arXiv subjects

Nobuo Hinohara

Publications and source records attributed to Nobuo Hinohara.

46 records · Page 3Linked to original sources

arXiv2011

Microscopic description of large-amplitude shape-mixing dynamics with local QRPA inertial functions

We introduce a microscopic approach to derive all the inertial functions in the five-dimensional quadrupole collective Hamiltonian. Local normal modes are evaluated on the constrained mean field in the quasiparticle random-phase approximation in order to derive the inertial functions. The collective Hamiltonians for neutron-rich Mg isotopes are determined with use of this approach, and the shape coexistence/mixing around the N = 20 region is analyzed.

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arXiv2011

Microscopic description of large-amplitude shape-mixing dynamics with inertial functions derived in local quasiparticle random-phase approximation

On the basis of the adiabatic self-consistent collective coordinate method, we develop an efficient microscopic method of deriving the five-dimensional quadrupole collective Hamiltonian and illustrate its usefulness by applying it to the oblate-prolate shape coexistence/mixing phenomena in proton-rich 68,70,72Se. In this method, the vibrational and rotational collective masses (inertial functions) are determined by local normal modes built on constrained Hartree-Fock-Bogoliubov states. Numerical calculations are carried out using the pairing-plus-quadrupole Hamiltonian including the quadrupole-pairing interaction. It is shown that the time-odd components of the moving mean-field significantly increase the vibrational and rotational collective masses in comparison with the Inglis-Belyaev cranking masses. Solving the collective Schroedinger equation, we evaluate excitation spectra, quadrupole transitions and moments. Results of the numerical calculation are in excellent agreement with recent experimental data and indicate that the low-lying states of these nuclei are characterized as an intermediate situation between the oblate-prolate shape coexistence and the so-called gamma unstable situation where large-amplitude triaxial-shape fluctuations play a dominant role.

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arXiv2010

Shape mixing dynamics in the low-lying states of proton-rich Kr isotopes

We study the oblate-prolate shape mixing in the low-lying states of proton-rich Kr isotopes using the five-dimensional quadrupole collective Hamiltonian. The collective Hamiltonian is derived microscopically by means of the CHFB (constrained Hartree-Fock-Bogoliubov) + Local QRPA (quasiparticle random phase approximation) method, which we have developed recently on the basis of the adiabatic self-consistent collective coordinate method. The results of the numerical calculation show the importance of large-amplitude collective vibrations in the triaxial shape degree of freedom and rotational effects on the oblate-prolate shape mixing dynamics in the low-lying states of these isotopes.

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arXiv2009

A Model Analysis of Triaxial Deformation Dynamics in Oblate-Prolate Shape Coexistence Phenomena

From a viewpoint of oblate-prolate symmetry and its breaking, we adopt the quadrupole collective Hamiltonian to study dynamics of triaxial deformation in shape coexistence phenomena. It accommodates the axially symmetric rotor model, the $γ$-unstable model, the rigid triaxial rotor model and an ideal situation for the oblate-prolate shape coexistence as particular cases. Numerical solutions of this model yield a number of interesting suggestions. (1) The relative energy of the excited 0+ state can be a signature of the potential shape along the $γ$ direction. (2) Specific E2 transition probabilities are sensitive to the breaking of the oblate-prolate symmetry. (3) Nuclear rotation may induce the localization of collective wave functions in the ($β, γ$) deformation space.

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arXiv2009

Microscopic description of oblate-prolate shape mixing in proton-rich Se isotopes

The oblate-prolate shape coexisting/mixing phenomena in proton-rich 68,70,72Se are investigated by means of the adiabatic self-consistent collective coordinate (ASCC) method. The one-dimensional collective path and the collective Hamiltonian describing the large-amplitude shape vibration are derived in a fully microscopic way. The excitation spectra, B(E2) and spectroscopic quadrupole moments are calculated by requantizing the collective Hamiltonian and solving the collective Schroedinger equation. The basic properties of the coexisting two rotational bands in low-lying states of these nuclei are well reproduced. It is found that the oblate-prolate shape mixing becomes weak as the rotational angular momentum increases. We point out that the rotational energy plays a crucial role in causing the localization of the collective wave function in the (beta,gamma) deformation space.

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arXiv2009

Dineutron correlations in quasi two-dimensional systems in a simplified model and possible relation to neutron-rich nuclei

Two-neutron correlation in the $^1S$ channel in quasi two-dimensional (2D) neutron systems at zero temperature is studied by means of the BCS theory with finite-range effective nuclear forces. The dineutron correlation in low density neutron systems confined in an infinite slab is investigated in a simplified model that neutron motion of one direction is frozen. When the slab is thin enough, two neutrons form a tightly bound dineutron with a small size in the quasi-2D system, and a Bose dineutron gas is found in low density limit. With increase of Fermi momentum, the neutron system changes from the Bose-gas phase to the superfluid Cooper pair phase. The density dependence of the neutron pairing shows the BCS-BEC crossover phenomena at finite low-density region. In the transition region, the size shrinking of neutron pair and enhancement of pairing gap are found. The relation to dineutron correlation at surface of neutron-rich nuclei is also discussed.

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arXiv2007

Microscopic Derivation of Collective Hamiltonian by Means of the Adiabatic Self-Consistent Collective Coordinate Method

Microscopic dynamics of the oblate-prolate shape coexistence/mixing phenomena in 68Se and 72Kr are studied by means of the adiabatic self-consistent collective coordinate (ASCC) method in conjunction with the pairing-plus-quadrupole (P+Q) Hamiltonian including the quadrupole pairing interaction. Quantum collective Hamiltonian is constructed, and excitation spectra, spectroscopic quadrupole moments and quadrupole transition properties are evaluated. The effect of the time-odd pair field on the collective mass (inertia function) of the large-amplitude vibration and the rotational moments of inertia about three principal axes is evaluated. Basic properties of the shape coexistence/mixing are well reproduced. The calculation indicates that the oblate-prolate shape mixing decreases as the angular momentum increases.

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arXiv2007

Microscopic Dynamics of Shape Coexistence Phenomena around 68Se and 72Kr

The adiabatic self-consistent collective coordinate (ASCC) method is applied to the pairing-plus-quadrupole (P + Q) model Hamiltonian including the quadrupole pairing, and the oblate-prolate shape coexistence phenomena in proton-rich nuclei, 68Se and 72Kr, are investigated. It is shown that the collective path connecting the oblate and prolate local minima runs along a triaxial valley in the beta-gamma plane. Quantum collective Hamiltonian is constructed and low-lying energy spectra and E2 transition probabilities are calculated for the first time using the ASCC method. Basic properties of the shape coexistence/mixing are well reproduced. We also clarify the effects of the time-odd pair field on the collective mass (inertial function) for the large-amplitude vibration and on the rotational moments of inertia about three principal axes.

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arXiv2007

Gauge-Invariant Formulation of Adiabatic Self-Consistent Collective Coordinate Method

The adiabatic self-consistent collective coordinate (ASCC) method is a practical microscopic theory of large-amplitude collective motions in nuclei with superfluidity. We show that its basic equations are invariant against transformations involving the gauge angle in the particle-number space. By virtue of this invariance, a clean separation between the large-amplitude collective motion and the pairing rotational motion can be achieved, enabling us to restore the particle-number symmetry broken by the Hartree-Fock-Bogoliubov (HFB) approximation. We formulate the ASCC method explicitly in a gauge-invariant form. In solving the ASCC equations, it is necessary to fix the gauge. Applying this new formulation to the multi-O(4) model, we compare different gauge-fixing procedures and demonstrate that calculations using different gauges indeed yield the same results for gauge-invariant quantities, such as the collective path and quantum spectra. We suggest a gauge-fixing prescription that seems most convenient in realistic calculations.

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arXiv2005

Effects of Time-Odd Components in Mean Field on Large Amplitude Collective Dynamics

We apply the adiabatic self-consistent collective coordinate (ASCC) method to the multi-O(4) model and study collective mass (inertia function) of the many-body tunneling motion. Comparing results with those of the exact diagonalization, we show that the ASCC method succeeds in describing gradual change of excitation spectra from an anharmonic vibration about the spherical shape to a doublet pattern associated with a deformed double-well potential possessing the oblate-prolate symmetry. The collective mass is significantly increased by the quadrupole-pairing contribution to time-odd components of the moving mean field. In contrast, the cranking (Inglis-Belyaev) mass based on the constrained mean field, which ignores the time-odd components, is smaller than the ASCC mass and fails to reproduce the exact spectra.

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