons and neutrons present in the clustering region(s). 12 C is shown to constitute the cluster configuration in prolate-deformed ground-states of 112–116 Ba and oblate-deformed first excited states of 118–122 Ba nuclei. Presence of other lighter clusters such as 2 H , 3 H and nuclei in the neighborhood of N = Z, 14 N , 34–36 Cl , 36 Ar and 42 Ca are also indicated in the ground and excited states of these nuclei. Cases with no cluster configuration are shown for 112–116 Ba in their first and second excited states. All these results are of interest for the observed intermediate-mass-fragments and fusion–fission processes, and the so far unobserved evaporation residues from the decaying Ba * compound nuclei formed in heavy ion reactions.

MICROSCOPIC STUDY OF NEGATIVE PARITY YRAST STATES IN NEUTRON-DEFICIENT 119–127Ba ISOTOPES

The negative parity yrast bands of neutron-deficient 119–127 Ba nuclei are studied by using the Projected Shell Model approach. Energy levels, transition energies and B(M1)/B(E2) ratios are calculated and compared with the available experimental data. The calculations reproduce the band head spins of negative parity yrast bands and indicate the multi-quasiparticle structure for these bands.

Interacting boson model-1 calculations for even-even <SUP align=right>122−132</SUP>Xe and <SUP align=right>126−136</SUP>Ba nuclei

In this study, we present the calculations of energy levels and B(E2) values of 122–132 Xe and 126–136 Ba nuclei using the Interacting Boson Model (IBM-1). Using the best fitted values of the parameters in the Hamiltonian of the IBM-1 we have calculated energy levels and B(E2) values for a number of transitions in 122–132 Xe and 126–136 Ba nuclei. Results are compared with the experimental data and other theoretical models. It has turned out that the IBM is fairly reliable for the calculation of spectra in the entire set of 122–132 Xe and 126–136 Ba nuclei.

SPECTROSCOPIC FEATURES OF LOW-ENERGY EXCITATIONS IN SKIN NUCLEI

Systematic studies of dipole and other multipole excitations in stable and exotic nuclei are discussed theoretically. Exploring the relation of the strengths of low-energy dipole and quadrupole pygmy resonances to the thickness of the neutron (proton) skin a close connection between static and dynamic properties of the nucleus is observed. The fine structure of low-energy dipole strength in 138 Ba nucleus is revealed from E1 and spin-flip M1 strengths distributions.

Microscopic description of spherical toγ-soft shape transitions in Ba and Xe nuclei

The rapid transition between spherical and $\gamma$-soft shapes in Ba and Xe nuclei in the mass region $A \geq 130$ is analyzed using excitation spectra and collective wave functions obtained by diagonalization of a five-dimensional Hamiltonian for quadrupole vibrational and rotational degrees of freedom, with parameters determined by constrained self-consistent relativistic mean-field calculations for triaxial shapes. The results reproduce the characteristic evolution of excitation spectra and E2 transition probabilities and, in general, a good agreement with available data is obtained. The calculated spectra display fingerprints of a second-order shape phase transition that can approximately be described by analytic solutions corresponding to the E(5) dynamical symmetry.