Narrow Results

The 3α resonances in ¹²C are investigated in a framework of the complex scaling method. Calculated resonance parameters well reproduce the experimental data and we can obtain the second 2⁺ state just above the third 0⁺ state.

We investigate the three-body Coulomb breakup reaction of two-neutron halo nuclei ¹¹Li, where we adopt the extended three-body model of ¹¹Li with paying attention to the pairing correlation of the nuclei, and also employ the complex scaling method (CSM) to solve the three-body unbound states of ¹¹Li. From the results, we cannot find any dipole resonances, at least, having small decay widths. This means that the breakup strength is exhausted by the continuum states. We compare the obtained strength showing the low energy enhancement to the several experimental data.

New cluster model based on the Generator Coordinate Method (GCM) is proposed for the studies on the molecular resonances recently observed in the neutron-rich Be isotope. The new model is applied to the ¹⁰Be=⁴He+⁶He system and its adiabatic energy surface is calculated. It is found that both the weak-coupling states and the strong-coupling ones are quite naturally generated depending on the ⁴He-⁶He relative distance. The stability of both states is also discussed.

We study ¹⁷O and ¹⁸O nuclei by using the core+n(+n) model. We perform the coupled-channel and the resonating group method (RGM) calculations not only for bound states but also for resonant states of ¹⁷O. We obtain the state dependent core-n folding potential and reasonable single-particle energy (SPE) in the ¹⁶O core. By using the same interaction for ¹⁷O, we study ¹⁸O in the core+n+n system.

We investigate the roles of the tensor correlation on the structures of ⁴He and ⁵He. For ⁴He, we take the high angular momentum states within the 2p2h excitations of the shell model type method to describe the tensor correlation explicitly. We found that the solutions show a good convergence and the obtained wave function has the large tensor correlation. We also found that three 2p2h configurations are largely coupled with (0s)⁴ one to describe the tensor correlation, which is understood from the selectivity of the tensor operator. This tensor correlation is also important to describe the scattering phenomena of the ⁴He+n system including the higher partial waves consistently.

We investigate the tensor and pairing correlations in ¹¹Li based on the ⁹Li+n+n model. For ⁹Li, we perform the configuration mixing with the shell model type wave function to introduce the core polarization caused by the tensor and pairing correlations. For ¹¹Li, we perform the coupled ⁹Li+n+n calculation, in which the couplings between the correlations in ⁹Li and the motion of the last two neutrons emerge Pauli-blocking for the p² configuration of ¹¹Li and increases the s² component to develop the halo structure.

We investigate the tensor correlations in He and Li isotopes systematically. We propose the tensor-optimized shell model (TOSM) to describe the strong tensor correlation arising from the bare nuclear force in nuclei. Using TOSM for Li isotopes, we investigate the anomalous structures of ^9,10,11Li based on the ⁹Li+n+n model where the ⁹Li cluster is described by TOSM. As a result, the couplings between the tensor correlation in ⁹Li and the extra two neutrons emerge Pauli-blocking, which naturally increases the s² component to develop the halo structure in ¹¹Li. We further describe the short-range correlation arising from the repulsive core in the bare nuclear force by the unitary correlation operator method (UCOM). We propose the new framework of TOSM+UCOM for the nuclear structure study starting from the bare nuclear force.

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.

To describe excited nuclear states, we developed the Brueckner-AMD combining the Brueckner theory with Antisymmetrized Molecular Dynamics (AMD), which has been recently proposed as a new framework to study nuclear structure of light nuclei based on the realistic nuclear force. In the present framework, we formulate a multi-configuration calculation with Generator Coordinate Method (GCM) in the Brueckner-AMD. An application is shown for the excited states with positive and negative parities in ⁴He, and the successful results and reliability of the present framework are discussed.

The α-condensed state in nuclear systems has been proposed by Tohsaki et al. and given rise to interesting discussions. The Hoyle state of ¹²C has been studied as the most typical example of such an α-condensed state. A new resonant state (E_r = 1.66 MeV, Γ = 1.48 MeV) is predicted as an excited α-condensed state in addition to the second 0⁺ state of the Hoyle state by calculations of the complex scaled 3α model. Based on this result, the breakup strengths of the inversion reaction for sequential (⁸Be + α → ¹²C + γ) and direct (α + α + α → ¹²C + γ) processes are calculated.

We present a new method of smoothing discrete breakup cross sections calculated by the method of continuum-discretized coupled-channels. In the four-body breakup reaction of ¹²C(⁶He, nn⁴He) at E_in = 229.8 MeV, the continuous breakup cross section is evaluated as a function of the excitation energy of ⁶He. Convergence of the cross section with respect to extending the modelspace is also confirmed.

We investigate the three-body Coulomb breakup of a two-neutron halo nucleus, ⁶He. The three-body scattering states of ⁶He are described by using the Complex-scaled solutions of the Lippmann-Schwinger equation. We calculate the breakup cross section and the invariant mass spectra, and discuss the relations between the structures in these observables and the n-n and α-n correlations of ⁶He.

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.

In order to investigate the particle capture reactions at the astrophysical energy, we consider that the structure of the negative-parity states near the threshold energy becomes important. To study the structure, it is necessary to extend the model space take into account the effect of the core excitation. In this paper, we discuss the effect of the core excitation for the reaction cross sections at the astrophysical energy.

We propose a new approach of the Brueckner-AMD that makes the antisymmetrized molecular dynamics (AMD) calculations possible with realistic nuclear forces. In this method, we solve the Bethe-Goldstone equation and calculate the G-matrix for every nucleon pair described by wave packets of AMD correctly. We report the results of applications to light nuclei with the Brueckner-AMD.

We show the importance of the tensor correlation on the structures of He and Li isotopes. We develop the tensor optimized shell model (TOSM) to describe the strong tensor correlation of the nuclear force in nuclei. We investigate the exotic structures of ^9,10,11Li based on the ⁹Li+n+n model where TOSM is used for ⁹Li. The coupling between the tensor correlation in ⁹Li and the extra two neutrons emerges Pauli-blocking, which increases the s² component and develops the halo structure in ¹¹Li.

We further treat the short range repulsion of the nuclear force by the unitary correlation operator method (UCOM), while the tensor correlation is described by TOSM. We propose a new approach of TOSM+UCOM to describe nuclei from the nuclear force.

We propose a new approach of the Brueckner-AMD that makes the antisymmetrized molecular dynamics (AMD) calculations possible with realistic nuclear forces. In this method, we solve the Bethe-Goldstone equation and calculate the G-matrix for every nucleon pair described by wave packets of AMD. In addition, we calculate the G-matrix in the spin and parity projection correctly using the two-body correlation functions derived from the solutions of the Bethe-Goldstone equation. We report the results of applications to light nuclei with the Brueckner-AMD plus the spin and parity projection.

A new method to describe the three-body decaying states is developed. In this method, the Lippmann–Schwinger equation is combined with the complex scaling method to take the correct boundary condition into account. For the application, the E1 transition strength of ⁶He is investigated. The energy and Dalitz distributions of the E1 transition are calculated, and the internal correlation of ⁶He is discussed. As results, it is found that the ⁶He → ⁵He(3/2^-)+n → ⁴He+n+n sequential decay process is dominant in the E1 transition reaction of ⁶He.

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 ⁷He into the ⁶He-n components, and 2) five-body 0⁺ resonance of ⁸He and its structure from the viewpoint of the neutron-pair coupling.

We investigate the three-body Coulomb breakup of a two-neutron halo nucleus, ⁶He. We calculate the breakup cross section and the invariant mass spectra by using the complex-scaled solutions of the Lippmann-Schwinger equation, and discuss the relations between the structures in these observables and the n-n and α-n correlations in ⁶He.