arXiv subjects

Hisashi Horiuchi

Publications and source records attributed to Hisashi Horiuchi.

At least 55 records · Page 3Linked to original sources

arXiv2014

Investigation of ${}^9$Be from nonlocalized clustering concept

The nonlocalized aspect of clustering, which is a new concept for self-conjugate nuclei, is extended for the investigation of the N{\not=}Z nucleus ${}^9$Be. A modified version of the THSR (Tohsaki-Horiuchi-Schuck-Röpke) wave function is introduced based on the container picture. It is found that the constructed negative-parity THSR wave function is very suitable for describing the cluster states of ${}^9$Be. Namely the nonlocalized clustering is shown to prevail in ${}^9$Be. The calculated binding energy and radius of ${}^9$Be are consistent with calculations in other models and with experimental values. The squared overlaps between the THSR wave function and the Brink+GCM wave function for the $3/2^-$ rotational band of ${}^9$Be are found to be near 96%. Furthermore, by showing the density distribution of the ground state of ${}^9$Be, the π-orbit structure is naturally reproduced by using this THSR wave function.

nucl-th↗

arXiv2014

The container picture with two-alpha correlation for the ground state of $^{12}$C

It is shown that the single $0^+$ THSR (Tohsaki-Horiuchi-Schuck-Röpke) wave function which is extended to include 2$α$ correlation is almost completely equivalent to the 3$α$ wave function obtained as the full solution of 3$α$ cluster model. Their squared overlap is as high as 98\% while it is 93\% if the 2$α$ correlation is not included. This result implies that, by incorporating the 2$α$ correlation in the 3$α$ model, the ground state of $^{12}$C is describable in the container picture which is valid for the Hoyle state for which the 2$α$ correlation is weak and a single $0^+$ THSR wave function without 2$α$ correlation is almost completely equivalent to the full solution of 3$α$ cluster model.

nucl-th↗

arXiv2013

Nonlocalized cluster dynamics and nuclear molecular structure

A container picture is proposed for understanding cluster dynamics where the clusters make nonlocalized motion occupying the lowest orbit of the cluster mean-field potential characterized by the size parameter $``B"$ in the THSR (Tohsaki-Horiuchi-Schuck-Röpke) wave function. The nonlocalized cluster aspects of the inversion-doublet bands in $^{20}$Ne which have been considered as a typical manifestation of localized clustering are discussed. So far unexplained puzzling features of the THSR wave function, namely that after angular-momentum projection for two cluster systems the prolate THSR wave function is almost 100$\%$ equivalent to an oblate THSR wave function is clarified. It is shown that the true intrinsic two-cluster THSR configuration is nonetheless prolate. The proposal of the container picture is based on the fact that typical cluster systems, 2$α$, 3$α$, and $α$+$^{16}$O, are all well described by a single THSR wave function. It will be shown for the case of linear-chain states with two and three $α$-clusters as well as for the $α$+$^{16}$O system that localization is entirely of kinematical origin, that is, due to the inter-cluster Pauli repulsion. It is concluded that this feature is general for nuclear cluster states.

nucl-th↗

arXiv2010

Triaxial superdeformation in $^{40}$Ar

Superdeformed (SD) states in $^{40}$Ar have been studied using the deformed-basis antisymmetrized molecular dynamics. Low energy states were calculated by the parity and angular momentum projection (AMP) and the generator coordinate method (GCM). Basis wave functions were obtained by the energy variation with a constraint on the quadrupole deformation parameter $β$, while other quantities such as triaxiality $γ$ were optimized by the energy variation. By the GCM calculation, an SD band was obtained just above the ground state (GS) band. The SD band involves a $K^π= 2^+$ side band due to the triaxiality. The calculated electric quadrupole transition strengths of the SD band reproduce the experimental values appropriately. Triaxiality is significant for understanding low-lying states.

nucl-th↗

arXiv2009

Internal One-Particle Density Matrix for Bose-Einstein Condensates with Finite Number of Particles in a Harmonic Potential

Investigations on the internal one-particle density matrix in the case of Bose-Einstein condensates with a finite number ($N$) of particles in a harmonic potential are performed. We solve the eigenvalue problem of the Pethick-Pitaevskii-type internal density matrix and find a fragmented condensate. On the contrary the condensate Jacobi-type internal density matrix gives complete condensation into a single state. The internal one-particle density matrix is, therefore, shown to be different in general for different choices of the internal coordinate system. We propose two physically motivated criteria for the choice of the adequate coordinate systems which give us a unique answer for the internal one-particle density matrix. One criterion is that in the infinite particle number limit ($N=\infty$) the internal one-particle density matrix should have the same eigenvalues and eigenfunctions as those of the corresponding ideal Bose-Einstein condensate in the laboratory frame. The other criterion is that the coordinate of the internal one-particle density matrix should be orthogonal to the remaining $(N - 2)$ internal coordinates. This second criterion is shown to imply the first criterion. It is shown that the internal Jacobi coordinate system satisfies these two criteria while the internal coordinate system adopted by Pethick and Pitaevskii for the construction of the internal one-particle density matrix does not. It is demonstrated that these two criteria uniquely determine the internal one-particle density matrix which is identical to that calculated with the Jacobi coordinates. The relevance of this work concerning $α$-particle condensates in nuclei, as well as bosonic atoms in traps, is pointed out.

nucl-th↗

arXiv2008

Monopole Excitation to Cluster States

We discuss strength of monopole excitation of the ground state to cluster states in light nuclei. We clarify that the monopole excitation to cluster states is in general strong as to be comparable with the single particle strength and shares an appreciable portion of the sum rule value in spite of large difference of the structure between the cluster state and the shell-model-like ground state. We argue that the essential reasons of the large strength are twofold. One is the fact that the clustering degree of freedom is possessed even by simple shell model wave functions. The detailed feature of this fact is described by the so-called Bayman-Bohr theorem which tells us that SU(3) shell model wave function is equivalent to cluster model wave function. The other is the ground state correlation induced by the activation of the cluster degrees of freedom described by the Bayman-Bohr theorem. We demonstrate, by deriving analytical expressions of monopole matrix elements, that the order of magnitude of the monopole strength is governed by the first reason, while the second reason plays a sufficient role in reproducing the data up to the factor of magnitude of the monopole strength. Our explanation is made by analysing three examples which are the monopole excitations to the $0^+_2$ and $0^+_3$ states in $^{16}$O and the one to the $0^+_2$ state in $^{12}$C. The present results imply that the measurement of strong monopole transitions or excitations is in general very useful for the study of cluster states.

nucl-th↗

arXiv2007

Clustering and Triaxial Deformations of $^{40}$Ca

We have studied the positive-parity states of $^{40}$Ca using antisymmetrized molecular dynamics (AMD) and the generator coordinate method (GCM). Imposing two different kinds of constraints on the variational calculation, we have found various kinds of $^{40}{\rm Ca}$ structures such as a deformed-shell structure, as well as $α$-$^{36}$Ar and $^{12}$C-$^{28}$Si cluster structures. After the GCM calculation, we obtained a normal-deformed band and a superdeformed band together with their side bands associated with triaxial deformation. The calculated $B(E2)$ values agreed well with empirical data. It was also found that the normal-deformed and superdeformed bands have a non-negligible $α$-$^{36}$Ar cluster component and $^{12}$C-$^{28}$Si cluster component, respectively. This leads to the presence of an $α$-$^{36}$Ar higher-nodal band occurring above the normal-deformed band.

nucl-th↗

arXiv2005

Explicit treatment of tensor force with a method of Antisymmetrized Molecular Dynamics

In order to treat tensor force explicitly, we propose a microscopic model for nuclear structure based on antisymmetrized molecular dynamics (AMD). As a result of the present study, it is found that some extentions of the AMD method are effective to incorporate the tensor correlation into wave functions. Calculating the deuteron, triton and $^4$He with the extended version of AMD, we obtained solutions that have large contribution of the tensor force. By analyzing the wave funtion of $^4$He, it is found that its single-particle orbits are composed of normal-size $0s$ orbits and shrunk $p$ orbits so as to gain the tensor force.

nucl-th↗

arXiv2004

New Constraint of Clustering for AMD and Its Application to the Study of $2α$-$^{12}$C Structure of $^{20}$Ne

A new constraint of clustering for the AMD calculation is proposed. This new constraint gives us large improvement in studying the cluster structure by AMD which sometimes meets difficulty in giving rise to some specific cluster configurations. The usefulness of this new constraint is verified by applying it to the the study of the third $K^π= 0^+$ band of $^{20}$Ne which has been discussed to have $2α$-$^{12}$C structure. This band has not been easy even to construct by AMD. We see that the AMD+GCM calculation by the use of the new constraint gives rise to the third $K^π= 0^+$ band which contains the $2α$-$^{12}$C structure as an important component.

nucl-th↗

arXiv2004

Coexistence of cluster structure and superdeformation in $^{44}$Ti studied with deformed-basis antisymmetrized molecular dynamics

The nucleus $^{44}$Ti has low-lying levels of various kinds of mutually very different nuclear structure displaying the richness of the nuclear many-body dynamics. It is shown that the deformed-basis antisymmetrized molecular dynamics by the use of the Gogny D1S force reproduces successfully and unifiedly two types of coexistence phenomena in $^{44}$Ti. Namely, on one hand, the coexistence of the mean field structure and the cluster structure is confirmed by verifying the normally deformed structure of the $K^π$=$3^-_1$ band with a 1-particle-jump intrinsic configuration and the $α+ ^{40}$Ca cluster structure of the $K^π$=$0^-_2$ band. The mixed character of the mean-field-like structure and the $α+ ^{40}$Ca cluster structure of the ground band is also shown. On the other hand, the coexistence of the normal deformed mean field and the superdeformed mean field is confirmed by verifying the triaxial superdeformation of the $K^π$=$0_2^+$ band and the $K^π$=$2^+_1$ band which has a 4-particle-jump intrinsic configuration. Good reproduction of the experimental data is shown for many kinds of quantities including the energy spectra, electric transition rates, alpha spectroscopic factors. Preliminary discussions are given on the existence of hyperdeformed excited states, the relation between superdeformation and clustering and so on.

nucl-th↗

arXiv2004

Many-Particle and Many-Hole States in Neutron-Rich Ne Isotopes Related to Broken N=20 Shell Closure

The low-lying level structures of $^{26}{\rm Ne}$, $^{28}{\rm Ne}$ and $^{30}{\rm Ne}$ which are related to the breaking of the N=20 shell closure have been studied by the framework of the deformed-basis antisymmetrized molecular dynamics plus generator coordinate method using Gogny D1S force. The properties of the many-particle and many-hole states are discussed as well as that of the ground band. We predict that the negative-parity states in which neutrons are promoted into $pf$-orbit from $sd$ orbit have the small excitation energy in the cases of $^{28}{\rm Ne}$ and $^{30}{\rm Ne}$ which, we regard, is a typical phenomena accompanying the breaking of N=20 shell closure. It is also found that the neutron $4p4h$ structure of $^{30}{\rm Ne}$ appears in low excitation energy which contains $α+ ^{16}{\rm O}$ correlations.

nucl-th↗

arXiv2003

Kaonic nuclei studied based on a new framework of Antisymmetric Molecular Dynamics

We have developed a new framework of Antisymmetrized Molecular Dynamics (AMD), to adequately treat the I=0 KN interaction, which is essential to study kaonic nuclei. The improved points are 1) pK$^-$/nK$^0$ mixing and 2) total spin and isospin projections. These improvements enable us to investigate various kaonic nuclei (ppnK$^-$, pppK$^-$, pppnK$^-$, $^6$BeK$^-$ and $^9$BK$^-$) systematically. We have found that they are deeply bound and extremely dense with a variety of shapes.

nucl-th↗

arXiv2003

Cluster Structures of the Ground and Excited States of 12Be Studied with Antisymmetrized Molecular Dynamics

The structures of the ground and excited states of 12Be were studied with antisymmetrized molecular dynamics. The ground state was found to be a state with a developed 2-alpha core with two neutrons occupying the intruder orbits. The energy levels of the newly measured spin-assigned states were described well, except for the $1^-_1$ state. The calculations indicated that many exotic cluster structures appear in the low-energy region. The widths concerning alpha and 6He decays were discussed by using reduced width amplitudes.

nucl-th↗

arXiv2002

Description of 8Be as Deformed Gas-like Two-Alpha-Paricle States

In order to study non-zero spin excitations of the recently proposed alpha-cluster condensation in the self-conjugate 4n nuclei, spatial deformation is introduced into the model wave function of the alpha-cluster condensate. The rotational band states of 8Be are investigated as a first step of a test case for the study of the deformation of the alpha-cluster condensate. Calculations reproduce well the binding energy of the 0+ ground state and also the excitation energy of the 2+ state. Our 0+ wave function is found to be almost exactly equal to the 0+ wave function obtained by the generator coordinate method using Brink's 2 alpha wave function. The study shows that both the 0+ ground and 2+ excited states can be considered as having a gas-like (i.e. weakly bound) 2 alpha-cluster structure. As for the 0+ ground state, the change of the wave function, due to the introduction of the deformation, is found to be very small.

nucl-th↗

arXiv1996

Antisymmetrized molecular dynamics of wave packets with stochastic incorporation of Vlasov equation

On the basis of the antisymmetrized molecular dynamics (AMD) of wave packets for the quantum system, a novel model (called AMD-V) is constructed by the stochastic incorporation of the diffusion and the deformation of wave packets which is calculated by Vlasov equation without any restriction on the one-body distribution. In other words, the stochastic branching process in molecular dynamics is formulated so that the instantaneous time evolution of the averaged one-body distribution is essentially equivalent to the solution of Vlasov equation. Furthermore, as usual molecular dynamics, AMD-V keeps the many-body correlation and can naturally describe the fluctuation among many channels of the reaction. It is demonstrated that the newly introduced process of AMD-V has drastic effects in heavy ion collisions of 40Ca + 40Ca at 35 MeV/nucleon, especially on the fragmentation mechanism, and AMD-V reproduces the fragmentation data very well. Discussions are given on the interrelation among the frameworks of AMD, AMD-V and other microscopic models developed for the nuclear dynamics.

nucl-th↗

arXiv1995

Statistical properties of antisymmetrized molecular dynamics for non-nucleon-emission and nucleon-emission processes

Statistical properties of the antisymmetrized molecular dynamics (AMD) are classical in the case of nucleon emission processes, while they are quantum mechanical for the processes without nucleon emission. We first clarify that there coexist mutually opposite two statistics in the AMD framework: One is the classical statistics of the motion of wave packet centroids and the other is the quantum statistics of the motion of wave packets which is described by the AMD wave function. We prove the classical statistics of wave packet centroids by using the framework of the microcanonical ensemble of the nuclear system. We show that the quantum statistics of wave packets emerges from the classical statistics of wave packet centroids. It is emphasized that the temperature of the classical statistics of wave packet centroids is different from the temperature of the quantum statistics of wave packets. We then explain that the statistical properties of AMD for nucleon emission processes are classical because nucleon emission processes in AMD are described by the motion of wave packet centroids. When we improve the description of the nucleon emission process so as to take into account the momentum fluctuation due to the wave packet spread, the AMD statistical properties for nucleon emission processes change drastically into quantum statistics. Our study of nucleon emission processes can be conversely regarded as giving another kind of proof of the fact that the statistics of wave packets is quantum mechanical while that of wave packet centroids is classical.

nucl-th↗

arXiv1995

Improvement of the nucleon emission process and the statistical property in molecular dynamics

We propose to introduce a new stochastic process in molecular dynamics in order to improve the description of the nucleon emission process from a hot nucleus. We give momentum fluctuations originating from the momentum width of the nucleon wave packet to the nucleon stochastically when it is being emitted from the nucleus. We show by calculating the liquid gas phase equilibrium in the case of antisymmetrized molecular dynamics, that with this improvement, we can recover the quantum mechanical statistical property of the nucleus for the particle emission process.

nucl-th↗

arXiv1995

Delta degrees of freedom in antisymmetrized molecular dynamics and (p,p') reactions in the delta region

Delta degrees of freedom are introduced into antisymmetrized molecular dynamics (AMD). This is done by increasing the number of basic states in the AMD wave function, introducing a Skyrme-type delta-nucleon potential, and including $NN\leftrightarrow NΔ$ reactions in the collision description. As a test of the delta dynamics, the extended AMD is applied to (p,p$'$) recations at $E_{\rm lab}=800$ MeV for a $^{12}$C target. It is found that the ratio and the absolute values for delta peak and quasielastic peak (QEP) in the $^{12}$C(p,p$'$) reaction are reproduced for angles $Θ_{\rm lab} \agt 40^\circ$, pointing to a correct treatment of the delta dynamics in the extended AMD. For forward angles the QEP is overestimated. The results of the AMD calculations are compared to one-step Monte Carlo (OSMC) calculations and a detailed analysis of multi-step and delta potential effects is given. As important side results we present a way to apply a Gallilei invariant theory for (N,N$'$) reactions up to $E_{\rm lab} \approx 800$ MeV which ensures approximate Lorentz invariance and we discuss how to fix the width parameter $ν$ of the single particle momentum distribution for outgoing nucleons in the AMD calculation.

nucl-th↗