Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1093/ptep/ptz136

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

Background: Low-lying collective excitations of the inner crust matter in neutron stars are expected to affect observables such as the quasiperiodic oscillation in giant flares or cooling of the inner crust in transient phenomena. The coupling between the Anderson-Bogoliubov (AB) superfluid phonon in superfluid neutron gas and collective excitations of nuclear clusters is crucially important.Purpose: Our aim is to describe the characteristics of the low-lying excitation modes of the superfluid inner crust matter, focusing on quadrupole excitations around a spherical nuclear cluster. We studied the effect of the inhomogeneous structure of the inner crust matter on the AB phonon of neutron superfluid and on the possible quadrupole shape vibration of clusters.Methods: The coordinate-space Hartree-Fock-Bogoliubov method and the quasiparticle random phase approximation formulated in a spherical Wigner-Seitz cell were used to describe the neutron superfluidity and low-lying collective excitations. We performed systematic numerical calculations for the quadrupole excitations by varying the neutron chemical potential and the number of protons in the cell.Results: The calculated results indicate the appearance of both AB phonon and quadrupole shape vibration of the cluster with small mixing between the two collective modes. The quadruple AB phonon is similar to that in the uniform superfluid, apart from the small admixture of the shape vibration of cluster. The excitation energy and the collectivity of the cluster vibration mode show a strong and oscillatory dependence on the neutron chemical potential (the neutron gas density), resulting in softening and instability under certain conditions. This is due to the resonance shell effect, where unbound, but resonant single-particle states of neutrons are crucially important.Conclusions: The AB phonon of the superfluid neutron gas and the quadrupole shape vibration of the nuclear cluster coexist in the inner crust. The coupling between the AB phonon and the quadrupole shape vibration is weak. The collectivity of the quadrupole shape vibration is controlled by the resonance shell effect, which suggests that the appearance of deformed nuclear clusters is possible in any layer of the inner crust.

DOI： 10.1103/PhysRevC.99.045801

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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 the inner crust of neutron stars. However, there are a 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 with the neutron density. At higher neutron densities (>= 0.006 fm(-3)) the AB phonon mode exhibits behavior 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.

DOI： 10.1103/PhysRevC.96.025806

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Language：English   Publishing type：Research paper (international conference proceedings)  

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The basic concepts and recent developments in the time-dependent density-functional theory (TDDFT) for describing nuclear dynamics at low energy are presented. The symmetry breaking is inherent in nuclear energy density functionals, which provides a practical description of important correlations at the ground state. Properties of elementary modes of excitation are strongly influenced by the symmetry breaking and can be studied with TDDFT. In particular, a number of recent developments in the linear response calculation have demonstrated their usefulness in the description of collective modes of excitation in nuclei. Unrestricted real-time calculations have also become available in recent years, with new developments for quantitative description of nuclear collision phenomena. There are, however, limitations in the real-time approach; for instance, it cannot describe the many-body quantum tunneling. Thus, the quantum fluctuations associated with slow collective motions are explicitly treated assuming that time evolution of densities is determined by a few collective coordinates and momenta. The concept of collective submanifold is introduced in the phase space associated with the TDDFT and used to quantize the collective dynamics. Selected applications are presented to demonstrate the usefulness and quality of the new approaches. Finally, conceptual differences between nuclear and electronic TDDFT are discussed, with some recent applications to studies of electron dynamics in the linear response and under a strong laser field.

DOI： 10.1103/RevModPhys.88.045004

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Language：English   Publisher：IOP PUBLISHING LTD  

We discuss the nature of the low-frequency quadrupole vibrations from small-amplitude to large-amplitude regimes. We consider full five-dimensional quadrupole dynamics including three-dimensional rotations restoring the broken symmetries as well as axially symmetric and asymmetric shape fluctuations. Assuming that the time evolution of the self-consistent mean field is determined by five pairs of collective coordinates and collective momenta, we microscopically derive the collective Hamiltonian of Bohr and Mottelson, which describes low-frequency quadrupole dynamics. We show that the five-dimensional collective Schrodinger equation is capable of describing large-amplitude quadrupole shape dynamics seen as shape coexistence/mixing phenomena. We summarize the modern concepts of microscopic theory of large-amplitude collective motion, which is underlying the microscopic derivation of the Bohr-Mottelson collective Hamiltonian.

DOI： 10.1088/0031-8949/91/6/063014

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Assuming that the time-evolution of the self-consistent mean field is determined by five pairs of collective coordinate and collective momentum, we microscopically derive the collective Hamiltonian for low-frequency quadrupole modes of excitation. We show that the five-dimensional collective Schrodinger equation is capable of describing large-amplitude quadrupole shape dynamics seen as shape coexistence/mixing phenomena. We focus on basic ideas and recent advances of the approaches based on the time-dependent mean-field theory, but relations to other time-independent approaches are also briefly discussed.

DOI： 10.1088/0954-3899/43/2/024006

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OXFORD UNIV PRESS INC  

We discuss the effects of pairing correlation on quasiparticle resonance. We analyze in detail how the width of the low-lying (Ex less than or similar to 1 MeV) quasiparticle resonance is governed by the pairing correlation in the neutron drip-line nuclei. We consider the Si-46 + n system to discuss the low-lying p-wave quasiparticle resonance. Solving the Hartree-Fock-Bogoliubov equation in coordinate space with the scattering boundary condition, we calculate the phase shift, the elastic cross section, the resonance width, and the resonance energy. We find that the pairing correlation has the effect of reducing the width of the quasiparticle resonance that originates from a particle-like orbit in weakly bound nuclei.

DOI： 10.1093/ptep/ptv175

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Language：Japanese   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.71.2.0_118

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Language：Japanese   Publishing type：Research paper (international conference proceedings)  

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

I formulate a many-body theory to calculate the cross section of direct radiative neutron capture reaction by means of the Hartree-Fock-Bogoliubov mean-field model and the continuum quasiparticle random-phase approximation (QRPA). A focus is put on very-neutron-rich nuclei and low-energy neutron kinetic energy in the range from 1 keV to several MeV, which is relevant to the rapid neutron capture process of nucleosynthesis. I begin with the photoabsorption cross section and the E1 strength function. Next, in order to apply the reciprocity theorem, I decompose the cross section into partial cross sections corresponding to different channels of one-and two-neutron emission decays of photo-excited states. A numerical example is shown for the photo-absorption of Sn-142 and the neutron capture of Sn-141.

DOI： 10.1103/PhysRevC.91.034604

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Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

DOI： 10.11316/jpsgaiyo.70.1.0_239

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

Low-lying quadrupole shape dynamics is a typical manifestation of large-amplitude collective motion in finite nuclei. To describe the dynamics on a microscopic foundation, we have formulated a consistent scheme in which the Bohr collective Hamiltonian for the five-dimensional quadrupole shape variables is derived on the basis of the time-dependent Hartree-Fock-Bogoliubov theory. It enables us to incorporate the Thouless-Valatin effect on the shape inertial functions, which has been neglected in previous microscopic Bohr Hamiltonian approaches. Quantitative successes are illustrated for the low-lying spectra in Se-68, Mg30-34 and Cr58-64, which display shape-coexistence, shape-mixing and shape-transitional behavior.

DOI： 10.1088/0031-8949/89/5/054020

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

We study microscopic structures of monopole pair vibrational modes and associated two-neutron transfer amplitudes in neutron-rich Sn isotopes by means of the linear response formalism of the quasiparticle random phase approximation (QRPA). For this purpose we introduce a method to decompose the transfer amplitudes with respect to two-quasiparticle components of the QRPA eigenmode. It is found that pair-addition vibrational modes in neutron-rich Sn132-140 and the pair rotational modes in Sn142-150 are commonly characterized by coherent contribution of quasaiparticle states having high orbital angular momenta l greater than or similar to 5, which suggests transfer of a spatially correlated neutron pair. The calculation also predicts a high-lying pair vibration, the giant pair vibration, emerging near the one-neutron separation energy in Sn110-130, and we find that they have the same di-neutron characters as that of the low-lying pair vibration in Sn132-140.

DOI： 10.1103/PhysRevC.88.054308

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We apply the continuum quasiparticle random phase approximation to calculate the direct neutron capture cross section relevant to the r-process nucleo-synthesis. The electric dipole strength function in an even-even n-rich nucleus is decomposed with respect to the channels of direct neutron decays. Using the detailed balance relation, the partial dipole strengths are converted to obtain the direct neutron-capture cross sections. Numerical examples are given for Sn-142.

DOI： 10.1088/1742-6596/445/1/012019

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：WORLD SCIENTIFIC PUBL CO PTE LTD  

We propose a practical method for determining the collective potential and inertial functions in the five-dimensional quadrupole collective Hamiltonian. We have applied this method to large-amplitude shape mixing dynamics in the low-lying states of proton-rich Kr isotopes.

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：WORLD SCIENTIFIC PUBL CO PTE LTD  

The miroscopic method of deriving the quadrupole collective Hamiltonian is presented. Shape changes and transitions in neutron-rich magnesium and chromium isotopes are discussed using the quadrupole collective Hamiltonian.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

The spherical-to-prolate shape transition in neutron-rich Cr isotopes from N = 34 to 42 is studied by solving the collective Schrodinger equation for the five-dimensional quadrupole collective Hamiltonian. The collective potential and inertial functions are microscopically derived with use of the constrained Hartree-Fock-Bogoliubov plus local quasiparticle random-phase approximation method. Nature of the quadrupole collectivity of low-lying states is discussed by evaluating excitation spectra and electric quadrupole moments and transition strengths. The result of calculation indicates that Cr isotopes around Cr-64 are prolately deformed but still possess transitional character; large-amplitude shape fluctuations dominate in their low-lying states.

DOI： 10.1103/PhysRevC.86.024316

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PROGRESS THEORETICAL PHYSICS PUBLICATION OFFICE  

We have analyzed large-amplitude quadrupole collective dynamics in neutron-rich nuclei Mg30-36 using the five-dimensional quadrupole collective Hamiltonian approach. The collective Hamiltonian is microscopically derived with the constrained HFB plus local quasi-particle RPA method. Enhancement of the quadrupole collectivity from Mg-30 to Mg-34 is well described by the calculation. The shape transitional behavior in the ground band and the shape coexistence/mixing properties in the ground and excited 0(+) states are analyzed.

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IOP PUBLISHING LTD  

We have developed a new method for determining microscopically the five-dimensional quadrupole collective Hamiltonian, on the basis of the adiabatic self-consistent collective coordinate method. This method consists of the constrained Hartree-Fock-Bogoliubov (HFB) equation and the local QRPA (LQRPA) equations, which are an extension of the usual QRPA (quasiparticle random phase approximation) to non-HFB-equilibrium points, on top of the CHFB states. One of the advantages of our method is that the inertial functions calculated with this method contain the contributions of the time-odd components of the mean field, which are ignored in the widely-used cranking formula. We illustrate usefulness of our method by applying to oblate-prolate shape coexistence in Kr-72 and shape phase transition in neutron-rich Cr isotopes around N = 40.

DOI： 10.1088/1742-6596/381/1/012103

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

Large-amplitude collective dynamics of shape phase transition in the low-lying states of Mg30-36 is investigated by solving the five-dimensional (5D) quadrupole collective Schrodinger equation. The collective masses and potentials of the 5D collective Hamiltonian are microscopically derived with use of the constrained Hartree-Fock-Bogoliubov plus local quasiparticle random phase approximation method. Good agreement with the recent experimental data is obtained for the excited 0(+) states as well as the ground bands. For Mg-30, the shape coexistence picture that the deformed excited 0(+) state coexists with the spherical ground state approximately holds. On the other hand, large-amplitude quadrupole-shaped fluctuations dominate in both the ground and the excited 0(+) states in Mg-32, providing a picture that is different from the interpretation of the "coexisting spherical excited 0(+) state" based on the naive inversion picture of the spherical and deformed configurations.

DOI： 10.1103/PhysRevC.84.061302

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DOI： 10.1103/PhysRevC.84.044317

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

Two-neutron transfer associated with the pair correlation in superfluid neutron-rich nuclei is studied with focus on low-lying 0(+) states in Sn isotopes beyond the N = 82 magic number. We describe microscopically the two-neutron addition and removal transitions by means of the Skyrme-Hartree-Fock-Bogoliubov mean-field model and the continuum quasiparticle random phase approximation formulated in the coordinate space representation. It is found that the pair transfer strength for the transitions between the ground states becomes significantly large for the isotopes with A >= 140, reflecting very small neutron separation energy and long tails of the weakly bound 3 p orbits. In (132) Sn-140, a peculiar feature of the pair transfer is seen in transitions to low-lying excited 0(+) states. They can be regarded as a kind of pair vibrational mode which is characterized by an anomalously long tail of the transition density extending to far outside of the nuclear surface, and a large strength comparable to that of the ground-state transitions. The presence of the weakly bound neutron orbits plays a central role for these anomalous behaviors.

DOI： 10.1103/PhysRevC.84.044317

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DOI： 10.1103/PhysRevC.83.054301

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：POLISH ACAD SCIENCES INST PHYSICS  

A new microscopic approach is proposed to derive the five-dimensional quadrupole collective Hamiltonian. It is based on the time-dependent mean-field theory and the adiabatic self-consistent collective coordinate method. We apply the method to studies of oblate-prolate shape coexistence/mixing phenomena and anharmonic vibrations. Experimental data for Se isotopes are well reproduced.

DOI： 10.5506/APhysPolB.42.443

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

We performed fluctuation analysis by means of the local scaling dimension for the strength function of the isoscalar (IS) giant quadrupole resonance (GQR) in Pb-208 where the strength function is obtained by the shell model calculation including 1p1h and 2p2h configurations. It is found that at almost all energy scales, fluctuation of the strength function obeys the Gaussian orthogonal ensemble (GOE) random matrix theory limit. This is contrasted with the results for the GQR in Ca-40, where at the intermediate energy scale of about 1.7 MeV, a deviation from the GOE limit was detected. It is found that the physical origin for this different behavior of the local scaling dimension is ascribed to the difference in the properties of the damping process.

DOI： 10.1103/PhysRevC.83.024314

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：AMER INST PHYSICS  

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.

DOI： 10.1063/1.3584067

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Language：Japanese   Publisher：素粒子論グループ 素粒子論研究 編集部  

DOI： 10.24532/soken.119.1_A119

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

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 (68,70,72)Se. 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 within the two major-shell active model spaces both for neutrons and protons. 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 Schrodinger equation, we evaluate excitation spectra, quadrupole transitions, and moments. The 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.

DOI： 10.1103/PhysRevC.82.064313

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DOI： 10.1103/PhysRevC.82.024318

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

We investigate the neutron pair transfer modes associated with the low-lying quadrupole states in neutron-rich Sn isotopes by means of the quasiparticle random phase approximation based on the Skyrme-Hartree-Fock-Bogoliubov mean-field model. The transition strength of the quadrupole pair-addition mode feeding the 2(1)(+) state is enhanced in the Sn isotopes with A >= 132. The transition density of the pair-addition mode has a large spatial extension in the exterior of the nucleus, reaching to r similar to 12-13 fm. The quadrupole pair-addition mode reflects sensitively a possible increase of the effective pairing interaction strength in the surface and exterior regions of neutron-rich nuclei.

DOI： 10.1103/PhysRevC.82.024318

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WORLD SCIENTIFIC PUBL CO PTE LTD  

We develop an efficient microscopic method of deriving the five-dimensional quadrupole collective Hamiltonian on the basis of the adiabatic self-consistent collective coordinate method. We illustrate its usefulness by applying it to the oblate-prolate shape coexistence/mixing phenomena and anharmonic vibrations in Se isotopes.

DOI： 10.1142/S0217732310000356

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WORLD SCIENTIFIC PUBL CO PTE LTD  

We discuss the pair transfer mode populating pair vibration 0(2)(+) state in neutron-rich Sn isotopes by means of the continuum quasi particle random phase approximation (continuum QRPA). It is seen that the strength of the two-neutron addition transfer from the ground state to the 0(2)(+) state is significantly enhanced beyond the N = 82 shell gap.

DOI： 10.1142/S0217732310000964

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WORLD SCIENTIFIC PUBL CO PTE LTD  

From a viewpoint of oblate-prolate symmetry and its breaking, we propose a simple model based on the quadrupole collective Hamiltonian to study dynamics of triaxial deformation in shape coexistence phenomena. The numerical results suggest that the oblate-prolate symmetry breaking in the rotational moments of inertia can play an important role for the oblate-prolate shape coexistence as well as that in the collective potential.

DOI： 10.1142/S0217732310000939

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WORLD SCIENTIFIC PUBL CO PTE LTD  

We develop a method of determining microscopically the collective potential and inertial masses in the five-dimensional quadrupole collective Hamiltonian on the basis of the adiabatic self-consistent collective coordinate method. We apply this method to shape coexistence/mixing phenomena in low-lying states of the proton-rich Kr isotopes.

DOI： 10.1142/S0217732310000940

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

Construction of the microscopic theory of large-amplitude collective motion, capable of describing a wide variety of quantum collective phenomena in nuclei, is a long-standing and fundamental subject in the study of nuclear many-body systems. The present status of the challenge toward this goal is discussed taking the shape coexistence/mixing phenomena as typical manifestations of the large-amplitude collective motion at zero temperature. Some open problems in rapidly rotating cold nuclei are also briefly discussed in this connection.

DOI： 10.1088/0954-3899/37/6/064018

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

Physics related to weakly bound nuclei and low-density asymmetric nuclear matter is discussed from a theoretical point of view. Especially, we focus our discussion on new correlations in nuclei near the drip lines and on open issues of the density functional theory with a proper account of the continuum.

DOI： 10.1088/0954-3899/37/6/064017

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Language：English   Publishing type：Part of collection (book)   Publisher：World Scientific Publishing Co.  

Large-amplitude oblate-prolate shape coexistence dynamics in proton-rich Se and Kr isotopes is analyzed using the five-dimensional quadrupole collective Hamiltonian. The potential and inertial functions in the collective Hamiltonian are calculated using the constrained Hartree-Fock-Bogoliubov (CHFB) equation and the local quasiparticle random-phase approximation (LQRPA). The excitation spectra and the electric quadrupole transitions between the low-lying states in 68Se are calculated by solving the collective Schrodinger equation, and the shape mixing dynamics in the low-lying collective states are discussed.

DOI： 10.1142/9789814313933_0042

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PROGRESS THEORETICAL PHYSICS PUBLICATION OFFICE  

From the viewpoint of oblate-prolate symmetry and its breaking, we adopt the quadrupole collective Hamiltonian to study the dynamics of triaxial deformation in shape coexistence phenomena. It accommodates the axially symmetric rotor model, the gamma-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 gamma 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 (beta, gamma) deformation space.

DOI： 10.1143/PTP.123.129

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：AMER INST PHYSICS  

We present a new microscopic approach which consists of the constrained Hartree-Fock-Bogoliubov (CHFB) and the local quasiparticle random-phase approximation (LQRPA) to construct the five-dimensional quadrupole collective Hamiltonian for large-amplitude collective dynamics. The excitation spectra and the electric quadrupole transitions between the low-lying states in Se-68 are calculated by solving the collective Schrodinger equation.

DOI： 10.1063/1.3442638

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：AMER INST PHYSICS  

Features of the neutron pair correlation characteristic to neutron-rich nuclei are discussed on the basis of the Hartree-Fock-Bogoliubov mean-field model and the continuum quasiparticle random phase approximations. We discuss the monopole and quadrupole pair transfer modes in neutron-rich Sn isotopes beyond the N = 82 shell closure. We investigate also how the pair correlation behaves in deformed weakly bound nuclei, and we show that the neutron pairing enhances as the binding energy of neutrons becomes small.

DOI： 10.1063/1.3442639

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：AMER INST PHYSICS  

The five-dimensional quadrupole collective Hamiltonian for large-amplitude collective dynamics is microscopically constructed by the constrained Hartree-Fock-Bogoliubov (CHFB) method and local quasiparticle random phase approximation (LQRPA). The excitation spectra and the electric quadrupole transitions between the low-lying states in Se-68 are calculated by solving the collective Schrodinger equation.

DOI： 10.1063/1.3455952

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WORLD SCIENTIFIC PUBL CO PTE LTD  

We formulate a new Hartree-Fock-Bogoliubov method applicable to weakly bound deformed nuclei using the coordinate-space Green's function technique. An emphasis is put on treatment of quasiparticle states in the continuum, on which we impose the correct boundary condition of the asymptotic out-going wave. We illustrate this method with numerical examples.

DOI： 10.1142/S0218301309014202

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DOI： 10.1103/PhysRevC.80.024301

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

We formulate a new scheme of the Hartree-Fock-Bogoliubov mean-field theory applicable to weakly bound and pair-correlated deformed nuclei using the coordinate-space Green's function technique. On the basis of a coupled-channel representation of the quasiparticle wave function expanded in terms of the partial waves, we impose the correct boundary condition of the asymptotically out-going waves on the continuum quasiparticle states. We perform numerical analysis for (38)Mg to illustrate properties of the continuum quasiparticle states and the pair correlation in deformed nuclei near the neutron drip line.

DOI： 10.1103/PhysRevC.80.024301

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

The oblate-prolate shape coexisting/mixing phenomena in proton-rich (68,70,72)Se 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 Schroumldinger 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.

DOI： 10.1103/PhysRevC.80.014305

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

A Monte Carlo simulation of the gamma decay of superdeformed nuclei has been developed. It is based on microscopic calculations for the energy levels, E2 decay probabilities, collective mass parameters, and potential energy barriers. The use of microscopically calculated quantities largely reduces the parameters of the simulation, allowing one to focus on the basic ingredients of the physical processes. Calculations are performed for the warm rotating superdeformed nuclei Tb-151 and Pb-196, for which high statistics Euroball IV data are available. The dependence on the simulation parameters is investigated, together with the basic features of the microscopic calculations.</p>.

DOI： 10.1103/PhysRevC.79.064307

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

The gamma decay associated with the warm rotation of the superdeformed nuclei Tb-151 and Pb-196 has been measured with the Euroball IV array. Several experimental quantities are presented, putting strong constraints on the decay dynamics in the superdeformed well. The data are successfully reproduced using a Monte Carlo simulation of the gamma decay based on microscopically calculated energy levels, E2 decay probabilities, collective mass parameters, and potential energy barriers between the wells associated with normal and super deformation. This allows one to test the basic ingredients of the physical process, such as the strength of the two-body residual interaction and the potential barriers as a function of spin and excitation energy. We also show that the data probe the E1 strength function, indicating an enhancement around 1-2 MeV gamma rays, which might be related to octupole vibrations.</p>.

DOI： 10.1103/PhysRevC.79.064306

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Language：English   Publishing type：Research paper (scientific journal)  

The γ-decay from the warm rotation in the transition region between order and chaos is studied in the superdeformed (SD) nuclei 151Tb and 196Pb, using the EUROBALL IV array. A number of observables, testing the decay dynamics in the SD well, are compared with predictions from a Monte Carlo simulation of the γ-decay based on microscopic calculations of discrete levels and decay probabilities. Agreement with the data is found only assuming an enhancement of the B(E1) strength around 1 MeV by a factor of 10-100, which is consistent with the evidence for octupole vibrations in both mass regions. The work shows the relevance of γ-spectroscopy in the order-to-chaos regime to highlight specific nuclear structure effects.

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DOI： 10.1103/PhysRevC.79.024313

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

We develop a new formulation of the continuum quasiparticle random-phase approximation in which the velocity-dependent terms of the Skyrme effective interaction are explicitly treated except the spin-dependent and the Coulomb terms. Numerical analysis using the SkM(*) parameter set is performed for the isovector dipole and the isovector/isoscalar quadrupole responses in (20)O and (54)Ca. It is shown that the energy-weighted sum rule, including the enhancement factors for the isovector responses, is satisfied with good accuracy. We investigate also how the velocity-dependent terms influence the strength distribution and the transition densities of the low-lying surface modes and the giant resonances.

DOI： 10.1103/PhysRevC.79.024313

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PROGRESS THEORETICAL PHYSICS PUBLICATION OFFICE  

We investigate the low-lying octupole response of neutron-rich Ni isotopes beyond the N = 50 shell closure using the Skyrme-Hartree-Fock-Bogoliubov mean fields and the continuum quasi-particle random phase approximation. Performing detailed numerical analyses employing the Skyrme parameter set SLy4 and a density-dependent delta interaction of the mixed type, we show that a neutron mode emerges above the neutron separation energy as a consequence of the weak binding of neutrons and that it strongly influences the di-neutron correlation.

DOI： 10.1143/PTP.121.97

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：AMER INST PHYSICS  

We formulate the coordinate-space Hartree-Fock-Bogoliubov (HFB) theory which can describe pair correlated and deformed nuclei near the drip-lines. In order to ensure the correct asymptotic form of weakly bound and continuum quasiparticle states, we adopt a coupled-channel representation based on the partial wave expansion, and then we construct the exact HFB Green's function. Numerical examples calculated for (38)Mg are discussed.

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：AMER INST PHYSICS  

Large-amplitude collective dynamics of oblate-prolate shape coexistence in the low-lying states of proton-rich Se-68,Se-70,Se-72 are studied. The collective path (collective submanifold) is extracted from the time-dependent Hartree-Fock-Bogoliubov (HFB) manifold by use of the adiabatic self-consistent collective coordinate (ASCC) method. The inertial functions for the large-amplitude collective vibration along the collective path and for the three-dimensional rotation are microscopically calculated. Solving the collective Schrodinger equation, excitation spectra, E2 transition probabilities, and spectroscopic quadrupole moments are evaluated.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

The gamma decay associated with the warm rotation of the superdeformed nuclei (151)Tb and (196)Pb has been measured with the EUROBALL IV array. Several independent quantities provide a stringent test of the population and decay dynamics in the superdeformed well. A Monte Carlo simulation of the gamma decay based on microscopic calculations gives remarkable agreement with the data only assuming a large enhancement of the B(E1) strength for 1-2 MeV gamma rays, which may be related to the evidence for octupole vibrations in both mass regions.

DOI： 10.1103/PhysRevLett.101.142502

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PROGRESS THEORETICAL PHYSICS PUBLICATION OFFICE  

We analyse the deformation mechanism in neutron-rich Cr, Fe and Ti isotopes with N = 32-44 using a Skyrme-Hartree-Fock-Bogoliubov mean-field code employing a two-dimensional mesh representation in the cylindrical coordinate system. Evaluating the quadrupole deformation energy systematically; we show that the Skyrme parameter set SkM* gives a quadrupole instability around the neutron numbers N similar to 38-42 in Cr isotopes, where the deformation energy curve suggests a transitional behavior with a shallow minimum extending to a. large prolate deformation. The roles of a deformed N = 38 gap and the position of the neutron g(9/2) orbit are analysed in detail.

DOI： 10.1143/PTP.120.143

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PROGRESS THEORETICAL PHYSICS PUBLICATION OFFICE  

The microscopic dynamics of oblate-prolate shape coexistence/mixing phenomena in (68) Se and Kr-72 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. A 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. It is found that the basic properties of the shape coexistence/mixing are qualitatively reproduced. The results of the calculation indicate that the oblate-prolate shape mixing decreases as the angular momentum increases.

DOI： 10.1143/PTP.119.59

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

We look for collective excitations originating from the strong surface pairing in unstable nuclei near the neutron drip-line. The soft dipole excitation is such a pairing mode as it exhibits a character of core-vs-dineutron motion. Possibility of the hydrodynamic phonon mode (the Anderson-Bogoliubov mode) is also discussed.

DOI： 10.1016/j.nuelphysa.2007.01.017

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The adiabatic self-consistent collective coordinate (ASCC) method is a practical microscopic theory of large-amplitude collective motion in nuclei with superfluidity. We show that its basic equations are invariant under transformations involving the gauge angle in particle-number space. By virtue of this invariance, a clean separation of the large-amplitude collective motion and the pairing rotational motion can be made, and this allows 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 propose a gauge-fixing prescription that seems most convenient in realistic calculations.

DOI： 10.1143/PTP.117.451

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Language：English   Publisher：Soryushiron Kenkyu Editorial Office  

DOI： 10.24532/soken.115.3_C88

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DOI： 10.24532/soken.115.3_C45

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PROGRESS THEORETICAL PHYSICS PUBLICATION OFFICE  

We apply the adiabatic self-consistent collective coordinate (ASCC) method to the multi-O(4) model and study the collective mass (inertia function) of many-body tunneling motion. Comparing the results with those obtained from the exact diagonalization, we show that the ASCC method is capable of describing the gradual change of the excitation spectra from an anharmonic vibration about a spherical shape to a doublet pattern associated with a deformed double-well potential possessing oblate-prolate symmetry. It is found that 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.

DOI： 10.1143/PTP.115.567

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Language：English   Publishing type：Research paper (international conference proceedings)  

By means of the adiabatic self-consistent collective coordinate method and the pairing-plus-quadrupole interaction, we have for the first time obtained a self-consistent collective path connecting the oblate and prolate local minima in 68Se and 72Kr. This self-consistent collective path is found to run approximately along the valley connecting the oblate and prolate local minima in the collective potential energy landscape. The result of this calculation clearly indicates the importance of triaxial deformation dynamics in oblate-prolate shape coexistence phenomena. © Società Italiana di Fisica / Springer-Verlag 2005.

DOI： 10.1140/epjad/i2005-06-039-7

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMERICAN PHYSICAL SOC  

The neutron pairing correlation and the soft dipole excitation in medium mass nuclei near the drip line are investigated from the viewpoint of the di-neutron correlation. Numerical analyses based on the coordinate-space Hartree-Fock-Bogoliubov method and the continuum quasiparticle random phase approximation are performed for even-even O18-24,Ca50-58, and Ni80-86. A clear signature of the di-neutron correlation is found in the ground state; two neutrons are correlated at short relative distances less than or similar to 2 fm with large probability similar to 50%. The soft dipole excitation is influenced strongly by the neutron pairing correlation, and it accompanies a large transition density for pair motion of neutrons. This behavior originates from a coherent superposition of two-quasiparticle configurations [l x (l + 1)](L=1) consisting of continuum states with high orbital angular momenta l reaching an order of l similar to 10. It suggests that the soft dipole excitation under the influence of neutron pairing is characterized by the motion of di-neutron in the nuclear exterior against the remaining A-2 subsystem. Sensitivity to the density dependence of the effective pair force is discussed.

DOI： 10.1103/PhysRevC.71.064326

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Language：English   Publisher：PROGRESS THEORETICAL PHYSICS PUBLICATION OFFICE  

By means of the adiabatic self-consistent collective coordinate method and the pairing-plus-quadrupole interaction, we have for the first time obtained a self-consistent collective path connecting the oblate and prolate local minima in Se-68 and Kr-72. This self-consistent collective path is found to run approximately along the valley connecting the oblate and prolate local minima in the collective potential energy landscape. The result of this calculation clearly indicates the importance of triaxial deformation dynamics in oblate-prolate shape coexistence phenomena.

DOI： 10.1143/PTP.113.129

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER  

On the basis of the coordinate-space Hartree-Fock-Bogoliubov and the continuum quasiparticle random phase approximation (QRPA) theories, we demonstrate that a di-neutron correlation exists in the ground states of medium-mass neutron-rich nuclei near the dripline, and we suggest that the soft dipole excitation has the character of di-neutron motion against the remaining A - 2 subsystem.

DOI： 10.1140/epjad/i2005-06-045-9

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IOP PUBLISHING LTD  

Investigating the pair correlation in medium-mass nuclei near the neutron drip-line, we find that the pairing involving several weakly bound neutrons exhibits a significant spatial correlation of the di-neutron type. We suggest that the strong spatial correlation is an inherent property of the pair correlation in nuclear matters at low densities. The di-neutron correlation influences strongly properties of the soft dipole and octupole excitations of the neutron-rich nuclei.

DOI： 10.1088/1742-6596/20/1/019

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Language：English   Publisher：PROGRESS THEORETICAL PHYSICS PUBLICATION OFFICE  

By means of the adiabatic self-consistent collective coordinate method and the pairing-plus-quadrupole interaction, we have obtained a self-consistent collective path connecting the oblate and prolate local minima in Se-68 for the first time. The result of the calculation indicates the importance of triaxial deformation dynamics in oblate-prolate shape coexistence phenomena.

DOI： 10.1143/PTP.112.363

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

The validity of the K-quantum number in rapidly rotating warm nuclei is investigated as a function of thermal excitation energy U and angular momentum I, for the rare-earth nucleus Er-163. The quantal eigenstates are described with a shell model which combines a cranked Nilsson mean-field and a residual two-body interaction, together with a term which takes into account the angular momentum carried by the K-quantum number in an approximate way. K-mixing is produced by the interplay of the Coriolis interaction and the residual interaction; it is weak in the region of the discrete rotational bands (U less than or similar to 1 MeV), but it gradually increases until the limit of complete violation of the K-quantum number is approached around U similar to 2-2.5 MeV The calculated matrix elements between bands having different K-quantum numbers decrease exponentially as a function of DeltaK, in qualitative agreement with recent data. (C) 2004 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.nuclphysa.2004.03.004

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Language：Japanese   Publisher：The Physical Society of Japan  

Presense of weakly bound nucleons in neutron-rich nuclei near the drip-line may lead to new features of nucleon correlations. We discuss illustrative examples concerning the soft dipole excitation and the neutron pair correlations.

DOI： 10.11316/butsuri1946.59.96

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Properties of thermally excited rotating nuclei are discussed by means of the cranked shell model. Focus is put on the violation of the K-quantum number in the rare-earth deformed nucleus Er-163 and on the peculiar features of rotational motion in superdeformed Hg nuclei, which appear to be precursory of ergodic rotational bands.

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：WORLD SCIENTIFIC PUBL CO PTE LTD  

Pair correlation effects on the soft dipole excitation in medium mass nuclei near neutron drip-line are investigated by means of the continuum quasiparticle random phase approximation. The correlation of di-neutron type found in the ground state affects strongly the soft dipole excitation, and enhances the transition amplitude for two-neutron pair transfer.

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：WORLD SCIENTIFIC PUBL CO PTE LTD  

By using the continuum quasiparticle random phase approximation, which we recently formulated on the basis of the coordinate-space Hartree-Fock-Bogoliubov theory, we investigate pairing effects on the low-lying dipole strength in neutron rich oxygen isotopes near the drip-line. The neutron pairing enhances the dipole strength near the threshold, especially in the case of the surface pairing. Analysis shows that spatially correlated spin-singlet neutron pairs (di-neutrons) are formed in the external region, and the low-lying dipole strength is characterized by motion of the correlated neutron pairs against the core.

DOI： 10.1142/9789812703972_0039

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We performed fluctuation analysis by means of the local scaling dimension for the strength function of the isoscalar (IS) and the isovector (IV) giant quadrupole resonances in [Formula Presented], where the strength functions are obtained by the shell model calculation within up to the [Formula Presented] configurations. It is found that at small energy scale, fluctuation of the strength function almost obeys the Gaussian orthogonal ensemble (GOE) random matrix theory limit. On the other hand, we found a deviation from the GOE limit at the intermediate energy scale of about [Formula Presented] for the IS and at [Formula Presented] for the IV. The results imply that different types of fluctuations coexist at different energy scales. Detailed analysis strongly suggests that GOE fluctuation at small energy scale is due to the complicated nature of [Formula Presented] states and that fluctuation at the intermediate energy scale is associated with the spreading width of the Tamm-Dancoff [Formula Presented] states. © 2003 The American Physical Society.

DOI： 10.1103/PhysRevC.68.054316

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

The gamma-decay of excited rotating nuclei in the high level density region a few MeV above the yrast line has been studied through a statistical analysis of the fluctuation of counts in gamma-gamma coincident spectra. In particular, making use of the covariance technique between spectra gated by different intrinsic configurations, one can measure how the cascades feeding into different selected bands are similar. The aim is to learn about the transition between order to chaos in the nuclear many-body system, in terms of the validity of selection rules associated with the quantum numbers of the intrinsic structure. Experimental results on the nucleus Yb-164 are presented and compared to model predictions based on cranked shell model calculations including a two-body residual interaction.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

The damping of collective rotational motion is studied microscopically, making use of shell model calculations based on the cranked Nilsson deformed mean-field and on residual two-body interactions, and focusing on the shape of the gamma-gamma correlation spectra and on its systematic behavior. It is shown that the spectral shape is directly related to the damping width of collective rotation, Gamma(rot), and to the spreading width of many-particle many-hole configurations, Gamma(mu). The rotational damping width is affected by the shell structure, and is very sensitive to the position of the Fermi surface, besides mass number, spill and deformation. This produces a rich variety of features in the rotational damping phenomena.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ACTA PHYSICA POLONICA B, JAGELLONIAN UNIV, INST PHYSICS  

The gamma-decay of excited rotating nuclei is studied as function of heat energy through a statistical analysis of the fluctuation of counts in gamma-gamma coincident spectra. In particular, making use of the covariance technique between spectra gated by different intrinsic configurations, one can find if there are similarities among cascades feeding into different selected bands. This can be used to learn about the transition between order to chaos in the nuclear many-body system, in terms of the validity of selection rules associated with the quantum numbers of the intrinsic structure. Experimental results on the nucleus Yb-164 Seem to indicate a possible weakening of the selection rules already at the moderate excitation energy greater than or equal to 1 MeV above yrast, probed by the rotational decay-flow.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

The role of the rotating mean field and residual interactions is discussed on the basis of recent experimental interaction matrix elements and distribution of level distances. Based on a careful identification of the rotational bands in four rare-earth nuclei, carried out earlier, most of the interactions are found to be generated by a two-body residual interaction. Some hindrance is observed with respect to changes in the K quantum number. Level distance distributions address in a more general way the question of the independence of excitations within rotational states. Both types of experimental information, band interactions and level distances, are in general accordance with mean field bands interacting with a standard surface-delta interaction.

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：AMER INST PHYSICS  

By performing a fully three dimensional Hartree-Fock calculation with use of the Skyrm forces, we demonstrate possibility of exotic deformations violating both the reflection and the axial symmetries of N = Z nuclei in A similar to 60 - 80 mass region. The Y-32 tetrahedral shape predicted in excited Zr-80 arises from a shell gap at N, Z = 40 which is enhanced for the tetrahedron deformation. Softness toward the Y-33 triangular deformation of the oblate state in Se-68 is also predicted.

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：AMER INST PHYSICS  

The gamma-decay of the continuum has been measured in two mass regions. The excitation function of the continuum decay as well as spectral shape and fractional Doppler shifts are discussed for both Te-114 and Yb-164 compound nuclei, and show the typical features of rotational collective motion. Moreover, in both cases an upper limit of Gamma(rot) is given and the number of decay-paths is determined from the fluctuation analysis method. Simulations based on microscopic calculations of the rotational damping model reproduce quite well the experimental findings for both N-path and the scaling of Gamma(rot) as a function of the mass number.

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：WORLD SCIENTIFIC PUBL CO PTE LTD  

We study static non-axial octupole deformations in proton-rich Z = N nuclei, Ge-64, Se-68, Kr-72, Sr-76 and Zr-80, by using the Skyrme Hartree-Fock plus BCS method with no restrictions on the nuclear shape. The calculation predicts that the oblate ground state in Se-68 is extremely soft for the Y-33 triangular deformation, and that in Zr-80 the low-lying local minimum state coexisting with the prolate ground state has the Y-32 tetrahedral deformation.

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：WORLD SCIENTIFIC PUBL CO PTE LTD  

A shell model diagonalization method utilizing the cranked deformed mean-field has been developed to investigate the rotational damping phenomena and the coexistence of order and chaos in rapidly rotating warm nuclei.

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：WORLD SCIENTIFIC PUBL CO PTE LTD  

Shell effect on rotational damping associated with single particle alignment is discussed. Dispersion of rotational frequency is shown to be sensitive to single particle alignment structure at the Fermi surface. It is illustrated that shell oscillation of s.p. alignment influences significantly the dispersion of rotational frequency. In superdeformed Hg-192 th, shell effect causes considerably small rotational damping width Gamma(rot) similar to 30 keV, and large number of rotational bands N-band similar to 150, which are quite different from those in A similar to 150 superdeformed nuclei and normal deformed nuclei.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMERICAN PHYSICAL SOC  

In order to identify double-gamma vibrational states in well-deformed regions, we have made a Coulomb excitation experiment for Er-168. We could observe 1235-keV and 962-keV gamma transitions decaying from the 2056-keV 4(+) state. The measured E2 transition probabilities support the assignment of the 4(+) state as a two-phonon gamma-vibrational state.

DOI： 10.1103/PhysRevC.52.3492

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Several new methods for the study of nuclear structure at low temperature are reviewed. The methods analyze the fluctuations of the intensity of E(gamma)1 - E(gamma)2 spectra, and the shape and width GAMMA(rot) of the correlated patterns with different characteristics of the rotational motion in cold and warm nuclei. New results are given for the rotational damping width, and the number of 2-step-paths below and above U0 almost-equal-to 800 keV, considered to be the energy of the borderline between undamped and damped rotational motion. The rotational damping width GAMMA(rot) is studied as function of rotational frequency for selected regions of entry states in Tm-163, and found to be rather constant almost-equal-to 80 keV, significantly smaller than current theoretical predictions. The fluctuation analysis supports the damping picture in general, and confirms that a strong branching of the transition strength for each step in the E2 cascades exists at high spin. This can be taken as evidence for damping of the rotational motion in warm nuclei.

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：PERGAMON PRESS LTD  

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DOI： 10.1143/PTP.76.372

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Other Link： https://projects.repo.nii.ac.jp/?action=repository_uri&item_id=348626

Language：English   Publishing type：Research paper (scientific journal)   Publisher：KYOTO UNIV  

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DOI： 10.1143/PTP.72.666

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Other Link： https://projects.repo.nii.ac.jp/?action=repository_uri&item_id=347894

Language：Japanese   Publisher：一般社団法人日本物理学会  

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The adiabatic self-consistent collective coordinate method is applied to an exactly solvable multi-O(4) model that is designed to describe nuclear shape coexistence phenomena. The collective mass and dynamics of large amplitude collective motion in this model system are analyzed, and it is shown that the method yields a faithful description of tunneling motion through a barrier between the prolate and oblate local minima in the collective potential. The emergence of the doublet pattern is clearly described.

DOI： 10.1143/PTP.110.65

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Language：Welsh   Publisher：AMER INST PHYSICS  

The rotational damping width Gammarot and the compound damping width Gammacomp are two fundamental quantities that characterize rapidly rotating compound nuclei having finite thermal excitation energy. A two-component structure in the strength function of consecutive E2 transitions reflects the two widths, and it causes characteristic features in the double and triple gamma-ray spectra. We discuss a new method to extract experimentally values of Gammarot and Gammacomp. The first preliminary result of this method is presented.

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Language：English   Publisher：PROGRESS THEORETICAL PHYSICS PUBLICATION OFFICE  

We discuss novel features of a new continuum RPA formulated in the coordinate-space Hartree-Fock-Bogoliubov framework. This continuum quasiparticle RPA takes into account both the one- and two-particle escaping channels. The theory is tested with numerical calculations for monopole, dipole and quadrupole excitations in neutron-rich oxygen isotopes near the drip-line. Effects of the particle-particle RPA correlation caused by the pairing interaction are discussed in detail, and importance of the selfconsistent treatment is emphasized.

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Language：English   Publisher：ELSEVIER SCIENCE BV  

We formulate a continuum linear response theory on the basis of the Hartree-Fock-Bogoliubov formalism in the coordinate space representation in order to describe low-lying and high-lying collective excitations which couple to one-particle and two-particle continuum states. Numerical analysis is done for the neutron drip-line nucleus O-24. A low-lying collective mode that emerges above the continuum threshold with large neutron strength is analyzed. The collective state is sensitive to the density-dependence of the pairing. The present theory satisfies accurately the energy weighted sum rule. This is guaranteed by treating the pairing self-consistently both in the static HFB and in the dynamical linear response equation. (C) 2001 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0375-9474(01)01133-2

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Language：English   Publisher：ELSEVIER SCIENCE BV  

We construct a microscopic model of thermally excited superdeformed states that describes both the barrier penetration mechanism, leading to the decay-out transitions to normal deformed states, and the rotational damping causing fragmentation of rotational E2 transitions. We describe the barrier penetration by means of a tunneling path in the two-dimensional deformation energy surface, which is calculated with the cranked Nilsson-Strutinsky model. The individual excited superdeformed states and associated E2 transition strengths are calculated by the shell-model diagonalization of the many-particle-many-hole excitations interacting with the delta-type residual two-body force. The effects of the decay-out on the excited superdeformed states are discussed in detail for Dy-152, Eu-143 and Hg-192. The model predicts that the decay-out brings about a characteristic decrease in the effective number of excited superdeformed rotational bands. (C) 2001 Elsevier Science B.V. All fights reserved.

DOI： 10.1016/S0375-9474(01)01123-X

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Language：English   Publisher：ELSEVIER SCIENCE BV  

By performing fully 3D symmetry-unrestricted Skyrme-Hartree-Fock-Bogoliubov calculations, we discuss shape coexistence and possibility of exotic deformations simultaneously breaking the reflection and axial symmetries in proton-rich N = Z nuclei: Ge-64, Se-68, Kr-72,Sr-76, Zr-80 and Mo-84. Results of calculation indicate that the oblate ground state of Se-68 is extremely soft against the Y-33 triangular deformation, and that the low-lying spherical minimum coexisting with the prolate ground state in Zr-80 is extremely soft against the Y-32 tetrahedral deformation. (C) 2001 Elsevier Science B.V. All rights reserved.

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Language：English   Publisher：ACTA PHYSICA POLONICA B, JAGELLONIAN UNIV, INST PHYSICS  

A general discussion and illustration is given of strength functions for rotational transitions in two-dimensional E-gamma1 x E-gamma2 spectra. Especially, a narrow component should be proportional to the compound damping width, related to the mixing of basis rotational bands into compound bands with fragmented transition strength. Three E-gamma1 x E-gamma2 spectra are made by setting gates on triple coincidences, selecting cascades which feed into specific low-lying bands in the nucleus Hf-168. In each of the gated spectra, we find a ridge, carrying about 100 decay paths. This ridge is ascribed to rotational transitions in the excitation energy range of 1.0 to 1.5 MeV above the yrast line. The FWHM of the ridges axe around 40 keV, about a factor of two smaller than calculated on the basis of mixed cranked mean field bands.

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Language：English   Publisher：ELSEVIER SCIENCE BV  

Two aspects of rotational motion of thermally excited nuclei are discussed. First, the schematic cases of ordered or chaotic motion of intrinsic and rotational motion are presented: discrete rotational bands, ergodic bands, damping of the rotational motion. Secondly, the strength functions of mixing of basis bands and of E2-transitions over one or two decay steps are discussed. The two-step E2-strength displays both a narrow and wide component, yielding different types of information about the basis bands and their interaction. Indications of the presence of a narrow component is found in energy correlations of consecutive transitions on displaced rotational bands of a three dimensional spectrum for the nucleus Yb-168.

DOI： 10.1016/S0375-9474(00)00671-0

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The decay of the superdeformed bands has been studied mainly concentrating upon the decay-out spin, which is sensitive to the tunneling probability between the super- and normal-deformed wells. Although the basic features are well understood by the calculations, it is difficult to precisely reproduce the decay-out spins in some cases. Comparison of the systematic calculations with experimental data reveals that values of the calculated decay-out spins scatter more broadly around the average value in both the A approximate to 150 and 190 regions, which reflects the variety of calculated tunneling probability in each band.

DOI： 10.1016/S0375-9474(00)00674-6

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Language：English   Publisher：AMER INST PHYSICS  

Strength functions for damped collective motion sometimes exhibit fluctuation that is called tine structure. Using two examples, i.e. the damped collective rotation of deformed compound nuclei and the giant resonances, we discuss statistical measures that characterize the fine structures, and demonstrate how such measures tell us important information on the microscopic mechanism of the damping phenomena.

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Unresolved gamma transitions of Te-114 and of Sn-112 sorted into one-dimensional and two-dimensional spectra have been studied. The reaction Ni-64 + Cr-54 at bombarding energies 230, 240, 250, 260, 270 MeV was used and the gamma-rays were detected with the EUROBALL array. In the case of the nucleus 114Te the values of the multiplicity as a function of bombarding energy and of the moment of inertia were obtained. The effective moment of inertia was found to be almost constant in the interval I = 20-40 h, in contrast to the decreasing behaviour of the dynamic moment of inertia for the terminating yrast band. The ridge valley structures in E-gamma 1 x E-gamma 2 spectra of Te-114 and of Sn-112 were analysed with the fluctuation analysis technique. The analysis of the two nuclei are compared to simulations based on microscopic cranking calculations with residual interactions included. A rather good agreement is found between data and predictions. (C) 2000 Elsevier Science B.V. All rights reserved.

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The gamma-cascades feeding specific intrinsic configurations of Yb-164 are studied making use of a statistical analysis of counts fluctuations in gamma-gamma coincident spectra. In particular, variance and covariance spectra are obtained starting from the measured (0, +), (0, -) and (1, -) gate-selected matrices. The analysis of the first ridge of the spectra yields about 25 excited bands carrying rotational energy correlations for the total spectrum, and about 10 in coincidence with each of the (alpha, pi) configurations. The covariance of count fluctuations between the different (alpha, pi) gates is expressed by an experimental correlation coefficient, r, which measures the degree of sharing of decay paths through the excited bands, and thereby the extent to which selection rules are obeyed by the decay. The correlation coefficient is around r approximate to 0.3 for the ridge, and also in general rather small for valley fluctuations, Only at the highest valley energies, a tendency to larger correlation coefficients is seen, indicating some weakening of the selection rules over longer decay cascades. The results of the experimental analysis are compared to rotational damping model predictions based on cranked shell model plus residual interactions, and rather good agreement is found. (C) 2000 Published by Elsevier Science B.V. All rights reserved.

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Language：English   Publisher：PROGRESS THEORETICAL PHYSICS PUBLICATION OFFICE  

An adiabatic approximation to the selfconsistent collective coordinate method is formulated in order to describe large amplitude collective motions in nuclei with pairing correlations on the basis of the time-dependent Hartree-Fock-Bogoliubov equations of motion. The basic equations are presented in a local harmonic form which can be solved in a manner similar to that of the quasiparticle RPA equations. The formalism guarantees the conservation of nucleon number expectation values. An extension to the multi-dimensional case is also discussed.

DOI： 10.1143/PTP.103.959

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The intrinsic width of (multiparticle-multihole) compound states is an elusive quantity, of difficult direct access, as it is masked by damping mechanisms which control the collective response of nuclei. Through microscopic cranked shell model calculations, it is found that the strength function associated with two-dimensional gamma-coincidence spectra arising from rotational transitions between states lying at energies > 1 MeV above the yrast line, exhibits a two-component structure controlled by the rotational (wide component) and compound (narrow component) damping width. This last component is found to be directly related to the width of the multiparticle-multihole autocorrelation function. (C) 1999 Published by Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0370-2693(99)01058-8

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Language：English   Publisher：AMERICAN PHYSICAL SOC  

We propose a new method to analyze fluctuations in the strength function phenomena in highly excited nuclei. Extending the method of multifractal analysis to the cases where the strength fluctuations do not obey power scaling laws, we introduce a new measure of fluctuation, called the local scaling dimension, which characterizes scaling behavior of the strength fluctuation as a function of energy bin width subdividing the strength function. We discuss properties of the new measure by applying it to a model system which simulates the doorway damping mechanism of giant resonances. It is found that the local scaling dimension well characterizes fluctuations and their energy scales of fine structures in the strength function associated with the damped collective motions. [80556-2813(99)01609-X].

DOI： 10.1103/PhysRevC.60.034307

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Language：English   Publisher：SPRINGER VERLAG  

The number of discrete rotational bands in the nucleus Yb-168 is Obtained by a fluctuation analysis of the rotational ridge structure in double and triple gamma coincidence matrices. The data are compared with cranked shell model calculations including a surface delta interaction. It is found that the number of calculated bands strongly depends on the interaction strength V-0, and agreement between data and calculations supports the standard value V-0=27.5/A MeV.

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Unresolved γ rays of 114Te sorted into one- and two-dimensional spectra were studied. The reaction 64Ni(Ebeam = 230-270MeV)+54 Cr was used and the γ rays were detected with the EUROBALL array. The effective moment of inertia for the quasicontinuum was found to be almost constant for I=(20-40)ħ, in contrast with the decreasing behavior of the terminating yrast band. A comparative analysis with the nucleus 164Yb is presented and the results from a fluctuation analysis were compared with cranked shell model calculations. The comparison shows consistency in the scaling of the rotational damping width with mass number. © 1999 The American Physical Society.

DOI： 10.1103/PhysRevLett.83.5234

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We study static non-axial octupole deformations in proton-rich Z=N nuclei, Ge-64, Se-68, Kr-72, Sr-76, Zr-80 and Mo-84, by using the Skyrme Hartree-Fock plus BCS calculation with no restrictions on the nuclear shape. The calculation predicts that the oblate ground state in Se-68 is extremely soft for the Y-33 triangular deformation, and that in Zr-80 the low-lying local minimum state coexisting with the prolate ground state has the Y-32 tetrahedral deformation. (C) 1998 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0370-2693(98)00545-0

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Damping of collective rotational motion in A similar to 190 and A similar to 150 superdeformed nuclei is studied by means of the cranked shell model with two-body residual force. Numerical calculations predict that in a typical A similar to 190 superdeformed nucleus, Hg-192, the rotational damping width is significantly small, Gamma(rot) similar to 30 keV, and that the number of superdeformed bands in the off-yrast region amounts up to 150 at a given rotational frequency. These features are quite different from the prediction for A similar to 150 superdeformed nuclei and rare-earth normally deformed nuclei. It is shown that the single-particle alignments of the cranked Nilsson orbits have strong shell oscillation. It affects significantly the properties of rotational damping in superdeformed Hg-192. (C) 1998 Elsevier Science B.V.

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The nearest neighbour level spacing distribution and the Delta(3) statistic of level fluctuations associated with very high spin states (I greater than or similar to 30) in rare-earth deformed nuclei are analysed by means of a cranked shell model, The many particle-many hole configurations created in the rotating Nilsson potential are mixed by the surface-delta two-body residual interaction, The levels in the near-yrast region show a Poisson-like level spacing distribution. As the intrinsic excitation energy U increases, the level statistics shows a gradual transition from order to chaos, reaching at U greater than or similar to 2 MeV the Wigner distribution typical of the Gaussian orthogonal ensemble of random matrices, This transition is caused by the residual two-body interaction, On the other hand, the level spacings between the yrast and the first excited state show a peculiar behaviour, displaying a Wigner-like distribution instead of the Poisson-like distribution seen for the other near-yrast rotational states, The lowest spacings reflect the properties of the single-particle orbits in the mean-field, and are only weakly affected by the residual two-body interaction. (C) 1997 Elsevier Science B.V.

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In order to provide a microscopic description of levels and E2 transitions in rapidly rotating nuclei with internal excitation energy up to a few MeV, use is made of a shell model which combines the cranked Nilsson mean-field and the residual surface delta two-body force. The damping of collective rotational motion is investigated in the case of a typical rare-earth nucleus, namely Yb-168. It is found that rotational damping sets in at around 0.8 MeV above the yrast line, and the number of levels which form rotational band structures is thus limited. We predict at a given rotational frequency the existence of about 30 rotational bands of various lengths, in overall agreement with the experimental findings. The onset of the rotational damping proceeds quite gradually as a function of the internal excitation energy. The transition region extends up to around 2 MeV above yrast and it is characterized by the presence of scars of discrete rotational bands which extend over few spin values and stand out among the damped transitions, and by a two-component profile in the E-gamma-E-gamma correlation. The important role played by the high-multipole components of the two-body residual interaction is emphasized. (C) 1997 Elsevier Science B.V.

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We discuss damping of the collective rotational motion in A similar to 150 superdeformed nuclei by means of a shell-model combining the cranked Nilsson mean field and the surface and volume delta two-body residual forces. It is shown that, because of the shell structure associated with the superdeformed mean field, onset energy of the rotational damping becomes E(x) similar to 1.5-3 MeV above the yrast line, with significant variation for different neutron and proton numbers. The mechanism of the shell structure effect is investigated through detailed analysis of level densities in superdeformed nuclei. The variation in onset of damping is associated with variation in the single-particle structure at the Fermi surface.

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Language：English   Publisher：PERGAMON PRESS LTD  

The rotational continuum for normally deformed nuclei of the rare earth region is investigated making use of statistical analysis methods, With these techniques it is possible to extract information on the rotational motion from the region of high level density, in this connection, two points will be discussed: i) the important role of the residual interaction in the description of the experimental data and ii) the dependence of the mixing among rotational bands on the symmetry quantum numbers of the nuclear states, This last point was investigated for the nucleus Er-163 for which it has been found that the gamma-cascades feeding into low-K bands are different from those feeding high-K bands, This result indicates that the K-selection rules are effective for excited rotational bands within the angular momentum 30h less than or equal to I less than or equal to 40h.

DOI： 10.1016/S0146-6410(97)00026-4

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Language：English   Publisher：SPRINGER VERLAG  

We present shell model calculations for warm rotating nuclei, combining the cranked Nilsson mean field and a residual surface-delta two-body interaction, The model is used to describe the transition from the region of well-defined rotational bands into the region dominated by rotational damping, and the results are in overall agreement with the experimental findings.

DOI： 10.1007/s002180050310

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Rotational motion loses its coherence as a function of the nuclear internal excitation energy. The damping process does not proceed in a continuous fashion and scars of discrete rotational bands are found, inbedded in a background of damped rotational states, regardless whether the calculations are carried out using effective or ''random'' forces. The complexity of the damping mechanism is revealed in the lineshape of the ridges in the gamma-gamma correlation spectrum.

DOI： 10.1007/s002180050178

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Language：English   Publisher：AMERICAN PHYSICAL SOC  

The gamma decay of the excited rotating Yb-168 nucleus has been simulated considering the competition between El and E2 transitions, using microscopically calculated rotational bands. The simulations were made for two different cases: (i) pure rotating mean field bands and (ii) rotational bands mixed by a residual interaction. Simulated gamma-gamma spectra were analyzed in the typical rotational ridge-valley region. The fluctuation analysis method, sensitive to the effective number of gamma-decay paths, was also applied. An overall agreement between experimental and simulated data is found for the case of mixed rotational bands.

DOI： 10.1103/PhysRevLett.76.4484

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Language：English   Publishing type：Book review, literature introduction, etc.   Publisher：ELSEVIER SCIENCE BV  

It is well established that nucleons in the atomic nucleus can organize their motion, leading to quadrupole deformed shapes of the average field and to rotations of the nucleus as a whole. At an excitation energy of few MeV above the yrast line, rotational bands become very closely spaced in energy. Any single band can be viewed as a collective sequence of related states embedded in a dense background of other (more or less complicated) states, to which ii will couple by residual interactions. This coupling leads to stationary states of the system (the compound nucleus) which are complicated mixtures of unperturbed configurations. The rotational degree of freedom is ''damped'' in these compound states in the sense that the electric quadrupole decay of a single quantum state with angular momentum I will not go to a unique final state with spin I - 2 (as for the unperturbed bands) but will exhibit a spectrum of final states all having spin I - 2. In other words, for each compound nucleus formed in an experiment, the cascade of similar to 20 gamma-rays, which eventually will cool the system, will find many transitions through which to proceed in the regions where bands mix strongly (damped region) and only few in the region of discrete bands. In actual experiments, the cascade of gamma-rays associated with each of the members of the ensemble of compound nuclei will use each of the ''discrete'' transitions many more times than the ''continuum'' transitions. Relatively large and small fluctuations in the recorded coincidence spectrum will ensue, respectively. The analysis of the fluctuations will be shown to be instrumental to gain insight into the phenomenon of rotational damping. For this purpose, two- and higher-fold coincidence spectra emitted from rotating nuclei are analyzed with respect to the count fluctuations. The coincidences from consecutive gamma-rays emitted from discrete rotational bands generate ridges in the E(gamma 1) . E(gamma 2) spectrum, and the fluctuation analysis of the ridges is based upon the ansatz of a random selection of transition energies from band to band. This ansatz is supported by a cranked mean-field calculation for the nucleus Yb-168, as well as by analyzing resolved bands in Yb-168 and its neighbors. Consecutive gamma-rays emitted from the region of rotational damping spread out more in the E(gamma 1) . E(gamma 2) plane than those associated with transitions between members of discrete rotational bands, and are studied most clearly in the central valley (E(gamma 1) = E(gamma 2)) The fluctuation analysis of the valley is based upon the ansatz of fluctuations in the intensity of the transitions of Porter-Thomas type superposed on a smooth spectrum of transition energies. This ansatz is again supported by a mixed-band calculation. The mathematical treatment of count fluctuations is formulated in general terms, and the connection to earlier treatments of one-fold spectra of high level density is established. The statistical assumptions underlying the fluctuation analysis imply the existence of a principal uncertainty, which is examined in detail. In the experimental section, the fluctuation analysis is applied to two-dimensional gamma-spectra, the only available data at present with sufficient intensity to warrant a meaningful analysis. Large fluctuations are observed in the ridge structures from the four cases analyzed, showing that only a rather low number( approximate to 30) of discrete rotational bands exist.
In contrast, only weak fluctuations are found along the central valley, revealing that the spectrum in the valley effectively contains different (of the order of 10(5)) coincidence combinations. This number is considerably larger than what is found assuming that the rotational decay leads to a unique final stare, showing that the transition strength through each decay step is spread over many states within a given energy interval, the damping width, and thus providing fairly direct evidence of the rotational damping picture.

DOI： 10.1016/0370-1573(95)00060-7

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Language：English   Publisher：AMERICAN PHYSICAL SOC  

In order to identify double-gamma vibrational states in well-deformed regions, we have made a Coulomb excitation experiment for Er-168. We could observe 1235-keV and 962-keV gamma transitions decaying from the 2056-keV 4(+) state. The measured E2 transition probabilities support the assignment of the 4(+) state as a two-phonon gamma-vibrational state.

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The number of excited superdeformed bands in Eu-143 is measured by use of the Fluctuation Analysis Method. Between 10 and 40 rotational bands, displaying typical rotational energy correlations over two consecutive transitions, are populated within a rather narrow range in transition energy, E(gamma) approximate to 1300-1500 keV. These numbers are close to the values found for normally deformed nuclei and agree with microscopic cranking + band mixing calculations for the specific superdeformed nucleus, which predict the onset of rotational damping to occur at the excitation energy U-0 = 1.3-1.6 MeV above the yrast line.

DOI： 10.1016/0370-2693(95)00549-Z

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The study of damping of rotational motion applying the rotational plane mapping (RPM) method is presented and discussed. The aim of this technique is to extract the distribution of the rotational transition strength from an analysis of the shape of the ''central valley'' of two- and three-dimensional gamma-ray spectra. The method is applied to a triple gamma-coincidence data set of Tm-162,Tm-163 nuclei formed in Cl-37+Te-130 reactions. The rotational transition strength is obtained as a function of rotational frequency for selected regions of entry states, and the width is found to be rather constant and approximately equal to 80 keV. This value is significantly smaller than the value predicted theoretically for the rotational damping width Gamma(rct). Also the ratio between the observed depth and width of both the 2D and 3D valleys does not agree with the simple model adopted in the RPM method, These discrepancies point to the presence of both a wide and a narrow component in the distribution of rotational strength as extracted by the RPM method. The analysis of simulated spectra obtained on the basis of realistic band-mixing calculations, including residual interactions, confirms this behaviour.

DOI： 10.1016/0375-9474(95)00024-U

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Language：English   Publisher：POLISH ACAD SCIENCES INST PHYSICS  

The progress in gamma-spectroscopy is discussed with special emphasis on the transition region in excitation energy, from the rather well known cold nuclei characterized by regular rotational motion built on specific single particle configurations with well defined quantum numbers, to the region above 800 keV in heat energy, where the rotational motion is damped, as a result of a spreading of the rotational transition strength, due to residual interactions acting between the close lying bands. A general analysis scheme is advocated, aiming at a more direct comparison between the experimental results and theoretical models to give a more complete picture of nuclear structure going from cold to warm nuclei. A simulation model for describing the rotational and statistical decay of high spin states has been developed based on microscopically calculated energies and the spreading of rotational transition strength due to residual interactions. The calculations predict that scars of regular rotational motion may be found at excitation energies as high as 2 MeV above yrast, far into the region characterized by damped rotational motion. Traces of this new phenomenon are identified and studied in the experimental spectra from high spin states in rare earth nuclei. A prominent example of isolated structures in the quasi-continuum region are bands built on high-K quantum numbers. Recent results from a fluctuation analysis of counts in low-K and high-X configurations in Er-163 are discussed, and indicate that states in the quasi-continuum feeding high-K bands are different from states feeding the low-K bands.

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Fluctuations associated with stretched E2 transitions from high-spin levels in nuclei around Yb-168 are investigated by a cranked shell model extended to include residual two-body interactions. In the cranked mean-field model without residual interactions, it is found that gamma-ray energies behave like random variables and the energy spectra show Poisson fluctuation. With two-body residual interactions included, the discrete transition pattern with unmixed rotational bands is still valid up to around 600 keV above yrast, in good agreement with experiments. At higher excitation energy, a gradual onset of rotational damping emerges. At 1.8 MeV above yrast, complete damping is observed with GOE-type fluctuations for both energy levels and transition strengths (Porter-Thomas fluctuations).

DOI： 10.1016/0375-9474(93)90509-V

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Several new methods for the study of nuclear structure at low temperature are reviewed. The methods analyze the fluctuations of the intensity of Eγ1 · Eγ2 spectra, and the shape and width Γrot of the correlated patterns with different characteristics of the rotational motion in cold and warm nuclei. New results are given for the rotational damping width, and the number of 2-step-paths below and above U0 ≈ 800 keV, considered to be the energy of the borderline between undamped and damped rotational motion. The rotational damping width Γrot is studied as function of rotational frequency for selected regions of entry states in 163Tm, and found to be rather constant ≈ 80 keV, significantly smaller than current theoretical predictions. The fluctuation analysis supports the damping picture in general, and confirms that a strong branching of the transition strength for each step in the E2 cascades exists at high spin. This can be taken as evidence for damping of the rotational motion in warm nuclei. © 1993.

DOI： 10.1016/0375-9474(93)90541-5

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The experimental data emerging from the fluctuation analysis of the rotational gamma-decay are used to provide evidence for three regimes in the rotational spectrum. Namely discrete bands, fragmented transitions and rotational damping.
The mechanisms which are expected to be at work in the damping of rotational motion are briefly reviewed and a parallel is made with the relaxation of giant resonances, focusing on the interplay of mean field (average) effects and of chaotic (fluctuation) behaviour. A simple, yet accurate model of rotational damping where chaotic behaviour emerges from effective, though realistic, two-body interactions acting among unperturbed rotational bands indicates the possibility of obtaining novel insight on the nuclear structure, through the study of rotational motion. In particular, the onset of chaos can be related to the high-multipole components of the nuclear force which are not able to generate mean field effects.

DOI： 10.1016/0375-9474(93)90540-E

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Language：English   Publisher：AMERICAN PHYSICAL SOC  

The rotational spectrum of Yb-168 is calculated by diagonalizing different effective interactions within the basis of unperturbed rotational bands provided by the cranked shell model. A transition between order and chaos taking place in the energy region between 1 and 2 MeV above the yrast line is observed, associated with the onset of rotational damping. It can be related to the higher multipole components of the force acting among the unperturbed rotational bands.

DOI： 10.1103/PhysRevLett.70.2694

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Band mixing calculations in rapidly rotating well-deformed nuclei are presented, investigating the properties of energy levels and rotational transitions as a function of excitation energy. Substantial fragmentation of E2 transitions is found for E(x) greater than or similar to 800 keV above yrast, which represents the onset of rotational damping. Above E(x) almost-equal-to 2 MeV, energy levels and E2 strengths display fluctuations typical of quantum chaotic systems, which are determined by the high multipole components of the two-body residual interaction.

DOI： 10.1016/0375-9474(93)90542-6

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The structure of excited rotational bands in well deformed nuclei is discussed. It is shown how fluctuations of 2-dimensional energy-energy gamma-ray spectra can give quite detailed information about both the region of discrete bands and the region of rotational damping.

DOI： 10.1016/0375-9474(93)90648-H

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A statistical method to analyze the gamma decay of excited, rapidly rotating nuclei is presented. It is based on the fact that the cooling path of these systems goes through regions of both suppressed and enhanced fluctuations typical of large and low level density, respectively. The method is applied to the study of the high-spin quasicontinuum of Yb-167, Yb-168.

DOI： 10.1103/PhysRevLett.68.3008

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Two new methods, the Rotational Plane Mapping, and the Fluctuation Analysis Method are reviewed, and applied to the study of high spin quasi-continuum states in 167,168Yb and Tm-163 nuclei. New results are given for the rotational damping width GAMMA(rot) and the number of different 2-step-paths below and above U0, defined to be the energy of the borderline between undamped regular rotational motion for bands along the yrast line and the region of heated nuclei with damped rotational motion. The results indicate that at least 30 bands with regular rotational structure exist in the I = 40 h region before damping becomes dominating. The fundamental concept of rotational damping may be questioned, and has never been verified experimentally. The analysis support the damping picture, giving evidence for a strong branching of the E2 decay, showing 10 times as many 2-step-paths through the continuum than expected if only regular rotational E2 decay, and E1 statistical branching were the decay modes.

DOI： 10.1016/0146-6410(92)90023-U

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DOI： 10.1143/PTP.85.281

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Language：English   Publisher：KYOTO UNIV  

Damping property of the collective vibration is numerically analyzed for a schematic shell model which simulates a giant collective vibration built on compound states. Microscopic mechanism of the motional narrowing of the damping width is investigated in reference to the residual interaction which causes configuration mixing. Statistical aspects of the damping mechanism are also discussed. It is shown that the response function method which we formulated in a preceding paper provides a consistent and microscopic description of the damped collective vibration embedded in the highly excited region.

DOI： 10.1143/PTP.84.1126

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DOI： 10.1143/PTP.84.269

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Language：English   Publisher：PROGRESS THEORETICAL PHYSICS PUBLICATION OFFICE  

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Language：English   Publisher：ACADEMIC PRESS INC JNL-COMP SUBSCRIPTIONS  

DOI： 10.1016/0003-4916(89)90031-6

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DOI： 10.1143/PTP.78.591

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DOI： 10.1143/PTP.78.609

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DOI： 10.1143/PTP.76.93

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Language：Japanese   Publisher：一般社団法人日本物理学会  

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