Rn-Th偶偶核的八级形变研究

用推转壳模型在多维形变空间系统研究了Rn-Th偶偶核的基态性质及高自旋情形下的性质, 其中选取的形变自由度为β₂, β₃, β₄和β₅. 计算结果很好的再现了实验提取的转动惯量值. 势能面的研究表明, 随中子数的增加, 基态形状由近球形(N≈130)逐渐演变为八极形变(N≈136)后又发展成为稳定的四极形变(N≥140). 推转计算表明Rn-Th偶偶核的八极形变非常软, 在推转到高自旋情形下, 逐渐变为反射对称形变.     

原子核形变与价核子数的系统关系

利用N_pN_n方法研究了A≥100的偶–偶核基态四极形变参数β的系统规律.根据质量数以及价质子(中子)是粒子还是空穴对原子核分组,发现β与(N_pN_n)^1/2的关系曲线是平滑的.不同组中原子核的β变化曲线的斜率和趋势显示,价核子和空穴对核四极形变的贡献不同.通过对近滴线原子核理论形变值的变化规律的研究表明,在N_pN_n方法中p-n价核子相互作用的一般关系可能依然适用于不稳定核.     

铂同位素的研究——费米子动力学对称模型和相互作用玻色子模型的比较

利用费米子动力学对称性模型(FDSM)系统研究了偶偶核铂的同位素,其跃迁可以很好地由对相互作用+四极相互作用来描述,计算了铂(^190—196Pt)同位素的能级、电四极矩、旋磁比、同质异能移和同位素移动,结果表明理论值与实验值符合的很好.计算结果还与相互作用玻色子模型(IBM)的结果进行了比较.计算结果表明即使在FDSM中质子–中子耦合系统(SO^π(8)×SP^ν(6))形式上不包括SO(6)动力学对称性,但¹⁹⁶Pt附近确实存在精确的等效SO(6)动力学对称性     

单粒子薛定谔液体和形变核的转动惯量

将单粒子薛定谔液体理论应用于轴对称形变核的集体运动.也给出了一个相反的例子,即在各向异性谐振子势中处于稳定形变的任意数目的独立核子.而且,通过填充与主量子数n_x,n_y和n_z的可能值相应的单粒子态来构成s-d壳偶偶核:²⁰Ne,²⁴Mg,²⁸Si,³²S和³⁶Ar的基态,并计算了作为谐振子参数hω_x,hω_y和hω_z的函数的这些核的推转模型、刚体模型和稳态模型转动惯量.这些谐振子参数用与质量数A、中子数N、质子数Z和形变参数β有关的非形变参数hω00来描述.这些核的推转模型转动惯量的理论计算结果与实验数据符合甚好.而且,所考虑的轴对称形变核可能是扁椭球形的,也可能不是扁椭球形的,其中²⁴Mg是惟一高度形变的.²⁰Ne和²⁴Mg这两个核的刚体模型和稳态模型转动惯量也与实验数据符合甚好.     

相对论平均场理论对A～130区E(5)关键点核的研究

利用形变约束的相对论平均场理论系统地研究了A～130区Ba,Xe和Te同位素偶－偶核的基态性质, 理论计算数据和实验数据符合得非常好. 详细分析了这些核的位能曲面、费米能和γ跃迁能量的分支比, 给出了¹³⁶Ba,^132,134Xe具有E(5)对称性的预言. 对于^128,130,132Te这3个核, 理论计算的结果表明其具有E(5)对称性, 但γ跃迁能量的分支比的实验值不支持理论结果. 此3个核是否为关键点核有待于实验的进一步检验.     

自洽半经典Sum rule方法研究巨共振的平均性质

从同一扩展Skyrme力出发,用自洽半经典方法确定球形核基态密度分布ρ_π和ρ^{p,用Sum rule方法计算强度函数矩m_－1,m₁和m₃,从而具体计算了isovector巨单极,巨偶极和巨四极共振的平均激发能量,以及isoscalar巨单极和巨四极共振的宽度,部分结果同实验事实做了比较.}     

A～50区同位素的相对论平均场研究

利用轴向形变相对论平均场理论计算了A～50区的核基态性质,结果表明,在Fe同位素链中最稳定的核是⁵⁶Fe和⁵⁸Fe而不是通常的⁵⁴Fe;给出了⁴⁶Cr,⁵⁰Fe和⁵⁴N(N=Z－2),⁴⁵Cr,⁴⁹Fe和⁵³Ni(N=Z－3)核的质子和中子分离能,分析了它们的稳定性.     

2-三氟甲基吡啶的转动光谱及分子结构研究

本文测定了2-三氟甲基吡啶在2∽20 GHz频率范围内的高分辨转动光谱. 测定了转动常数、¹⁴N核四极耦合常数及离心畸变常数等一系列光谱参数. 同时还在自然丰度下测定了5个¹³C和1个¹⁴N单取代同位素异数体的光谱数据. 实验结果结合从头算准确地推导出2-三氟甲基吡啶的骨架结构. 实验测得同位素异数体的平面转动惯量P_cc数值均为44.46 u?²，表明此分子具有C_s对称性. 此外，本文计算了吡啶、2-氟吡啶、2-甲基吡啶和2-三氟甲基吡啶的分子表面静电势，以此分析了三氟甲基的取代对电子分布的影响.     

sdg IBM对稀土偶偶核基态形变的计算

用sdg IBM的内禀态,解析计算了稀土区的^152—164Dy、^154—168)Er、^170—186W、^168—194Os等偶偶同位素的基态形变,与其它理论及实验结果进行系统比较,表明sdg IBM能对核的形变作出很好的描述.     

O同位素的相对论平均场计算中对能隙参数的研究

在相对论平均场理论框架下, 研究了各种对能隙参数对O同位素偶偶核的适用性. 通过对原子核结合能和四极形变的系统计算表明, 在O同位素区域, 对能隙参数Λ_n和Λ_p均可取为0.5, 这样既简化了计算, 又可得到比较满意的结果.     

High-spin g factors and proton alignment in Pt

The average g factors of high-spin states in ^180,182,184Pt were measured by the transient-field technique. In all three isotopes the quasicontinuum g factor at an angular momentum of 20 is g0.37. This contrasts with similar measurements on other nuclei that have 70Z80, where typical values of g0.22 have been attributed to the influence of quasineutron alignments. Evidently proton and neutron configurations are about equally important at high spin in the Pt isotopes near mid-shell. This inference is consistent with the discrete spectroscopy, including the contention, supported by g_K−g_R values, that h_9/2 proton pairs align along with the i_13/2 neutrons at rotational frequencies of ω≈0.3 MeV in ¹⁸⁴Pt. Links between the quasicontinuum g factors and features in the discrete spectroscopy are explored by comparing and contrasting the behavior of ¹⁸⁴Pt and ¹⁶⁶Hf.     

原子核单粒子共振态的研究进展

共振是自然界普遍存在的有趣现象。在核物理领域，存在许多奇特现象，共振在其中扮演着重要角色。介绍了近期发展的RMF-CSM、RMF-CGF和RMF-CMR方法及其对原子核单粒子共振态的研究。给出了120Sn，31Ne等核的单粒子共振态的能量和宽度及其随质量数、形变的变化规律，分析了19C，31Ne和39Mg等核的晕形成的物理机制和在N=20附近能级反转的原因。特别是新发展的RMF-CMR方法，在描述稳定核和奇特核方面都取得了成功，支持Zr同位素存在巨晕的预言。Resonance is an interesting phenomenon in nature. In nuclear physics, resonance plays an important role in the formation of many exotic phenomena. This paper introduces the recently developed RMF-CSM, RMFCGF, and RMF-CMR methods and their researches on nuclear single-particle resonances. The energies and widths of the single-particle resonant states in 120Sn and 31Ne and their evolution to mass number and deformation are given. In addition, the physical mechanism of the halo formation in 19C, 31Ne and 39Mg and the cause of energy level inversion near N=20 are analyzed. In particular, the newly developed RMF-CMR approach has been successful in describing stable and exotic nuclei and supports the prediction that Zr isotopes exist in a giant halo.     

质子数Z 分别位于Ru 之上和之下的A~(100~126) 丰中子原子核三轴形变在原子核形状变迁和共存中的重要作用(英文)

基于Ru (Z = 44) 丰中子同位素中存在最大三轴形变的理论预言和实验证据,综述了近年来Rh (Z = 45),Pd (Z =46), Ag (Z =47), Cd (Z =48)(质子数Z 位于Ru,Z =44 之上)及Zr (Z =40), Nb (Z =41), Mo (Z =42),Tc (Z =43)(质子数Z 位于Ru,Z =44 之下) 的A~ (100~126) 丰中子同位素中关于三轴形变的形状变迁和形状共存系统性研究的重要进展。252Cf 自发裂变瞬发 射线-- 三重符合、特别是新建立的--- 四重符合数据的系统观测和研究,在Ru, Pd, Cd 和Nb 丰中子同位素中显著扩展或首次观测到了一系列能带,为这个核区原子核形状的研究提供了新的、重要的实验数据。联系此前报道的有关进展,使用PES, TRS, PSM, CCCSM 和SCTAC 理论模型计算拟合新的实验数据,在该核区沿同中素和同位素链,并随自旋和激发能变化各自由度,跟踪原子核形状渐进变化,获得了新的系统性研究成果,显著扩展和深化了人们对原子核形状变迁和形状共存的认知。对于Ru 及其上的Rh (Z = 45), Pd (Z = 46), Ag (Z = 47) 和Cd (Z = 48) 丰中子同位素的研究表明:Rh 丰中子核具有比最大值稍小的三轴形变,γ = 28°,并在103{106Rh 同位素链上鉴别出了手征对称破缺;在三轴形变核112Ru和114Pd(N = 68)中发现了三轴原子核的摆动运动,该摆动运动也可能在114Ru (N = 70)中存在;观察到了从具有最大三轴形变的110,112Ru 中手征破缺到稍小三轴形变的112,114,116Pd 中扰动的手征破缺的过渡;在较软的Ag 核中观察到了丰富的谱学结构,在104,105Ag 中鉴别出了可能的手征对称破缺,在较重的115,117Ag 中提出了趋于三轴形变的软度;具有小形变的Cd核的能级结构被解释为准粒子耦合、准转动和软三轴形变;最近的库伦激发的研究提供了Z = 50, N = 82满壳附近122,124,126Cd 核中出现核集体性的实验和理论证据;上述研究成果展现出从Ru中的最大三轴形变(γ=30°,三轴形变极小增益为0.67 MeV), 经具有大三轴形变的Rh核γ=28°),到Pd核中的稍小、但稳定于中等自旋到高自旋区的三轴形变(γ~41°,三轴形变极小增益为0.32 MeV),再经Ag核中的软度,最后到具有很小形变、但仍出现集体性质、包括软三轴形变的Cd核的过渡。对于Pd核转动带交叉系统性的研究揭示了其第一带交叉(νh_11/2)2 中子转动顺排的上行驱动,和第二带交叉(πg_9/2)2质子转动顺排的下行驱动效应,成功地解释了114Pd 中的三轴摆动运动,并给出了110-118Pd同位素链中理论早已预言、而比早期理论预言更为完整准确的形状渐进变迁和形状共存的图像。根据该核区的系统研究,发现最大三轴形变出现在112Ru,而在相邻的偶Z(Pd)同位素链,三轴形变极小的中心在114Pd, 两者均为N = 68。上述系统性研究沿相邻的Ru和Pd偶Z同位素链,在N =68同中素中鉴别出最大三轴形变,均比理论预言的108Ru 和110Pd 多4个中子。在Z值位于Ru (Z = 44) 之下的Zr (Z = 40), Nb (Z = 41), Mo (Z = 42) and Tc (Z = 43) 丰中子同位素中,Y和Zr核具有很强的轴对称四极形变,而在较重的Zr同位素中出现了自由度;较重的Nb核(A = 104~106) 基态具有中等程度的软三轴形变和强四极形变,随着自旋和激发能的增加,过渡到接近于轴对称的强四极形变;而较轻的Nb核(A≤103) 基态均接近轴对称形状;在Nb同位素链上基态由球形到强四极形变的形状突变发生在100Nb(N = 59),在100-106Nb同位素链中基态的软三轴形变随中子数增加而增加;在Nb核中还观察到关于软三轴形变的形状共存;Mo核具有大的三轴形变,观察到了振动和手征对称破缺;Tc核具有比最大值稍小的三轴形变,γ=26°,并观察到了手征对称破缺。质子数Z从41到48的A~(100~126)丰中子同位素,特别是Pd和Nb 同位素,呈现出关于三轴形变的过渡特征。This paper reviews the systematic investigations and understanding for the shape transitions and coexistence with regard to triaxial deformations in A s 100 to 126 neutron-rich Rh (Z = 45), Pd (Z = 46), Ag (Z = 47), Cd (Z = 48) and Zr (Z = 40), Nb (Z = 41), Mo (Z = 42), Tc (Z = 43) isotopes with Z beyond and below Ru (Z = 44), respectively, in Ru the maximal triaxial deformation having been predicted and deduced. The recent measurements and studies of prompt triple- and four-fold, γ-γ-γ and γ-γ-γ-γ, coincidence data from the spontaneous fission of 252Cf using Gammasphere have yielded considerable expansion and extension or first observation of the bands in Ru, Pd, Cd, and Nb isotopes,which provided important data for the studies of nuclear shapes in this region. Combined with previous investigations, recent systematic studies of the new data well reproduced by PES, TRS, PSM, CCCSM and SCTAC model calculations have traced shape changes along the isotonic and isotopic chains, respectively,and with changing excitations/spins as well, significantly expanding our knowledge of shape transitions/coexistence in nuclei.For the neutron-rich Ru and beyond, Rh, Pd, Ag and Cd isotopes, triaxial deformations γ= 28°,slightly smaller than the maximal value, were deduced in Rh (Z = 45) isotopes, with chiral symmetry breaking proposed in 103-106Rh; onset of wobbling motions were identified in 112Ru and 114Pd (N =68),and probably also in 114Ru (N =70); evolution from chiral symmetry breaking in 110,112Ru with maximal triaxial deformations to disturbed chirality in 112,114,116Pd with less pronounced triaxial deformations was proposed; rich nuclear structure was proposed in soft Ag isotopes with possible chiral doubling structure suggested in 104,105Ag, and softness towards triaxial deformation proposed in heavier 115,117Ag;quasi-particle couplings, quasi-rotations and soft triaxiality were suggested in Cd (Z =48) isotopes with small deformations; onset of collectivity was recently suggested in 122,124,126Cd in the vicinity of Z =50 and N = 82 closed shells by studies of Coulomb excitations; shape evolutions from maximal triaxial deformations in Ru (γ=30°, with triaxial minimum energy gain of 0.67 MeV), through Rh with large triaxial deformations ( γ=28°), to less pronounced triaxiality in Pd (with triaxial minimum energy gain of 0.32 MeV), then soft triaxiality in Ag, and finally to slightly deformed Cd isotopes but with emergence of collectivity and soft triaxiality were proposed. The systematic studies of the band crossings in Pd revealed up-rising drivings of the first band crossings caused by (νh_11/2)2 and down-sloping drivings of the second band crossings by (πg_9/2)2, explained the onset of wobbling motions in 114Pd,and showed a long-sought picture of shape evolution and coexistence in the Pd isotopic chain which is more complete but complex than earlier predictions. Based on the systematic studies in the mass region,maximal triaxial deformation is found to be reached in 112Ru and less-pronounced triaxiality centered at 114Pd, both for N =68, four neutrons more than predicted in earlier theoretical calculations.In the neutron-rich Zr (Z =40), Nb (Z =41), Mo (Z =42) and Tc (Z =43) isotopes with Z just below Ru, large quadrupole deformations of axially symmetric shapes were deduced in Y and Zr isotopes, with emergence of the degree of freedom having been suggested for heavier Zr isotopes; medium triaxial deformations were deduced for the ground states of heavier (A > 104) Nb isotopes, and, with increasing excitations and spins, evolution from medium triaxial deformations with strong quadrupole deformations at ground states to nearly axially-symmetric shapes were deduced; light Nb isotopes (A6103) have near axially-symmetric shapes with strong quadrupole deformations; combining with the identification of onset of strong quadrupole deformation at 100Nb in the Nb isotopic chain, an increase of soft triaxiality with increasing neutron number was proposed in 100-106Nb. Shape coexistence with regard to soft triaxiality is also proposed in Nb isotopes; large triaxial deformations, vibrations and chiral doublets were proposed in Mo isotopes; chiral doubling and large triaxial deformations (γ ~26°) slightly smaller than the maximal triaxiality were suggested in Tc isotopes.The neutron-rich nuclei with Z ranging from 41 through 48 and A ~100 to 126, especially the Pd and Nb isotopes are thus found to be transitional nuclei with regard to triaxiality.     

稀土区奇A核晕带存在从转动到振动形状演化的直接证据(英文)

原子核的形状演化效应是核结构研究的重要基础问题之一。通常认为，A=160质量区的奇A核位于大形变核区域，它们的激发态能谱将呈现出典型的转动激发特征。然而，基于E-GOS曲线方法，发现随着角动量的增加，该质量区奇A核的晕带具有显著地从转动激发演化成为振动激发的形状演化现象。此外，为深入理解原子核形状演化的微观机制，采用Total-Routhian-Surface（TRS）方法针对稀土区的奇A核进行了理论计算，结果表明，165Yb和157Dy同位素在低激发态时具有稳定的长椭形变，当角动量大于0.50 MeV后，核芯的四极形变显著减小并开始产生三轴形变。The phase transition of nuclei with increasing angular momentum (or spin) and excitation energy is one of the most fundamental topics of nuclear structure research. The odd-N nuclei with A ≈160 are widely considered belonging to the well-deformed region, and their excitation spectra are energetically favored to exhibit the rotational characteristics. In this work, however, the evidence suggesting that the nuclei changes from rotation to vibration along the yrast lines as a function of spin was found. The simple method, named as E-Gamma Over Spin (E-GOS) curves, would be used to discern the evolution from rotational to vibrational structure in nuclei for various spin ranges. Meanwhile, in order to understand the band structure properties of nuclei, theoretical calculations have been performed for the yrast bands of the odd-A rare-earth nuclei within the framework of the total routhian surface (TRS) model. The TRS plots predict that the 165Yb and 157Dy isotopes have large quadrupole shapes at low spin states. At higher rotational frequency (hω~ >0.50 MeV), a clear reduction of the quadrupole deformation is indicated by the present results, and the isotopes become rigid in the γ deformation.     

RMF理论对N=60同中子核素形状演化的研究

利用形变约束的相对论平均场理论系统研究了N=60同中子核素的形状演化， 给出了这些核的基态结合能、 形变、 单粒子能级以及形变激发的位能曲线。 通过比较和分析发现， 随着质子数的增加， N=60同中子核的基态形变向轴对称形变方向演化， 114Xe和116Ba位于球形U（5）和轴对称SU（3）的过渡区， 存在形状相变的临界点结构， 这些结果与实验观测一致。 The shape phase transition between spherical U（5）and axially SU（3）deformed nuclei is investigated systemically for N=60 isotonic chain by the constrained relativistic mean|field theory with the interactions NL3 and PK1. The values of bind energy and quadruple deformation β2 are calculated and a good agreement is obtained as compared with the experiments. By examining the potential energy curve and single particle spectra obtained with this microscopic approach, the possible critical point nuclei with the structure of shape phase transition are suggested to be 114Xe and 116Ba, which is favored by the experiments.     

Macroscopic-microscopic calculations of fission potential surface of uranium isotopes in the three quadratic surfaces parametrization

Five-dimensional (5D) fission potential energy surfaces (PES) for uranium nuclei are investigated based on the macroscopic-microscopic Lublin-Strasbourg drop model in the three-quadratic-surface parametrization, and the heights of static fission barriers are obtained. Asymmetric and symmetric fission paths are presented on the 5D PES of ²³⁶U for different nuclear shapes. The calculated barrier heights, E_A and E_B, are quite consistent with the experimental data for all even-even nuclei of uranium isotopes, from ²³⁰U to ²⁴⁴U.     

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     

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.     

Quasi-exactly solvable decatic model description of nuclei near the X(5) critical point

The Bohr Hamiltonian with axially deformed shape confined in a quasi-exactly solvable decatic β-part potential is studied.It is shown that the decatic model can well reproduce the X(5)model results as far as the energy ratios in the ground and beta band and related B(E2)values are concerned.Fitting results to the low-lying energy ratios and relevant B(E2)values of even-even X(5)candidates ¹⁵⁰Nd,¹⁵⁶Dy,¹⁶⁴Yb,¹⁶⁸Hf,¹⁷⁴Yb,^176,178,180Os,and ^188,190Os show that the decatic model provides the best fitting results for the energy ratios,while the X(5)model is the best at reproducing the B(E2)values of these nuclei,in which the beta-bandhead energy is lower than that of the gamma band.While for even-even nuclei,such as ^154,156,158Gd,with bandhead energies of the beta and gamma bands more or less equal within the X(5)critical point to the axially deformed region,our numerical analysis indicates that the decatic model is better than the X(5)model in describing both the low-lying level energies and related B(E2)values.     

轴对称奇A核系统的强耦合临界点对称性

鉴于临界点对称性方法在描述原子核形状相变中的成功应用，在强耦合方案下对原有描述偶偶核球形到长椭形状相变的临界点对称性模型X（n）（n=3，4，5）进行扩展，据此建立描述轴对称奇A核系统的SX（n）临界点对称性。通过对X（n）模型与SX（n）模型的转动谱结构进行对比分析，揭示了SX（n）临界点模型的动力学结构受模型维数n的影响较小且更接近刚性转子的模型特征，这些模型特征进一步通过检验过渡区核素150，151，152，153Sm以及172，173，174，175Os中的相关转动带结构得到了初步证实。In view of the successful application of the methods based on critical point symmetries (CPSs) in nuclear shape phase transitions, the new CPSs named SX(n) are established in this work for axially-symmetric odd-A nuclei through extending the original X(n) CPSs with n=3,4,5, which were used to describe the spherical to prolate shape phase transitions in even-even nuclei, in the strong-coupling scheme. By comparing the spectral structures in between the X(n) and the SX(n) CPSs, it is revealed that the dynamical structures of SX(n) are closer to the rigid rotor and less changed with the model dimension in comparison with X(n). Moreover, these features of SX(n) are preliminarily verified by checking the rotational structures of 150,151,152,153Sm and 172,173,174,175Os nuclei.