Toshio Suzuki

Nihon University, Edo, Tōkyō, Japan

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Publications (137)351.57 Total impact

  • Toshio Suzuki · Takaharu Otsuka · Cenxi Yuan · Navin Alahari
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    ABSTRACT: The formation of two-neutron “halo”, a low-density far-extended surface of weakly-bound two neutrons, is described using the neutron–neutron (nn) interaction fixed at the low-energy nn scattering limit. This method is tested for loosely-bound two neutrons in 24O, where a good agreement with experimental data is found. It is applied to halo neutrons in 22C in two ways: with the 20C core being closed or correlated (due to excitations from the closed core). This nn interaction is shown to be strong enough to produce a two-neutron halo in both cases, locating 22C on the drip line, while 21C remains unbound. A unique relation between the two neutron separation energy, S2n, and the radius of neutron halo is presented. New predictions for S2n and the radius of neutron halo are given for 22C. The appearance of Efimov states is also discussed.
    No preview · Article · Dec 2015 · Physics Letters B
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    Toshio Suzuki · Hiroshi Toki · Ken'ichi Nomoto
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    ABSTRACT: Electron capture and beta-decay rates for nuclear pairs in sd-shell are evaluated at high densities and high temperatures relevant to the final evolution of electron-degenerate O-Ne-Mg cores of stars with the initial masses of 8-10 solar mass. Electron capture induces a rapid contraction of the electron-degenerate O-Ne-Mg core. The outcome of rapid contraction depends on the evolutionary changes in the central density and temperature, which are determined by the competing processes of contraction, cooling, and heating. The fate of the stars are determined by these competitions, whether they end up with electron-capture supernovae or Fe core-collapse supernovae. Since the competing processes are induced by electron capture and beta-decay, the accurate weak rates are crucially important. The rates are obtained for pairs with A=20, 23, 24, 25 and 27 by shell-model calculations in sd-shell with the USDB Hamiltonian. Effects of Coulomb corrections on the rates are evaluated. The rates for pairs with A=23 and 25 are important for nuclear URCA processes that determine the cooling rate of O-Ne-Mg core, while those for pairs with A=20 and 24 are important for the core-contraction and heat generation rates in the core. We provide these nuclear rates at stellar environments in tables with fine enough meshes at various densities and temperatures for the studies of astrophysical processes sensitive to the rates. In particular, the accurate rate tables are crucially important for the final fates of not only O-Ne-Mg cores but also a wider range of stars such as C-O cores of lower mass stars.
    Full-text · Article · Nov 2015 · The Astrophysical Journal
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    ABSTRACT: The roles of nuclear weak processes in stars are discussed. Neutrino-nucleus reactions on 12C, 56Fe and 40Ar are studied with new shell-model Hamiltonians. New cross sections, which give good account of experimental data, are applied to nucleosynthesis of light elements in supernova explosions. Effects of ν-oscillations are investigated, and the abundance ratio of 7Li/11B is pointed out to be sensitive to the ν mass hierarchy. Then, e-capture and β-decay rates in sd-shell nuclei are evaluated at stellar environments, and applied to study cooling of O-Ne-Mg core stars by nuclear URCA processes. The fate of 8-10 M❿ stars is sensitive to the cooling of the core. Finally, β-decay half-lives of r-process waiting-point nuclei with N=126 are evaluated by shell-model calculations taking into account both the Gamow-Teller and first-forbidden transitions. The half-lives obtained are short compared with standard FRDM values.
    No preview · Article · Oct 2015
  • Toshio Suzuki
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    ABSTRACT: New shell-model Hamiltonians which can successfuly describe spin-dependent transition rates in nuclei are applied to study nuclear weak processes in stars. New v-induced reaction cross sections in 12C and 56Fe evaluated by the new Hamiltonians are shown to reproduce well the experimental data. Nucleosynthesis of light elements in supernova explosions (SNe) as well as v oscillation effects are discussed with the new cross sections. Electron capture and β-decay rates in stellar environments are re-evaluated in fp- and sd-shell nuclei. Nucleosynthesis in Type-Ia SNe, rp-process and X-ray burst are discussed with the new reaction rates in Ni isotopes. Important roles of accurate e-capture and β-decay rates in sd-shell nuclei on the cooling of stars with 8-10 solar masses by nuclear URCA processes and the fate of the stars are demonstrated. β-decay half-lives of waiting-point nuclei at N =126 are evaluated by shell- model calculations, and r-process nucleosynthesis up to Th and U region in both core-collapse SNe and binary neutron star mergers are studied.
    No preview · Article · Apr 2015 · Journal of Physics Conference Series
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    ABSTRACT: Spin-dependent modes in nuclei are studied by shell-model method with the use of new shell-model Hamiltonians which properly take into account important roles of tensor interactions. New Hamiltonians can describe spin degrees of freedom in nuclei remarkably well. Nuclear weak processes at stellar environments are investigated based on these successes. New neutrino-nucleus reaction cross sections on 12C are applied to light-element synthesis in supernova explosions. The production rate for 11B/7Li is pointed out to be useful to determine v-oscillation parameters, in particular, v-mass hierarchy. New e-capture rates in Ni isotopes are obtained and implications for element synthesis are discussed. The monopole-based universal interaction is applied to study structure of p-sd shell nuclei and 40Ar as well as v-induced reactions on 40Ar. Repulsive corrections in the isospin T=1 monopoles are shown to be important for proper shell evolutions in neutron-rich carbon isotopes. The repulsive correction is pointed out to be due to three-body forces, in particular, the Fujita-Miyazawa force. Roles of the three-body forces on the shell evolution of neutron-rich calcium isotopes, the closed- shell nature of 48 Ca and M1 transition in 48 Ca are studied on top of the two-body G-matrix obtained by including core-polarization effects in larger spaces (≤24ω). Effects of the inclusion of g9/2-shell are also discussed.
    Preview · Article · Feb 2015 · Journal of Physics Conference Series
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    ABSTRACT: When carbon is ignited off-center in a CO core of a super-AGB star, its burning in a convective shell tends to propagate to the center. Whether the C flame will actually be able to reach the center depends on the efficiency of extra mixing beneath the C convective shell. Whereas thermohaline mixing is too inefficient to interfere with the C-flame propagation, convective boundary mixing can prevent the C burning from reaching the center. As a result, a C-O-Ne white dwarf (WD) is formed, after the star has lost its envelope. Such a "hybrid" WD has a small CO core surrounded by a thick ONe zone. In our 1D stellar evolution computations the hybrid WD is allowed to accrete C-rich material, as if it were in a close binary system and accreted H-rich material from its companion with a sufficiently high rate at which the accreted H would be processed into He under stationary conditions, assuming that He could then be transformed into C. When the mass of the accreting WD approaches the Chandrasekhar limit, we find a series of convective Urca shell flashes associated with high abundances of 23Na and 25Mg. They are followed by off-center C ignition leading to convection that occupies almost the entire star. To model the Urca processes, we use the most recent well-resolved data for their reaction and neutrino-energy loss rates. Because of the emphasized uncertainty of the convective Urca process in our hybrid WD models of SN Ia progenitors, we consider a number of their potentially possible alternative instances for different mixing assumptions, all of which reach a phase of explosive C ignition, either off or in the center. Our hybrid SN Ia progenitor models have much lower C to O abundance ratios at the moment of the explosive C ignition than their pure CO counterparts, which may explain the observed diversity of the SNe Ia.
    Full-text · Article · Nov 2014
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    Cenxi Yuan · Chong Qi · Furong Xu · Toshio Suzuki · Takaharu Otsuka
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    ABSTRACT: The properties of loosely bound proton-rich nuclei around A = 20 are investigated within the framework of nuclear shell model. In these nuclei, the strength of the effective interactions involving the loosely bound proton s1=2 orbit are significantly reduced in comparison with those in their mirror nuclei. We evaluate the reduction of the effective interaction by calculating the monopole-baseduniversal interaction (VMU) in the Woods-Saxon basis. The shell-model Hamiltonian in the sd shell, such as USD, can thus be modified to reproduce the binding energies and energy levels of the weakly bound proton-rich nuclei around A = 20. The effect of the reduction of the effective interaction on the structure and decay properties of these nuclei is also discussed.
    Full-text · Article · Apr 2014 · Physical Review C
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    ABSTRACT: Remarkable improvements in the evaluation of neutrino-nucleus reaction cross sections are obtained based on new shell-model Hamiltonians with proper tensor components. New ν-induced reaction cross sections on 12C, 13C, 56Fe, 56Ni and 40Ar are presented, and predictions for nucleosynthesis in supernova explosions, ν-oscillation effects and low-energy reactor and solar neutrino detection are discussed based on these new cross sections.
    No preview · Article · Feb 2014 · The European Physical Journal Conferences
  • Takaharu Otsuka · Toshio Suzuki
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    ABSTRACT: Physics of three-body forces in connection to exotic nuclei will be discussed. Three-nucleon forces (3NF), especially Fujita–Miyazawa 3NF, are shown to be the key for the solution to the long-standing problem of oxygen drip line, which deviates from basic trend towards the stability line. Three-body forces produce repulsive modifications to effective interaction between valence neutrons, and make the ground states less bound. The oxygen drip line is then located at the right place. The relation to the neutron matter is presented. Applications to Ca isotopes will be presented. The shell evolution due to the 3NF depicts the raising of single-particle energies and the widening of splitting among the orbits. This is in contrast to the so-called shell quenching. The 2+ levels are calculated for Ca isotopes, suggesting about the same sub-magic structure for N = 32 and 34.
    No preview · Article · Aug 2013 · Few-Body Systems
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    ABSTRACT: We calculate β-transition rates for URCA nuclear pairs using the sd-shell-model framework of Wildenthal [ B. H. Widenthal Prog. Part. Nucl. Phys. 11 5 (1984)] with the modified Hamiltonian. We consider many β transitions including excited states necessary for electron capture and β decay with high Fermi energy of electrons at high electron density ρYe and temperature T relevant for the massive star and super-asymptotic-giant-branch star evolution. We provide β-transition rates for URCA nuclear pairs (A=23, 25, and 27) in the range of density 8.0 <log10ρYe< 9.2 in steps of 0.02 (Ye is the electron mole number and ρ is the nucleon density in units of g cm−3) and temperature 8.0 <log10T< 9.2 in steps of 0.05 (T is the temperature in units of K). This fine mesh is able to provide clearly the URCA density at log10ρYe=8.92 for A=23 and at log10ρYe=8.81 for A=25, while the URCA density is not clear for A=27. For the evolution of 8–10M⊙ stars, the use of the fine mesh is found to increase the cooling effect and affects the final fate of these stars.
    No preview · Article · Jul 2013 · Physical Review C
  • Toshio Suzuki · Toshitaka Kajino
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    ABSTRACT: Neutrino–nucleus reaction processes play important roles in the synthesis of 7Li, 11B, 138La, 180Ta and other elements in explosive environments realized in supernovae. We have constructed new shell-model Hamiltonians based on recent progress in the physics of exotic nuclei. The shell evolutions toward drip-lines and the spin responses of nuclei are found to be remarkably improved by the new Hamiltonians. Proper tensor components in the Hamiltonians are shown to be important for the improvements. We then applied these Hamiltonians to calculate the neutrino–nucleus reaction cross sections, and obtained more precise theoretical estimates of supernova nucleosynthesis of 7Li, 11B and 55Mn etc, including the neutrino processes. Finally, we propose a new method for determining the neutrino oscillation parameter, the mixing angle θ13, and the mass hierarchy, by making use of the strong dependence of the yields of 7Li and 11B on these parameters.
    No preview · Article · Jun 2013 · Journal of Physics G Nuclear and Particle Physics
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    ABSTRACT: The stellar mass range 8 M/M ☉ 12 corresponds to the most massive asymptotic giant branch (AGB) stars and the most numerous massive stars. It is host to a variety of supernova (SN) progenitors and is therefore very important for galactic chemical evolution and stellar population studies. In this paper, we study the transition from super-AGB (SAGB) star to massive star and find that a propagating neon-oxygen-burning shell is common to both the most massive electron capture supernova (EC-SN) progenitors and the lowest mass iron-core-collapse supernova (FeCCSN) progenitors. Of the models that ignite neon-burning off-center, the 9.5 M ☉ star would evolve to an FeCCSN after the neon-burning shell propagates to the center, as in previous studies. The neon-burning shell in the 8.8 M ☉ model, however, fails to reach the center as the URCA process and an extended (0.6 M ☉) region of low Y e (0.48) in the outer part of the core begin to dominate the late evolution; the model evolves to an EC-SN. This is the first study to follow the most massive EC-SN progenitors to collapse, representing an evolutionary path to EC-SN in addition to that from SAGB stars undergoing thermal pulses (TPs). We also present models of an 8.75 M ☉ SAGB star through its entire TP phase until electron captures on 20Ne begin at its center and of a 12 M ☉ star up to the iron core collapse. We discuss key uncertainties and how the different pathways to collapse affect the pre-SN structure. Finally, we compare our results to the observed neutron star mass distribution.
    Full-text · Article · Jun 2013 · The Astrophysical Journal
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    Toshio Suzuki · Michio Honma
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    ABSTRACT: Gamow-Teller (GT) strength in $^{40}$Ar is studied by shell-model calculations with monopole-based universal intearction, which has tensor components of $\pi$\rho$-meson exchanges. Calculated GT strength is found to be consistent with the experimental data obtained by recent ($p, n$) reactions. Neutrino capture cross sections on $^{40}$Ar for solar neutrinos from $^{8}$B are found to be enhanced compared with previous calculations. The reaction cross sections for multipoles other than $0^{+}$ and $1^{+}$ are obtained by random-phase approximation (RPA). Their contributions become important for neutrino energies larger than 50 MeV.
    Preview · Article · Jan 2013 · Physical Review C
  • Takaharu Otsuka · Toshio Suzuki
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    ABSTRACT: We present recent developments in the understanding of exotic nuclei and their relevance to nuclear astrophysics particularly of explosive stellar processes.
    No preview · Article · Nov 2012
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    ABSTRACT: Beta decays of N=126 isotones are studied by shell model calculations by including both the Gamow-Teller (GT) and first-forbidden (FF) transitions. The half-lives of the isotones are found to be reduced considerably by the the contributions from the FF transitions, and short compared to the standard half-lives usually used for the nucleosynthesis network calculations. Possible implications of the short half-lives of the waiting point nuclei on the r-process nucleosynthesis during the supernova explosions are discussed.
    No preview · Article · Nov 2012
  • Toshio Suzuki · Takaharu Otsuka · Michio Honma
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    ABSTRACT: Spin-dependent modes in nuclei are studied and important roles of tensor and three-body forces on nuclear structure are discussed. New shell model Hamiltonians, which have proper tensor components, are shown to explain spin properties of both stable and exotic nuclei. Gamow-Teller (GT) strengths in Ni isotopes, especially in 56Ni, are found to be well described by pf-shell Hamiltonian GXPF1J, which leads to a remarkable improvement in the evaluation of electron capture rates in stellar environmnets. GT strength in 40Ar obtained with VMU (monopole-based universal interaction) is found to be consistent with the experimental strength, and neutrino capture reaction cross sections for solar neutrinos from 8B are found to be enhanced compared with previous calculations. The repulsive monopole corrections to the microscopic two-body interactions in isospin T=1 channel are important for the proper shell evolutions in neutron-rich isotopes. The three-body force, in particular the Fujita-Miyazawa force induced by δ excitations, is pointed out to be responsible for the repulsive corrections among the valence neutrons. The important roles of the three-body force on the energies of exotic calcium isotopes as well as on the closed-shell nature of 48Ca and M1 transition in 48Ca are demonstrated.
    No preview · Article · Oct 2012
  • Toshio Suzuki · Michio Honma
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    ABSTRACT: Nuclear weak processes are investigated based on new shell model Hamiltonians, which give successful description of spin responses in nuclei, and applied to astrophysical problems. Neutrino-induced reactions on 12C and synthesis of light elements by supernova neutrinos, and effects of contamination of 13C, whose natural isotopic abundance is 1.1%, on inclusive ν-12C reactions are discussed. Spin-dipole transitions and ν-induced reactions on 16O are studied by using a new Hamiltonian with proper tensor components, and compared with conventional calculations and previous CRPA results. Gamow-Teller transition strength in 40Ar and ν-induced reactions on 40Ar by solar neutrinos are studied based on monopole-based-universal interaction (VMU). We finally discuss electron capture reactions on Ni isotopes in stellar environments.
    No preview · Article · Sep 2012 · Journal of Physics Conference Series
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    ABSTRACT: We study boron, carbon, nitrogen, and oxygen isotopes with a newly constructed shell-model Hamiltonian developed from a monopole-based universal interaction (VMU). The present Hamiltonian can reproduce well the ground-state energies, energy levels, electric quadrupole properties, and spin properties of these nuclei in full psd model space including (0−3)ℏω excitations. Especially, it correctly describes the drip lines of carbon and oxygen isotopes and the spins of the ground states of 10B and 18N while some former interactions such as WBP and WBT fail. We point out that the inclusion of 2ℏω excitations is important in reproducing some of these properties. In the present (0+2)ℏω calculations small but constant E2 effective charges appear to work quite well. As the inclusion of the 2ℏω model space makes a rather minor change, this seems to be related to the smallness of the 4He core. Similarly, the spin g factors are very close to free values. The applicability of tensor and spin-orbit forces in free space, which are taken in the present Hamiltonian, is examined in shell-model calculations.
    Full-text · Article · Jun 2012 · Physical Review C
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    ABSTRACT: We investigate the effects of newly measured beta-decay half-lives on r-process nucleosynthesis. These new rates were determined by recent experiments at the radioactive isotope beam factory facility in the RIKEN Nishina Center. We adopt an r-process nucleosynthesis environment based on a magnetohydrodynamic supernova explosion model that includes strong magnetic fields and rapid rotation of the progenitor. A number of the new beta-decay rates are for nuclei on or near the r-process path, and hence they affect the nucleosynthesis yields and time scale of the r-process. The main effect of the newly measured beta-decay half-lives is an enhancement in the calculated abundance of isotopes with mass number A = 110 -- 120 relative to calculated abundances based upon beta-decay rates estimated with the finite-range droplet mass model. This effect slightly alleviates, but does not fully explain, the tendency of r-process models to underproduce isotopes with A = 110 -- 120 compared to the solar-system r-process abundances.
    Full-text · Article · Mar 2012 · Physical Review C
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    ABSTRACT: Gamow-Teller strengths in Ni isotopes are evaluated by using a new shell model Hamiltonian, GXPF1J, and applied to nuclear weak processes in stars. The calculated strengths are found to reproduce recent experimental data fairly well. Neutral current reactions on 56Ni induced by supernova neutrinos are studied. The cross section for proton emission channel is found to be increased comapared to previous calculations. The enhancement of the cross section is pointed out to lead to the enhancement of the production amount of 55Mn and 59Co in population III stars. The electron capture reactions on Ni isotopes at stellar environments are investigated. Considerable improvements of the evaluation of the capture rates are obtained by using GXPF1J compared to previous calculations.
    No preview · Article · Jan 2012 · Progress of Theoretical Physics Supplement

Publication Stats

2k Citations
351.57 Total Impact Points


  • 1982-2015
    • Nihon University
      • Department of Physics
      Edo, Tōkyō, Japan
  • 2013
    • University of Notre Dame
      • Department of Physics
      South Bend, Indiana, United States
  • 2011
    • National Astronomical Observatory of Japan
      • Division of Theoretical Astronomy
      Edo, Tokyo, Japan
  • 2010
    • Michigan State University
      • Department of Physics and Astronomy
      East Lansing, Michigan, United States
  • 1998-2005
    • Fukui University
      Фукуй, Fukui, Japan
    • Chiba University
      • Department of Physics
      Tiba, Chiba, Japan
  • 2004
    • The University of Aizu
      Hukusima, Fukushima, Japan
  • 1997-2003
    • RIKEN
      Вако, Saitama, Japan
  • 2002
    • University of Milan
      • Department of Physics
      Milano, Lombardy, Italy
  • 1984-1989
    • Kyoto University
      Kioto, Kyōto, Japan
  • 1988
    • Massachusetts Institute of Technology
      Cambridge, Massachusetts, United States