Octupole deformation for Ba isotopes in a reflection-asymmetric relativistic mean-field approach

The potential energy surfaces of even-even 142-156Ba are investigated in the constrained reflectionasymmetric relativistic mean-field approach with parameter set PK1. It is shown that for the ground states, 142Ba is near spherical,156Ba well quadrupole-deformed, and in between 144-154Ba octupole deformed. In particular, the nuclei 148,150Ba with N=92, 94 have the largest octupole deformations. By including the octupole degree of freedom, energy gaps N = 88, N = 94 and Z = 56 near Fermi surfaces for the singleparticle levels in 148Ba with β2 ～ 0.26 and β3 ～ 0.17 are found. Furthermore, the performance of the octupole deformation driving pairs (ν2f7/2, ν1i13/2) and (π2d5/2, π1h11/2) is demonstrated by analyzing the singleparticle levels near Fermi surfaces in 148Ba.     

偶偶 Ra 同位素的八极形变研究

用反射不对称的相对论平均场理论(RAS-RMF)对偶偶Ra同位素的八极形变进行了系统研究,并与实验数据和有限力程小液滴模型(FRDM)结果进行了比较.结果表明：RAS-RMF理论很好地描述了Ra同位素的基态性质,计算的结合能、双中子分离能和形变与实验数据和FRDM一致.RAS-RMF理论获得的中子、质子密度分布清晰地展现出偶偶Ra同位素由球形逐渐转变为八极形变,到四极形变的过程,与实验观察的八极形变不稳定现象一致.     

偶偶 Ra 同位素的八极形变研究

用反射不对称的相对论平均场理论(RAS-RMF)对偶偶Ra同位素的八极形变进行了系统研究,并与实验数据和有限力程小液滴模型(FRDM)结果进行了比较.结果表明：RAS-RMF理论很好地描述了Ra同位素的基态性质,计算的结合能、双中子分离能和形变与实验数据和FRDM一致.RAS-RMF理论获得的中子、质子密度分布清晰地展现出偶偶Ra同位素由球形逐渐转变为八极形变,到四极形变的过程,与实验观察的八极形变不稳定现象一致. 关键词： 反射不对称平均场(RAS-RMF) 八极形变 偶偶核     

Shape evolution for Sm isotopes in relativistic mean-field theory

The evolution of shape from the spherical to the axially deformed shapes in the Sm isotopes is investigated microscopically in relativistic mean-field theory. The microscopic and self-consistent quadrupole deformation constrained relativistic mean-field calculations show a clear shape change for the even-even Sm isotopes with N = 82-96. The potential surfaces for ¹⁴⁸Sm, ¹⁵⁰Sm and ¹⁵²Sm are found to be relatively flat, which may be the possible critical-point nuclei. By examining the single-particle spectra and nearest-neighbor spacing distribution of the single-particle levels, one finds that the single-particle levels in ¹⁴⁸Sm , ¹⁵⁰Sm, and ¹⁵²Sm distribute more uniformly.     

Restoration of rotational symmetry in deformed relativistic mean-field theory

We report on a very recently developed three-dimensional angular momentum projected relativistic mean-field theory with point-coupling interaction (3DAMP+RMF-PC). Using this approach the same effective nucleon-nucleon interaction is adopted to describe both the single-particle and collective motions in nuclei. Collective states with good quantum angular momentum are built projecting out the intrinsic deformed meanfield states. Results for 24Mg are shown as an illustrative application.     

Deformation constrained relativistic mean-field approach with fixed configuration and time-odd component

Deformation constrained relativistic mean-field (RMF) approach with fixed configuration and timeodd component has been developed and applied to investigate magnetic moments of light nuclei near doublyclosed shells. Taking 17O as an example, the results and discussion are given in detail.     

八级形变系统的集体运动

利用一组内部坐标和三个欧拉角描述八极形变系统的集体运动,动能被分解成三部分:体坐标系下的形变振动,体坐标系围绕实验室系的转动以及振动和转动的耦合.量子化的动能算符被导出,一些特殊八极形变下的集体谱被讨论.     

相对论平均场理论框架下对能的系统研究

在相对论平均场模型的框架内,沿原子核的稳定线,以每隔4个质子或中子提取样本的方法,计算了核谱图上数十个原子核的对能,特别是研究了氧同位素偶-偶核的对能随核子数的变化规律,发现在固定能隙Δ的条件下,对能的大小和核的壳结构有关,由此提出了一种检验闭壳效应的简便方法,进而发现中子数N=6不仅在轻核的丰中子区是一个新幻数,而且在丰质子区也是一个可能的新幻数. 关键词： 相对论平均场模型 对能 能隙 幻数     

Deformation constrained relativistic mean-field approach with fixed configuration and time-odd component

Deformation constrained relativistic mean-field (RMF) approach with fixed configuration and time-odd component has been developed and applied to investigate magnetic moments of light nuclei near doubly-closed shells. Taking ¹⁷O as an example, the results and discussion are given in detail.     

Restoration of rotational symmetry in deformed relativistic mean-field theory

We report on a very recently developed three-dimensional angular momentum projected relativistic mean-field theory with point-coupling interaction (3DAMP+RMF-PC). Using this approach the same effective nucleon-nucleon interaction is adopted to describe both the single-particle and collective motions in nuclei. Collective states with good quantum angular momentum are built projecting out the intrinsic deformed mean-field states. Results for ²⁴Mg are shown as an illustrative application.     

Constrained relativistic mean-field approach with fixed configurations

A diabatic (configuration-fixed) constrained approach to calculate the potential energy surface (PES) of the nucleus is developed in the relativistic mean-field model. As an example, the potential energy surfaces of ²⁰⁸Pb obtained from both adiabatic and diabatic constrained approaches are investigated and compared. It is shown that the diabatic constrained approach enables one to decompose the segmented PES obtained in usual adiabatic approaches into separate parts uniquely characterized by different configurations, to follow the evolution of single-particle orbits till the very deformed region, and to obtain several well-defined deformed excited states which can hardly be expected from the adiabatic PESs.     

相对论平均场理论对Rn同位素链原子核基态性质的研究

在相对论平均场理论的框架下,对Rn同位素链原子核的结合能、形变、同位素位移等若干基态性质进行了较详细的研究.结果表明,理论计算结果与已有的实验数据符合较好.原子核的四极形变主要出现在远离幻数的区域(N=110-124和N=129-142).而在中子数大于幻数的区域(N=127-142),十六级形变也非常明显.对电荷半径的研究显示,Rn同位素链的同位素位移曲线的斜率在中子幻数处出现明显的变化. 关键词： 相对论平均场理论 电荷半径 同位素位移 单粒子能级     

丰中子核144,146Ce的八极形变

通过对²⁵²Cf自发裂变所产生的瞬发γ谱的实验研究，建立并扩展了丰中子核^144,146Ce的高自旋和八极形变集体带,最高自旋态可达15^－.对这两个核的八极形变特性进行了讨论.     

相对论平均场理论对Pt同位素形状演化的研究

利用形变约束的相对论平均场理论研究了Pt同位素偶-偶核的形状演化,比较了基态结合能和四极形变的理论计算值和实验值, 分析了这些核的位能曲线、单粒子能级及其随四极形变β₂ 的变化规律,发现从N=88到N=126, Pt同位素的基态变形从球形对称核经X(5)对称性核、演化为具有稳定形变的核,再演化为球形核的变化过程.其中, ^166-172Pt是近球形核, ¹⁷⁴Pt和^192-196Pt位于球形和稳定形变之间,可能具有X(5)对称性, ^176-190Pt具有稳定的变形, ^198-202Pt是近球形核, ²⁰⁴Pt是球形核,这些结果与实验一致.     

Resonant Continuum in the Relativistic Mean-Field Theory

Energies, widths and wave functions of the single-particle resonant continuum are determined by solvingscattering states of the Dirac equation with proper asymptotic conditions for the continuous spectrum in the relativisticmean-field theory. The relativistic regular and irregular Coulomb wave functions are calculated numerically. Theresonance states in the continuum for some closed- or sub-closed-shell nucleus in Sn-isotopes, such as 1 14Sn, 1 16Sn, 1 18Sn,and 120Sn are calculated. Results show that the S-matrix method is a reliable and straightforward way in determiningenergies and widths of resonant states.     

丰中子核145,147La的八极形变

通过对²⁵²Cf自发裂变产生的瞬发γ谱的实验研究,建立与扩展了丰中子核^145,147La的高自旋态能级图,最高自旋态达到(41/2⁺)与(43/2^－).测得的交叉相联的相反宇称带及带间的强化E1跃迁说明在^145,147La中形成强的八极形变.对¹⁴⁵La的研究表明,具有轴对称形状的四极形变与具有反演不对称形状的八极形变在同一核中产生共存与竞争.在πh_11/2带中观测到的带交叉位于ω≈0.26—0.30MeV附近,由推转壳模型计算表明,它是由一对i_13/2中子的顺排所引起的.     

用相对论平均场理论研究近滴线区原子核传统幻数的消失和新幻数的产生

提出了一种从理论上检验壳效应的方法.在考虑了由Bardeen，Cooper和Schrieffer提出的金属超导理论(BCS方法)的相对论平均场理论框架内，通过计算粒子数的涨落，发现涨落的大小和核的壳结构有紧密的关系，进而研究了滴线区一些传统幻数的消失和新幻数的产生. 关键词： 相对论平均场理论 粒子数涨落 幻数 壳效应     

经典粒子在轴对称八极形变势场中的混沌运动

在自然界中长的变形核数目多于扁的变形核数目, 这一事实发现与核子的混沌运动有关. 经典理论的初步研究表明, 粒子在扁椭球加八极形变场中比在长椭球加八极形变场中的运动能在更小的形变参数下产生混沌运动, 原因是前者的势能面能在更小的形变参数下出现负曲率.