168Hf三轴超形变核态的研究

采用TRS方法研究了¹⁶⁸Hf核的三轴超形变核态. 通过位能面计算给出了平衡形变参数, 证实了高自旋态下该核存在三轴不对称性. 通过分析各部分修正能量, 研究了其三轴超形变形成的机制: 主要原因是中子壳修正, 同时高j闯入轨道πi_13/2的形变驱动效应和转动能也起到重要作用.     

原子核内新的转动不变性的探索

对于λ=2,4,6…的偶极性轴对称形变核, 除存在着R(π)不变性外, 在某些核中可能还存在着R(π/2)不变性. 本文从理论上一般地分析了出现新的形变对称性的可能. 主要分析了出现R(π/2)不变性的条件, 满足R(π/2)不变性的波函数和矩阵元中所谓的记号因子σ⁽⁴⁾相关项. 用此可以解释实验能谱和B(E2)值中出现的一些I/2奇偶现象. 本文还提出了可能存在R(2π/3)不变性的条件.     

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.     

90Mo电磁跃迁几率的测量

利用束流能量为116MeV的⁵⁹Co(³⁵Cl,2p2n)⁹⁰Mo反应布居⁹⁰Mo的高自旋态.用10台反康普顿HPGe探测器组成的探测阵列进行γγ符合测量.通过多普勒展宽峰的形状分析测定⁹⁰Mo高自旋态的寿命.在正宇称衰变系观察到增强的M1跃迁,推断I=13以上是扁椭形变.负宇称高自旋态具有大的B(E2)值,并随自旋增大而起伏变化.正、负宇称态之间的跃迁显示增大的E1跃迁,似有八极关联的可能.但是,⁹⁰Mo并不处在理论预言的存在八极形变的核区内.     

奇A Tl核超形变的形状演化

利用粒子-转子模型研究了奇A Tl核yrast超形变核态的能谱,能量的旋称分离以及低自旋区的M1跃迁,理论值和实验值符合较好,研究表明奇A Tl超形变核态具有小的三轴形变,随着N的增加,重的Tl核比轻的Tl核四极形变要稍大.     

相对论平均场理论对Se，Kr，Sr和Zr同位素链形状共存的系统研究

在约束形变的相对论平均场理论下,用NL3参数组系统地研究了Se,Kr,Sr和Zr四个同位素链中的偶-偶核,理论计算的基态束缚能和实验值符合得非常好.通过对这些核的位能曲面的分析,发现在此区域内有着丰富的形状共存现象,系统地指出可能存在形状共存现象的原子核,并且进一步指出在这些核的位能曲面上两个能量极小点的能量差.另外通过对位能曲面以及单中子能级的研究,提出在此区域内N＝70可能是一个中子幻数. 关键词： 形状共存 相对论平均场 位能曲面 幻数     

稀土区奇A核M1和E2跃迁的性质

利用推广的粒子-转子模型研究了稀土区奇A核的M1和E2跃迁的性质,指出核心的十六极形变、转动哈密顿量中的二级科里奥利作用对M1(ΔI=1)和E2跃迁几率的Signature依赖性以及对Signature的平均值有着不容忽略的影响.对¹⁵⁷Ho的计算得到了能谱的Signature分离、B(M1;ΔI=1)值和[B(E2;ΔI=1)/B(E2;ΔI=2)]^1/2比值都同实验定性相符的结果.     

154Er核三轴超形变核态存在的微观机制

利用TRS方法计算了154Er核的总位能面,讨论了其存在三轴超形变核态的微观机制. Based on TRS theory the total routhian surface for~(154)Er nuclei is calculated, the result indicates it exists TSD state.     

用类B原子波函数对H2+7团簇的正八面体中心结构与能量的研究

在单中心球模型近似下,选用类B原子解析波函数,用变分法计算了H2+7团簇正八面体中心结构与能量.结果表明当中心氢原子核到顶角氢原子核之间的距离R=2.83α0时,体系能量有一极小值E=-3.918h0(a0=0.529177×10-10m,h0=27.2 eV).这表明H27+团簇的正八面体中心结构是稳定的结构,H2+7团簇是可能存在的.     

轴对称超形变和三轴超形变核态性质的研究

利用轴对称超形变和三轴超形变模型研究了¹⁶⁵Lu π[660 1/2]带.两种模型计算的γ跃迁能量都和实验值较好地符合.然而,能量的signature颤动指数,三轴因子,两类动力学电四极矩之比存在明显的差别,这些差别可以用来识别三轴超形变核态.     

Calculation of multidimensional potential energy surfaces for even-even transuranium nuclei: systematic investigation of the triaxiality effect on the fission barrier

Static fission barriers for 95 even-even transuranium nuclei with charge number Z = 94-118 have been systematically investigated by means of pairing self-consistent Woods-Saxon-Strutinsky calculations using the potential energy surface approach in multidimensional(β_2, γ, β_4) deformation space. Taking the heavier (252)~Cf nucleus(with the available fission barrier from experiment) as an example, the formation of the fission barrier and the influence of macroscopic, shell and pairing correction energies on it are analyzed. The results of the present calculated β_2 values and barrier heights are compared with previous calculations and available experiments. The role of triaxiality in the region of the first saddle is discussed. It is found that the second fission barrier is also considerably affected by the triaxial deformation degree of freedom in some nuclei(e.g., the Z =112-118 isotopes). Based on the potential energy curves, general trends of the evolution of the fission barrier heights and widths as a function of the nucleon numbers are investigated. In addition, the effects of Woods-Saxon potential parameter modifications(e.g.,the strength of the spin-orbit coupling and the nuclear surface diffuseness) on the fission barrier are briefly discussed.     

Evidence for a smooth onset of deformation in the neutron-rich Kr isotopes

The neutron-rich nuclei 94,96Kr were studied via projectile Coulomb excitation at the REX-ISOLDE facility at CERN. Level energies of the first excited 2(+) states and their absolute E2 transition strengths to the ground state are determined and discussed in the context of the E(2(1)(+)) and B(E2;2(1)(+)→0(1)(+)) systematics of the krypton chain. Contrary to previously published results no sudden onset of deformation is observed. This experimental result is supported by a new proton-neutron interacting boson model calculation based on the constrained Hartree-Fock-Bogoliubov approach using the microscopic Gogny-D1M energy density functional.     

ON THE MECHANISM OF BACKBENDING PHENOMENA OF SOME EVEN-EVEN NUCLEI

The energy levels, B(E2) values and gyromagnetic ratio g of some even-even nuclei have been calculated with a double band scheme of band-crossing. Based on these results, the mechanism of backbending phenomena is analyzed, and the possible criterion to distinguish the effects of shape transition, rotation-alignment and pairing collapse are also discussed.     

A microscopic study of the octupole degree of freedom at high angular momentum

A microscopic parity and number projected calculation after the variation was used to describe the rotational bands of the octupole deformed nuclei ¹⁴⁴Ba, ¹⁴⁶Ce and ²²⁴Ra. The states obtained in a cranked Hartree-Fock-Bogoliubov approach are taken as intrinsic states for the parity and number projection. Dipole moments, deformation parameters, B(E1), B(E2) and B(E3) transition probabilities along the band are obtained and compared with the available experimental data. The calculations have been done with the finite range density dependent Gogny force.     

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.     

IBM-2 calculations of some even-even selenium nuclei

In this study, we determined the most appropriate Hamiltonian that is needed for present calculations of nuclei in the A≅ 80 region by the view of interacting boson model (IBM-2). Using the best-fitted values of parameters in the Hamiltonian, we have calculated energy levels and B(E2) values for a number of transitions in some doubly even Se nuclei. The results were compared with the previous experimental and theoretical data and it is observed that they are in good agreement. The calculations have been extended to Se isotopes with A < 76 for which some B(E2) values are still not known.     

Nuclear Structure and Electromagnetic Transitions Investigation in Er Isotopes within Framework of Interacting Boson Model

Interacting Boson Model-2 (IBM-2) is used to determine the Hamiltonian for Er nuclei. Fit values of parameters are used to construct the Hamiltonian, energy levels and electromagnetic transitions (B(E2), B(M1)) multipole mixing ratios (δ(E2/M1)) for some even-even Er nuclei and monopole transition probability are estimated. New ideas are used for counting bosons number at N = 64 and results are compared with previous works.     

生成超重核的熔合反应中的动力学形变效应

利用包含动力学势能面的双核模型对超重核的生成机制中的一些问题进行了研究。对双核系统的粒子交换势能面进行的计算结果表明,反应过程中原子核动力学形变对于粒子交换势能面的结构有显著的影响。进一步计算了生成超重核的熔合几率,结果显示,原子核的动力学形变导致内熔合位垒升高,进而明显降低了生成超重核的熔合几率。Some aspects in the fusion mechanism for the production of superheavy nuclei are investigated with the dinuclear system model with dynamical potential energy surface. The calculation results about the potential energy surface indicate that the inclusion of nuclear dynamical deformation affects the structure of potential energy surface significantly.The investigation on the fusion probability to synthesize superheavy nuclei indicates that the fusion probability decreases significantly due to the increase of the inner fusion barrier for the inclusion of the nuclear dynamical deformation.     

Nuclear Structure of 12,14Be Within Deformed Quasi-Particle Random Phase Approximation (DQRPA)

We developed a deformed quasi-particle random phase approximation (DQRPA) to describe the Gamow–Teller (GT) transitions on even–even neutron-rich nuclei. To describe deformed nuclei, we exploited the deformed axially symmetric Woods–Saxon potential, the deformed BCS, and the deformed QRPA with realistic two-body interaction calculated by Brueckner G-matrix based on Bonn CD potential. The deformed single particle states are expanded in terms of the spherical harmonic oscillator basis in order to take the realistic G-matrix stored in the spherical basis. We calculated GT strength distributions, B(GT), of two nuclei ^12,14Be for many different deformation parameter β ₂ values as a function of the excitation energy E _ex w.r.t. the ground state of a parent nucleus. Our results for ¹²Be predict to prefer a prolate shape and B(GT) results of ¹⁴Be turn out to be independent of the β ₂ values.     

Potential energy surfaces for<Emphasis Type="Italic">N</Emphasis> =<Emphasis Type="Italic">Z</Emphasis>,<Superscript>20</Superscript>Ne-<Superscript>112</Superscript>Ba nuclei

We have calculated the potential energy surfaces forN = Z,²⁰Ne-¹¹²Ba nuclei in an axially deformed relativistic mean field approach. A quadratic constraint scheme is applied to determine the complete energy surface for a wide range of the quadrupole deformation. The NL3, NL-RA1 and TM1 parameter sets are used. The phenomenon of (multiple) shape coextistence is studied and the calculated ground and excited state binding energies, quadrupole deformation parameters and root mean square (rms) charge radii are compared with the available experimental data and other theoretical predictions.