“全同”超形变核转动带的量子群Uqp(u2)模型的理论分析

利用量子群U_qp(u₂)模型计算了^{191-192-193-194Hg}超形变(SD)带的γ跃迁能E_γ,运动学转动惯量J⁽¹⁾和动力学转动惯量J⁽²⁾,顺排角动量之差(i=ω(J⁽¹⁾(^{191-192-193-194}Hg)-J⁽¹⁾(¹⁹²Hg))),并与实验值进行比较得到了满意的结果,此外,还利用U_qp(u₂)模型的形变参量与核软度的关系式,计算出各SD带的核软度参数σ₁与唯象分析给出的组态结构进行了比较分析.     

粒子–转子模型分析超形变转动带

利用三轴粒子-转子模型计算了¹⁹³Tl超形变带γ跃迁能量,运动学转动惯量J⁽¹⁾和动力学转动惯量J⁽²⁾,并与实验值进行比较得到了满意的结果;预言了B(M1)值以及动力学电四极矩Q⁽¹⁾和Q⁽²⁾指出在超形变带的分析中粒子-转子模型是一种可以采用的方法.     

A～190区超形变带能谱分析和自旋的决定

利用宏观模型系统地分析了A～190区七个超形变核十五条超形变带的能谱,决定了超形变带的自旋值,用三参数公式计算了能谱,运动学转动惯量J⁽¹⁾和动力学转动惯量J⁽²⁾,并与实验进行了比较,得到了较满意的结果.     

超形变带Staggering现象的SUq(2)描述

利用SU_q(2)转动谱公式分析了¹⁴⁹Gd(1),¹⁴⁸Gd(6)和¹⁴⁸Eu(1)超形变带的staggering现象.当选择合适的带首自旋,计算的ΔI=4的分岔和实验提取的结果惊人地吻合,表明q形变或许是产生原子核超形变带staggering现象的原因之一.     

超形变带的两带混合模型

用参数化的两带混合模型解释了A～190区两条反常的超形变带((193)Hg(b1)和¹⁹³Hg(b4)).预言在hω≈0.42MeV时,¹⁹⁴Hg(b1)动力学转动惯量J⁽²⁾将开始下降.     

178 72Hf和179 72Hf稀土核高K低激发带

用处理推转壳模型的粒子数守恒(PNC)方法,分析了稀土变形核^178,179Hf的基态带和低激发高K多准粒子带的运动学转动惯量J⁽¹⁾随角频率ω的变化及其微观机制,特别是被拆散核子的Pauli堵塞效应的重要影响.本文分析和计算了¹⁷⁸₇₂Hf的2准粒子和4准粒子及的¹⁷⁸₇₂Hf3准粒子的高K低激发带.实验观测到的J⁽¹⁾随ω的变化,在PNC计算中得到较好的重现.分析表明, 高K多准粒子带的J⁽¹⁾随ω的变化与基态带的不同,主要来自高N(j)闯入态的堵塞效应.     

全同超形变带转动惯量的粒子数守恒计算

利用推转壳模型的粒子数守恒方法计算了超形变(SD)转动带¹⁹²Hg和¹⁹⁴Hg(1,2,3)的带首转动惯量.分析了带首附近的组态结构及带首转动惯量随对力强度的变化.带首转动惯量之差δJ₀对对力强度十分敏感,而对Nilsson能级参数K、μ及形变参数并不敏感.对力及堵塞效应是造成带首转动惯量差别的主要因素.但与正常形变核相比,对力强度似有较大程度减弱.     

超变形核中四极对力形式的探讨

用粒子数守恒方法分析了对力对于超变形(SD)带的转动惯量随角动量(角频率)变化的规律.计算中如包含了单极对力和Y₂₀四极对力,晕SD带¹⁹⁴Hg(1)和¹⁹²Hg(1)的转动惯量在观测的全部角动量范围中的变化规律,都可得到极好的重现,特别是ω≥0.40MeV时,¹⁹⁴Hg(1)的J⁽²⁾下弯和¹⁹²Hg(1)J⁽²⁾的变平.而考虑Y_2±1和Y_2±2四极对力的计算结果,都与实验不符.粒子数守恒计算中极清楚地展现了J⁽²⁾随ω变化的微观机制(可分别给出各大壳、各推转Nilsson能级上的粒子填布几率和对J⁽²⁾的贡献).J⁽²⁾随ω变化是粒子壳效应(变形场中单粒子运动)、对关联、Pauli堵塞效应以及Chriolis(反配对)作用相互竞争的结果.     

奇A核超形变全同带分析

利用三轴粒子-转子模型研究了A～190区奇A核超形变全同带,采用标准的BCS方法处理对关联,分析了(¹⁹¹Au,¹⁹¹Hg(b1)),(¹⁹¹Hg(b2),¹⁹³Hg(b2))和(¹⁹¹Hg(b3),¹⁹³Hg(b3))三对全同带,指出特定轨道的填充是造成全同带的重要原因.     

用I(I+1)展开式分析超形变带

用Bohr–MottelsonI(+1)展开四参数转动谱公式系统分析了A～190、150区的超形变转动带.结果表明:四参数ABCD公式能够相当好地描述上述两个区的超形变带,若干核第二类转动惯量J⁽²⁾的理论计算值与实验提取值符合较好;A～190区超形变带的四参数数值关系并不支持Harris公式及ab公式的理论预期值,但相对而言,ab公式的理论预期值与实验提取值更为接近.     

转动谱的若干理论及其对超形变带的研究

简述了若干转动谱理论及其对超形变带的应用 ,并用 Bohr- Mottelson的 I(I+1 )展开公式分析了 A=1 90区超形变带的性质和指定了它们的能级自旋 ,用 Harris的ω2 展开公式 J(1) =2α+(4/3 )βω2 +(6 /5 )γω4分析了 A=1 5 0区 Tb和 Dy同位素 2 0条超形变带的性质 ,指定了它们的能级自旋 .对于首次发现的152 Dy(1 )超形变带 ,带首自旋指定为 2 6 h,与实验结果更加符合. The recent developments of rotational spectral theories and its application to superdeformed bands were briefly reviewed. The superdeformed bands in A ≈190 region were analyzed and the spins of energy level were determined by the least square fitting experimental transition energy with the formula of Bohr Mottelson’s I(I+1) expansions. The superdeformed bands in A ≈150 region were analyzed by using the kinematic moments of inertia formula J (1) =2α+(4/3)βω 2+(6/5)γω 4 in...     

190区超形变带自旋指定的再讨论

利用两类转动惯量随转动频率的变化及其相互关系,对190区Bohr-Mottelson的两参数、三参数和四参数I(I+1)展开公式指定自旋不一致的27条超形变带进行分析,发现其中18条超形变带,它们的带首自旋I₀能够从两类转动惯量随转动频率的变化及其相互关系中可靠地定出.¹⁹²Hg(2)等发生带交叉的超形变带,它们的带首自旋也可通过分析带交叉以前、两类转动惯量随转动频率的变化及其相互关系定出.     

Further Discussion on the Spin-Determination of Superdeformed Bands in the A～190 Region

The 27 superdeformed bands, whose spin determinations aren't in agreement with two-parameter, three-parameter and four-parameter I(I+1) expansions, are analyzed. The results show that the angular momenta of 18 superdeformed bands can be determined by comparison with the variation of the kinematic and dynamic moments of inertia with rotational frequency and their mutual relation. The angular momenta of superdeformed bands like ¹⁹²Hg(2), which have bands cross, can also determined by analyzing the spectra before bands cross and by comparison with the variation of the kinematic and dynamic moments of inertia with rotational frequency and their mutual relation.     

Odd-Even Difference of Moment of Inertia of NuclearSuperdeformed States in A～190 Region

By fitting the E2 transition spectra of superdeformed bands in A～190 region, the coefficients of Bohr-Mottelson's I(I+1) expansion are determined and moments of inertia of band head are calculated out. All results show that the moments of inertia of odd-A nuclei are systematically larger than those of the neighboring even-even nuclei, and the moments of inertia of odd-odd nuclei are systematically larger than those of the neighboring odd-A nuclei. The odd-even difference of moment of inertia of nuclear superdeformed states is obvious.     

Energy Staggering in Ground Bands of 232Th and 236,238U Nuclei Using the Interacting Vector Boson Model

The ΔI=2 and ΔI=4 staggering parameters of transition energies E_γ for normally deformed positive parity ground bands in ²³²Th and ^236,238U nuclei are studied in framework of the symplectic extension of the interacting vector boson model. The model parameters are obtained from the fitting procedure between the calculated excitation energies and the corresponding experimental ones. The staggering parameters represent the finite difference approximations to higher order derivatives dⁿE_γ/d Iⁿ of the γ -ray transition energies in a ΔI=2 and ΔI=4 bands, which yielding multipoint formulae. The first order derivative (two-point formula) provides us with information about the dynamical moment of inertia. The staggering oscillation for the fourth order derivative (five-point formula) is about 0.5 KeV and is even larger than that in superdeformed bands. The quite similarity in dynamical moments of inertia of the isotopes ^236,238U up to high spin states indicate that the phenomenon of identical bands is not restricted to superdeformed bands.     

A comparison of the known SD bands in the mass A≈80 region

The mass A≈80 region is now firmly established as the newest region of superdeformation, with up to 11 nuclei exhibiting as many as 21 superdeformed bands. The dynamic moments of inertia of these bands reveal a variety of interesting features, such as superdeformed band crossings and the first pair of identical superdeformed bands in the mass A≈80 region. Cranked shell model calculations have been performed and the bands are interpreted in terms of the number of high-N intruder orbitals occupied. The differences in dynamic moments of inertia and the proposed single particle configurations are discussed.     

Description of the Superdeformed Bands of the Lutetium Isotopes

In the cases with and without a perturbation possessing the S0_sdg(5) (or SU_sdg(5)) symmetry in the supersymmetry scheme with many-body interactions, superdeformed bands in the odd-A Lu isotopes ^163,165,167Lu are investigated. Quantitatively good results of γ-ray energies and dynamical moments of inertia are obtained in both of the two cases. It shows that the supersymmetry scheme with many-body interactions has almost the same power to describe the triaxial superdeformed bands as to the other superdeformed bands.     

Identical bands: two steps forward

The identical bands phenomenon has been studied in detail both experimentally and theoretically. A first step has been done by analysing the distributions of the fractional changes in the dynamical moments of inertia of superdeformed nuclei. They showthat there is a clear excess of identical bands in superdeformed nuclei compared to normally-deformed nuclei at low spin. Furthermore, this difference can be traced back to some special properties of superdeformed bands. The second step consists in the precise lifetime measurements that have been performed in superdeformed nuclei of the rare earth region. The derived quadrupole moments support the picture that alignments and deformation effects cancel in identical bands.     

Identification of Bandhead Spin and Identical Bands for Odd-A Nuclei in $A\sim190$ Superdeformed Mass Region

The dynamical moment of inertia is estimated with its even-power expansion of the rotational frequency and in accordance we determine the intermediate spins of the superdeformed (SD) rotational bands. Using Marquardt method of nonlinear least-squares routines, we determine the expansion coefficients by fitting the proposed dynamical moment of inertia with its recent experimental data of the SD nuclei in the A=190 mass region. The comparison between our theoretical and available experimental data for the dynamic moment of inertia and spin shows good agreements. Also, we have calculated the static moment of inertia at three alternative values of spin. The value of spin at which the two moments of inertia are nearly equals is to be regarded as a bandhead spin of the corresponding band. These studies are carried out for eighteen bands of odd-A nuclei of the superdeformed region 190, namely ¹⁸⁹Hg(b1), ¹⁹¹Hg(b1, b2, b3, b4), ¹⁹³Hg(b2, b3, b5), ¹⁹⁵Hg(b1, b2, b3, b4), ¹⁹³Tl(b1, b2, b3, b5), ¹⁸⁹Tl(b1), and ¹⁹⁷Bi(b1). We also notice the occurrence of identical SD bands with near identical transition energies among the considered SD bands.     

Double-Blocking Effects in Odd-odd Superdeformed Nucleus 194Tl

Six superdeformed bands of odd-odd nucleus ¹⁹⁴Tl in A～190 mass region are studied using the particle-number conserving method for treating the cranked shell model with pairing interactions. Calculated results agree with experiments very well. Based on our calculation the configurations of the six superdeformed bands are assigned and the influence of blocking effects of proton and neutron on moments of inertia is investigated in detail. The variation of moments of inertia with rotational frequency is mainly attributed to the intruder shells (neutron N=7 and proton N=6), whereas the contributions to moment of inertia from other shells remain almost unchanged with rotational frequency.