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DOI： 10.1103/PhysRevC.107.024309

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DOI： 10.1038/s41467-022-29582-0

Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

DOI： 10.1103/physrevc.106.044330

Other URL： http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevC.106.044330/fulltext

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Authorship：Lead author,　Last author,　Corresponding author   Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

DOI： 10.1016/j.physletb.2022.137067

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DOI： 10.1103/PhysRevC.105.064314

Authorship：Lead author,　Last author,　Corresponding author   Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

DOI： 10.1103/PhysRevC.105.024314

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DOI： 10.1103/PhysRevC.105.024304

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DOI： 10.1103/physrevc.104.034613

Other URL： http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevC.104.034613/fulltext

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DOI： 10.1016/j.physletb.2021.136283

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The triple alpha reaction is one of the most important reactions in the nuclear astrophysics. However, its reaction rate in high temperature environments at T₉>2 was still uncertain. One of the major origins of the uncertainty was that the radiative-decay probability of the 3⁻₁ state in ¹²C was unknown. In the present work, we have determined the radiative-decay probability of the 3⁻₁ state to be 1.3[+1.2][-1.1] × 10⁻⁶ by measuring the ¹H(¹²C, ¹²Cp) reaction for the first time, and derived the triple alpha reaction rate in high temperature environments from the measured radiative-decay probability. The present result suggests that the 3⁻₁ state noticeably enhances the triple alpha reaction rate although the contribution from the 3⁻₁ state had been assumed to be small.

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DOI： 10.1103/PhysRevC.103.044303

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DOI： 10.4028/www.scientific.net/MSF.1016.863

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DOI： 10.1103/physrevc.102.024332

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DOI： 10.1103/physrevc.101.034304

Other URL： https://link.aps.org/article/10.1103/PhysRevC.101.034304

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<title>Abstract</title>
We use a microscopic multicluster model to investigate the structure of $^{10}{\rm Be}$ and of $^{11}{\rm Be}$. These nuclei are described by $\alpha +\alpha+n+n$ and $\alpha +\alpha+n+n+n$ configurations, respectively, within the Generator Coordinate Method (GCM). The 4- and 5-body models raise the problem of a large number of generator coordinates (6 for $^{10}{\rm Be}$ and 9 for $^{11}{\rm Be}$), which requires specific treatment. We address this issue by using the Stochastic Variational Method (SVM), which is based on an optimal choice of the basis functions, generated randomly. The model provides good energy spectra for low-lying states of both nuclei. We also compute rms radii and densities, as well as electromagnetic transition probabilities. We analyze the structure of $^{10}{\rm Be}$ and of $^{11}{\rm Be}$ by considering energy curves, where one of the generator coordinates is fixed during the minimization procedure.

DOI： 10.1093/ptep/ptz169

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DOI： 10.1007/978-3-030-32357-8_15

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DOI： 10.11316/jpsgaiyo.75.1.0_201

CiNii Article

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DOI： 10.11316/jpsgaiyo.75.1.0_196

CiNii Article

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DOI： 10.11316/jpsgaiyo.75.1.0_200

CiNii Article

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The stability of the linear chain structure of three ff clusters for 12C against the bending and fi ssion is investigated in the cranking covariant density functional theory, in which the equation of motion is solved on a 3D lattice with the inverse Hamiltonian and the Fourier spectral methods. Starting from a twisted three ff initial con fi guration, it is found that the linear chain structure is stable when the rotational frequency is within the range of 2.0- 2.5 MeV. Beyond this range, the fi nal states are not stable against fi ssion. By examining the density distributions and the occupation of single-particle levels, however, these fi ssions are found to arise from the occupation of unphysical continuum with large angular momenta. To properly remove these unphysical continuum, a damping function for the cranking term is introduced. Eventually, the stable linear chain structure could survive up to the rotational frequency 3.5 MeV, but the fi ssion still occurs when the rotational frequency approaches 4.0 MeV.

DOI： 10.1007/s11433-019-9412-3

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© 2019 The Author(s) Two new mechanisms active in rotating nuclei located in the vicinity of neutron drip line have been discovered. Strong Coriolis interaction acting on high-j orbitals transforms particle-unbound (resonance)nucleonic configurations into particle-bound ones with increasing angular momentum. The point of the transition manifests the birth of particle-bound rotational bands. Alternative possibility of the transition from particle-bound to resonance rotational band (the death of particle-bound rotational bands)with increasing spin also exists but it is less frequent in the calculations. The birth of particle-bound rotational bands provides a mechanism for the extension of nuclear landscape to neutron numbers which are larger than those of the neutron drip line in non-rotating nuclei.

DOI： 10.1016/j.physletb.2019.05.021

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© 2019 The Author(s) 2019. Published by Oxford University Press on behalf of the Physical Society of Japan. We apply the tensor version of the antisymmetrized quasi-cluster model (AQCM-T) to $4\textrm{He}$ and $8\textrm{Be}$ while focusing on the $NN$ correlations in $\alpha$ clusters. We adopt the $NN$ interactions including realistic ones containing a repulsive core for the central part in addition to the tensor part. In $4\textrm{He}$, the $pn$ pair in the $3D$ channel has been known to play a decisive role in the tensor correlation and the framework is capable of treating not only this channel but also the $NN$ correlations in the $1S$ and $3S$ channels. In $8\textrm{Be}$, when two $\alpha$ clusters approach, the $3D$ pair is suppressed because of the Pauli blocking effect, which also induces a decrease in the $3S$ component through the $3S$-$3D$ coupling. These coherent effects result in the reduction of the attractive effect of the central-even interaction in the middle-range region and keep the distance between two $\alpha$ clusters.

DOI： 10.1093/ptep/ptz046

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We focus on the raison d'etre of the alpha-chain states on the basis of the fully microscopic framework, where the Pauli principle among all the nucleons is fully taken into account. Our purpose is to find the limiting number of alpha clusters on which the linear alpha-cluster state can stably exist. How many alpha clusters can stably make an alpha-chain state? We examine the properties of equally separated alpha clusters on a straight line and compare its stability with that on a circle. We also confirm its stability in terms of binary and ternary disintegrations including alpha-decay and fission modes. For the effective nucleon-nucleon interaction we employ the F1 force, which has finite-range three-body terms and guarantees overall saturation properties of nuclei. This interaction also gives a reasonable binding energy and size of the alpha particle, and the alpha-alpha scattering phase shift. The result astonishes us because we can point out the possible existence of alpha-chain states with vast numbers of alpha clusters.

DOI： 10.1093/ptep/ptz045

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DOI： 10.11316/jpsgaiyo.74.1.0_229

CiNii Article

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DOI： 10.11316/jpsgaiyo.74.2.0_287

CiNii Article

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DOI： 10.11316/jpsgaiyo.74.1.0_219

CiNii Article

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DOI： 10.1557/adv.2019.28

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DOI： 10.11316/jpsgaiyo.74.2.0_244

CiNii Article

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DOI： 10.1557/adv.2019.17

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DOI： 10.11316/jpsgaiyo.74.2.0_245

CiNii Article

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© 2018 American Physical Society. In this paper, we extend the framework of the improved version of a simplified method to take into account the tensor contribution (iSMT) and propose the AQCM-T, a tensor version of the antisymmetrized quasicluster model (AQCM). Although the AQCM-T is phenomenological, we can treat the S3-D3 coupling in the deuteronlike T=0NN pair induced by the tensor interaction in a very simplified way, which allows us to proceed to heavier nuclei. Using the AQCM-T and the V2m interaction, where the triplet-even channel of the Volkov no. 2 interaction is weakened to 60% so as to reproduce the binding energy of He4 after including the tensor term of a realistic interaction, the significant tensor contribution in He4 is shown, which is almost comparable to the central interaction, where the D state mixes by 8% to the major S state. The AQCM-T with the new interaction is also applied to Be8. It is found that the tensor suppression gives a significant contribution to the short-range repulsion between two α clusters.

DOI： 10.1103/PhysRevC.98.054306

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© 2018 American Physical Society. The Tohsaki-Horiuchi-Schuck-Röpke (THSR) wave function has been successfully used for the studies of gaslike nature of α clusters in various nuclei, including the so-called Hoyle state of C12 and four α states of O16. In standard α cluster models, however, each α cluster wave function has spin zero because of its spatial symmetry and antisymmetrization effect. Thus the noncentral interactions do not contribute, and this situation is the same in the THSR wave function. In this work, the spin-orbit contribution, which is found to be quite important at short α-α distances, is taken into account in the THSR wave function by combing it with antisymmetrized quasicluster model (AQCM). The application to C12 is presented. The multi-integration in the original THSR wave function is carried out by using a Monte Carlo technique, which is called the Monte Carlo THSR wave function. For the nucleon-nucleon interaction, the Tohsaki interaction, which contains finite-range three-body terms and simultaneously reproduces the saturation properties of nuclear systems, the α-α scattering phase shift, and the size and binding energy of He4, is adopted.

DOI： 10.1103/PhysRevC.98.044306

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We study the property of alpha aggregates distributed on Archimedean solids within a microscopic framework, which takes full account of the Pauli principle. We pay special attention to the Coulomb energy for such exotic shapes of nuclei, and we discuss the advantage of alpha clusters with geometric configurations compared with the uniform density distributions in reducing the repulsive effect. We consider four kinds of configurations of alpha clusters distributed on Archimedean solids: dual polyhedra composed of a dodecahedron and an icosahedron, an octacontahedron, and two types of truncated icosahedrons, that is, two kinds of Archimedean solids. The latter two are an icosidodecahedron and a fullerene shape. Putting an alpha cluster on each vertex of the polyhedra, four alpha-cluster aggregates correspond to the following four nuclei: Gd (64 protons), Po (84 protons), Nd (60 protons), and a nucleus with 120 protons, respectively.

DOI： 10.1103/PhysRevC.98.014302

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© 2018 American Physical Society. Herein, we investigated the channel coupling (CC) effect on the elastic scatterings of lithium (Li) isotopes (A=6-9) for C12 and Si28 targets at E/A=50-60 MeV. The wave functions of the Li isotopes were obtained using the stochastic multi-configuration mixing method based on the microscopic-cluster model. The proton radii of the Li7, Li8, and Li9 nuclei became smaller as the number of valence neutrons increased. The valence neutrons in the Li8 and Li9 nuclei exhibited a glue-like behavior, thereby attracting the α and t clusters. Based on the transition densities derived from these microscopic wave functions, the elastic-scattering cross section was calculated using a microscopic coupled-channel method with a complex G-matrix interaction. The existing experimental data for the elastic scatterings of the Li isotopes and Be10 nuclei were well reproduced. The Li isotope elastic cross sections were demonstrated for the C12 and Si28 targets at E/A=53 MeV. The glue-like effect of the valence neutrons on the Li isotope was clearly demonstrated by the CC effect on elastic scattering. Finally, we realize that the valence neutrons stabilized the bindings of the core parts and the CC effect related to core excitation was indeed reduced.

DOI： 10.1103/PhysRevC.97.044602

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© 2018 American Physical Society. We use microscopic Be9 wave functions defined in a α+α+n multicluster model to compute Be9+target scattering cross sections. The parameter sets describing Be9 are generated in the spirit of the stochastic variational method, and the optimal solution is obtained by superposing Slater determinants and by diagonalizing the Hamiltonian. The Be9 three-body continuum is approximated by square-integral wave functions. The Be9 microscopic wave functions are then used in a continuum-discretized coupled-channel (CDCC) calculation of Be9+Pb208 and of Be9+Al27 elastic scattering. Without any parameter fitting, we obtain a fair agreement with experiment. For a heavy target, the influence of Be9 breakup is important, while it is weaker for light targets. This result confirms previous nonmicroscopic CDCC calculations. One of the main advantages of the microscopic CDCC is that it is based on nucleon-target interactions only; there is no adjustable parameter. The present work represents a first step towards more ambitious calculations involving heavier Be isotopes.

DOI： 10.1103/PhysRevC.97.014612

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© 2018 American Physical Society. The anomalous large radii are exotic phenomena observed around the neutron dripline. Around the neutron dripline, the weak binding of the last bound neutron(s) causes the drastic increase of the radius, which is called the neutron halo structure. Although the nucleus O24 is located at the dripline of oxygen isotopes, the separation energies of one and two neutron(s) are 4.19 MeV and 6.92 MeV, respectively. In spite of this sufficient binding, the enhancement of the matter radius is observed. In this study, we microscopically describe the structure change of the O22 core in O24 and explain the observed large radius based on the cluster model. Two degrees of freedom for the large radius, the relative distances among four α clusters and the size of each α cluster, are examined, where the Tohsaki interaction, which has finite range three-body terms, is employed. The nucleus O22 has smaller α-α distance compared with O16 owing to the gluelike effect of six valence neutrons around four α clusters. When two neutrons are added at the center of O22, the expansion of each α cluster is energetically more favored than increasing the α-α distances for reducing the kinetic energy of the neutrons. The calculated rms matter radii of O22 and O24 are 2.75 fm and 2.92 fm, respectively. Although these are slightly smaller than the experimental values, the jump at O24 from O22 is reproduced.

DOI： 10.1103/PhysRevC.97.014307

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© 2018 American Physical Society. The tensor contribution can be directly incorporated in the cluster model in a simplified way. In conventional α cluster models, the contribution of the noncentral interactions exactly cancels because of the antisymmetrization effect and spatial symmetry of α clusters. The mixing of breaking components of α clusters to take into account the spin-orbit and tensor effects is needed. Previously, we proposed a simplified method to include the spin-orbit effect, and also for the tensor part, a simplified model to directly take into account the contribution of the tensor interaction (called SMT) was introduced; however, the contribution of the tensor interaction was quite limited. Here we improve SMT, which is called iSMT. Using newly proposed iSMT, the contribution of the tensor interaction in He4 is more than -40 MeV, four times larger than the previous version. The method is applied to four-α cluster structure of O16. In O16, the tensor contribution is also large, and this is coming from the finite size effect for the distances among α clusters with a tetrahedral configuration.

DOI： 10.1103/PhysRevC.97.014304

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We study alpha-cluster structure based on the geometric configurations with a microscopic framework, which takes full account of the Pauli principle, and which also employs an effective internucleon force including finite-range three-body terms suitable for microscopic alpha-cluster models. Here, special attention is focused upon the alpha clustering with a hollow structure; all the alpha clusters are put on the surface of a sphere. All the platonic solids (five regular polyhedra) and the fullerene-shaped polyhedron coming from icosahedral structure are considered. Furthermore, two configurations with dual polyhedra, hexahedron-octahedron and dodecahedron-icosahedron, are also scrutinized. When approaching each other from large distances with these symmetries, alpha clusters create certain local energy pockets. As a consequence, we insist on the possible existence of alpha clustering with a geometric shape and hollow structure, which is favored from Coulomb energy point of view. Especially, two configurations, that is, dual polyhedra of dodecahedron-icosahedron and fullerene, have a prominent hollow structure compared with the other six configurations.

DOI： 10.1103/PhysRevC.97.011301

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Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

© The Author(s) 2017. The antisymmetrized quasi-cluster model (AQCM) was proposed to describe α-cluster and jj-coupling shell models on the same footing. In this model, the cluster–shell transition is characterized by two parameters, R representing the distance between α clusters and Λ describing the breaking of α clusters, and the contribution of the spin–orbit interaction, very important in the jj-coupling shell model, can be taken into account starting with the α-cluster model wave function. Not only the closure configurations of the major shells but also the subclosure configurations of the jj-coupling shell model can be described starting with the α-cluster model wave functions; however, the particle–hole excitations of single particles have not been fully established yet. In this study we show that the framework of AQCM can be extended even to the states with the character of single-particle excitations. For 12C, two-particle–two-hole (2p2h) excitations from the subclosure configuration of 0p3/2 corresponding to a BCS-like pairing are described, and these shell model states are coupled with the three α-cluster model wave functions. The correlation energy from the optimal configuration can be estimated not only in the cluster part but also in the shell model part. We try to pave the way to establish a generalized description of the nuclear structure.

DOI： 10.1093/ptep/ptx161

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© The Author(s) 2017. We investigate cluster structures and E0 transitions of 0+ states in 16O. In particular, we discuss the mixing effect of 3α and α breaking components in the 12C cluster on the E0 transitions. To this end, we perform a microscopic calculation including α cluster and cluster-breaking model spaces. By analyzing the obtained results, we confirm that the 0+2 and 0+3 states of 16O are indeed the weak-coupling 12C(0+) + α and 12C(2+) + α cluster states, respectively. We find mainly two important mechanisms for reducing the E0 transition: (i) the difference in intrinsic spin configurations between the initial and final states caused by the cluster breaking and (ii) the mixing of planar 4α configurations in the excited states. We show that the E0 operator excites the initial (ground) state not to planar 4α configurations but predominantly to triangular pyramid 4α configurations. Thus, the mixture of the planar 4α configurations in the 0+2 state significantly reduces the E0 transition matrix elements to this state.We conclude that the E0 transitions tend to be enhanced by cluster states, but they are affected by various mechanisms originating in the detailed structures of the final states.

DOI： 10.1093/ptep/ptx065

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© 2016 American Physical Society. Consistent description of C12 and O16 has been a long-standing problem of microscopic α cluster models, where the wave function is fully antisymmetrized and the effective interaction is applied not between α clusters but between nucleons. When the effective interaction is designed to reproduce the binding energy of O16 (four α), the binding energy of C12 (three α) becomes underbound by about 10 MeV. In the present study, by taking into account the coupling with the jj-coupling shell model components and utilizing the Tohsaki interaction, which is phenomenological but has finite-range three-body interaction terms, it is shown that consistent understanding of these nuclei can be achieved. The original Tohsaki interaction gives a small overbound value of about 3 MeV for O16, and this is improved by slightly modifying the three-body Majorana exchange parameter. Also, the coupling with the jj-coupling shell model wave function strongly contributes to the increase of the binding energy of C12. So far the application of the Tohsaki interaction has been limited to 4N nuclei; here, Bartlet and Heisenberg exchange terms are added in the two-body interaction part for the purpose of applying it to neutron-rich systems, and it is applied to He6.

DOI： 10.1103/PhysRevC.94.064324

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© 2016 The Author(s). The antisymmetrized quasi-cluster model (AQCM) is a method to describe transitions from the α cluster wave functions to jj-coupling shell model wave functions. In this model, the cluster-shell transition is characterized by only two parameters: R representing the distance between α clusters and describing the breaking of α clusters. The contribution of the spin-orbit interaction, very important in the jj-coupling shell model, can be taken into account starting with the α cluster modelwave function. In this article we showthe generality ofAQCMby extending the application to heavier regions: various 4N nuclei from 4He to 100Sn. The characteristic magic numbers of the jj-coupling shell model, 28 and 50, are described starting with the α cluster model. The competition of two different configurations is discussed in 20Ne (16O + one quasi-cluster and 12C + two quasi-clusters) and 28Si (pentagon shape of five quasi-clusters and 12C+16O). Also, we compare the energy curves for the α+40Ca cluster configuration calculated with and without the α breaking effect in 44Ti.

DOI： 10.1093/ptep/ptw125

Publishing type：Research paper (international conference proceedings)   International / domestic magazine：International journal  

© 2015 AIP Publishing LLC. In this presentation I discussed two subjects. One is the persistence of threefold symmetry in the ground state of 12C. Recently D3h symmetry has been established in 12C, which reflects the geometric symmetry of the three α particles. Although the spin-orbit interaction plays a significant role and this interaction breaks the α clusters, we show that threefold symmetry of 12C is still there. We use AQCM approach and discuss that inclusion of spin-orbit interaction, which is absent in the conventional microscopic α cluster models, is possible keeping the threefold symmetry. The second subject is the appearance of rod shape in C isotopes, which has been investigated in the framework of the cranking covariant density functional theory. The relationship between the stability of such states and the spin and isospin degrees of freedom is discussed; adding valence neutrons and rotating the system. These two effects stabilize the rod shape, and in addition, their coherent effect has been found; the σ-orbits (parallel to the symmetry axis) of the valence neutrons, which enhances the rod shape, is lowered by the rotation of the system, and this σ-orbit pulls down the single particle energies of protons with linear configuration owing to the proton-neutron interaction effect.

DOI： 10.1063/1.4932241

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© 2015 American Physical Society. The stable existence of rod-shaped structures in highly excited states of Mg24 is studied based on a systematic cranked Hartree-Fock calculation with various Skyrme-type interactions. Its stability is examined by allowing the transition of the clusterlike structure to the shell-model-like structure. Especially, the rod-shaped state is exposed to two major instabilities: the bending motion, which is the main path for the transition to low-lying states, and the spin-orbit interaction, which is the driving force to break the α clusters and enhance the independent motion of the nucleons. The rod-shaped structure with large angular momentum is obtained as a metastable stationary state.

DOI： 10.1103/PhysRevC.92.011303

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© 2015 American Physical Society. © 2015 American Physical Society. The anomalous rod shape in carbon isotopes has been investigated in the framework of the cranking covariant density functional theory, and two mechanisms to stabilize such a novel shape with respect to the bending motion, extreme spin, and isospin are simultaneously discussed for the first time in a self-consistent and microscopic way. By adding valence neutrons and rotating the system, we have found the mechanism stabilizing the rod shape; i.e., the σ orbitals (parallel to the symmetry axis) of the valence neutrons, important for the rod shape, are lowered by the rotation due to the Coriolis term. The spin and isospin effects enhance the stability of the rod-shaped configuration. This provides a strong hint that a rod shape could be realized in nuclei towards extreme spin and isospin.

DOI： 10.1103/PhysRevLett.115.022501

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A study of the 4 alpha linear-chain structure in high-lying collective excitation states of O-16 with covariant density functional theory is presented. The low-spin states are obtained by configuration mixing of particle-number and angular-momentum projected quadrupole deformed mean-field states with the generator coordinate method. The high-spin states are determined by cranking calculations. These two calculations are based on the same energy density functional PC-PK1. We have found a rotational band at low spin with the dominant intrinsic configuration considered to be the one whereby 4 alpha clusters stay along a common axis. The strongly deformed rod shape also appears in the high-spin region with the angular momentum 13 (h) over bar to 18 (h) over bar; however, whether the state is a pure 4 alpha linear chain is less obvious than for the low-spin states.

DOI： 10.1103/PhysRevC.90.054307

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© 2014 American Physical Society. Background: In our previous study, we found that an exotic isomer with a torus shape may exist in the high-spin, highly excited states of Ca40. The z component of the total angular momentum, Jz=60, of this torus isomer is constructed by totally aligning 12 single-particle angular momenta in the direction of the symmetry axis of the density distribution. The torus isomer executes precession motion with the rigid-body moments of inertia about an axis perpendicular to the symmetry axis. The investigation, however, has been focused only on Ca40. Purpose: We systematically investigate the existence of exotic torus isomers and their precession motions for a series of N=Z even-even nuclei from Si28 to Ni56. We analyze the microscopic shell structure of the torus isomer and discuss why the torus shape is generated beyond the limit of large oblate deformation. Method: We use the cranked three-dimensional Hartree-Fock method with various Skyrme interactions in a systematic search for high-spin torus isomers. We use the three-dimensional time-dependent Hartree-Fock method for describing the precession motion of the torus isomer. Results: We obtain high-spin torus isomers in Ar36,Ca40,Ti44,Cr48, and Fe52. The emergence of the torus isomers is associated with the alignments of single-particle angular momenta, which is the same mechanism as found in Ca40. It is found that all the obtained torus isomers execute the precession motion at least two rotational periods. The moment of inertia about a perpendicular axis, which characterizes the precession motion, is found to be close to the classical rigid-body value. Conclusions: The high-spin torus isomer of Ca40 is not an exceptional case. Similar torus isomers exist widely in nuclei from Ar36 to Fe52 and they execute the precession motion. The torus shape is generated beyond the limit of large oblate deformation by eliminating the 0s components from all the deformed single-particle wave functions to maximize their mutual overlaps.

DOI： 10.1103/PhysRevC.90.034314

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We investigate the precession motion of the exotic torus configuration in high-spin excited states of 40Ca. For this aim, we use the three-dimensional time-dependent Hartree-Fock (TDHF) method. Although the high-spin torus isomer is a unique quantum object characterized by the alignment of angular momenta of independent single-particle motions, we find that the obtained moment of inertia for rotations about an axis perpendicular to the symmetry axis is close to the rigid-body value. We also analyze the microscopic structure of the precession motion using the random-phase approximation (RPA) method for high-spin states. In the RPA calculation, the precession motion of the torus isomer is generated by coherent superposition of many one-particle-one-hole excitations across the sloping Fermi surface that strongly violates the time-reversal symmetry. By comparing results of the TDHF and the RPA calculations, we find that the precession motion obtained by the TDHF calculation is a pure collective motion well decoupled from other collective modes. © 2014 American Physical Society.

DOI： 10.1103/PhysRevC.89.011305

Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

We investigate the precession motion of the exotic torus configuration in high-spin excited states of Ca-40. For this aim, we use the three-dimensional time-dependent Hartree-Fock (TDHF) method. Although the high-spin torus isomer is a unique quantum object characterized by the alignment of angular momenta of independent single-particle motions, we find that the obtained moment of inertia for rotations about an axis perpendicular to the symmetry axis is close to the rigid-body value. We also analyze the microscopic structure of the precession motion using the random-phase approximation (RPA) method for high-spin states. In the RPA calculation, the precession motion of the torus isomer is generated by coherent superposition of many one-particle-one-hole excitations across the sloping Fermi surface that strongly violates the time-reversal symmetry. By comparing results of the TDHF and the RPA calculations, we find that the precession motion obtained by the TDHF calculation is a pure collective motion well decoupled from other collective modes.

DOI： 10.1103/PhysRevC.89.011305

Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

The low-lying states of the 9Li nucleus are investigated with a unified framework of microscopic structure and reaction models. In the structure model, the wave function is fully antisymmetrized and the 9Li nucleus is described as an α+t+n+n four-body system, and low-lying 1/2-, 3/2 -, 5/2-, and 7/2- states are obtained by the stochastic multiconfiguration mixing method. Using these wave functions, the quasielastic cross section at E/A = 60 MeV and the elastic and inelastic cross sections at E/A = 50 MeV on the 12C target are calculated in the framework of the microscopic coupled channel (MCC) method. The characteristic inelastic angular distribution is seen in the 3/22- state, whose α+t cluster structure and valence neutron configurations are discussed in detail. We find the possibility of triaxial deformation and mixing of dineutron components in the 9Li nucleus. © 2013 American Physical Society.

DOI： 10.1103/PhysRevC.87.064320

Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

We propose an improved version of the antisymmetrized quasicluster model (AQCM) to describe a smooth transition from the alpha-cluster wave function to the j j-coupling shell model wave function and apply it to the ground state of C-12. The cluster-shell transition in C-12 is characterized in AQCM by only two parameters: R representing the distance between alpha clusters and the center of mass and Lambda describing the break of alpha clusters. The optimal AQCM wave function for the ground state of C-12 is an intermediate state between the three-alpha cluster state and the shell model state with the p(3/2) subshell closure configuration. The result is consistent with that of the antisymmetrized molecular dynamics (AMD), and the optimal AQCM wave function quantitatively agrees with the AMD one, although the number of degrees of freedom in AQCM is significantly fewer.

DOI： 10.1103/PhysRevC.87.054334

Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

We investigate the possibility of the existence of the exotic torus configuration in the high-spin excited states of Ca40. We here consider the spin alignments about the symmetry axis. To this end, we use a three-dimensional cranked Skyrme Hartree-Fock method and search for stable single-particle configurations. We find one stable state with the torus configuration at the total angular momentum J=60 and an excitation energy of about 170MeV in all calculations using various Skyrme interactions. The total angular momentum J=60 consists of aligned 12 nucleons with the orbital angular momenta Λ=+4, +5, and +6 for spin-up or -down neutrons and protons. The obtained results strongly suggest that a macroscopic amount of circulating current breaking the time-reversal symmetry emerges in the high-spin excited state of Ca40. © 2012 American Physical Society.

DOI： 10.1103/PhysRevLett.109.232503

PubMed

Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

We investigate the existence of weakly coupled gaslike states comprised of three α particles around an 16O core in 28Si. We calculate the excited states in 28Si using the multiconfiguration mixing method based on the 16O+3α cluster model. We also include the 16O+12C and 24Mg+α basis wave functions prepared by the generator coordinate method. To identify the gaslike states, we calculate the isoscalar monopole transition strengths and the overlap of the obtained states with the geometrical cluster wave function and the Tohsaki-Horiuchi-Schuck-Röpke (THSR) wave function. The results show that the obtained fourth and twelfth states significantly overlap with the THSR wave function. These two states clearly coexist with the 16O+12C cluster states, emerging at similar energies. The calculated isoscalar monopole strengths between those two states are significantly large, indicating that the states are members of the excitation mode. Furthermore, the calculated root-mean-square radii for these states also suggest that a layer of gaslike three α particles could exist around the surface of the 16O core, which can be described as a "two-dimensional gas" in the intermediate state before the Hoyle-like three-α states emerge. © 2012 American Physical Society.

DOI： 10.1103/PhysRevC.86.031303

Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

We investigate the existence of weakly coupled gaslike states comprised of three a particles around an O-16 core in Si-28. We calculate the excited states in Si-28 using the multiconfiguration mixing method based on the O-16+3 alpha cluster model. We also include the O-16+C-12 and Mg-24+alpha basis wave functions prepared by the generator coordinate method. To identify the gaslike states, we calculate the isoscalar monopole transition strengths and the overlap of the obtained states with the geometrical cluster wave function and the Tohsaki-Horiuchi-Schuck-Ropke (THSR) wave function. The results show that the obtained fourth and twelfth states significantly overlap with the THSR wave function. These two states clearly coexist with the O-16+C-12 cluster states, emerging at similar energies. The calculated isoscalar monopole strengths between those two states are significantly large, indicating that the states are members of the excitation mode. Furthermore, the calculated root-mean-square radii for these states also suggest that a layer of gaslike three alpha particles could exist around the surface of the O-16 core, which can be described as a "two-dimensional gas" in the intermediate state before the Hoyle-like three-alpha states emerge.

DOI： 10.1103/PhysRevC.86.031303

Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

The formation of intruder states in the low-lying states of 12Be=α+α+4N is studied by applying the generalized two-center cluster model, which can optimize the excess neutrons' orbits depending on the α-α distance. The correlation energy for the intruder states is analyzed from the viewpoint of two different pictures based on the cluster structure: the covalent picture around two α clusters and the binary He-cluster picture. In the covalent picture, the binding energy of (π32-)2(σ12 +)2, corresponding to ν(0p)4 (1s0d)2 in a naive shell model, gains largely owing to the spin-triplet pairing of the 0d-wave neutrons, which is induced by the two-body spin-orbit interaction. The spin-triplet pairing gives rise to the reduction of the kinetic energy and the increase of the attractive spin-orbit interaction for the excess neutrons. As a result of these correlation energies, the ν(0p)4(1s0d)2 configuration becomes dominant in the ground state. In the binary cluster picture, the correlation energy is investigated from the coupled channels among α+8He, 6He+6He, and 5He+7He. The coupling to 5He+7He, which is neglected in usual binary-cluster models, plays an important role for a large reduction of kinetic energy and the formation of a pair of the low-lying 0+ states with a close energy spacing recently observed in experiment. The rotational bands are also discussed from the viewpoint of these two cluster pictures. © 2012 American Physical Society.

DOI： 10.1103/PhysRevC.85.014302

Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

We apply a simple model to describe the cluster-shell competition in Ne-20 due to the spin-orbit interaction, which is called Antisymmetrized Quasi Cluster approach. By introducing one additional parameter in the trial wave function, the transformation of one a cluster into a quasi cluster, i.e. the transition from a cluster state [O-16+alpha] to a shell model state [O-16+4N], can be studied in details. Such approach can be applied to the case of 3 alpha + four neutrons in C-16, and cluster-shell competition is investigated in a neutron-rich nucleus.

DOI： 10.1143/PTPS.196.192

J-GLOBAL

Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

DOI： 10.1093/ptpsupp.196.i

Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

Publishing type：Research paper (international conference proceedings)   International / domestic magazine：International journal  

© Owned by the authors, published by EDP Sciences, 2011. We give a brief overview of recent work examining the presence of α-clusters in light nuclei within the Skyrme-force Hartree-Fock model. Of special signif cance are investigations into α-chain structures in carbon isotopes and 16O. Their stability and possible role in fusion reactions are examined in static and time-dependent Hartree-Fock calculations. We f nd a new type of shape transition in collisions and a centrifugal stabilization of the 4α chain state in a limited range of angular momenta. No stabilization is found for the 3α chain.

DOI： 10.1051/epjconf/20111707002

Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

We investigate the linear chain configurations of four-α clusters in O16 using a Skyrme cranked Hartree-Fock method and discuss the relationship between the stability of such states and angular momentum. We show the existence of a region of angular momentum (13-18) where the linear chain configuration is stabilized. For the first time we demonstrate that stable exotic states with a large moment of inertia (2/2Θ∼0.06-0.08MeV) can exist. © 2011 American Physical Society.

DOI： 10.1103/PhysRevLett.107.112501

Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

We investigate whether three-triton states appear or not in excited states of 9Li. We also search for a signature of the gaslike three-triton state, which is partly an analogy to the the case of the three-α state in 12C (Hoyle state). For this purpose, we use both three-triton and α+t+n+n wave functions to describe the low-lying states of 9Li and take into account the coupling effect between them. We show that the states in which the three-triton components dominate indeed appear below the three-triton threshold energy, although the root-mean-square radii of those states are not so much expanded in comparison with the gaslike state of three α's. © 2011 American Physical Society.

DOI： 10.1103/PhysRevC.84.034305

Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

We have studied gas-like states of α clusters around an O16 core in Mg24 based on a microscopic α-cluster model. The 0+ states below the 16O+α+α threshold, which are candidates for the resonance solution judging from the energy convergence behavior, are strongly excited by an isoscalar monopole (E0) operator from the ground state, which could be observed as an experimental signature of well-developed α gas-like states in the excited states. These states have significant overlaps with the THSR (Tohsaki-Horiuchi-Schuck-Röpke) wave functions with large spatial extension. © 2011 American Physical Society.

DOI： 10.1103/PhysRevC.83.061301

Publishing type：Research paper (international conference proceedings)   International / domestic magazine：International journal  

The question of phases and phase transitions of cluster states is reviewed. First some features of the vibron model are recalled, then its extensions are investigated. Preliminary results are also presented from a study on the cluster-shell competition. © 2011 World Scientific Publishing Company.

DOI： 10.1142/S0218301311018721

Publishing type：Research paper (international conference proceedings)   International / domestic magazine：International journal  

We have studied three-α states around 40Ca based on a microscopic α-cluster model.Quite recently experimental evidence for such states has been obtained. This study was performed by introducing a Monte Carlo technique for the description of the THSR (Tohsaki Horiuchi Schuck Röpke) wave function, which is called the "virtual THSR" wave function. The three α cluster state around 40Ca has an energy below the Coulomb barrier top energy with a spatial extension comparable to the second 0+ state of 12C. There is possibility that such gas-like structure of α clusters is stabilized with geometric shape when valence neutrons are added. We also discussed the appearance of geometric α cluster configurations, especially for the linear chain configurations of three α clusters, in neutron-rich C isotopes. © 2011 World Scientific Publishing Company.

DOI： 10.1142/S0218301311019167

Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

The relation between the monopole transition strength and existence of cluster structure in the excited states is discussed based on an algebraic cluster model. The structure of C12 is studied with a 3α model, and the wave function for the relative motions between α clusters are described by the symplectic algebra Sp(2,R)z, which corresponds to the linear combinations of SU(3) states with different multiplicities. Introducing Sp(2,R)z algebra works well for reducing the number of the basis states, and it is also shown that states connected by the strong monopole transition are classified by a quantum number Λ of the Sp(2,R) z algebra. © 2011 American Physical Society.

DOI： 10.1103/PhysRevC.83.024301

Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

We investigate properties of the generator coordinate method (GCM) on a collective basis of antisymmetrized quasicluster states to describe the cluster-shell competition in Ne-20 and Mg-24 owing to the spin-orbit interaction. By introducing a single additional parameter in the antisymmetrized-cluster basis function, a continuous transformation of the alpha cluster(s) into independent nucleons can be described. We apply this GCM trial wave function to study in detail the transition from cluster states [O-16 + alpha] and [O-16 + alpha + alpha] to shell-model states [O-16 + 4N] and [O-16 + 8N], respectively. An optimal value of the strength of the spin-orbit interaction is deduced by reproducing level spacing in Ne-20. A possible connection to the group theoretical understanding of the cluster-shell configuration transition is also discussed.

DOI： 10.1103/PhysRevC.83.014302

Publishing type：Research paper (international conference proceedings)   International / domestic magazine：International journal  

We give a brief overview of recent work examining the presence of alpha-clusters in light nuclei within the Skyrme-force Hartree-Fock model. Of special signif cance are investigations into alpha-chain structures in carbon isotopes and O-16. Their stability and possible role in fusion reactions are examined in static and time-dependent Hartree-Fock calculations. We f nd a new type of shape transition in collisions and a centrifugal stabilization of the 4 alpha chain state in a limited range of angular momenta. No stabilization is found for the 3 alpha chain.

DOI： 10.1051/epjconf/20111707002

J-GLOBAL

Publishing type：Research paper (international conference proceedings)   International / domestic magazine：International journal  

We study the di-neutron correlations in the super neutron-rich nucleus 7H with the AMD triple-S (AMD superposition of selected snapshots). 7H is the most neutron-rich nucleus in the neutron ratio to the proton (N/Z = 6). And the strong di-neutron correlations are expected due to the weak binding properties. In this paper, the mixing of di-neutron cluster components is estimated by calculating the squared overlap with the di-neutron condensate type wave function. The calculated results show significant mixing of di-neutron (t + 2n + 2n) components (70 ∼ 80%). © 2010 World Scientific Publishing Company.

DOI： 10.1142/S0217732310000423

Publishing type：Research paper (international conference proceedings)   International / domestic magazine：International journal  

We have studied three α states around 40Ca based on a microscopic α-cluster model, which has been succeeded experimentally quite recently. This was performed by introducing a Monte Carlo technique for the description of the THSR (Tohsaki Horiuchi Schuck Röpke) wave function, which is called the "virtual THSR" wave function. The three α cluster state around 40Ca has an energy below the Coulomb barrier top energy with a spatial extension comparable to the second 0+ state of 12C. © 2010 World Scientific Publishing Company.

DOI： 10.1142/S021773231000071X

Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

We have studied three-α states around Ca40 based on a microscopic α-cluster model. Quite recently experimental evidence for such states has been obtained. This study was performed by introducing a Monte Carlo technique for the description of the Tohsaki-Horiuchi-Schuck-Röpke (THSR) wave function, which is called the "virtual THSR" wave function. The three-α-cluster state around Ca40 has an energy below the Coulomb-barrier top energy with a spatial extension comparable to the second 0+ state of C12. © 2010 The American Physical Society.

DOI： 10.1103/PhysRevC.82.014312

Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

We present Skyrme-force Hartree-Fock calculations of metastable three-alpha chain-state configurations in C-12, C-16, and C-20. A microscopic dynamical study of reactions involving three He-4 clusters shows that the triple-alpha linear chain configuration of C-12 is formed with a certain lifetime and subsequently decays into a triangular configuration of C-12 and then to a configuration near the ground state.

DOI： 10.1142/S0217732310000514

Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

We have studied three alpha states around Ca-40 based on a microscopic alpha-cluster model, which has been succeeded experimentally quite recently. This was performed by introducing a Monte Carlo technique for the description of the THSR (Tohsaki Horiuchi Schuck Ropke) wave function, which is called the "virtual THSR" wave function. The three alpha cluster state around Ca-40 has an energy below the Coulomb barrier top energy with a spatial extension comparable to the second 0(+) state of C-12.

DOI： 10.1142/S021773231000071X

Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

We have studied three alpha states around Ca-40 based on a microscopic alpha-cluster model, which has been succeeded experimentally quite recently. This was performed by introducing a Monte Carlo technique for the description of the THSR (Tohsaki Horiuchi Schuck Ropke) wave function, which is called the "virtual THSR" wave function. The three alpha cluster state around Ca-40 has an energy below the Coulomb barrier top energy with a spatial extension comparable to the second 0(+) state of C-12.

DOI： 10.1142/S021773231000071X

DOI： 10.1103/PhysRevLett.104.252501

PubMed

Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

We present a microscopic dynamical study of the reactions involving three He4 clusters. We show that the much discussed triple-α linear chain configuration of C12 is formed with a certain lifetime and subsequently makes a transition to a triangular configuration of C12 and then to a configuration near the ground state. Time-dependent Hartree-Fock theory coupled with a density constraint is used to study the properties of these configurations. © 2010 The American Physical Society.

DOI： 10.1103/PhysRevLett.104.212503

Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

Nucleon transfer is studied with a focus on charge equilibration. It is completely classified into six types. The preferred nucleon transfer (i.e. neutron transfer, proton transfer, dual-way transfer, etc.) is predictable based on this classification, which is verified within the framework of microscopic time-dependent density functional calculations. This classification gives a simple explanation for the reason why the proton-richness does not necessarily result in the enhancement of proton transfer contrary to the neutron-richness in neutron transfer. © 2010 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.nuclphysa.2010.01.242

Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

Using a Skyrme mean-field model, we investigate the linear-chain configurations of three α-clusters with four or eight additional valence neutrons in 16C and 20C and discuss the relation between the stability of such states and the neutron number. The Hartree-Fock solution is sought from an initial configuration with three α-clusters and the additional neutrons are prepared in wave functions of various symmetries. We find at least five different chain configurations in 16C and one "closed shell" configuration in 20C that appear as highly converged states in the Hartree-Fock iterations. We investigate their stability with respect to quadrupole and octupole distortions and find that they appear unstable with respect to bending deformations, but show lifetimes that may lead to observable resonances. © 2009.

DOI： 10.1016/j.nuclphysa.2009.12.005

Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

DOI： 10.1142/9789814313933_0036

Publishing type：Research paper (international conference proceedings)   International / domestic magazine：International journal  

The mass-dependent structure of the composite nucleus is shown based on three-dimensional time-dependent Hartree-Fock calculations with Skyrme interactions (SLy4d and SkM*). One remarkable result is that the isovector monopole excitation dominantly appears for collisions of heavy nuclei, and the isovector dipole excitation for those of light ones. Such a difference found in the dynamical structure of composite nucleus plays a role in the equilibration of charge.

DOI： 10.1051/epjconf/20100213002

Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

DOI： 10.1140/epja/i2009-10874-6

Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

The charge equilibration upper energy-limit formula is proposed. It shows not only the basic mechanism of charge equilibration but also does imply the possibility of controlling the exotic nuclear synthesis. To understand the mechanism of charge equilibration, charge and mass distributions of final fragments of the heavy-ion collisions are studied based on three-dimensional time-dependent Hartree-Fock calculations with a Skyrme interaction. © Società Italiana di Fisica / Springer-Verlag 2009.

DOI： 10.1140/epja/i2009-10851-1

Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

We investigate the dineutron correlations in H7. The ground state of H7 is solved by superposing many AMD (antisymmetrized molecular dynamics) Slater determinants with various t+n+n+n+n configurations based on AMD triple-S (AMD superposition of selected snapshots). The mixing of dineutron cluster components is estimated by calculating the squared overlap with the wave function of the dineutron condensate, which is an extension of the studies on the α condensate in 4N nuclei. The calculated results show significant mixing of components of dineutron clusters (t+2n+2n) with a spatially extended distribution (~70%) much larger than that of He8, where the core nucleus is changed from t to He4. © 2009 The American Physical Society.

DOI： 10.1103/PhysRevC.80.021304

Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

We investigate the dineutron correlations in H-7. The ground state of H-7 is solved by superposing many AMD (antisymmetrized molecular dynamics) Slater determinants with various t+n+n+n+n configurations based on AMD triple-S (AMD superposition of selected snapshots). The mixing of dineutron cluster components is estimated by calculating the squared overlap with the wave function of the dineutron condensate, which is an extension of the studies on the alpha condensate in 4N nuclei. The calculated results show significant mixing of components of dineutron clusters (t+(2)n+(2)n) with a spatially extended distribution (similar to 70%) much larger than that of He-8, where the core nucleus is changed from t to He-4.

DOI： 10.1103/PhysRevC.80.021304

Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

The generalized two-center cluster model (GTCM), which can treat various single particle configurations in general two center systems, is applied to the light neutron-rich system, Be-12 =alpha+alpha+4N. We discuss the change of the neutrons' configuration around two alpha-cores as a variation of an excitation energy. We show that the covalent, ionic and atomic configurations appear in the unbound region above the alpha+He-8(g.s.) particle-decay threshold, and they coexist within a quite small energy interval.

DOI： 10.1142/S0217732309000462

Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

The condensed states of alpha-clusters or di-neutrons are studied by introducing a Monte Carlo technique for the description of the THSR (Tohsaki Horiuchi Schuck Ropke) wave function. The condensed state of five alpha particles is shown to be stable around the threshold energy even after taking into account the coupling effect between normal cluster states with O-16+alpha configurations. Next, the mixing of di-neutron components in He-8 is studied. The ground state of 8He corresponds to the sub-closed-shell configuration of the spin-orbit favored orbits (p(3/2)) for the neutrons, and the shell-model-like configuration is considered to be dominant. However, He-8 is a drip-line nucleus with a two-neutron separation energy of 2.1 MeV, and the di-neutron configuration, which is a characteristic feature of the weakly bound systems, mixes in the ground state. Finally, characteristic mechanism for the binding of clusters in neutron-rich nuclei (s(2) bond) is discussed.

DOI： 10.1142/S0217751X09045571

Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

We study the structure of low-lying states of C13 with a microscopic cluster model. In addition to the 3α-n model space, the breaking effect of one of the α clusters due to the spin-orbit interaction is also taken into account. The isoscalar E0 transition probabilities from the ground 1/2- state to the excited ones are discussed associated with the cluster structure of these states. © 2009 The American Physical Society.

DOI： 10.1103/PhysRevC.79.034308

Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

We systematically investigate the possibility that the s2 configuration of the two neutrons in the middle of the nucleus is a characteristic bond of α-clusters in light neutron-rich nuclei. The series of cluster states seen in Be10(2α+2n) and C14(3α+2n) is extended to the cases of heavier nuclei, O18(4α+2n) and Ne22(5α+2n), and we show the appearance of cluster structure with the s2 bond in the excited states by using a microscopic Nα+2n model, in which the coupling with low-lying states is included. © 2009 The American Physical Society.

DOI： 10.1103/PhysRevC.79.034312

Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

The alpha+He-8 low-energy reactions and the exotic structures of Be-12 are studied using the generalized two-center cluster (alpha+alpha+N) model. In the two-neutron transfer reactions, alpha+He-8(g.s.) -> He-6(g.s.)+He-6(g.s.), a resonant peak with J(pi) = 0(+) appears around E similar to 1.3 MeV above the He-6(g.s.) + He-6(g.s.) threshold as the result of the formation of the covalent superdeformation, which has a hybrid structure of covalent and ionic configurations for the valence neutrons. The covalent superdeformation gives rise to an isomeric state with a sharp width of Gamma similar to 400keV.

DOI： 10.1142/S0218301308011094

Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

Two principal reaction dynamics are introduced. One is the spin displacement, which is caused from the spin-dependence of the interaction, and the other is the isovector displacement, which is caused from the isospin-dependence of it. The competition of these two dynamics is a rather important factor as the target or projectile has more excess neutrons or protons. In this paper the competitive reaction mechanism is theoretically formulated, where the time-dependent mean field calculations are performed for justification.

DOI： 10.1142/S0218301308010672

Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

The α+He8 low-energy reactions and the exotic structures of Be12 are studied using the generalized two-center cluster (α+α+4N) model. In the two-neutron transfer reactions, α+He8g.s.→He6g.s.+He6g.s., a resonant peak with Jπ=0+ appears around E~ 1.3 MeV above the He6g.s.+He6g.s. threshold as the result of the formation of the covalent superdeformation, which has a hybrid structure of covalent and ionic configurations for the valence neutrons. The covalent superdeformation gives rise to an isomeric state with a sharp width of Γ~400 keV, which is smaller by about one order of magnitude than the typical width observed in molecular resonances above the Coulomb barrier. The energy-spin systematics for the two-neutron transfer reactions is investigated, and our calculation predicts a sequence of resonant structures in the range of 3-14 MeV in the center-of-mass energy with spins 0-8. © 2008 The American Physical Society.

DOI： 10.1103/PhysRevC.78.011602

Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

The mixing of di-neutron components in He-8 is studied. The ground state of He-8 corresponds to the sub-closed-shell configuration of the spin-orbit favored orbits (p(3/2)) for the neutrons, and the shell-model-like configuration is considered to be dominant. However, He-8 is a drip-line nucleus with a two-neutron separation energy of 2.1 MeV, and the di-neutron configuration, which is a characteristic feature of the weakly bound systems, mixes in the ground state. The motion of four neutrons around the He-4 core is solved by superposing the wave functions of antisymmetrized molecular dynamics. The mixing of di-neutron configurations is estimated by coupling the THSR (Tohsaki-Horiuchi-Schuck-Ropke) wave function, which successfully describes the alpha-condensed state of light nuclei.

DOI： 10.1103/PhysRevC.78.017306

Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

The coexistence of the α+α+n+n and α+t+t cluster structures in the excited states of Be10 has been discussed. In the previous analysis, all the low-lying states of Be10 were found to be well described by the motion of the two valence neutrons around two α clusters. However, the α+t+t cluster structure was found to coexist with the α+α+n+n structure around Ex=15 MeV, close to the corresponding threshold. We have introduced a microscopic model to solve the coupling effect between these two configurations. The K=0 and K=1 states are generated from the α+t+t configurations due to the spin coupling of two triton clusters. The present case of Be10 is one of the few examples in which completely different configurations of triton-type (α+t+t three-center) and α-type (α+α+n+n two-center) clusters coexist in a single nucleus in the same energy region. © 2008 The American Physical Society.

DOI： 10.1103/PhysRevC.77.067301

Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

The coexistence of the alpha + alpha + n + n and alpha + t + t cluster structures in the excited states of Be-10 has been discussed. In the previous analysis, all the low-lying states of Be-10 were found to be well described by the motion of the two valence neutrons around two alpha clusters. However, the alpha + t + t cluster structure was found to coexist with the alpha + alpha + n + n structure around E-x=15 MeV, close to the corresponding threshold. We have introduced a microscopic model to solve the coupling effect between these two configurations. The K=0 and K=1 states are generated from the alpha + t + t configurations due to the spin coupling of two triton clusters. The present case of Be-10 is one of the few examples in which completely different configurations of triton-type (alpha + t + t three-center) and alpha-type (alpha + alpha + n + n two-center) clusters coexist in a single nucleus in the same energy region.

DOI： 10.1103/PhysRevC.77.067301

Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

The coexistence of the alpha + alpha + n + n and alpha + t + t cluster structures in the excited states of Be-10 has been discussed. In the previous analysis, all the low-lying states of Be-10 were found to be well described by the motion of the two valence neutrons around two alpha clusters. However, the alpha + t + t cluster structure was found to coexist with the alpha + alpha + n + n structure around E-x=15 MeV, close to the corresponding threshold. We have introduced a microscopic model to solve the coupling effect between these two configurations. The K=0 and K=1 states are generated from the alpha + t + t configurations due to the spin coupling of two triton clusters. The present case of Be-10 is one of the few examples in which completely different configurations of triton-type (alpha + t + t three-center) and alpha-type (alpha + alpha + n + n two-center) clusters coexist in a single nucleus in the same energy region.

DOI： 10.1103/PhysRevC.77.067301

Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

The generalized two-center cluster model, which can treat static structures and dynamical reactions in excited states, is applied to the light neutron-rich system, Be12=α+α+4N. We discuss the change of the neutrons' configuration around two α cores from the covalent structure to the ionic one. We show that, in the unbound region above particle-decay thresholds, the ionic configurations appear as the molecular resonances of α+He8, He6+He6, and He5+He7. A new type of superdeformation is possible, and we find here a covalent superdeformation with a hybrid configuration of both the covalent and ionic structures. The excitation of these exotic structures through the two-neutron transfer reaction is also discussed. © 2008 The American Physical Society.

DOI： 10.1103/PhysRevLett.100.182502

Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

We have studied the α-condensed states of O16 and Ne20 based on a microscopic α-cluster model. This was performed by introducing a Monte Carlo technique for the description of the THSR (Tohsaki Horiuchi Schuck Röpke) wave function, which is called the "virtual THSR" wave function. Earlier microscopic calculations pointed out the possibility of the existence of four-α-cluster condensed states. Here, in addition to studying the four-α case, we also studied the case of five-α particles, for which the states are shown to be stable around the threshold energy even after taking into account the coupling effect between normal cluster states with O16+α configurations. © 2008 The American Physical Society.

DOI： 10.1103/PhysRevC.77.037301

Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

We have studied the alpha-condensed states of O-16 and Ne-20 based on a microscopic alpha-cluster model. This was performed by introducing a Monte Carlo technique for the description of the THSR (Tohsaki Horiuchi Schuck Ropke) wave function, which is called the "virtual THSR" wave function. Earlier microscopic calculations pointed out the possibility of the existence of four-alpha-cluster condensed states. Here, in addition to studying the four-alpha case, we also studied the case of five-alpha particles, for which the states are shown to be stable around the threshold energy even after taking into account the coupling effect between normal cluster states with O-16+alpha configurations.

DOI： 10.1103/PhysRevC.77.037301

Publishing type：Research paper (international conference proceedings)   International / domestic magazine：International journal  

The alpha+He-6,He-8 low-energy reactions and the structural changes of Be-10 in the microscopic alpha+alpha+2N model are studied by the generalized two-center cluster model with the Kohn-Hulthen-Kato variation method. It is found that in the inelastic scattering to the alpha+He-6(2(1)(+)) channel, characteristic enhancements are expected as the results of the parity-dependent non-adiabatic dynamics. The similar method is applied to the resonant scattering of a+He-8, and the coupling with the compound configurations of alpha+alpha+4N are discussed.

DOI： 10.1063/1.2943573

Publishing type：Research paper (international conference proceedings)   International / domestic magazine：International journal  

© 2008 American Institute of Physics. We study the structure of low-lying states of 13C with a microscopic cluster model. The second 0+ state of 12C, which is known as the Hoyle state and is important for astrophysical reactions, has been clarified to have dilute α-cluster structure. On the basis of the α-cluster model, we discuss the effect of one valence neutron in 13C on the α-cluster configuration of the Hoyle state. For these purpose, we investigate the iso-scalar E0 transition probability from the ground 1/2- state to this excited states.

DOI： 10.1063/1.2943623

Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

The t + t cluster components in the ground-state structure of He-isotopes are analysed through a new AMD approach. The method is called AMD triple-S which has been developed on the basis of the anti-symmetrized molecular dynamics (AMD), the generator coordinate method (GCM) and the stochastic variational method (SVM). In the AMD triple-S, variational calculations are carried out by means of the GCM with the AMD wave functions produced by the SVM procedure. © 2007 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.nuclphysa.2007.03.055

Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

We study the cluster-shell competition in carbon isotopes. Two parameters are introduced for the C12 core to characterize the transition from a cluster state to a shell-model state as a measure of the cluster-shell competition: one expresses the relative distance between α clusters and the other does the dissolution of one of the α clusters. We show the energy curves as functions of these parameters. The calculation is performed by combining the simplified modeling of cluster-shell competition for the C12 core and AMD triple-S. As the neutron number increases, the α-α distance becomes smaller; on the contrary, the dissolution of α clusters is enhanced. The origins of the anomalously small B(E2) value of C16 are discussed from cluster-shell competition point of view, and the appearance of pure cluster state around the 10 MeV region is suggested. © 2007 The American Physical Society.

DOI： 10.1103/PhysRevC.75.054309

Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

We demonstrate based on a microscopic α-cluster model that α-condensed states appear not only in light nuclei such as C12 and O16 but also in heavier nuclei with a core at excitation energies corresponding to multi-α-threshold energies. To extend the study of normal α-condensed state to the cases of heavier nuclei with an inner strongly bound core (O16) and also to non-4N-nuclei (e.g., 2α+dineutron), we introduce a Monte Carlo technique for the description of the Schuck wave function, which are called "virtual Schuck" wave function. © 2007 The American Physical Society.

DOI： 10.1103/PhysRevC.75.037303

Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

DOI： 10.24532/soken.115.3_C33

CiNii Article

Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

We investigate a linear-chain configuration of three alpha clusters with a neutron in C-13. To characterize this configuration, an operator P is introduced, which is the sum of parity inversion operators for each proton. The states with positive expectation values for this operator are found to form a rotational band structure, and the moment of inertia agrees well with the experimentally suggested value. Allowing a small bending angle stabilizes the linear-chain configuration of three alpha clusters with a valence neutron, which is a hyper-deformed state.

DOI： 10.1103/PhysRevC.74.067304

Publishing type：Research paper (international conference proceedings)   International / domestic magazine：International journal  

t+t clustering in He isotopes is investigated by using two theoretical approaches. A role of the t+t cluster component in the ground state is examined with AMD triple-S, allowing the wider configuration space containing simultaneously the "t+t+valence neutrons" structure and "4He+valence neutrons" structure. We understand the importance of the t+t component even for the ground state. Further, t+t resonances are investigated with RGM type approach. We obtained many t+t states as resonances near to t+t threshold. © World Scientific Publishing Company.

Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

A systematic study on the ground-state structure of He isotopes (including He-10) is presented through a new method developed on the basis of antisymmetrized molecular dynamics (AMD), the generator coordinate method (GCM), and the stochastic variational method (SVM). In this approach, variational calculations are carried out by means of the GCM with the AMD wave functions produced by means of the SVM. A role of the t+t cluster component is examined with the present method, allowing the wider configuration space containing simultaneously the "t+t+valence neutrons" structure and "He-4+valence neutrons" structure.

DOI： 10.1103/PhysRevC.74.017307

Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

An experimental way of testing Bose-Einstein condensation of alpha clusters in the atomic nucleus is reported. The enhancement of cluster emission and the multiplicity partition of possible emitted clusters could be direct signatures for the condensed states. The barrier for the emission of clusters, such as Be-8 and C-12(*)(0(2)(+)), is calculated and compared with the barrier for the sequential emission of 2 or 3 alpha particles from the compound nucleus. For the calculations, a simple approach using a folded Woods-Saxon potential is used.

DOI： 10.1103/PhysRevLett.96.192502

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We propose a simplified model to directly take into account the contribution of the tensor interaction ( SMT) for light nuclei by extending the alpha-cluster model. In Be-8, the energy curve with respect to the relative distance between the two He-4 clusters suggests that the cluster structure persists even though the tensor interaction contributes strongly. In addition to SMT, a simplified method to take into account the strong spin-orbit contribution is introduced and the coupling effects of these two models is shown to be important in C-12, in contrast to Be-8.

DOI： 10.1103/PhysRevC.73.034310

Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

We investigate a linear-chain configuration of three α clusters with a neutron in C13. To characterize this configuration, an operator P is introduced, which is the sum of parity inversion operators for each proton. The states with positive expectation values for this operator are found to form a rotational band structure, and the moment of inertia agrees well with the experimentally suggested value. Allowing a small bending angle stabilizes the linear-chain configuration of three α clusters with a valence neutron, which is a hyper-deformed state. © 2006 The American Physical Society.

DOI： 10.1103/PhysRevC.74.067304

Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

A systematic study on the ground-state structure of He isotopes (including He10) is presented through a new method developed on the basis of antisymmetrized molecular dynamics (AMD), the generator coordinate method (GCM), and the stochastic variational method (SVM). In this approach, variational calculations are carried out by means of the GCM with the AMD wave functions produced by means of the SVM. A role of the t+t cluster component is examined with the present method, allowing the wider configuration space containing simultaneously the "t+t+valence neutrons" structure and "He4+valence neutrons" structure. © 2006 The American Physical Society.

DOI： 10.1103/PhysRevC.74.017307

Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

We propose a simple model to describe cluster-shell competition. Introducing only one parameter (Λ) to the wave function makes it possible to describe the asymptotic transition of two valence neutrons in Be10 (α+α+n+n) from a di-neutron to independent particles when the contribution of the spin-orbit interaction is taken into account. Similarly in C12, a transition from a 3α configuration to a 2α+4N configuration is represented, and we show a strong contribution of the spin-orbit interaction in the ground state. We investigate further this transition from the cluster state (α+O16) to the shell-model state (O16 + four nucleons) in Ne20. In these examples, the wave functions for cluster-breaking states are prepared in the same general way. © 2005 The American Physical Society.

DOI： 10.1103/PhysRevC.71.064307

Publishing type：Research paper (international conference proceedings)   International / domestic magazine：International journal  

The ground state properties of the carbon isotopes are investigated using the extended version of the Antisymmetrized Molecular Dynamics (AMD) Multi Slater Determinant method. We can reproduce reasonably well many experimental data for C-12-C-22. In this contribution we present a systematic calculation of binding energies, energies of the 2(+)(1) states and B(E2) transition strengths.

Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

The problem of the long life time of the pentaquark Theta(+) is investigated on the basis of the color molecular dynamics simulation. We find that it takes a long time (typically of 50-100 fm/c) for the initial pentaquark state to rearrange its color and spatial positions to decay into the nucleon+kaon final state. Structure of the potential surface in the color and position spaces also supports this picture. Pentaquark wanders on the potential surface to find a narrow channel to decay.

DOI： 10.1556/APH.22.2005.1-2.7

Publishing type：Research paper (international conference proceedings)   International / domestic magazine：International journal  

Life time of the pentaquark Theta(+) is investigated on the basis of the color molecular dynamics simulation. We find that it takes a long time (typically of 50 - 100 fm/c) for the initial pentaquark-state to rearrange its color and spatial configurations to decay into the nucleon+kaon final state. The potential surface in the color and position spaces also supports this picture: Pentaquark wanders on the potential surface to find a narrow channel to decay.

Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

The structure of low-lying states of the carbon isotopes is investigated using the improved version of the Antisymmetrized Molecular Dynamics (AMD) Multi-Slater Determinant model. The theoretical method is found to be very useful to study ground-state properties of various nuclei covering light unstable nuclei. The calculations succeed to reproduce reasonably well many experimental data for the carbon isotopes 12C-22C such as binding energies, the energies of the 21+ states in the even-even isotopes, radii and electromagnetic transition strengths. We investigate the structure change with the increasing neutron number and observe the existence of various exotic phenomena, like the development of a neutron skin and large deformations which appear in unstable nuclei. Our calculations clearly support the existence of the N = 8 and N = 16 neutron magic numbers. The role of the spin-orbit interaction in the description of the studied isotopes and in the development of cluster structures is discussed. A special approach, important for weakly bound systems, is adopted for 15C. It enables us to better describe the tail of the wave function. © Società Italiana di Fisica/Springer-Verlag 2004.

DOI： 10.1140/epja/i2004-10053-5

Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

We demonstrate whether the cluster structure dissolves or remains when the shell-model-like model space is introduced in addition to the cluster model space in light nuclei. Although the binding energies of 8Be, 10Be, and 10B become larger by about 1-2 MeV by adding shell-model-like basis states to the α+α+N+N+⋯ basis states, the α-α structure is a dominant configuration of the ground states. However, α-breaking wave functions strongly mix in 12C, and the decrease of the energy from the 3α configuration by about 6 MeV is a clue to resolving a long-standing problem of the binding energies of 12C and 12O. The improved version of antisymmetrized molecular dynamics (AMD), AMD superposition of selected snapshots (AMD triple-S), is used to show the cluster-shell competition of these nuclei.

DOI： 10.1103/PhysRevC.70.054307

Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

The ground state properties and the properties of low-lying states of the even-even 6Be- 12Be beryllium isotopes are investigated using the extended version of the Antisymmetrized Molecular Dynamics Multi-Slater Determinant model. The theoretical method is found to be very useful to study ground state properties of various nuclei covering light unstable nuclei. Many experimental data can be successfully reproduced by the adopted approach. Binding energies, the energies of the 2 +1 states, electromagnetic transition strengths and quadrupole moments of proton and neutron distribution are calculated.

DOI： 10.1023/B:CJOP.0000038527.84719.ee

Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

A new method to calculate the low-lying states of light nuclei is proposed: Antisymmetrized Molecular Dynamics (AMD) - Superposition of Selected Snapshots (AMD triple S). In addition to the cluster features of the core nucleus, the properties of the wave of the valence nucleons are well expressed in terms of a superposition of selected AMD wave functions. Our previous results based on Molecular-orbits are justified using this new framework. For example, the three O+ states of 10Be are found to be well described. Here, the importance of solving the cooling equation for the imaginary part of the Gaussian centers for the nucleons is examined. For 12Be, the newly observed J = 0 state at 2.24 MeV is analyzed to be the second O+ state. The method is further applied to Ne isotopes with 5α-core, and parity mixing of the single-particle orbit around parity-asymmetric core is discussed. © 2004 Published by Elsevier B.V.

DOI： 10.1016/j.nuclphysa.2004.04.006

Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

We study systematically H- and He-isotopes using an extended AMD (Antisymmetrized Molecular Dynamics) approach. In this approach, AMD combined with the generator coordinate method is extended with the idea of the stochastic variational method. By using this new method, we study many body-cluster states of extremely neutron-rich nuclei such as 7H (t+n+n+n+n) or 10He (4He+n+n+n+n+n+n . © 2004 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.nuclphysa.2004.04.062

Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

The molecular-orbit (MO) model of an equilateral-triangular shape of three α clusters surrounded by excess neutrons was investigated. An equilateral-triangular symmetry was determined by an attractive interaction between an excess neutron and α particle was found to stabilize K πx = 0+ and 3- rotational bands. The rotational band with 3- value at 3 MeV below the 10Be + α threshold energy corresponded to the band built on top of second 3 - state. The molecular 3-α structure stabilization was suggested by excess neutrons which were observed as realization of α crystallization in dilute nuclear medium.

DOI： 10.1103/PhysRevLett.92.142501

Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

The structure of stable and unstable light nuclei in the carbon region is investigated using the extended version of the Antisymmetrized Molecular Dynamics Multi-Slater Determinant model. This method has proved to be very flexible when describing structure of light nuclei where both shell model and cluster structure can appear. In this paper we address specifically the development of cluster structure in the 02+ state in the 10Be isotope. The possibility of description of halo structure within the adopted method is discussed in the case of 15C. Systematic calculations for even-even oxygen isotopes support the development of new magic number N=16.

DOI： 10.1023/B:CJOP.0000018129.75918.e8

Publishing type：Research paper (international conference proceedings)   International / domestic magazine：International journal  

A new method for calculating the low-lying states of light nuclei is proposed: Antisymmetrized Molecular Dynamics (AMD) - Superposition of Selected Snapshots (AMD triple-S). In addition to the cluster features of the core nucleus, the properties of the wave of valence nucleons are well expressed in terms of a superposition of selected AMD wave functions. For He-6, the binding energy and the halo nature are reproduced using effective interactions determined from a phase-shift analysis. For the deformed core cases, in Be-12, the newly observed J = 0 state at 2.24 MeV is analyzed to be the second 0(+) state.

Publishing type：Research paper (international conference proceedings)   International / domestic magazine：International journal  

The structure of low-lying states of the carbon isotopes is investigated using the extended version of the Antisymmetrized Molecular Dynamics (AMD) Multi-Slater Determinant model. We can reproduce reasonably well many experimental data for carbon isotopes C-12-C-22. A special approach is adopted for C-15 to better describe the tail of the wave function.

Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

A new method for calculating the low-lying states of light nuclei is proposed: antisymmetrized molecular dynamics (AMD)-superposition of selected snapshots. In addition to the cluster features of the core nucleus, the properties of the wave of valence nucleons are well expressed in terms of a superposition of selected AMD wave functions. For 6He, the binding energy and the halo nature are reproduced using effective interactions determined from a phase-shift analysis. For the deformed core cases, the three 0+ states of 10Be are well described. Here, the importance of solving the cooling equation for the imaginary part of the Gaussian centers for the nucleons is examined. For 12Be, the newly observed J=0 state at 2.24 MeV is analyzed to be the second 0+ state.

DOI： 10.1103/PhysRevC.68.054302

Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

We discuss two topics about the cluster structure in light neutron-rich nuclei with the astrophysical interests. One is 9Be: using a microscopic α + α + n model, the photodisintegration cross section is analyzed. It is shown that good agreement is achieved with the recently measured B(E1) transition probability from the ground 3/2- state to the first excited state (1/2+), which is 2 times larger than the previous measurement. The other topic is the cluster-shell mixing in 12C, which is crucial to explain the B(E2) value from the second O+ state to the first 2+ state in triple-α reaction.

DOI： 10.1016/S0375-9474(03)00918-7

Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

The low-lying structure of the C isotopes is investigated using the Antisymmetrized Molecular Dynamics (AMD) Multi-Slater Determinant model. The calculated 2± energies of the even-even isotopes indicate the change from spherical to deformed structure at N = 8. This is consistent with the isotope change of the single particle energy deduced from recent experiments. Binding energies and r.m.s. radii are also calculated and compared with the experimental data.

DOI： 10.1016/S0375-9474(03)00939-4

Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

An isomeric 0+ state in 12Be was found at Ex = 2.24 MeV. The isomer was identified by measuring coincident two γ-rays from in-flight 12Be nuclei, 12mBe → 12Be* (21+) → 12Beg.s., produced by the projectile fragmentation of 18O at 100 A MeV on a beryllium target. Its spin was determined to be 0+ by the angular correlation of the two γ-rays. The low excitation energy of the 0+ state is a strong evidence of the break of the N = 8 shell closure in the 12Be nucleus. © 2003 Published by Elsevier Science B.V.

DOI： 10.1016/S0370-2693(03)00341-1

Publishing type：Research paper (international conference proceedings)   International / domestic magazine：International journal  

The triaxial deformation in Be-10 is investigated using a microscopic alpha+alpha+n+n model. The states of two valence neutrons are classified based on the molecular-orbit (MO) model, and the pi-orbit is introduced about the axis connecting the two alpha-clusters for the description of the rotational bands. There appear two rotational bands comprised mainly of K-pi = 0(+) and K-pi = 2(+), respectively, at low excitation energy, where the two valence neutrons occupy K-pi = 3/2(-) or K-pi = 1/2(-) orbits. The triaxiality and the K-mixing are discussed in connection to the molecular structure, particularly, to the spin-orbit splitting. The extent of the triaxial deformation is evaluated in terms of the electro-magnetic transition matrix elements (Davydov-Filippov model). The obtained values turned out to be gamma = 15 degrees similar to 20 degrees. Furthermore, the mirror symmetry breaking of the triaxial deformation of C-10 is investigated. The triaxiality of protons in C-10 is much larger than that of neutrons in Be-10 due to the weak binding nature of the valence particles. This agrees with the recent experiment which suggests the mirror symmetry breaking of these nuclei through the beta-decay transition strength.

Publishing type：Research paper (international conference proceedings)   International / domestic magazine：International journal  

The low-lying structure of the even-even C isotopes is investigated using the Multi-Slater Determinant AMD model. The calculated 2(+) energies show the change from spherical to deformed structure at N = 8 and it is consistent with the isotope change of the single particle energy deduced from recent experiments. Binding energies and r.m.s. radii are also calculated and compared with the experimental data.

Publishing type：Research paper (international conference proceedings)   International / domestic magazine：International journal  

The cluster structure of C isotopes is investigated using a microscopic α+α+α+n+n... model based on the molecular orbit (MO) model. The stability of the linear chain of 3α with respect to the breathing mode and the bending mode for various neutron configurations is investigated. The combination of the valence neutrons in the π- and σ-orbits is promising to stabilize for these modes, and the excited states of 16C with the (3/2π-)2(1/2σ-)2 configuration for the four valence neutrons are one of the most promising candidates for such structure. Furthermore, the equilateral-triangular shape of 3α surrounded by valence neutrons is suggested for 14C. The 3-, 4-, and 5 - members of this rotational band appear around the 10Be+α threshold, and these calculated states correspond to the experimentally observed 3- state (9.80 MeV) and 4- state (11.67 MeV). A positive-parity rotational band (0+, 2+, 4+) also arises around this threshold energy, and these results suggest that the picture of inversion doublet structure works also in neutron-rich nuclei.

DOI： 10.1556/APH.18.2003.2-4.9

Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

The triaxial deformation in Be-10 is investigated using a microscopic alpha+alpha+n+n model. The states of two valence neutrons are classified based on the molecular-orbit (MO) model, and the pi orbit is introduced about the axis connecting the two alpha clusters for the description of the rotational bands. There appear two rotational bands comprised mainly of K-pi=0(+) and K-pi=2(+), respectively, at low excitation energy, where the two valence neutrons occupy K-pi=3/2(-) or K-pi=1/2(-) orbits. The triaxiality and the K mixing are discussed in connection to the molecular structure, particularly to the spin-orbit splitting. The extent of the triaxial deformation is evaluated in terms of the electromagnetic transition matrix elements (Davydov-Filippov model, Q-invariant model) and density distribution in the intrinsic frame. The obtained values turned out to be gamma=15degrees-20degrees.

DOI： 10.1103/PhysRevC.65.044302

Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

The structure of C isotopes are investigated using a microscopic alpha+alpha+alpha+n+n... model based on the molecular orbit (MO) model. The stability of the linear-chain of 3alpha with respect to the breathing mode and the bending mode for various neutron configurations is investigated. The combination of the valence neutrons in the pi- and the sigma-orbit is promising to stabilize for these modes, and the excited state of C-16 with the (3/2(pi)(-))(2) (1/2(sigma)(-))(2) configuration for the four valence neutrons is one of the most promising candidates for such structure. Furthermore, the equilateral-triangular shape of 3alpha surrounded by valence neutrons is suggested for C-14 based on a microscopic cluster model. The 3(-), 4(-) and 5(-) members of this rotational band appear around the Be-10+alpha threshold, and these calculated states correspond to the experimentally observed 3(-) state (9.80 MeV) and 4(-) state (11.67 MeV). A positive-parity rotational band (0(+), 2(+), 4(+)) also arises around this threshold energy, and these results suggest that the picture of inversion doublet structure works also in neutron-rich nuclei.

Publishing type：Research paper (international conference proceedings)   International / domestic magazine：International journal  

DOI： 10.1143/ptps.146.565

Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

The structure of Be and C isotopes are investigated based on the molecular-orbit (MO) model. The low-lying states are characterized by several configurations of valence neutrons, which are constructed as combinations of basic orbits. In 10Be, all of the observed positive-parity bands and the negative-parity bands are described within the model. The second 0 + state of 10Be has a large α-α cluster structure, and this is characterized by a (1/2+σ) 2 configuration. An enlargement of the α-α distance due to two-valence neutrons along the α-α axis makes their wave function smooth and reduces the kinetic energy drastically. Furthermore, the contribution of the spin-orbit interaction due to coupling between the S z = 0 and the S z = 1 configurations, is important. In the ground state of 12Be, the calculated energy exhibits similar characteristics, that the remarkable α clustering and the contribution of the spin-orbit interaction make the binding of the state with (3/2-π)2(1/2+σ)2 configuration properly stronger in comparison with the closed p-shell (3/2 -π)2(1/2-π) 2 configuration. This is related to the breaking of the N = 8 (closed p-shell) neutron magic number. Also, the molecule-like structure of the C isotopes is investigated using a microscopic α+α+α+n+n+ . . . model. The combination of the valence neutrons in the π- and the σ-orbit is promising to stabilize the linear-chain state against the breathing and bending modes, and it is found that the excited states of 16C are the most promising candidates for such structure. © Società Italiana di Fisica and Springer-Verlag 2002.

DOI： 10.1007/s10050-002-8716-2

Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

We use a microscopic three-cluster model with the [Formula Presented] configuration to analyze with astrophysical interests the photodisintegration cross section of [Formula Presented] The valence neutron in [Formula Presented] is treated in the molecular orbit model, including continuum states by the box discretization method. It is shown that good agreement is achieved with the recently measured [Formula Presented] transition probability from the ground state to the first [Formula Presented] state when the box size is enlarged, resulting in reasonable reproduction of the experimental data for the photodisintegration cross section. The Coulomb dissociation of [Formula Presented] is also discussed. © 2002 The American Physical Society.

DOI： 10.1103/PhysRevC.66.057301

Publishing type：Research paper (international conference proceedings)   International / domestic magazine：International journal  

The molecule-Re structure of the C isotopes is investigated using a microscopic alpha+alpha+alphaln+n+(.) (.) (.) model. The valence neutrons are classified based on the molecular-orbit (MO) model, and both pi-orbit and sigma-orbit are introduced around three alpha-clusters. The excited states of C-16 is one of the most promising candidates for the linear-chain structure. The equilateral-triangular shape of 3alpha surrounded by valence neutrons is also suggested for C-14. The cluster around the Be-10+alpha threshold energy corresponds to the experimentally observed band built on top of the second 3(-) state.

Publishing type：Research paper (international conference proceedings)   International / domestic magazine：International journal  

The structure of C isotopes are investigated using a microscopic α+α+α+n+n. . . model based on the molecular orbit (MO) model. The stability of the linear-chain of 3α with respect to the breathing mode and the bending mode for various neutron configurations is investigated. The combination of the valence neutrons in the π- and the σ-orbit is promising to stabilize for these modes, and the excited state of 16C with the (3/2π-)2 (1/2σ-)2 configuration for the four valence neutrons is one of the most promising candidates for such structure. Furthermore, the equilateral-triangular shape of 3α surrounded by valence neutrons is suggested for 14C based on a microscopic cluster model. The 3-, 4- and 5- members of this rotational band appear around the 10Be+α threshold, and these calculated states correspond to the experimentally observed 3- state (9.80 MeV) and 4- state (11.67 MeV). A positive-parity rotational band (0+, 2+, 4+) also arises around this threshold energy, and these results suggest that the picture of inversion doublet structure works also in neutron-rich nuclei.

DOI： 10.1143/ptps.146.207

Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

The moleculelike structure of the C isotopes (A = 12, 14, 16) is investigated using a microscopic α + α + α + n + n + ⋯ model. The valence neutrons are classified based on the molecular-orbit model, and both π orbit and σ orbit are introduced around three α clusters. The valence neutrons which occupy the π orbit increase the binding energy and stabilize the linear chain of 3 α against the breathinglike breakup. However, 14C with the π orbit does not show a clear energy minimum against the bendinglike path. The combination of the valence neutrons in the π and σ orbits is promising to stabilize the linear-chain state against the breathing and bending modes, and it is found that the excited states of 16C with the (3/2-π)2(1/2-σ)2 configuration for the four valence neutrons is one of the most promising candidates for such a structure.

DOI： 10.1103/PhysRevC.64.014301

Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

The structure of Be-12 is investigated using a microscopic alpha+alpha +4n model based on the molecular-orbit (MO) model. It is shown that the remarkable alpha -clustering and the contribution of the spin-orbit interaction make the binding of the state with the (3/2(-))(2)(1/2(+))(2) configuration for the valence neutrons properly stronger in comparison with the closed p-shell (3/2(-))(2)(1/2(-))(2) configuration. The molecular-like structure of the C isotopes is also investigated using a microscopic alpha+alpha+alpha +n+n+(...) model.

Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

The structures of Be isotopes and C isotopes are investigated using a microscopic α+α+n+n· · · model and α+α+α+n+n· · · model, respectively, based on the molecular orbit (MO) model. The low-lying states of the Be isotopes are characterized by several configurations of valence neutrons, which are constructed as combinations of three basic orbits. The model space employed is extended from that of conventional MO models, and the orbits are expressed as linear combinations of local Gaussians. Their positions are determined variationally. In 10Be, all of the observed positive-parity bands and negative-parity bands are described within the model. It is found that the second 0+ state of 10Be has a large α-α structure with a (1/2+)2 configuration. Increase of the α-α distance due to the existence of two valence neutrons along the α-α axis makes their wave function smooth and reduces the kinetic energy drastically. Here, the contribution of the spin-orbit interaction due to coupling between the Sz = 0 and the Sz = 1 configurations is important. The energy surface of 12Be is found to exhibit similar characteristics, with a significant α clustering and the contribution of the spin-orbit interaction causing the binding of the ground state with the (1/2+)2 configuration to become much stronger. As a result, the (3/2-)2(1/2+)2 configuration for the four valence neutrons almost degenerate with the (3/2-)2(1/2-)2 configuration. This is related to the breaking of the N = 8 magic number. For the C isotopes, the stability of the linear chain of 3α with respect to the breathing-like mode and the bending-like mode are investigated for various neutron configurations. It appears likely that a combination of the valence neutrons in the π-and the σ-orbit is to stabilize the system with respect to such modes, and it is found that the excited states of 16C with the (3/2-π)2(1/2-σ)2 configuration for four valence neutrons is one of the most probable of such structures.

DOI： 10.1143/PTPS.142.297

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The structure of the second 0(+) state of Be-10 is investigated using a microscopic alpha+alpha+n+n model based on the molecular-orbit (MO) model. The second 0(+) state, which has dominantly the(1/2(+))(2) configuration, is shown to have a particularly enlarged alpha-alpha structure. The kinetic energy of the two valence neutrons occupying along the alpha-alpha axis is reduced remarkably due to the strong alpha clustering and, simultaneously, the spin-orbit interaction unexpectedly plays an important role in making the energy of this state much lower. The mixing of states with different spin structure is shown to be important in negative-parity states. The experimentally observed small-level spacing between 1(-) and 2(-) (similar to 300 keV) is found to be evidence of this spin-mixing effect. Be-12 is also investigated using the alpha+alpha+4n model, in which four valence neutrons are considered to occupy the (3/2(-))(2)(1/2(+))(2) configuration. The energy surface of Be-12 is shown to exhibit similar characteristics, that the remarkable alpha clustering and the contribution of the spin-orbit interaction make the binding of the state with the (3/2(-))(2)(1/2(+))(2) configuration properly stronger in comparison with the closed p-shell (3/2(-))(2)(1/2(-))(2) configuration.

DOI： 10.1103/PhysRevC.62.034301

Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

We study the structure of He isotopes systematically using a model in which the frameworks of the anti-symmetrized molecular dynamics (AMD) and the generator coordinate method (GCM) are combined. The present AMD+GCM can reproduce basic features of the isotopes, for example halo structures in 6He and tendency of the binding energies of the isotopes within relatively small number of basis functions. In 7He, the importance of two configurations, 6He-n and (4He-n)-2n, is shown for the ground state. In 8He, the calculated rms radius is smaller than the experimental one.

DOI： 10.1103/PhysRevC.61.024303

Publishing type：Research paper (international conference proceedings)   International / domestic magazine：International journal  

Be-10 and Be-12 are investigated by a microscopic alpha+alpha +n+n ... model based on the Molecular Orbit (MO) model. The low-lying states are characterized by several configurations of valence neutrons which are constructed as combinations of three basic orbits: K-pi=3/2(-), 1/2(-) and 1/2(+). In Be-10, all the observed positive parity bands and negative parity bands are described within the model, and the second 0(+) state has large alpha - alpha structure. The configuration is (1/2(+))(2) corresponding to the sd-shell, and two valence neutrons along the alpha - alpha axis enhance the alpha - alpha distance. In Be-12, this configuration strongly mixes in the ground state, and due to this, the observed slow beta -decay to B-12 is explained. This is the breaking of N = 8 magic number in Be-12.

Publishing type：Research paper (international conference proceedings)   International / domestic magazine：International journal  

We discuss the importance of clustering in light neutron-rich nuclei. As examples, we analyse Be-10 and Be-12 based on a microscopic alpha+alpha +valence n model and show that the alpha-alpha clustering is enlarged due to valence neutrons.
In Be-10, all the observed positive parity bands and negative parity bands are described within the model (alpha+alpha +n+n), and the second 0(+) state is shown to have a large alpha-alpha distance. Here, the two valence neutrons occupy along the alpha-alpha axis and they enlarge the alpha-alpha distance. The configuration of the valence neutrons corresponds to (1/2(+))(2) (sigma -orbit in terms of MO), and these neutrons reduce their kinetic energy caused by the Pauli principle as the increase of the alpha-alpha distance.
This mechanism is related to the breaking of N = 8 magic number in Be-12. In Be-12, this (1/2(+))(2) component plays an important role in the ground state. The calculated energy of this configuration is lower than the closed p-shell configuration for neutrons. Due to this effect, the observed slow beta -decay probability from Be-12 to B-12 can be explained.

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The structure of [Formula Presented] is investigated using a microscopic [Formula Presented] model based on the molecular orbit (MO) model. The low-lying states are characterized by several configurations of valence neutrons, which are constructed as combinations of three basic orbits. The model space employed is extended from the traditional MO models, and the orbits are expressed as linear combinations of local Gaussians. Their positions are determined variationally. Using this model, we reanalyze the structure of [Formula Presented] and show that this extension enables us to use the original two-body spin-orbit interaction determined from a scattering phase-shift analysis of [Formula Presented] In [Formula Presented] all of the observed positive-parity bands and the negative-parity bands are described within the model. The [Formula Presented] ground state of [Formula Presented] is described by a dominant [Formula Presented] configuration. The state has a rather large binding energy (8.38 MeV from the [Formula Presented] threshold experimentally), and the mechanism leading to binding, such as a pairing effect and reduction of the kinetic energy between two clusters, is discussed in detail. In spite of this large binding, the [Formula Presented] clustering in the ground state persists due to a coupling effect between the [Formula Presented] configuration and the [Formula Presented] configuration, which provides a smooth potential for the valence neutrons. The second [Formula Presented] state of [Formula Presented] has a large [Formula Presented] structure with a [Formula Presented] configuration. An enlargement of the [Formula Presented] distance due to two-valence neutrons along the [Formula Presented] axis makes their wave function smooth and reduces the kinetic energy drastically. Furthermore, the contribution of the spin-orbit interaction due to coupling between the [Formula Presented] and the [Formula Presented] configurations is important. We also show the mediation effect of two valence neutrons between two [Formula Presented] clusters. © 2000 The American Physical Society.

DOI： 10.1103/PhysRevC.61.044306

Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

The structure of the second [Formula Presented] state of [Formula Presented] is investigated using a microscopic [Formula Presented] model based on the molecular-orbit (MO) model. The second [Formula Presented] state, which has dominantly the [Formula Presented] configuration, is shown to have a particularly enlarged [Formula Presented]-[Formula Presented] structure. The kinetic energy of the two valence neutrons occupying along the [Formula Presented]-[Formula Presented] axis is reduced remarkably due to the strong [Formula Presented] clustering and, simultaneously, the spin-orbit interaction unexpectedly plays an important role in making the energy of this state much lower. The mixing of states with different spin structure is shown to be important in negative-parity states. The experimentally observed small-level spacing between [Formula Presented] and [Formula Presented] keV) is found to be evidence of this spin-mixing effect. [Formula Presented] is also investigated using the [Formula Presented] model, in which four valence neutrons are considered to occupy the [Formula Presented] configuration. The energy surface of [Formula Presented] is shown to exhibit similar characteristics, that the remarkable [Formula Presented] clustering and the contribution of the spin-orbit interaction make the binding of the state with the [Formula Presented] configuration properly stronger in comparison with the closed p-shell [Formula Presented] configuration. © 2000 The American Physical Society.

DOI： 10.1103/PhysRevC.62.034301

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By using the complex scaling method, the C-10+p resonance parameters are determined in order to investigate the spectroscopic property of the proton-rich nucleus N-11 in comparison with the mirror nucleus Be-11 which has a typical neutron halo structure. The obtained resonance energy (E-r) and width (Gamma) of N-11 are (E-r, Gamma)=(1.29 MeV, 1.39 MeV) and (2.12 MeV, 0.95 MeV) for s(1/2) and p(1/2) states, respectively. These results are in good agreement with the recent experimental data reported by Axelsson et nl. Thomas-Ehrman effect on the 1/2(-) and 1/2(+) resonance states in N-11 is discussed in association with the weakly bound states in Be-11.

DOI： 10.1103/PhysRevC.57.975

Publishing type：Research paper (international conference proceedings)   International / domestic magazine：International journal  

We investigate the structure of Be-10 within the microscopic cluster model based on the Molecular Orbit and show the presence of a rotational band consisting of states with large cu-cu clustering. The configuration of valence neutrons corresponding to 1/2(+) orbit enhances alpha-alpha clustering. The existence of these clusterized states is proven by the large E2 transition probability from 2(3)(+) to 0(2)(+).

Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

By using the complex scaling method, the [Formula Presented] resonance parameters are determined in order to investigate the spectroscopic property of the proton-rich nucleus [Formula Presented] N in comparison with the mirror nucleus [Formula Presented] Be which has a typical neutron halo structure. The obtained resonance energy [Formula Presented] and width [Formula Presented] of [Formula Presented] N are [Formula Presented] Γ)=(1.29 MeV, 1.39 MeV) and (2.12 MeV, 0.95 MeV) for [Formula Presented] and [Formula Presented] states, respectively. These results are in good agreement with the recent experimental data reported by Axelsson et al. Thomas-Ehrman effect on the [Formula Presented] and [Formula Presented] resonance states in [Formula Presented] N is discussed in association with the weakly bound states in [Formula Presented] Be. © 1998 The American Physical Society.

DOI： 10.1103/PhysRevC.57.975

Publishing type：Research paper (international conference proceedings)   International / domestic magazine：International journal  

We discuss molecular structures of Be and C nuclei by a multi-configuration cluster model. Especially, both an E2-transition and an alpha-decay width from 0(2)(+) state of C-12 nuclei are well reproduced, which determines nucleosynthesis of C-12.

Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

In many previous calculations within microscopic models, the binding energy difference between C-12 and O-16 nuclei has been too large compared with the experimental data, and it has not been possible to describe these nuclei reasonably by the same effective interaction simultaneously. In this paper, we apply the N alpha-cluster model so as to clarify what is the most essential problem in the description of C-12 and O-16 by using a very large functional space and various effective interactions. This procedure is carried out by combining frameworks of the constraint cooling method introduced in Antisymmetrized Molecular Dynamics (AMD) and generator coordinate method (GCM). The resultant energy levels of O-16 show that various effective interactions give the second O+ slate of O-16 just around the C-12 + alpha threshold energy. This result agrees with the picture of the Ikeda diagram. However, even if we use some density dependent interactions, the binding energy difference between C-12 and O-16 cannot be remarkably improved.

DOI： 10.1143/PTP.94.1019

DOI： 10.11316/jpsgaiyo.72.2.0_156

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DOI： 10.11316/jpsgaiyo.71.1.0_180

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DOI： 10.11316/jpsgaiyo.71.1.0_205

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© Copyright owned by the author(s). Recently, we proposed the microscopic structure and reaction models. The model firstly constructs the nuclear structure by the stochastic multi-configuration mixing (SMCM) method based on the cluster model. Next, the cross section is obtained by the microscopic coupled-channel (MCC) calculation based on the folding model with the complex G-matrix interaction. In this work, we compare the 9Li nucleus with the 10Be nucleus from the viewpoint of the nuclear structure and reaction. The 9Li (10Be) nucleus is described as an α + t (α) + n + n four-body system based on the cluster model. The elastic and inelastic scattering cross sections for the 9Li + 12C and 10Be + 12C systems are obtained by the MCC calculation with the MPa interaction which is the latest version of the complex G-matrix interaction derived from the ESC nucleon-nucleon interaction model. The excitation energies of the low-lying states for the 9Li and 10Be nuclei well reproduce the data. The MCC model including the excitation effect of the projectile and target shows the visible channel coupling effect on the elastic cross section. The contribution of the 10Be excitation effect is clearly larger than that of the 9Li excitation effect.

DOI： 10.11316/butsuri.71.6_350

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DOI： 10.11316/jpsgaiyo.71.2.0_144

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DOI： 10.11316/jpsgaiyo.71.2.0_143

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The stable existence of rod-shaped structures in highly excited states of Mg-24 is studied based on a systematic cranked Hartree-Fock calculation with various Skyrme-type interactions. Its stability is examined by allowing the transition of the clusterlike structure to the shell-model-like structure. Especially, the rod-shaped state is exposed to two major instabilities: the bending motion, which is the main path for the transition to low-lying states, and the spin-orbit interaction, which is the driving force to break the alpha clusters and enhance the independent motion of the nucleons. The rod-shaped structure with large angular momentum is obtained as a metastable stationary state.

DOI： 10.1103/PhysRevC.92.011303

DOI： 10.11316/jpsgaiyo.70.1.0_313

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DOI： 10.1103/PhysRevC.90.039902

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We illustrate the formation of a thin, long structure of heavy nuclei by three-nucleus simultaneous collisions within time-dependent density functional theory. The impact parameter dependence for such a formation is systematically demonstrated through clarifications of the difference between binary and ternary collision events. A new method for producing thin, long heavy nuclei in the laboratory is suggested, as well as the possible formation of the thin, long structure in hot dense matter such as that encountered in core collapse supernovae. DOI: 10.1103/PhysRevC.87.014609

DOI： 10.1103/PhysRevC.87.014609

DOI： 10.11316/jpsgaiyo.68.2.1.0_61_3

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DOI： 10.11316/jpsgaiyo.68.2.1.0_32_4

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DOI： 10.11316/jpsgaiyo.68.2.1.0_61_4

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We investigate the properties of the states observed around the α-cluster breakup threshold region in 12C and 16O. We apply the orthogonality condition model (OCM), where the model space is given by the SU3 algebra. From bases of this SU3 configuration, two algebraic approaches of the symplectic (sp) method and μ-truncation method are introduced. In 12C, we show that the sp-quanta are important to understand the mechanism of the appearance of the large E0 transition strength. With these methods, both strong- and weak-coupling configurations are taken into account at the same time. Therefore, the properties of gas-like and linear-chain states are investigated easily. In 16O, a simpler truncation utilizing the μ quanta is applied. Here, the energy levels and the linear-chain (L. C.) configurations are investigated.

DOI： 10.1088/1742-6596/436/1/012035

Investigations of exotic cluster-like phenomena in the framework of the Skyrme-Hartree-Fock approach are reported. The occurrence of highly excited isomeric states is discussed in connection with the question of their stability in static and time-dependent Hartree Fock (TDHF) calculations. We find rotational stabilization of a 4α chain structure in 16O occurring for a limited range of angular momenta. A toroidal configuration of 40Ca was also stabilized by rotation and provides a very interesting example of rotation about a symmetry axis with a strictly quantized total angular momentum. Finally we look at the formation of nuclear pasta phases in a time-dependent approach and their classification.

DOI： 10.1088/1742-6596/445/1/012036

We discuss the appearance of various cluster structures in light nuclei. One of the examples is the appearance of geometric cluster configurations; gas-like α cluster states found in 12C and 16O could be stabilized with geometric shapes by adding neutrons or giving large angular momentum. We show in 16O that four α particles can have linear configurations with large angular momentum, which is very stable with respect to the bending motion using Skyrme cranked Hartree-Fock method. There exists a region of angular momentum (13-18 strok h sign) where the linear chain configuration is stabilized. The calculated moment of inertia (strok h sign 2/2(- ∼ 0.06-0.08 MeV) agrees well with conventional cluster model calculations. Another example of exotic cluster structure is the gas-like state of α clusters. The most famous example is the second 0+ state in 12C, the so called Hoyle state, which plays a dominant role in the synthesis of 12C and the heavier elements in the stars. We go one step further that such a dilute state of α particles exists around a strongly bound core in heavier systems. This study is performed by introducing a Monte Carlo technique for the description of the THSR (Tohsaki Horiuchi Schuck Röpke) wave function, and first we apply such method to three α state around a 40Ca core. Furthermore, coupling effect to other low-lying cluster states is taken into account; a large isoscalar monopole (E0) transition strength from the ground to the gas-like state is discussed in 24Mg. The gas-like state of two α clusters in 24Mg around the 16O core appears slightly below the 2α-thresliold energy.

DOI： 10.1088/1742-6596/420/1/012080

We construct nuclear wave functions from alpha clusters and some additional valence nucleons, and allow the inter-cluster distance to change and one alpha to dissolve from the (0s)4 structure as a result of the nuclear interaction. The change of the inter-cluster distance and the dissolution of the alpha particle can be interpreted as resulting from the competition of the 'shell model' and 'cluster model'. We demonstrate this competition through a few parameters.

DOI： 10.1088/1742-6596/436/1/012028

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DOI： 10.11316/jpsgaiyo.67.2.1.0_58_1

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DOI： 10.11316/jpsgaiyo.67.1.1.0_78_4

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DOI： 10.11316/jpsgaiyo.67.2.1.0_47_1

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DOI： 10.11316/jpsgaiyo.67.2.1.0_46_3

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Both from theoretical and experimental sides, the existence of cluster structure in light nuclei has been studied for a few decades and the appearance has been confirmed. To confirm the properties of these states is important also from the astrophysical view point. We investigate the properties of the structure of 12C above the α cluster threshold. Here, we apply orthogonality condition model (OCM), where the model space is given by SU(3) and its symplectic (sp) configuration. This enables us to treat both strong and weak coupling configuration. We show that sp-quanta is important to understand the mechanism of the appearance of large E0 strength. We also show that the other transition properties have good correspondence with experiments. © 2012 American Institute of Physics.

DOI： 10.1063/1.4763441

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DOI： 10.1103/PhysRevC.83.024301

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© 2010 Owned by the authors, published by EDP Sciences. The mass-dependent structure of the composite nucleus is shown based on three-dimensional timedependent Hartree-Fock calculations with Skyrme interactions (SLy4d and SkM∗). One remarkable result is that the isovector monopole excitation dominantly appears for collisions of heavy nuclei, and the isovector dipole excitation for those of light ones. Such a difference found in the dynamical structure of composite nucleus plays a role in the equilibration of charge.

DOI： 10.1051/epjconf/20100213002

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© 2010 by World Scientific Publishing Co. Pte. Ltd. All rights reserved. Algebraic nuclear models have successfully applied for various mass regions. In 12C, we couple this model space with treatment of the so-called complex scaling method for resonance states. We use the Sp(2, R), algebra to create ladder states on SU(3) bases which have large harmonic oscillation quanta. One advantage of this method is that it is possible naturally to extend to Nα: systems. The wave function is semi-microscopic and satisfies the Pauli principle (orthogonal to the Pauli forbidden states). We study basic properties of this wave function.

DOI： 10.1142/9789814313933_0036

The structure change of nuclear systems as a function of excitation energy is discussed. In the nuclear systems, protons and neutrons are considered to perform independent particle motion in low-lying states close to the ground state, however α cluster structure appears around the α-threshold energy to decay into subsystems. Until now, such cluster states have been investigated in light stable nuclei with equal numbers of protons and neutrons, and gas-like nature of α cluster structure has been well studied. In the present study, we discuss in neutron-rich nuclei how the gas-like cluster structure changes when excess neutrons are added. We show the appearance of cluster states with geometric shapes due to the &quot;glue effect&quot; of the excess neutrons.

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The generalized two-center cluster model (GTCM), which can treat various single particle configurations in general two center systems, is applied to the light neutron-rich system, 12Be= α+α+4N. We discuss the change of the neutrons' configuration around two α-cores as a variation of an excitation energy. We show that the covalent, ionic and atomic configurations appear in the unbound region above the α+ 8Heg.s. particle-decay threshold, and they coexist within a quite small energy interval. © 2009 World Scientific Publishing Company.

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Nucleon transfer is studied with focusing on the charge equilibration. The proposed classification of nucleon transfer in deep inelastic collisions at intermediate energies is verified by three-dimensional TDHF calculations. © 2009 American Institute of Physics.

DOI： 10.1063/1.3258252

The alpha+He-8 low-energy reactions and the exotic structures of Be-12 are studied using the generalized two-center cluster (alpha+alpha+4N) model. The energy-spin systematics for the two-neutron transfer reactions is investigated, and our calculation predicts a sequence of resonant structures in the range of 3 - 14 MeV in the center-of-mass energy with spins 0h - 8h.

DOI： 10.1063/1.3108806

A condition for the upper energy-limit of charge equilibration is proposed based on a Fermi gas-like treatment. The validity of this condition is confirmed by three-dimensional time-dependent Hartree-Fock calculations with a full Skyrme interaction. © 2009 American Institute of Physics.

DOI： 10.1063/1.3108840

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The generalized two-center cluster model (GTCM), which can treat static structures and dynamical reactions in excited states, is applied to the light neutron-rich system, 12Beα+α+4N. We discuss the change of the neutrons' configuration around two α-cores from the covalent structure to the ionic one. It is shown that, in the unbound region above particle-decay thresholds, the ionic configurations appear as the molecular resonances of α+8He, 6He+6He and 5He+7He. A new type of superdeformation is possible, and we find here the covalent superdeformation which has a hybrid configuration of the covalent and ionic ones. The excitation of these exotic structures through the two neutron transfer reaction is also discussed. © 2008 IOP Publishing Ltd.

DOI： 10.1088/1742-6596/111/1/012010

Nuclear systems are usually considered to be in the liquid phase, however, here we discuss the competition between the shell (liquid phase) and cluster structure in light neutron-rich nuclei. The appearance of molecular structure of α clusters with a geometric (equilateral triangular) shape is stabilized by the valence neutrons, and the nuclear systems with specific shapes are considered to be in the solid state. Also, α-condensed states originally suggested in 12C and 16O are extended to heavier nuclei with core nucleus, which are in the gas phase. © 2008 IOP Publishing Ltd.

DOI： 10.1088/1742-6596/111/1/012006

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DOI： 10.24532/soken.115.4_D4

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DOI： 10.24532/soken.115.4_D4

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DOI： 10.24532/soken.115.3_C115

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DOI： 10.1103/PhysRevC.75.054309

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Structure of Ne isotopes are investigated by a microscopic model, where thousands of Slater determinants are stochastically generated, and important ones are selected out of them. The importance of the α-cluster correlation is systematically shown, and also, the singleparticle parity of each nucleon is studied, and deviation from the pure shell-model-like picture is discussed. © 2006 IOP Publishing Ltd.

DOI： 10.1088/1742-6596/49/1/027

The competition between the cluster and shell structure of light nuclei is discussed. First, we demonstrate in 12C by superimposing many Slater determinants that the cluster structure dissolute when the shell-model-like model space is introduced. The decrease of the energy from the 3α configuration by about 6 MeV is a clue to resolve a long-standing problem of the binding energies of 12C and 16O. As a next step, we propose a simple model to include the spin-orbit interaction (SMSO). By introducing only one parameter (Γ) to the wave function, describing an asymptotic transition of 12C from a 3α configuration to a 2α+4N configuration is represented, and we show a strong contribution of the spin-orbit interaction in the ground state. Furthermore, we propose a simplified model to directly take into account the contribution of the tensor interaction (SMT) for light nuclei by extending α-cluster model. The coupling effect of SMSO and SMT is shown to be important in 12C, contrary to 8Be. © 2006 IOP Publishing Ltd.

DOI： 10.1088/1742-6596/49/1/025

To investigate structure of 21Ne, where the core has a parity asymmetric property, we superpose thousands of Slater determinants. Applying the method we can see importance of α-correlation for several low-lying states and also property of a valence neutron. The 13C nucleus is studied as parity asymmetric core with 3α. We confirm the change of spin quantization. © 2005 IOP Publishing Ltd.

DOI： 10.1088/1742-6596/20/1/044

The problem of the long life time of the pentaquark θ+ is investigated on the basis of the color molecular dynamics simulation. We find that it takes a long time (typically of 50-100 fm/c) for the initial pentaquark state to rearrange its color and spatial positions to decay into the nucleon+kaon final state. Structure of the potential surface in the color and position spaces also supports this picture. Pentaquark wanders on the potential surface to find a narrow channel to decay. © 2005 Akadémiai Kiadó, Budapest.

DOI： 10.1556/APH.22.2005.1-2.7

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We use a microscopic three-cluster model with the α + α + n configuration to analyze with astrophysical interests the photodisintegration cross section of 9Be. the valence neutron in 9Be is treated in the molecular orbit model, including continuum states by the box discretization method. It is shown that good agreement is achieved with the recently measured B(E1) transition probability from the ground state the the first 1/2+ state when the box size is enlarged, resulting in reasonable reproduction of the experimental data for the photodisintegration cross section. The Coulomb dissocitaion of 9Be is also discussed.

DOI： 10.1103/PhysRevC.66.057301

The triaxial deformation in [Formula Presented] is investigated using a microscopic [Formula Presented] model. The states of two valence neutrons are classified based on the molecular-orbit (MO) model, and the π orbit is introduced about the axis connecting the two α clusters for the description of the rotational bands. There appear two rotational bands comprised mainly of [Formula Presented] and [Formula Presented] respectively, at low excitation energy, where the two valence neutrons occupy [Formula Presented] or [Formula Presented] orbits. The triaxiality and the K mixing are discussed in connection to the molecular structure, particularly to the spin-orbit splitting. The extent of the triaxial deformation is evaluated in terms of the electromagnetic transition matrix elements (Davydov-Filippov model, Q-invariant model) and density distribution in the intrinsic frame. The obtained values turned out to be γ=15°–20°. © 2002 The American Physical Society.

DOI： 10.1103/PhysRevC.65.044302

The structure of the second 0+ state of 10Be is investigated using a microscopic α + α + n + n model based on the molecular-orbit (MO) model. The second 0+ state, which has dominantly the (1/2+)2 configuration, is shown to have a particularly enlarged α-α structure. The kinetic energy of the two valence neutrons occupying along the α-α axis is reduced remarkably due to the strong α clustering and, simultaneously, the spin-orbit interaction unexpectedly plays an important role in making the energy of this state much lower. The mixing of states with different spin structure is shown to be important in negative-parity states. The experimentally observed small-level spacing between 1- and 2- (∼300 keV) is found to be evidence of this spin-mixing effect. 12Be is also investigated using the α + α + 4n model, in which four valence neutrons are considered to occupy the (3/2-)2(1/2+)2 configuration. The energy surface of 12Be is shown to exhibit similar characteristics, that the remarkable α clustering and the contribution of the spin-orbit interaction make the binding of the state with the (3/2-)2(1/2+)2 configuration properly stronger in comparison with the closed p-shell (3/2-)2(1/2-)2 configuration.

DOI： 10.1103/PhysRevC.62.034301

The structure of 10Be is investigated using a microscopic α+α+n+n model based on the molecular orbit (MO) model. The low-lying states are characterized by several configurations of valence neutrons, which are constructed as combinations of three basic orbits. The model space employed is extended from the traditional MO models, and the orbits are expressed as linear combinations of local Gaussians. Their positions are determined variationally. Using this model, we reanalyze the structure of 9Be and show that this extension enables us to use the original two-body spin-orbit interaction determined from a scattering phase-shift analysis of α-n. In 10Be, all of the observed positive-parity bands and the negative-parity bands are described within the model. The 0+ ground state of 10Be is described by a dominant (3/2-)2 configuration. The state has a rather large binding energy (8.38 MeV from the α+α+n+n threshold experimentally), and the mechanism leading to binding, such as a pairing effect and reduction of the kinetic energy between two clusters, is discussed in detail. In spite of this large binding, the α-α clustering in the ground state persists due to a coupling effect between the 6He+α configuration and the 5He+5He configuration, which provides a smooth potential for the valence neutrons. The second 0+ state of 10Be has a large α-α structure with a (1/2+)2 configuration. An enlargement of the α-α distance due to two-valence neutrons along the α-α axis makes their wave function smooth and reduces the kinetic energy drastically. Furthermore, the contribution of the spin-orbit interaction due to coupling between the Sz=0 and the Sz=1 configurations is important. We also show the mediation effect of two valence neutrons between two α clusters.

DOI： 10.1103/PhysRevC.61.044306

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By using the complex scaling method, the 10C+p resonance parameters are determined in order to investigate the spectroscopic property of the proton-rich nucleus 11N in comparison with the mirror nucleus 11Be which has a typical neutron halo structure. The obtained resonance energy (Er) and width (Γ) of 11N are (Er, Γ)=(1.29 MeV, 1.39 MeV) and (2.12 MeV, 0.95 MeV) for s1/2 and p1/2 states, respectively. These results are in good agreement with the recent experimental data reported by Axelsson et al. Thomas-Ehrman effect on the 1/2- and 1/2+ resonance states in 11N is discussed in association with the weakly bound states in 11Be.

DOI： 10.1103/PhysRevC.57.975

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この論文は国立情報学研究所の電子図書館事業により電子化されました。

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Publishing type：Internal/External technical report, pre-print, etc.  

We study 4$\alpha$ linear-chain states in 16O in comparison with 3$\alpha$
states in 12C by using the Generator Coordinate Method within a microscopic
$N\alpha$-cluster model. It is shown to be very important to solve relative
motion of $\alpha$-clusters by taking into account the orthogonality between
the linear-chain states and other low-lying states including the ground state.
For 12C, the 3$\alpha$ chain state disappears because of this orthogonality.
The $4\alpha$ chain state in 16O, on the other hand, is hardly affected by
low-lying states and persists to remain above the 4$\alpha$ threshold. The
calculated moment of inertia of the $4\alpha$ linear-chain rotational band (88
keV) reproduces the experimentally suggested value qualitatively.

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DOI： 10.24532/soken.92.2_B68

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Presentation type：Oral presentation (invited, special)