Takayuki Myo

Resonance and Continuum Components of the Strength Function.

It is shown that the strength function can be expressed in a sum of the contributions from bound, resonance and continuum terms and the role of each term can be investigated complementarily by using the complex scaling method (CSM). The mechanism of the Coulomb breakup reaction of Be is analyzed and we confirm the fact that the breakup is direct but not through resonances. The present method is also applied to other systems and its usefulness is discussed.

Partial Decay Widths in Coupled-Channel Systems with the Complex-Scaled Jost Function Method

Partial decay widths of resonant states in a coupled-channel system are studied by using the complex-scaled Jost function method (CSJFM). With CSJFM, we use the ratio of the S-matrices to calculate partial decay widths, and then we need not introduce any “channel radius”, which is used in standard scattering theory. Combining the Jost function method (JFM) and the complex scaling method (CSM), we can easily obtain many resonant states even for a large total width and partial decay widths simultaneously. Several methods to calculate partial decay widths in CSM are also discussed and are shown to give the same values in CSJFM.

Extended 9Li+n+n three-body model of 11Li with a pairing correlation in 9Li

We investigate the binding mechanism of 11 Li on the basis of an extended three-body model of 9 Li+n+n. In the model, we take into account the pairing correlation of p-shell neutrons in 9 Li, in addition to that of valence neutrons outside the 9 Li nucleus, and solve the coupled-channel two- and three-body problems of 10 Li and 11 Li, respectively. The results show that the degrees of freedom of the pairing correlation in 9 Li play an important role in the structure of 10 Li and 11 Li. In 10 Li, the pairing correlation in 9 Li produces a socalled pairing-blocking effect due to the presence of a valence neutron, which causes the sand p-wave neutron orbits to become energetically degenerate. In 11 Li, contrastingly, the pairing-blocking effect is overwhelmed by the core-n interaction due to the two degrees of freedom of the two valence neutrons surrounding 9 Li, and as a result, the ground state is dominated by the p-shell closed configuration and does not exhibit spatial extension with a large r.m.s. radius. These results indicate that the pairing correlation is realized differently in odd- and even-neutron systems of 10 Li and 11 Li. In addition, we further improve the tail part of the 9 Li-n interaction, which yields reasonable reproductions of the observed large r.m.s. radius in 11 Li.

The Binding Mechanism and a Low-Lying Resonance in 11Li

Using a new 9 Li-n interaction taking into account the 9 Li-core excitation, it is shown that the 9 Li+n+n model reproduces the observed binding energy of 11 Li. This 9 Li-n interaction naturally explains the degeneracy of single particle s1/2- and p1/2-orbital states above the 9 Li+n threshold. Furthermore, by using the 9 Li-n interaction, a low-lying excited resonant state is obtained in 11 Li together with the ground state, and they are found to be partners in mixed configurations of (0p1/2) 2 and (1s1/2) 2 .

Study of virtual states in 5He and 10Li with the Jost function method

Abstract We study virtual states in 5 He and 10 Li by using the Jost function method (JFM). In 5 He, we obtained an s -wave pole with the complex energy E=7.50−44.7 i MeV using a 4 He–n potential called KKNN. In 10 Li, we investigated s -wave virtual poles with the 9 Li–n interaction microscopically constructed by taking into account the Pauli-blocking effect. We obtained a virtual state at E=−0.135 MeV ( k=−0.077 i fm −1 ). The attractive property of the s -wave 9 Li–n potential for 10 Li is discussed in comparison with the 5 He ( 4 He + n) system and also calculational results for the 9 Li–n potential of Thompson and Zhukov.

Beyond the core + n + n model for the neutron halo nucleus 11Li

Abstract A new model beyond the core + n + n model is discussed for two-neutron halo nucleus 11 Li. In this model, pairing correlations among two halo neutrons and p -orbital neutrons in the 9 Li core are taken into account as an important ingredient of the exotic binding mechanism. The 10 L= 9 Li+ n system, which is a subsystem of 9 Li+ n + n , is studied, and it is shown that the Pauli-blocking effect of pairing correlations of the 9 Li-core cluster due to a p 1 2 - valence neutron brings about the degeneracy of the single particle energies of p 1 2 and s 1 2 orbitals. For 11 Li, three-body coupled-channel calculations are performed, and it is shown that the results explain observed exotic properties of very small separation energy S 2 n , large matter radius and large amplitude of the s -orbital configuration.

Resonances and continuums in the three-body breakup of halo nuclei

Abstract We investigate the three-body Coulomb breakup reaction of two-neutron halo nuclei 11 Li, where we adopt the extended three-body model of 11 Li with paying attention to the pairing correlation of the nuclei. We also employ the complex scaling method (CSM) to solve the three-body unbound states of 11 Li. From the results, we cannot find any dipole resonances, at least, having small decay widths. This means that the breakup strengrth is exhausted by the continuum states. We discuss which component of the continuum states in the three-body system determines the structure of the breakup strength such as the low energy enhancement observed in the experiments.

Description of three‐body scattering for astrophysics

A new and simple discription of the three‐body scattering states, which is based on the Lippmann‐Schwinger equation and the complex scaling method, is developed. As applications of this method, the energy distribution of the E1 transition strength for 6He is calculated. It is also shown that the correlations of subsystems in 6He are well reproduced.

Role of the Tensor Correlation on the Spin-Orbit Splitting in Neutron Halo Nuclei

We investigate the tensor correlation in neutron halo nuclei 6He and 11Li. We use the extended (4He/9Li)+n+n models for two nuclei and a special attention is paid for core nuclei (4He and 9Li) to incorporate the tensor correlation in the shell model type wave function. We discuss the Pauli‐blocking between core nuclei and last two neutrons and its effect on the spin‐orbit splitting of halo nuclei. For 6He, 02+ state is affected by this blocking from the 0s1/2 → 0p1/2 excitation in 4He. For 11Li, the blocking makes the (1s)2 and (0p)2 configurations close to each other in energy and hence mix equal amount of two configurations to develop the halo structure.

Tensor Correlation in Neutron Halo Nuclei

We investigate the effect of the tensor correlation on the light neutron‐rich nuclei. We extend the model space of 4He core with the shell model approach to incorporate the tensor correlation, and π‐like 0− particle‐hole correlation is strongly favored. This affects the LS splitting in 5He and the 02+ state of 6He. We also investigate that the tensor correlation is suppressed in 11Li for p2 configuration of the last two neutrons. This suppression can be reduced by the large mixing of the (1s)2 component in the ground state, which naturally produces the halo structure.