Publications (86)173.96 Total impact

Article: Mirror energy difference and the structure of loosely bound protonrich nuclei around A = 20
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ABSTRACT: The properties of loosely bound protonrich 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 monopolebaseduniversal interaction (VMU) in the WoodsSaxon basis. The shellmodel Hamiltonian in the sd shell, such as USD, can thus be modified to reproduce the binding energies and energy levels of the weakly bound protonrich 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.04/2014; 
Article: New neutrinonucleus reaction cross sections at solar, reactor and supernova neutrino energies
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ABSTRACT: Remarkable improvements in the evaluation of neutrinonucleus reaction cross sections are obtained based on new shellmodel Hamiltonians with proper tensor components. New νinduced reaction cross sections on 12C, 13C, 56Fe, 56Ni and 40Ar are presented, and predictions for nucleosynthesis in supernova explosions, νoscillation effects and lowenergy reactor and solar neutrino detection are discussed based on these new cross sections.02/2014;  [Show abstract] [Hide abstract]
ABSTRACT: We calculate βtransition rates for URCA nuclear pairs using the sdshellmodel 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 superasymptoticgiantbranch star evolution. We provide βtransition 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.Physical Review C 07/2013; 88(1). · 3.72 Impact Factor  [Show abstract] [Hide abstract]
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 shellmodel Hamiltonians based on recent progress in the physics of exotic nuclei. The shell evolutions toward driplines 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.Journal of Physics G Nuclear and Particle Physics 06/2013; 40(8):083101. · 5.33 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: The stellar mass range 8<M/Mo<12 corresponds to the most massive AGB stars and the most numerous massive stars. It is host to a variety of supernova progenitors and is therefore very important for galactic chemical evolution and stellar population studies. In this paper, we study the transition from superAGB star to massive star and find that a propagating neonoxygen burning shell is common to both the most massive electron capture supernova (ECSN) progenitors and the lowest mass ironcore collapse supernova (FeCCSN) progenitors. Of the models that ignite neon burning offcenter, the 9.5Mo model would evolve to an FeCCSN after the neonburning shell propagates to the center, as in previous studies. The neonburning shell in the 8.8Mo model, however, fails to reach the center as the URCA process and an extended (0.6 Mo) region of low Ye (0.48) in the outer part of the core begin to dominate the late evolution; the model evolves to an ECSN. This is the first study to follow the most massive ECSN progenitors to collapse, representing an evolutionary path to ECSN in addition to that from SAGB stars undergoing thermal pulses. We also present models of an 8.75Mo superAGB star through its entire thermal pulse phase until electron captures on 20Ne begin at its center and of a 12Mo star up to the iron core collapse. We discuss key uncertainties and how the different pathways to collapse affect the presupernova structure. Finally, we compare our results to the observed neutron star mass distribution.The Astrophysical Journal 06/2013; 772(2). · 6.73 Impact Factor 
Article: Neutrino capture reactions on 40Ar
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ABSTRACT: GamowTeller (GT) strength in 40Ar is studied by shellmodel calculations with monopolebased universal interaction, which has tensor components of π+ρmeson exchanges. Calculated GT strength is found to be consistent with the experimental data obtained by recent (p,n) reactions. Neutrino capture cross sections on 40Ar for solar neutrinos from 8B are found to be enhanced compared with previous calculations. The reaction cross sections for multipoles other than 0+ and 1+ are obtained by randomphase approximation (RPA). Their contributions become important for neutrino energies larger than 50 MeV.Physical Review C 01/2013; 87(1). · 3.72 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: We present recent developments in the understanding of exotic nuclei and their relevance to nuclear astrophysics particularly of explosive stellar processes.AIP Conference Proceedings. 11/2012; 1484(1).  [Show abstract] [Hide abstract]
ABSTRACT: Beta decays of N=126 isotones are studied by shell model calculations by including both the GamowTeller (GT) and firstforbidden (FF) transitions. The halflives of the isotones are found to be reduced considerably by the the contributions from the FF transitions, and short compared to the standard halflives usually used for the nucleosynthesis network calculations. Possible implications of the short halflives of the waiting point nuclei on the rprocess nucleosynthesis during the supernova explosions are discussed.11/2012;  [Show abstract] [Hide abstract]
ABSTRACT: Spindependent modes in nuclei are studied and important roles of tensor and threebody 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. GamowTeller (GT) strengths in Ni isotopes, especially in 56Ni, are found to be well described by pfshell 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 (monopolebased 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 twobody interactions in isospin T=1 channel are important for the proper shell evolutions in neutronrich isotopes. The threebody force, in particular the FujitaMiyazawa force induced by δ excitations, is pointed out to be responsible for the repulsive corrections among the valence neutrons. The important roles of the threebody force on the energies of exotic calcium isotopes as well as on the closedshell nature of 48Ca and M1 transition in 48Ca are demonstrated.10/2012;  [Show abstract] [Hide abstract]
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. Neutrinoinduced 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 ν12C reactions are discussed. Spindipole transitions and νinduced reactions on 16O are studied by using a new Hamiltonian with proper tensor components, and compared with conventional calculations and previous CRPA results. GamowTeller transition strength in 40Ar and νinduced reactions on 40Ar by solar neutrinos are studied based on monopolebaseduniversal interaction (VMU). We finally discuss electron capture reactions on Ni isotopes in stellar environments.Journal of Physics Conference Series 09/2012; 381(1):2118.  [Show abstract] [Hide abstract]
ABSTRACT: We study boron, carbon, nitrogen, and oxygen isotopes with a newly constructed shellmodel Hamiltonian developed from a monopolebased universal interaction (VMU). The present Hamiltonian can reproduce well the groundstate 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 spinorbit forces in free space, which are taken in the present Hamiltonian, is examined in shellmodel calculations.Physical Review C 06/2012; 85(6). · 3.72 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: We investigate the effects of newly measured betadecay halflives on rprocess nucleosynthesis. These new rates were determined by recent experiments at the radioactive isotope beam factory facility in the RIKEN Nishina Center. We adopt an rprocess 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 betadecay rates are for nuclei on or near the rprocess path, and hence they affect the nucleosynthesis yields and time scale of the rprocess. The main effect of the newly measured betadecay halflives is an enhancement in the calculated abundance of isotopes with mass number A = 110  120 relative to calculated abundances based upon betadecay rates estimated with the finiterange droplet mass model. This effect slightly alleviates, but does not fully explain, the tendency of rprocess models to underproduce isotopes with A = 110  120 compared to the solarsystem rprocess abundances.Physical Review C 03/2012; 85(4). · 3.72 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: Neutrino‐nucleus reactions at MeV region are evaluated by using new shell model Hamiltonians, which are found to improve the description of spin degrees of freedom in nuclei as well as shell evolutions. The light element synthesis by neutrino processes in supernova explosions is discussed with the use of the new reaction cross sections for 12C and 4He. Possible constraints on the mixing angle θ13 and the neutrino mass hierarchy are pointed out to be imposed by the production yields of 7Li and 11B. Spin‐dipole transition strengths in 16O and neutrino‐induced reactions on 16O are investigated with the new improved Hamiltonian. The Gamow‐Teller transition strength in 56Ni for the new Hamiltonian, which is more fragmented compared to previous calculations, is found to lead to the enhancement of the production yield of 55Mn in population III stars.AIP Conference Proceedings. 11/2011; 1405(1):271276.  [Show abstract] [Hide abstract]
ABSTRACT: Beta decays of the isotones with N=126 are studied by shell model calculations taking into account both the GamowTeller (GT) and firstforbidden (FF) transitions. The FF transitions are found to be important to reduce the halflives, by nearly twice to several times, from those by the GT contributions only. Possible implications of the short halflives of the waiting point nuclei on the rprocess nucleosynthesis during the supernova explosions are discussed. A slight shift of the third peak of the element abundances in the rprocess toward higher mass region is found.Physical Review C 10/2011; · 3.72 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: Spin modes in stable and unstable exotic nuclei are studied and important roles of tensor and threebody forces on nuclear structure are discussed. New shell model Hamiltonians, which have proper tensor components, are shown to explain shell evolutions toward driplines and spin properties of both stable and exotic nuclei, for example, GamowTeller transitions in 12C and 14C and an anomalous M1 transition in 17C. The importance and the necessity of the repulsive monopole corrections in isospin T = 1 channel to the microscopic twobody interactions are pointed out. The corrections are shown to lead to the proper shell evolutions in neutronrich isotopes. The threebody force, in particular the FujitaMiyazawa force induced by Δ excitations, is pointed out to be responsible for the repulsive corrections among the valence neutrons. The important roles of the threebody force on the energies and transitions in exotic oxygen and calcium isotopes are demonstrated.AIP Conference Proceedings. 05/2011; 1355(1):4550.  [Show abstract] [Hide abstract]
ABSTRACT: Electron capture rates in Ni isotopes are studied in stellar environments, that is, at high densities and high temperatures during the corecollapse and postbounce explosive nucleosynthesis in supernovae. Reaction rates in 58Ni and 60Ni, as well as in 56Ni, 62Ni, and 64Ni, are evaluated by shellmodel calculations with the use of a new shellmodel Hamiltonian in the fp shell, GXPF1J. While the previous shellmodel calculations failed to reproduce the measured peaks of GamowTeller strength in 58Ni and 60Ni, the present new Hamiltonian is found to reproduce them very well, as well as the capture rates obtained from the observed strengths. Strengths and energies of the GamowTeller transitions in 56Ni, 62Ni, and 64Ni are also found to be consistent with the observations.Physical Review C 04/2011; 83(4). · 3.72 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: Spin dependent nuclear weak processes and nucleosynthesis in stars are investigated based on recent advances in shell model studies of stable and unstable exotic nuclei. Three topics on (1) neutrino–nucleus reactions in supernova explosions and nucleosynthesis of light elements as well as Mn, (2) electron capture reaction rates on Ni and Co isotopes at high densities and temperatures in the corecollapse process, and (3) new βdecay halflives of N=126 isotones obtained by including both the Gamow–Teller and the firstforbidden transitions, and the effects on the element abundance in the rprocess at the third peak region (A∼195), are studied with the use of new shell model Hamiltonians.Progress in Particle and Nuclear Physics 01/2011; 66(2):385389. · 2.26 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: GamowTeller (GT) and firstforbidden (FF) transitions in nuclei and their possible consequences on astrophysical processes in stars are discussed. GT transition strengths in fpshell nuclei are studied by shell model calculations with the use of new shell model Hamiltonians, GXPF1. Neutrinonucleus reaction cross sections are reevaluated and compared with previous investigations. Proton emission cross sections on 56Ni are pointed out to be enhanced and lead to the enhancement of the production yields of 55Mn and 59Co in population III supernovae. Next, electron capture reactions on Ni and Fe isotopes in steller environments are studied. The capture rates depend sensitively on the distributions of the GT strengths. Capture rates on 58Ni and 60Ni obtained by GXPF1 are found to reproduce rather well those obtained from experimental GT strengths. Finally, beta decays of the N = 126 isotones are studied by shell model calculations taking into account both the GT and FF transitions. The FF transitions are found to be important to reduce the halflives by twice to several times of those by the GT contributions only. Possible implications on the short halflives of the waiting point nuclei on the rprocess nucleosynthesis are discussed for certain astrophysical conditions.Journal of Physics Conference Series 01/2011; 312(4).  [Show abstract] [Hide abstract]
ABSTRACT: Understanding and predicting the formation of shell structure from nuclear forces is a central challenge for nuclear physics. While the magic numbers N=2,8,20 are generally well understood, N=28 is the first standard magic number that is not reproduced in microscopic theories with twonucleon forces. In this Letter, we show that threenucleon forces give rise to repulsive interactions between two valence neutrons that are key to explain 48Ca as a magic nucleus, with a high 2+ excitation energy and a concentrated magnetic dipole transition strength. The repulsive threenucleon mechanism improves the agreement with experimental binding energies.Journal of Physics G Nuclear and Particle Physics 09/2010; 39(8). · 5.33 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: Beta decays of N = 126 isotones are studied by shell model calculations. Both the GamowTeller (GT) and firstforbidden (FF) transitions are taken into account to evaluate the halflives of the isotones (Z = 6472) with the use of shell model interactions based on Gmatrix. The FF transitions are found to be important to reduce the halflives by twice to several times of those obtained by the GT contributions only. Possible implications of the short halflives of the waiting point nuclei on the rprocess nucleosynthesis during the supernova explosions are discussed.AIP Conference Proceedings 08/2010; 1269:339.
Publication Stats
969  Citations  
173.96  Total Impact Points  
Top Journals
Institutions

1995–2014

Nihon University
 • Department of Physics
 • Graduate School of Integrated Basic Sciences
Edo, Tōkyō, Japan


2013

University of Notre Dame
South Bend, Indiana, United States


2006–2012

The University of Tokyo
 Department of Physics
Edo, Tōkyō, Japan


2010

Michigan State University
 Department of Physics and Astronomy
East Lansing, Michigan, United States
