超形变核全同带的研究

简述了超形变原子核全同带的研究进展情况,并以Bohr-Mottelson的I(I+1)展开转动谱公式对部分典型的超形变带进行了分析.发现所谓全同带的确只是两个带的J⁽²⁾比较接近,它们的J⁽¹⁾和J₀并不相等,而且signature对偶带更接近全同.     

Microscopic Mechanism of Large Fluctuation in Odd-Even Differences in Moments of Inertia for Actinide Nuclei

The experimental large fluctuation in odd-even differences in moments of inertia of deformed actinide nuclei is investigated using the particle-number conserving (PNC) method for treating the cranked shell model with monopole and quadrupole pairing interactions. PNC calculations show that the large odd-even difference in moments of inertia mainly comes from the interference contributions j(μν) from particles in high j intruder orbitals μ and ν quite near the Fermi surface, which have no counterpart in the BCS formalism. The effective monopole and quadrupole pairing interaction strengths are determined to fit the experimental odd-even differences in binding energies and bandhead moments of inertia. The experimental results for the variation of moments of inertia with rotational frequency ω are reproduced well by the PNC calculation. The nearly identical experimental moments of inertia between ²³⁶U(gsb) and ²³⁸U(gsb) at low frequencies ħω≤0.20 MeV are also reproduced quite well.     

Single Particle Schr dinger Fluid and Moments of Inertia of Deformed Nuclei

We have applied the theory of the single-particle Schrodinger fluid to the nuclear collective motion of axially deformed nuclei. A counter example of an arbitrary number of independent nucleons in the anisotropic harmonic oscillator potential at the equilibrium deformation has been also given. Moreover, the ground states of the doubly even nuclei in the s-d shell ²⁰Ne,²⁴Mg,²⁸Si,³²S and ³⁶Ar are constructed by filling the single particle states corresponding to the possible values of the number of quanta of excitations n_x,n_y, and n_z. Accordingly, the cranking-model, the rigid-body model and the equilibrium-model moments of inertia of these nuclei are calculated as functions of the oscillator parameters ω_x,ω_yand ω_z which are given in terms of the non deformed value ω00 , depending on the mass number A, the number of neutrons N, the number of protons Z, and the deformation parameter β. The calculated values of the cranking-model moments of inertia of these nuclei are in good agreement with the corresponding experimental values and show that the considered axially deformed nuclei may have oblate as well as prolate shapes and that the nucleus ²⁴Mg is the only one which is highly deformed. The rigid body model and the equilibrium model moments of inertia of the two nuclei ²⁰Ne and ²⁴Mg are also in good agreement with the corresponding experimental values.     

Correlation of Moments and Critical Phenomenon in Disassembly of Hot Nuclei

We used Monte Carlo method to generate the configurations of disassembly of hot nucleus Au* based on the Atomic Mass Table and the conservation of mass and charge number.The resulted charge distribution of fragments was then used to calculate the conditional moments.The logarithm correlation between second and third moments of experimental charge distribution is very well reproduced by theory.It seems that no connection to the critical phenomenon of concerned system exists.     

QCD类规范的南部模型中费米子与动力学产生的介子的密度效应

将两味(N_f=2)情况下的QCD类规范的南部模型应用到核物质中并得到了费米子的能隙方程.与四费米子相互作用部分相比,胶子部分对费米子质量约有1/4的贡献.手征序参量与QCD求和规则所预言的结果符合得很好.基于能隙方程,得到了标量与赝标量介子的一系列动力学性质,理论结果很好地符合了实验.     

q形变壳模型中奇A核的磁矩

将核磁矩算符定义为量子群SU_q(2)的一阶张量算符的形式.计算结果显示,q形变参数依赖于最后一个主壳层中的价核子数.在对满单j壳层外仅有一个价核子的奇A核磁矩值进行拟合后发现,在大多数情况下,较Schmidt值有所改进.     

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.     

Some Approximations in the Theorie of Moments and Transitions for Even-Odd Nuclei

In the framework of Green's functions, the theory of moments and transitions for even-odd-nuclei is developed. It is shown, how these quantities are connected with the effective particle-hole force and the generalized linear response function for the neighbour even-even nuclei. The response function describes the change of the single-particle propagator due to an external perturbation. For superfluid systems the Nambu [1] – Engelsberg [2] – Belyaev [3] technique has been used. The connection between earlier treatments is established, especially with the semiphenomenological approach of Migdal [4] and co-workers. Some approximations for the relevant effective particle-hole force emerging from the many-body theory are discussed in detail. Furthermore the generalization of the RPA-approximation for the auto-correlation function of density fluctuations in the case of superfluidity is given.     

Investigation of the Type of Quadrupole Pairing Force in Superdeformed Nuclei

The variations of moments of inertia of superdeformed (SD) bands ¹⁹⁴Hg(1)and ¹⁹²Hg(1) with angular momentum (rotational frequency) are investigated using the particlenumber conserving (PNC) method for treating the cranked shell model. Calculations show that if both the monopole and Y₂₀ quadrupole pairing forces are taken into account, the observed co variation of the moments of inertia of ¹⁹⁴Hg(1) and ¹⁹²Hg(1) can be reproduced very well both in the low-and high- ranges, in particular the J⁽²⁾ downturn of ¹⁹⁴Hg(1) and the flattening in J⁽²⁾ of ¹⁹²Hg(1) at>0.40MeV. On the contrast, the calculated J⁽²⁾'s with the Y_2±1 or Y_2±2 quadrupole pairing forces are in disagreement with the experiments. The microscopic mechanism of the co variation of J⁽²⁾ is clearly exhibited in the PNC calculation (the contributions to J⁽²⁾ from various major Shells and individual cranked Nilsson orbitals, the occupancy of each cranked Nilsson Orbital etc). The variation of moment of inertia is the result of the competition among the shell effect (single particle motion in a deformed potential), pairing correlation, Pauli blocking effect and Coriolis (anti-pairing) interaction.     

核子(强子)结构和性质的QCD研究

核子 (强子 )是夸克、胶子的束缚态 ,由量子色动力学 QCD描述。由于 QCD的基本特性(高能标度下的渐近自由、低能标度下色禁闭及动力学手征对称性破缺 ) ,对核子 (强子 )结构和性质的 QCD图象是标度相关的 .在高能标度下描述强子的是与探测强子结构的硬过程相联系的QCD部分子模型 .强子的夸克、胶子结构信息通过 QCD部分子求和规则得到 .QCD微扰论是适用的理论 .在低能标度时 ,必须发展 QCD非微扰途径来描述核子 (强子 )物理 .这里简要地讨论各种非微扰途径 (格点 QCD、Dyson- Schwinger方程、有效场论、QCD求和规则 )的某些结果和进展 ,并指出 QCD真空结构在描述低能标度下强子物理中担任重要角色 . The nucleon (hadron) is the bound state of guarks and gluons, which is described by the quantum chromodynamics (QCD). Due to the basic properties of QCD (the asymptotic freedom at the high energy scale, the color confinement and the dynamical chiral symmetry breaking at the low energy scale), the QCD picture for the nucleon’s (hadron’s) structure and property is scale dependent. At high energy scale, the QCD parton model, which is relative to the hard process for testing the...     

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.     

Mass relations for heavy mesons

In a non-relativistic quark model, by parametrizing the quark-antiquark potentials, some mass relations have been obtained. Algebraic expressions for the masses of higher flavour meson isosinglets have been given in terms of the meson masses of lower symmetries. Hallock and Oneda’s contention of two types of sumrules for nonet mesons in SU(3) has been examined and the possibilities of such different sum-rules of this type in SU(4) and SU(5) have been explored.     

用BCS理论计算稀土核转动惯量的奇偶差

用BCS理论计算了稀土区偶偶核和奇A核的转动惯量.计算结果表明,尽管转动惯量的计算值系统地小于实验值,但实验上观测到的转动惯量奇偶差的大幅度变化能够用BCS理论定性地描述. 这个结论与人们普遍认为的BCS理论给出的奇A核转动惯量应比相邻的偶偶核基态转动惯量大15%的看法相悖,但却证实了20多年以前Gregory和Volkov等人得出的结论,有助于人们在BCS平均场理论框架下理解正常形变核中出现全同带的现象.     

Features of Triaxial Superdeformed Bands in Odd Mass Nuclei Using the Cranked Nilsson–Strutinsky Model

Physics of Atomic Nuclei - The axial asymmetry deformation parameter $$\gamma$$ , the gamma transition energies, rotational frequencies, kinematic and dynamic moments of inertia in triaxial...     

Calculation of the Critical Distances in a System of Two Colliding Nuclei Beyond the Monopole Approximation

A method for calculating electronic levels in compact superheavy nuclear quasimolecules based on solving the Dirac equation in spherical coordinates using a multipole expansion of a two-center potential is developed. It is shown that, for internuclear distances up to ∼100 fm, such a technique enables fast convergence, which allows one to calculate the electronic energy levels with an accuracy better than 10−6. Moreover, all the multipole moments can be calculated analytically. The critical distances between the similar colliding nuclei have been calculated in the range Z ∼ 87–100 for bottom electronic levels: even 1σg and odd 1σu, respectively.     

Magnetic Moments of Odd A Nuclei in q-Deformed Nuclear Shell Model

q-deformed nuclear magnetic moment operatoris defined in terms of rank 1tensor operator of the quantum algebra SU_q(2).The results show that the q-deformation parameter depends on valence nucleon number in major shell.The magnetic moments of odd A nuclei with only one valence nucleon outside closed single-j shell are fitted.It shows that in most cases the results are improved in comparison with the Schmidt values.     

平均场加邻近轨道对力模型描述N=94同中异质素性质

利用严格可解的Nilsson平均场加邻近轨道对力模型,在区分质子和中子情况下,研究了大形变核的性质,主要计算了中子数为N=94的同中异质素的结合能、奇偶能差和转动惯量,并与相应的实验值进行了系统比较,结果表明此模型可以合理描述这些性质,正确反映原子核奇偶性质的变化规律。然后以偶偶核160Dy为例,研究了基态中各角动量J=0,1,...,12价核子对的占有率。结果表明,偶角动量占有率远高于奇角动量占有率,其中S,D,G价核子对各组份在基态波函数中是主要的。The Nilsson mean-field plus the nearest orbit pairing model for deformed nuclei is applied to investigate systematically the properties of the N=94 nuclei,employing both proton-proton and neutron-neutron pairing interactions.The binding energies,even-odd mass differences,moments of inertia are calculated and compared with the corresponding experimental data.The results show that this model can reasonably describe these properties.Further,the ground-state occupation probabilities of valence nucleon pairs with angular momentum J=0,1,...,12 for even-even 160Dy are calculated,and the results show that it is much higher for the even angular momenta than the odd angular momenta,and the S,D,G components in the ground-state wave function are dominant.     

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.     

Total Nuclear Reaction Cross Section Induced by Halo Nuclei and Stable Nuclei

We develop a method for calculation of the total reaction cross sections induced by the halo nuclei and stable. nuclei. This approach is based on the Glauber theory, which is valid for nuclear reactions at high energies. It is extended for nuclear reactions at low energies and intermediate energies by including both the quantum correction and Coulomb correction under the assumption of the effective nuclear density distribution. The calculated results of the total reaction cross section induced by stable nuclei agree well with 30 experimental data within 10 percent accuracy. The comparison between the numerical results and 20 experimental data for the total nuclear reaction cross section induced by the neutron halo nuclei and the proton halo nuclei indicates a satisfactory agreement after considering the halo structure of these nuclei, which implies quite different mean fields for the nuclear reactions induced by halo nuclei and stable nuclei. The halo nucleon distributions and the root-mean-square radii of these nuclei can be extracted from the above comparison based on the improved Glauber model, which indicates clearly the halo structures of these nuclei. Especially,it is clear to see that the medium correction of the nucleon-nucleon collision has little effect on the total reaction cross sections induced by the halo nuclei due to the very weak binding and the very extended density distribution.