Cluster-orbital Shell Model Research Articles

Structure of neutron-rich He Λ hypernuclei using the cluster orbital shell model

We calculated the energy spectra of the neutron-rich He $\Lambda$ hypernuclei with $A=6$ to 9 within the framework of an $\alpha + \Lambda +Xn$ ($X=1$--4) cluster model using the cluster orbital shell model. The employed constituent particles reproduce their observed properties. For resonant states of core nuclei such as $^5$He, $^6$He, and $^7$He, the complex scaling method is employed to obtain energies and decay widths. The calculated ground states of $^6_{\Lambda}$He and $^7_{\Lambda}$He are in good agreement with published data. The energy levels of $^8_{\Lambda}$He and $^9_{\Lambda}$He are predicted. In $^9_{\Lambda}$He, we find one deeply bound state and two excited resonant states, which are proposed to be produced at the Japan proton accelerator research complex (J-PARC) by the double-charge-exchange reaction $(\pi^-, K^+)$ using a $^9$Be target.

Two-neutron halo structure of F31 and a novel pairing antihalo effect

Background: A newly identified dripline nucleus $^{31}$F offers a unique opportunity to study the two-neutron ($2n$) correlation at the east shore of the island of inversion where the $N = 28$ shell closure is lost. Purpose: We aim to present the first three-body theoretical results for the radius and total reaction cross sections of $^{31}$F. This will further help to investigate how the pairing and breakdown of the $N = 28$ shell closure influence the formation of the $2n$-halo structure and the anti-halo effect in this mass region. Methods: A $^{29}$F$+n+n$ three-body system is described by the cluster orbital shell model, and its total reaction cross section is calculated by the Glauber theory. Results: Our three-body calculations predict 3.48-3.70 fm for the root-mean-square radius of $^{31}$F, which corresponds to the total reaction cross section of 1530 (1410)-1640 (1500) mb for a carbon target at 240 (900) MeV/nucleon. The binding mechanism and halo formation in $^{31}$F are discussed. Conclusions: The present study suggests a novel anti-halo effect in this mass region: When the pairing overcome the energy gap between the $p_{3/2}$ and $f_{7/2}$ orbits, the inversion of the occupation number of these orbits takes place, and it diminishes the $2n$-halo structure.

Structure and decays of nuclear three-body systems: The Gamow coupled-channel method in Jacobi coordinates

${\bf Background:}$ Weakly bound and unbound nuclear states appearing around particle thresholds are prototypical open quantum systems. Theories of such states must take into account configuration mixing effects in the presence of strong coupling to the particle continuum space. ${\bf Purpose:}$ To describe structure and decays of three-body systems, we developed a Gamow coupled-channel (GCC) approach in Jacobi coordinates by employing the complex-momentum formalism. We benchmarked the new framework against the complex-energy Gamow Shell Model (GSM). ${\bf Methods:}$ The GCC formalism is expressed in Jacobi coordinates, so that the center-of-mass motion is automatically eliminated. To solve the coupled-channel equations, we use hyperspherical harmonics to describe the angular wave functions while the radial wave functions are expanded in the Berggren ensemble, which includes bound, scattering and Gamow states. ${\bf Results:}$ We show that the GCC method is both accurate and robust. Its results for energies, decay widths, and nucleon-nucleon angular correlations are in good agreement with the GSM results. ${\bf Conclusions:}$ We have demonstrated that a three-body GSM formalism explicitly constructed in cluster-orbital shell model coordinates provides similar results to a GCC framework expressed in Jacobi coordinates, provided that a large configuration space is employed. Our calculations for $A=6$ systems and $^{26}$O show that nucleon-nucleon angular correlations are sensitive to the valence-neutron interaction. The new GCC technique has many attractive features when applied to bound and unbound states of three-body systems: it is precise, efficient, and can be extended by introducing a microscopic model of the core.

Deuteron-Like Correlation for the T = 0 Channel in 18F Studied within the Continuum Contributions

We study the deuteron-like correlation of the valence proton and neutron for the T = 0 channel in 18F using the cluster-orbital shell model approach. In this study, the deuteron-like correlation is examined in terms of two key ingredients, cross-shell configuration and continuum contribution. We discuss the cross-shell configuration contributes to the restoration of the symmetry to form the LS-coupling in 1+, and the continuum contributions plays an important role of the spatial localization of the proton and neutron.

Deuteron-like neutron–proton correlation in18F studied with the cluster-orbital shell model approach

Deuteron-like neutron–proton correlation in¹⁸F studied with the cluster-orbital shell model approach

Deuteron-like correlation of valence nucleons for theT= 0 channel in18F

We study the deuteron-like correlation of the valence proton and neutron with the T = 0 channel in 18 F using an efficient calculational formalism; the cluster-orbital shell model approach. In this study, we show a particular configuration [j 1 ⊗ j 2 ]T J = [d 5/2 ⊗ d 3/2 ]0 1 is the key ingredient for the T = 0 pair formation. Also, the continuum contributions plays an important role of the spatial correlation of the proton and neutron.

Coupled-channel picture of the core nucleus for the expansion of the nuclear size in the drip-line region

We study the energy and radius of neutron rich nuclei toward to the drip-line region. We employ the cluster-orbital shell model approach to calculate the radius of the oxygen isotopes. The result shows that the calculated radius underestimates the observed one at 23O, though the binding energy and the drip-line of the oxygen isotopes are reproduced. Therefore, we propose a coupled-channel approach to explain the sudden increase of the radius of the oxygen isotopes at 23O. As a result, the sudden change of the radius can be descried in terms of the competition between the available valence neutron orbits and occupied orbits in the core nucleus. For the 23O case, we show that the excitation to the 1s1/2-orbit in the core nucleus is a key configuration to reproduce the radius.

Precise comparison of the Gaussian expansion method and the Gamow shell model

We perform a detailed comparison of results of the Gamow Shell Model (GSM) and the Gaussian Expansion Method (GEM) supplemented by the complex scaling (CS) method for the same translationally-invariant cluster-orbital shell model (COSM) Hamiltonian. As a benchmark test, we calculate the ground state $0^{+}$ and the first excited state $2^{+}$ of mirror nuclei $^{6}$He and $^{6}$Be in the model space consisting of two valence nucleons in $p$-shell outside of a $^{4}$He core. We find a good overall agreement of results obtained in these two different approaches, also for many-body resonances.

Interplay between the02+resonance and the nonresonant continuum of the drip-line two-neutron halo nucleus22C

The breakup cross section (BUX) of 22C by 12C at 250 MeV/nucleon is evaluated by the continuum-discretized coupled-channels method incorporating the cluster-orbital shell model (COSM) wave functions. Contributions of the low-lying 0+_2 and 2+_1 resonances predicted by COSM to the BUX are investigated. The 2+_1 resonance gives a narrow peak in the BUX, as in usual resonant reactions, whereas the 0+_2 resonant cross section has a peculiar shape due to the coupling to the nonresonant continuum, i.e., the Fano effect. By changing the scattering angle of 22C after the breakup, a variety of shapes of the 0+_2 resonant cross sections is obtained. Mechanism of the appearance of the sizable Fano effect in the breakup of 22C is discussed.

Cluster-Orbital Shell Model Approach with a Treatment of Partially Pauli-Forbidden States

We study the origin of a sudden change of the radius of oxygen isotopes at 23O in terms of a coupled-channel model approach. We use the cluster-orbital shell model approach for describing the system. Qualitatively, the sudden change of the radius can be understood as the competition of occupation of the valence neutrons and the component of the core configuration. For the 23O case, the effect of the partially Pauli-forbidden states of the 1s1/2-orbit is small in the excited-core configuration.

Expansion of the 16O-core in neutron drip-line nuclei: 23O and 24O

Abstract We study an effect of the expansion of the core nucleus to the radius of 23 O and 24 O. In order to clarify the importance of the expansion of the core, we perform two calculations; an m -scheme approach of the cluster-orbital shell model for O 16 + X n systems and a simplified model approach for core + n and core + 2 n systems. We calculate the energy and r.m.s. radius of oxygen isotopes by using these two approaches and discuss the effect of the expansion of the 16 O-core and the relation to the presence of valence neutrons. Furthermore, we propose a new approach of a coupled-channel model including a particle–hole excitation in the 16 O-core and the motion of the valence neutron.

Investigation for a Drastic Change of the Core in 23O and 24O

We study the radius and energies of oxygen isotopes towards the neutron drip-line. The abrupt increase of the radius at 23O is investigated with two different approaches; the m-scheme cluster-orbital shell model (COSM) and a simplified model approach with the core plus one and two valence neutrons. We investigate properties of the oxygen isotopes by changing the radius of the 16O-core in the m-scheme COSM approach and obtain the result that the broad structure of 16O is favored in the 23O and 24O. In the simplified model approach, we estimate the magnitude of the change of the size of 22O in 23O and 24O.

Recent Development of CDCC and Future

Recent development of the continuum-discretized coupled-channels method (CDCC) is reviewed. The following three topics are covered: i) four-body CDCC with the clusterorbital shell-model (COSM) wave functions, COSM-CDCC, and its application to the study of nuclear breakup of C, ii) the eikonal reaction theory (ERT) that accurately describes inclusive breakup processes within the framework of CDCC, and iii) some applications of CDCC to nuclearastrophysics.

Resonances and continuum states of drip-line nuclei using the complex scaling method

Resonances and continuum states of He isotopes are investigated using the cluster orbital shell model (COSM) with the complex scaling method (CSM). We discuss the following subjects: 1) Spectroscopic factors of the unbound nucleus 7He into the 6He-n components and their relation to the one-neutron removal strengths of 7He. The importance of the 6He(2+) resonance is shown. 2) Structure of five-body 0+ resonance of 8He from the viewpoint of the two-neutron pair coupling. The monopole strengths into five-body unbound states are also investigated. It is found that the sequential breakup process of 8He → 7He+n → 6He+n+n is dominant in the monopole excitation, while the contribution of 8He(0+2) is negligible.

Properties of drip-line nuclei with an m-scheme cluster-orbital shell model approach

In the drip-line region of oxygen isotopes, an abrupt increase of the r.m.s.radius of 23O is observed from the analysis of the reaction cross section. We develop an m-scheme approach of COSM and perform calculations for oxygen isotopes. We examine the interaction dependence to the calculated energies and r.m.s.radii. Further, the relation between the density and nucleon-nucleon interaction is discussed.

RESONANCES AND CONTINUUM STATES OF HALO NUCLEI USING THE COMPLEX SCALING METHOD

The resonances and continuum states of He isotopes are investigated using the cluster orbital shell model with the complex scaling method. We discuss the following subjects; 1) spectroscopic factors of 7 He into the 6 He -n components, and 2) five-body 0+ resonance of 8 He and its structure from the viewpoint of the neutron-pair coupling.

CLUSTER-ORBITAL SHELL MODEL APPROACH FOR STUDY OF EXOTIC NUCLEI NEAR THE NEUTRON DRIP-LINE

We have developed an m -scheme cluster-orbital shell model approach to study neutron- and proton-rich nuclei toward the drip-lines. We discuss the property of the neutron-rich oxygen isotopes with analyzing the relation between the energy and r.m.s. radius.

Study of neutron-rich nuclei with an m -scheme cluster-orbital shell model approach

We propose an m -scheme approach of the cluster-orbital shell model (COSM) formalism. In order to take into account the contribution of the unbound states, the radial wave function is treated as the super position of the Gaussian functions with different width parameters. We apply the m -scheme COSM to oxygen isotopes. Energies and r.m.s. radii of oxygen isotopes are studied.

M-SCHEME CLUSTER-ORBITAL SHELL MODEL APPROACH FOR NEUTRON-RICH SYSTEMS

We developed an m-scheme approach of the cluster-orbital shell model formalism. The radial wave function is treated as the super position of the Gaussian functions with different width parameters. Energies and r.m.s. radii of oxygen isotopes are studied.

Microscopic model analysis ofLi11+pelastic scattering at 62, 68.4, and 75 MeV/nucleon

{sup 11}Li+p elastic scattering data at three energies, 62, 68.4, and 75 MeV/nucleon, are analyzed with density-dependent M3Y and KH effective nucleon-nucleon (NN) interactions in the framework of the single folding model. The parameters of the density-dependent term are adjusted to fulfill saturation of nuclear matter. The optical potentials (OP's) and cross sections are calculated using four model densities of {sup 11}Li, G (one-parameter Gaussian), GG (Gaussian-Gaussian), GO (Gaussian- oscillator), and the COSMA (cluster orbital shell model approximation). Comparative studies are performed for real, imaginary, and spin-orbit potentials with the phenomenological and microscopic forms. The microscopic volume and surface imaginary potentials are constructed from both the renormalized folded potentials and their derivatives. The sensitivity of the differential cross section to the four densities is tested. It is found that the {sup 11}Li+p elastic scattering cross sections depend strongly upon the behavior of the corresponding potentials. The GG and GO densities obtained from analyzing the data, using Glauber multiple scattering theory at high energies, give good results at energies below 100 MeV/nucleon in the framework of the folding model. The OP's calculated in the microscopic form using few parameters give good agreement with the data. Thus, it is not necessary tomore » introduce a large number of arbitrary fitting parameters as done in the phenomenological and semimicroscopic OP's. The KH effective interaction successfully describes {sup 11}Li+p elastic scattering as the popular M3Y interaction. The obtained results of the reaction cross section are in good agreement with previous calculations.« less