Pairing Effects on Bubble Nuclei

In the framework of the Skyrme–Hartree–Fock–Bogoliubov approach with the Sk T interaction, the pairing effects on the proton bubble structures of ^(46)Ar and ^(206)Hg are discussed. In calculations, three kinds of pairing forces (volume, surface and mixed pairing interactions) are used. For ^(46)Ar, it is shown that the bubble structure with the volume pairing is almost the same as that with the mixed pairing. The bubble with the surface pairing is less pronounced than those with the volume and mixed pairings. Analyzing the density distributions and occupation probabilities of the proton s states and the quasi-degeneracy between the proton 2s_(1/2) and 1d_(3/2) orbitals, we explain the difference between the bubble structure with the surface pairing and those with the volume and mixed pairings. For ^(206)Hg, it is seen that the proton density distribution with the surface pairing is different from those with the volume and mixed pairings in the whole region of the radial distance. In addition, it is found that the bubbles with the three pairing forces are different from each other and the least pronounced bubble is obtained with the surface pairing. Thus the selection of the pairing force is important for the study of the nuclear bubble structure.

Eigen-Property of Single-j System and Seniority Conservation Condition

In this paper we study the system with three nucleons within a single-j shell, which can be described as the angular momentum coupling of a nucleon pair and the odd nucleon. The overlaps between these non-orthonormal states form a special matrix coincidental with the one obtained by Rowe and Rosensteel. They proposed a proposition related to the eigenvalue problems of that matrix and dimensions of the associated subspaces. We prove their proposition with the help of the symmetric properties of the six-j symbols. We also derive algebraic expressions for eigen energies as well as conditions for conservation of seniority through the decomposition of the angular momentum.

中重核中单粒子与集体运动的竞争效应（英文）

从原子核的电四极跃迁强度B(E2)中可以提取出原子核集体性和单粒子性质竞争的重要信息,其中一个重要的观测量是B(E2; 4_1^+→2_1^+)/B(E2; 2_1^+→g.s.)的比值(B_(4/2))。B_(4/2)一般要大于1,而且对于原子核转动和振动,我们应有B_(4/2)=1.4和2.0,但球形半满壳核一般会有不一样的性质。这些核的性质主要受对关联效应影响。介绍了几种超出我们一般认识的奇特衰变性质。Te同位素的基态带有鲜明的振动特性,但114Te的E2跃迁性质却更符合转动性。这些性质可以通过大规模壳模型计算来描述。对于填充j=9/2轨道的半满壳核,它们的4+和6+显示出很强的辛若数部分守恒性质。这种奇特的部分守恒可以被解析证明。而且我们的计算表明辛若数部分守恒对相关的E2跃迁影响很大。对于N=90附近具有量子相变行为的核素,其B_(4/2)也会也表现出相似的奇异特性。

轻质量及中质量核结构的壳模型研究

壳模型被广泛应用于研究轻质量及中质量核的性质,它能很好地描述这些原子核的基态和低激发态的能量、电磁矩和电磁跃迁以及β衰变等性质。本文简要介绍了原子核壳模型的基本框架,如何选择单粒子基矢和构建模型空间和有效哈密顿量。对不同区域的原子核的壳模型最新研究做了回顾。在psd区,介绍一个新的相互作用成功地描述碳、氮、氧的中子滴线及其它性质以及A=20附近弱束缚丰质子核的谱学性质;在fp区,介绍了N=Z奇奇核中不同同位旋形成的转动带,以及通过N=Z附近的镜像核研究核力的电荷对称性破缺;在更重的区域,介绍了92Pd这个N=Z的原子核中同位旋标量质子中子对起主导作用,以及Sn同位素的研究。

Alpha Decay as a Probe of the Structure of Neutron-deficient Nuclei Around Z=82

In this contribution I would like to review briefly our recent studies on nuclear α formation probabilities in heavy nuclei and their indication on the underlying structure of the nuclei involved.In particular, I will show that the empirical α-formation probabilities, which can be extracted from experimental half-lives, exhibit a rather smooth function with changing proton or neutron numbers. This allows us to distinguish the role played by pairing collectivity in the clustering process. The sudden hindrance of the clustering of the nucleons around the N = 126 shell closure is due to the fact that the configuration space does not allow a proper manifestation of the pairing collectivity. The influence of the Z = 82 shell closure on the α formation properties will also be discussed. Moreover, we have evaluated the α-decay fine structure to excited 0+states in Hg and Rn isotopes as well as the α-decay from the excited 0+states in the mother nucleus. It is thus found that the α decay is sensitive to the mixture of configurations corresponding to different nuclear shapes.

Alignments in the nobelium isotopes

Total-Routhian-Surface calculations have been performed to investigate the deformation and alignment properties of the No isotopes. It is found that normal deformed and superdeformed states in these nuclei can coexist at low excitation energies. In neutron-deficient No isotopes, the superdeformed shapes can even become the ground states. Moreover, we plotted the kinematic moments of inertia of the No isotopes, which follow very nicely available experimental data. It is noted that, as the rotational frequency increases, alignments develop at hω = 0.2- 0.3 MeV. Our calculations show that the occupation of the νj15/2 orbital plays an important role in the alignments of the No isotopes.

Shell-model studies of the N=14 and 16 shell closures in neutron-rich nuclei

Shell-model studies on the N =14 and 16 shell closures in neutron-rich Be, C, O and Ne isotopes are presented. We calculate, with the WBT interaction, the excited states in these nuclei. The calculations agree with recent experiment data. Excited energies and B(E2) values are displayed to discuss the shell closures. Our results support the N =16 shell closure in these isotopes, while indicating a disappearance of N =14 shell closure in Be and C isotopes.

Tensor force effect on the exotic structure of neutron-rich Ca isotopes

The structure of neutron-rich Ca isotopes is studied in the spherical Skyrme-Hartree-Fock-Bogoliubov(SHFB)approach with SLy5,SLy5+T,and 36 sets of TIJ parametrizations.The calculated results are compared with the available experimental data for the average binding energies,two-neutron separation energies and charge radii.It is found that the SLy5+T,T31,and T32 parametrizations reproduce best the experimental properties,especially the neutron shell effects at N=20,28 and 32,and the recently measured two-neutron separation energy of 56Ca.The calculations with the SLy5+T and T31 parametrizations are extended to isotopes near the neutron drip line.The neutron giant halo structure in the very neutron-rich Ca isotopes is not seen with these two interactions.However,depleted neutron central densities are found in these nuclei.By analyzing the neutron mean-potential,the reason for the bubble-like structure formation is given.

Shape transitions in proton-rich Ho and Tm isotopes

Total Routhian Surface (TRS) calculations have been performed for even-even nuclei along proton drip line to study nuclear ground-state deformations, as well as the odd proton nuclei Ho and Tm isotopes. The drip line nuclei show the expected shape transition with the shell e?ects. Ground-state shape changes from prolate to oblate at 143Ho and 145Tm in these two isotopes, which is due to the γ instability around N =76.