Masayuki Yamagami

Symmetry-unrestricted Skyrme–Hartree–Fock–Bogoliubov calculations for exotic shapes in N=Z nuclei from 64Ge to 84Mo

Abstract 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: 64Ge, 68Se, 72Kr, 76Sr, 80Zr and 84Mo. Results of calculation indicate that the oblate ground state of 68Se is extremely soft against the Y 33 triangular deformation, and that the low-lying spherical minimum coexisting with the prolate ground state in 80Zr is extremely soft against the Y 32 tetrahedral deformation.

High-spin yrast structure of 32S suggested by symmetry-unrestricted, cranked Hartree–Fock calculations

The high-spin yrast structure of 32 S is investigated by means of the cranked Skyrme‐Hartree‐ Fock method in the three-dimensional Cartesian-mesh representation without imposing restrictions on spatial symmetries. The result suggests that (1) a crossover from the superdeformed to the hyperdeformed-like configurations takes place on the yrast line at angular momentum I’ 24, which corresponds to the “band termination” point in the cranked harmonic-oscillator model, and (2) nonaxial octupole deformations of the Y31 type play an important role in the yrast states in the range 56I6 13.

Cranked Skyrme–Hartree–Fock calculation for superdeformed and hyperdeformed rotational bands in N=Z nuclei from 32S to 48Cr

Abstract With the use of the symmetry-unrestricted cranked Skyrme–Hartree–Fock method in the three-dimensional coordinate-mesh representation, we have carried out a systematic theoretical search for the superdeformed and hyperdeformed rotational bands in the mass A =30–50 region. Along the N = Z line, we have found superdeformed solutions in 32 S, 36 Ar, 40 Ca, 44 Ti, and hyperdeformed solutions in 36 Ar, 40 Ca, 44 Ti, 48 Cr. The superdeformed band in 40 Ca is found to be extremely soft against both the axially symmetric ( Y 30 ) and asymmetric ( Y 31 ) octupole deformations. An interesting role of symmetry breaking in the mean field is pointed out.

Mixed representation RPA calculation for octupole excitations on superdeformed states in the 40Ca and neutron-rich sulfur regions

Abstract By means of the mixed representation RPA based on the Skyrme–Hartree–Fock mean field, we investigate low-frequency octupole excitations built on the superdeformed (SD) states in the N = Z nuclei around 40Ca and the neutron-rich sulfur isotopes. The RPA calculation is carried out fully self-consistently on the three-dimensional Cartesian mesh in a box, and yields a number of low-frequency octupole vibrations built on the SD states in 32S, 36Ar, 40Ca and 44Ti. In particular, a strongly collective K π = 1 − octupole vibration is suggested to appear on top of the SD state in 40Ca. For 48,50S close to the neutron drip line, we find that the low-lying state created by the excitation of a single neutron from a loosely bound low Ω level to a high Ω resonance level acquires an extremely strong octupole transition strength due to the spatially very extended structure of the particle–hole wave functions.

Pairing and continuum effects on low-frequency quadrupole vibrations in deformed Mg isotopes close to the neutron drip line

Abstract Low-frequency quadrupole vibrational modes in deformed 36,38,40 Mg close to the neutron drip line are studied by means of the quasiparticle-random-phase approximation based on the coordinate-space Hartree–Fock–Bogoliubov formalism. Strongly collective K π = 0 + and 2 + excitation modes carrying 10–20 Weisskopf units in the intrinsic isoscalar quadrupole transition strengths are obtained at about 3 MeV. There are two reasons for the enhancement of the transition strengths. First, the quasiparticle wave functions generating these modes possess spatially very extended structure. The asymptotic selection rules characterizing the β and γ vibrations in stable deformed nuclei are thus strongly violated. Second, the dynamic pairing effects act strongly to enhance the collectivity of these modes. It is suggested that the lowest K π = 0 + collective mode is a particularly sensitive indicator of the nature of pairing correlations in deformed nuclei close to the neutron drip line.

Low-frequency K{sup {pi}}=0{sup +} modes in deformed neutron-rich nuclei: Pairing- and {beta}-vibrational modes of neutrons

Low-frequency K{sup {pi}}=0{sup +} states in deformed neutron-rich nuclei are investigated by means of the quasiparticle-random-phase approximation based on the Hartree-Fock-Bogoliubov formalism in the coordinate space. We have obtained the very strongly collective K{sup {pi}}=0{sup +} modes not only in neutron-rich Mg isotope but also in Cr and Fe isotopes in N=40 region, where the onset of nuclear deformation has been discussed. It is found that the spatially extended structure of neutron quasiparticle wave functions around the Fermi level brings about a striking enhancement of the transition strengths. It is also found that the fluctuation of the pairing field plays an important role in generating coherence among two-quasiparticle excitations of neutron.

Comparative Study of Octupole Excitations on Superdeformed States in 32S, 36S, 40Ca and 50S

By means of an RPA calculation based on the deformed Woods-Saxon potential in the coordinate-mesh representation, we make a comparative study of octupole excitations built on superdeformed states in the 40 Ca region and those in 50 S. For the N = Z stable nuclei, 32 Sa nd 40 Ca, enhancement of octupole transition strengths results from the coherence of the proton and neutron excitations. Contrastingly, for 50 S close to the neutron drip line, we find that the low-lying state created by the excitation of a single neutron from a loosely bound low Ω state to ah ighΩ resonance state acquires an extremely large transition strength. A similar enhancement of the octupole strength is also found in oblately deformed 40 Mg close to the neutron drip line.

Superdeformed bands in neutron-rich sulfur isotopes suggested by cranked Skyrme–Hartree–Fock calculations

Abstract On the basis of the cranked Skyrme–Hartree–Fock calculations in the three-dimensional coordinate-mesh representation, we suggest that, in addition to the well-known candidate 32 S, the neutron-rich nucleus 36 S and the drip-line nuclei, 48 S and 50 S, are also good candidates for finding superdeformed rotational bands in sulfur isotopes. Calculated density distributions for the superdeformed states in 48 S and 50 S exhibit superdeformed neutron skins.

Rotational Frequency Dependence of Octupole Vibrations on Superdeformed States in 40Ca

By means of the random phase approximation (RPA) calculation based on cranked deformed Woods-Saxon potential, we investigate how rotational motion affects the properties of octupole vibrations built on superdeformed states in 40 Ca. A major structure change of the superdeformed yrast states toward a reflection-asymmetric shape is suggested to take place in the region of angular momentum a little higher than the observed maximum value 16~, owing to a cooperative effect of octupole vibrational correlation and the rotation-aligned particle-hole excitations from the f7/2 to the g9/2 shell. Subject Index: 213

Triaxiality Dependence of Octupole Excitations on Superdeformed States in 44Ti

By random phase approximation (RPA) calculation based on triaxially deformed WoodsSaxon potential, we investigate how axial-symmetry breaking in the mean field affects the properties of octupole vibrational excitations built on superdeformed states in 44 Ti. We find a remarkable dependence of their properties on signature quantum number with respect to rotation about an axis perpendicular to the longest axis by the angle of π. Detailed numerical analysis of the signature dependence is made by considering the magnitude of the triaxial deformation γ as a parameter.