arXiv subjects

Tsunenori Inakura

Publications and source records attributed to Tsunenori Inakura.

At least 19 recordsLinked to original sources

arXiv2025

Exploring highly-deformed ground states involving the second intruder orbit in Z>50 even-even nuclei

We present a systematic survey of even-even nuclei with $Z>50$ to identify where a very large prolate configuration driven by the second intruder orbit emerges. Within the energy density functional theory framework, we find in representative cases a pronounced prolate minimum at quadrupole deformation $β_2\approx$ 0.3--0.4. A characteristic feature of these minima is a local enhancement of the hexadecapole ($β_4$) component relative to nearby deformations, which is a clear fingerprint of the $β_2$--$β_4$ coupling expected for the second intruder orbit. Representative comparisons among three Skyrme interactions show a similar appearance of the highly deformed minimum and a local enhancement of $β_4$ at the prolate minimum, indicating qualitative robustness with respect to the interaction. The resulting maps highlight specific heavy nuclei where highly deformed ground states are anticipated.

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arXiv2022

Effects of triaxiality and pairing interaction on fission barriers of actinide nuclei studied by density-dependence relativistic mean-field theory

We employ density-dependent relativistic mean-field theory to study how the triaxiality and pairing interaction affect the inner fission barriers of actinide nuclei. It was found that triaxiality reduced the inner fission barriers and improved agreement with experimental values for many actinides. However, about 1-2 MeV discrepancy to the experimental values still remained for some of the considered nuclei. Such a discrepancy could be made further smaller by increasing the BCS pairing strength parameter. In this work, we demonstrated that adjusting the paring strength was effective to reproduce the experimental inner fission barriers as well as "pairing rotational energy" and binding energy in a consistent manner for nuclei where the effect of the triaxiality on the inner fission barriers was significant.

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arXiv2022

Uncertainty evaluation of peak energy of giant dipole resonance propagated from uncertainties of Skyrme parameters

We evaluate uncertainty of peak energy of giant dipole resonance (GDR), propagated from uncertainty of parameters of Skyrme interaction. The Monte Carlo calculation of the random phase approximation using randomized Skyrme parameters is performed. Under the condition that the correlations between each of the Skyrme parameters is considered, the GDR peak energy has the uncertainty of $\sim$ 1 MeV irrespective of nuclear mass and is strongly correlated with the Skyrme parameters, in present calculations. This serves a guide for a new parametrization of effective interactions.

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arXiv2021

Pairing strength in the relativistic mean-field theory determined from fission barrier heights of actinide nuclei and verified by pairing rotation and binding energies

We have studied strength in the BCS pairing force, used as a residual interaction to the relativistic mean-field to reproduce the height of the inner fission barriers for actinide nuclei. It was found that increasing the pairing strength by about 13% makes reproduce the inner fission barriers better over a wide range of actinide nuclei. This result was verified by using the moment-of-inertia of pairing rotational energy, which was introduced to avoid mean-field and odd-mass effects in the pairing interaction to deduce purely the pairing strength. The pairing interaction thus determined could simultaneously improve the description of the binding energy of heavy nuclei as well. As a result, a consistent picture among inner fission barrier, binding energy, and pairing moment of inertia could be obtained in terms of the relativistic mean-field + BCS theory for a broad region of the actinide nuclei.

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arXiv2021

Deformation effect on nuclear density profile and radius enhancement in light- and medium-mass neutron-rich nuclei

Mass number dependence of the nuclear radii is closely related to the nuclear matter properties. It is known that the most of nuclei exhibit some deformation. We discuss how the nuclear density profile is modified by the nuclear deformation to elucidate the enhancement mechanism of the nuclear radii through a systematic investigation of neutron-rich Ne, Mg, Si, S, Ar, Ti, Cr, and Fe isotopes. Skyrme-Hartree-Fock calculations are performed in a three-dimensional Cartesian grid to describe the nuclear deformation in a non-empirical way. The role of the nuclear deformation on the nuclear density profiles is explored in comparison to calculations with spherical limit. We find correlations between the nuclear deformation and the internal nuclear density. The evolution of the nuclear radii appears to follow the core swelling mechanism recently proposed in spherical nuclei [Phys. Rev. C 101, 061301(R) (2020)], and the radius is further enhanced by the nuclear deformation. This study demands further theoretical and experimental investigations for the internal density.

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arXiv2017

Anderson-Bogoliubov phonon in inner crust of neutron stars: Dipole excitation in spherical Wigner-Seitz cell

Background: The Anderson-Bogoliubov (AB) phonon, called also the superfluid phonon, has attracted attentions since it may influence the thermal conductivity and other properties of inner crust of neutron stars. However, there are limited number of microscopic studies of the AB phonon where the presence of clusters is explicitly taken into account.\\ Purpose: We intend to clarify how the presence of clusters affects the AB phonon in order to obtain microscopic information relevant to the coupling between the AB phonon and the lattice phonon. \\ Methods: The Hartree-Fock-Bogoliubov model and the quasiparticle random-phase approximation formulated in a spherical Wigner-Seitz cell are adopted to describe neutron superfluidity and associated collective excitations. We perform systematic numerical calculations for dipole excitation by varying the neutron chemical potential and the number of protons in a cell. \\ Results:The model predicts systematic emergence of the dipole AB phonon mode, which however exhibits strong suppression of phonon amplitude inside the cluster. We find also that the phonon amplitude around the cluster surface varies as the neutron density. At higher neutron densities the AB phonon mode exhibits behaviour similar to the pygmy dipole resonance in neutron-rich nuclei.\\ Conclusions: The dipole AB phonon mode does not penetrate into the clusters. This suggests that the coupling between the AB phonon and the lattice phonon may be weak.

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arXiv2014

Systematic investigation of low-lying dipole modes using the canonical-basis time-dependent Hartree-Fock-Bogoliubov theory

Systematic investigations of the electric dipole (E1) modes of excitation are performed using the canonical-basis time-dependent Hartree-Fock-Bogoliubov (Cb-TDHFB) theory. The Cb-TDHFB is able to describe dynamical pairing correlations in excited states of nuclear systems. We apply the method to the real-time calculation of linear response in even-even nuclei with Skyrme functionals. Effects of shell structure, neutron skin, deformation, and neutron chemical potential (separation energy) are studied in a systematic way. This reveals a number of characteristic features of the low-energy E1 modes. We also find a universal behavior in the low-energy E1 modes for heavy neutron-rich isotopes, which suggests the emergence of decoupled E1 peaks beyond N = 82.

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arXiv2014

Mean-field analysis of ground state and low-lying electric dipole strength in $^{22}$C

Properties of neutron-rich $^{22}$C are studied using the mean-field approach with Skyrme energy density functionals. Its weak binding and large total reaction cross section, which are suggested by recent experiments, are simulated by modifying the central part of Skyrme potential. Calculating $E1$ strength distribution by using the random-phase approximation, we investigate developments of low-lying electric dipole ($E1$) strength and a contribution of core excitations of $^{20}$C. As the neutron Fermi level approaches the zero energy threshold ($\varepsilon_F >\sim -1$ MeV), we find that the low-lying $E1$ strength exceeds the energy-weighted cluster sum rule, which indicates an importance of the core excitations with the $1d_{5/2}$ orbit.

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arXiv2013

Low-energy E1 strength in select nuclei: Possible constraints on the neutron skins and the symmetry energy

Correlations between low-lying electric dipole (E1) strength and neutron skin thickness are systematically investigated with the fully self-consistent random-phase approximation using the Skyrme energy functionals. The presence of strong correlation among these quantities is currently under dispute. We find that the strong correlation is present in properly selected nuclei, namely in spherical neutron-rich nuclei in the region where the neutron Fermi levels are located at orbits with low orbital angular momenta. The significant correlation between the fraction of the energy-weighted sum value and the slope of the symmetry energy is also observed. The deformation in the ground state seems to weaken the correlation.

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arXiv2013

Time-dependent density-functional studies on strength functions in neutron-rich nuclei

The electric dipole (E1) strength functions have been systematically calculated based on the time-dependent density functional theory (TDDFT), using the finite amplitude method and the real-time approach to the TDDFT with pairing correlations. The low-energy E1 strengths in neutron-rich isotopes show peculiar behaviors, such as sudden enhancement and reduction, as functions of the neutron numbers.They seem to be due to the interplay between the neutron shell effect and the deformation effect.

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arXiv2013

Systematic investigation of E1 strength for the isotopes from Z = 28 to 50

We carry out a systematic study of electric dipole mode (E1) for neutron-rich isotopes from nickel (Z=28) to tin (Z=50) using a time-dependent mean-field theory. Our time-dependent scheme is the canonical-basis time-dependent Hartree-Fock-Bogoliubov theory which can self-consistently describe nuclear dynamics with pairing correlation. We focus our discussion on the pygmy dipole resonance (PDR) and E1 polarizability. The correlation between neutron-skin thickness and PDR strongly depends on the neutron number, but the correlation between the skin thickness and E1 polarizability is much more stable.

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arXiv2012

Linear-response calculation in the time-dependent density functional theory

Linear response calculations based on the time-dependent density-functional theory are presented. Especially, we report results of the finite amplitude method which we have recently proposed as an alternative and feasible approach to the (quasiparticle-)random-phase approximation. Calculated properties of the giant resonances and low-energy E1 modes are discussed. We found a universal linear correlation between the low-energy E1 strength and the neutron skin thickness.

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arXiv2012

Systematic study of low-lying E1 strength using the time-dependent mean field theory

We carry out systematic investigation of electric dipole (E1) mode from light to heavy nuclei, using a new time-dependent mean field theory: the Canonical-basis Time-Dependent Hartree-Fock-Bogoliubov (Cb-TDHFB) theory. The Cb-TDHFB in the three-dimensional coordinate space representation can deal with pairing correlation and any kind of deformation in the time-dependent framework. We report the neutron-number dependence of the low-energy E1 mode for light (A < 40) and heavy isotopes (A > 100) around N = 82.

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arXiv2011

Study of pygmy dipole resonance with a new time-dependent mean field theory

We carry out a systematic investigation on the low-energy electric dipole strength, which is often called pygmy dipole resonances (PDR), using the canonical-basis time-dependent Hartree-Fock-Bogoliubov (Cb-TDHFB) method. The Cb-TDHFB is a new method which is derived from TDHFB with an approximation analogous to the BCS theory that the pair potential is assumed to be diagonal in the time-dependent canonical basis. We apply the method to linear-response calculation for even-even nuclei. We report the neutron-number dependence of PDR in light (A < 70) and heavy isotopes (A > 100) around N = 82.

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arXiv2011

Emergence of pygmy dipole resonances: Magic numbers and neutron skins

The pygmy dipole resonances (PDR) for even-even nuclei in 8=<Z=<40 are studied performing a systematic calculation of the random-phase approximation with the Skyrme functional of SkM*. The calculation is fully self-consistent and does not assume any symmetry in the nuclear shape of the ground state. In every isotopic chain, the PDR emerges by showing a peak of the E1 strength at energies less than 10 MeV. The E1 strength of the PDR strongly depends on the position of the Fermi level and shows a clear correlation with the occupation of the orbits with the orbital angular momenta less than 3\hbar (l =< 2). We also found a strong correlation between the isotopic dependence of the neutron skin thickness and the pygmy dipole strength. The fraction of the energy weighted strength exhausted by the PDR and the neutron skin thickness show a linear correlation with the universal rate of about 0.2/fm.

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arXiv2011

Self-consistent description of nuclear photoabsorption cross sections

Several approaches to photonuclear reactions, based on the time-dependent density-functional theory, have been developed recently. The standard linearization leads to the random-phase approximation (RPA) or the quasiparticle-random-phase approximation (QRPA). We have developed a parallelized QRPA computer program for axially deformed nuclei. We also present a feasible approach to the (Q)RPA calculation, that is the finite amplitude method (FAM). We show results of photoabsorption cross sections for deformed nuclei using the QRPA and FAM calculations. Finally, the canonical-basis approach to the time-dependent Hartree-Fock-Bogoliubov method is presented, to demonstrate its feasibility and usefulness.

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arXiv2010

Canonical-basis time-dependent Hartree-Fock-Bogoliubov theory and linear-response calculations

We present simple equations for a canonical-basis formulation of the time-dependent Hartree-Fock-Bogoliubov (TDHFB) theory. The equations are obtained from the TDHFB theory with an approximation that the pair potential is assumed to be diagonal in the canonical basis. The canonical-basis formulation significantly reduces the computational cost. We apply the method to linear-response calculations for even-even light nuclei and demonstrate its capability and accuracy by comparing our results with recent calculations of the quasi-particle random-phase approximation with Skyrme functionals. We show systematic studies of E1 strength distributions for Ne and Mg isotopes. The evolution of the low-lying pygmy strength seems to be determined by the interplay of several factors, including the neutron excess, separation energy, neutron shell effects, deformation, and pairing.

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arXiv2009

Self-consistent calculation of nuclear photoabsorption cross section: Finite amplitude method with Skyrme functionals in the three-dimensional real space

The finite amplitude method (FAM), which we have recently proposed (T. Nakatsukasa, T. Inakura, and K. Yabana, Phys. Rev. C 76, 024318 (2007)), simplifies significantly the fully self-consistent RPA calculation. Employing the FAM, we are conducting systematic, fully self-consistent response calculations for a wide mass region. This paper is intended to present a computational scheme to be used in the systematic investigation and to show the performance of the FAM for a realistic Skyrme energy functional. We implemented the method in the mixed representation in which the forward and backward RPA amplitudes are represented by indices of single-particle orbitals for occupied states and the spatial grid points for unoccupied states. We solve the linear response equation for a given frequency. The equation is a linear algebraic problem with a sparse non-hermitian matrix, which is solved with an iterative method. We show results of the dipole response for selected spherical and deformed nuclei. The peak energies of the giant dipole resonance agree well with measurements for heavy nuclei, while they are systematically underestimated for light nuclei. We also discuss the width of the giant dipole resonance in the fully self-consistent RPA calculation.

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