Naoki Tajima

Self-consistent calculation of charge radii of Pb isotopes

Abstract Charge radii of lead isotopes are calculated with the HF plus BCS method, using Skyrme forces (SkM∗, SIII and SGII) for the mean field. When these forces are combined with a seniority pairing force, all of them fail to reproduce the experiment. Neither higher-order corrections, nor ground-state correlations due to the collective modes can resolve the discrepancy. However, by introducing a density-dependent pairing force quenched inside the nucleus, one can explain the odd-even staggering as well as the large kink of charge radii at 208Pb when plotted versus A.

Extensive Hartree-Fock+BCS calculation with Skyrme SIII force

Abstract We have performed deformed Hartree-Fock+BCS calculations with the Skyrme SIII force for the ground states of even-even nuclei with 2 ⩽ Z ⩽ 114 and N ranging from outside the proton drip line to beyond the experimental frontier in the neutron-rich side. We obtained spatially localized solutions for 1029 nuclei, together with the second minima for 758 nuclei. The single-particle wavefunctions are expressed in a three-dimensional Cartesian-mesh representation, which is suitable to describe nucleon skins, halos, and exotic shapes as well as properties of ordinary stable nuclei. After explaining some of the practical procedures of the calculations, we compare the resulting nuclear masses with experimental data and the predictions of other models. We also discuss the quadrupole ( m =0, 2) and hexadecapole ( m =0, 2, 4) deformations, the skin thicknesses, the halo radii, and the energy difference between the oblate and prolate solutions. Our results can be obtained via internet.

Roles of triaxiality and residual interaction in signature inversions of A ∼ 130 odd-odd nuclei

Abstract Rotational bands with (π h 11 2 ) 1 (ν h 11 2 ) 1 configurations are studied using a particle-rotor model in which a proton and a neutron quasiparticle interacting through a zero-range force are coupled with a triaxial rotor. It is shown for 124Cs that one can reproduce the signature dependence of the energy and the B ( M 1) B( E 2) ratio best when one takes into account γ-deformations with irrotational-flow moment of inertia in addition to the proton-neutron interaction proposed by Semmes and Ragnarsson. Including both effects, a systematic calculation of signature splittings is performed for Cs, La isotopes and N = 75 isotones to be compared with experiments. The deficiencies of the cranking model are also discussed concerning its applicability to signature-inversion phenomena in odd-odd nuclei.

Diabatic effects in 186Pb: A generator-coordinate analysis

Abstract We examine a possibility for quadrupole collective wavefunctions in 186Pb to remain localized within a diabatic potential. Our study uses the generator-coordinate method on a basis generated by the Hartree-Fock + BCS calculations. The mean field is constructed with the Skyrme force SIII while a seniority force describes pairing effects. The collective basis includes both Oqp states constrained on mass quadrupole moment and 2qp states built on the shape-driving intruder orbital π[514 9 2 ] (1 h 9 2 ) . We find that the seniority pairing force, with strengths compatible with systematic trends, generates a too strong coupling between diabatic configurations. For such a state-independent pairing interaction, low-excitation-energy collective wavefunctions are not trapped at oblate deformations.

Prolate dominance of nuclear shape caused by a strong interference between the effects of spin-orbit and l 2 terms of the Nilsson potential

The origin of the dominance of prolate shapes over oblate ones of the ground states of atomic nuclei is investigated with the Nilsson-Strutinsky method. The number of prolate nuclei among all the deformed even-even nuclei is calculated as a function of the strengths of the spin-orbit and the

SIGNATURE AND ANGULAR MOMENTUM IN 3D-CRANKED HFB STATES

{l}^{2}

Generator coordinate kernels between zero- and two-quasiparticle BCS states

terms of the Nilsson potential. The latter simulates a square-well-like radial profile of the mean potential. The proportion of prolate nuclei is 86% with the standard strengths corresponding to the actual atomic nuclei. By weakening the spin-orbit potential, the proportion oscillates strongly, having a local minimum value of 42% with about half of the standard strength and a local maximum value of 79% without the spin-orbit potential.

K-isomerism and γ-softness

Abstract In terms of the exact angular momentum projection, properties of the three dimensional cranked HFB (3d-CHFB) states are analyzed quantitatively in the context of the relation between the signature of an intrinsic symmetry and the parity of angular momentum, (−1) I . We found that the tilted states have favorable features to describe states involved with high- K quantum number and/or odd total angular momentum I . This implies that 3d-CHFB can describe properly the backbending phenomena like a “t-band and g-band” crossing, which is suggested in N =106 isotones.

Hartree-Fock+BCS Approach to Unstable Nuclei with the Skyrme Force

Abstract We give a method with which the matrix elements of operators between BCS states can be evaluated with the generalized Wicks theorem even when the excitation of a pair of quasiparticles leads to a vanishing of the overlap. We analyze the behavior of the mean field and the pairing contributions to the matrix elements of two-body operators versus the gauge angle of the orbital and find that each of them diverges as the overlap vanishes while their sum remains finite. A new definition of these quantities is proposed which removes the divergence occurring at zero overlap. A numerical application to a deformed heavy nucleus is done, which tests the feasibility of our prescription.

Nodal lines in the cranked HFB overlap kernels

Abstract The decay rates from K π = 10 + isomers into the ground-band states for 182 W and 184 Os are calculated by employing a particle-plus-γ-soft-rotor model and a particle-plus-triaxial-rotor model. As for the description of the degree of freedom of axial asymmetry, Bohrs model of γ-vibration around γ = 0 and Davydovs model of statically deformed triaxial rotor are shown to give clearly distinct results about the degree of violation of the K -selection rule, although they give similar values for quantities of collective character. This result implies a possibility to obtain information about the size of the quantum fluctuation in γ from the decay rates of K -isomers, using the knowledge of the mean value of γ determined from quantities of collective character.