Giant-dipole resonance and the deformation of hot,rotating nuclei

The development of nuclear shapes under the extreme conditions of high angular momentum and/or temperature is examined. Scaling properties are used to demonstrate universal properties of both thermal expectation values of nuclear shapes as well as the minima of the free energy, which can be used to understand the Jacobi transition. A universal correlation between the width of the giant-dipole resonance and quadrupole deformation is found, providing a novel probe to measure the nuclear deformation in hot nuclei.     

The swelling of nucleons and quark antisymmetrization

Antisymmetrization of the nuclear wavefunction at the quark level implies that quarks belonging to different nucleons are exchanged in proportion to the degree of nucleon overlap. This leads to an additional contribution to the quark-quark correlation beyond that expected in a conventional picture. We first explore this in a simple solvable one-dimensional model. Subsequently an extension is made to a model of nuclear matter for which divergences are encountered in the limit of large N. These are traced to the existence of unlinked quark clusters. After renormalization, the quarkquark correlation is computed. It is concluded that quark antisymmetrization leads to an effective nucleon size which depends on the nuclear density. A simple analytic formula for the effective nucleon radius is obtained.     

Al~+离子3s~2 ~1S_0→3s3p~ (3,1)P_1~o跃迁同位素偏移的理论研究

在多组态Dirac-Hartree-Fock方法对Al~+离子3s~2~1S_0→3s3p~(3,1)p_1~o两个跃迁同位素偏移因子精细计算工作的基础上,细致研究了同位素偏移因子和能量本征值(或跃迁能)随着电子关联的收敛过程.研究发现:单个能级的同位素质量偏移因子随电子关联的收敛性与能量本征值随电子关联的收敛性之间有线性关系;对于跃迁而言,对电子关联的描述越充分,质量偏移因子和跃迁能随电子关联的收敛性之间的线性关系越明显.因此,在计算模型中包含大规模的电子关联的情况下,可以利用该线性关系根据跃迁能的误差评估同位素偏移因子的不确定度.     

Nuclear radii of Na and Mg isotopes

The effective root-mean-square (rms) matter radii of ^ANa (A = 20–23, 25–32) and ^AMg (A = 20, 22, 23, 27, 29–32) have been deduced from the measured interaction cross sections using a Glauber-type calculation. It was found that the increase of rms matter radii in Na isotopes is primarily a consequence of the increase of rms neutron radii. A correlation between the radii, corrected for quadrupole deformation, and the Fermi-energy difference was observed for both Na and Mg isotopes. This correlation can be explained by a model that assumes the valence nucleons are responsible for the changes in nuclear radii. The presence of a neutron skin is suggested for neutron-rich Na and Mg isotopes. An application to the nuclear equation of state (EOS) is discussed.     

Nuclear spin-lattice relaxation of V in TIxV5S8 and TIxV6S8

Temperature dependence of the nuclear spin-lattice relaxation rate of ⁵¹V has been studied in metallic vanadium sulfides with quasi-one-dimensional structures. The ternary sulfide TI_0.54V₅S₈ is suggested to be an exchange-enhanced Pauli-parammagnet with antiferromagnetic correlation.     

基于252Cf裂变中子源的核信息系统频谱分析

 针对²⁵²Cf裂变中子源所构造的核信息系统,在阐述随机核信号功率谱密度的算法原理基础上,借助于Matlab分析工具,采用分块平均法,对系统3个测量通道的随机核信号,先做相关计算,再对总的相关函数进行傅里叶变换,求得总功率谱,最后做平均得到所需的功率谱密度,得到了核信息系统的频谱图,并获得了相关函数多重性、相干性和功率谱密度比等重要参数。     

壳模型哈密顿量本征值的美与奇

本征值问题是自然科学中基本运算之一，对于超大矩阵的对角化是当今许多科学问题的瓶颈。在应用原子核壳模型理论研究较重的原子核结构时，因为壳模型组态太大，通常的方法是基于各种物理考虑做某些组态截断，另一个思路是利用新的算法和飞速发展的计算机资源对这些大矩阵对角化或者近似对角化。总结了本课题组近年来在壳模型哈密顿量本征值近似方面研究的主要结果，包括最低本征值半经验公式及多种外推方法、本征值与对角元的相关性等。The eigenvalue problem is one of the fundamental issues of sciences. Many research fields have been challenged by diagonalizing huge matrices. The nuclear structure theorists face this problem in studies of medium-heavynuclei in terms of the nuclear shell model, in which the configuration space is too gigantic to handle. Thus one usually truncates the nuclear shell model configuration space based on various considerations. Another approach is to make use of super computers by various algorithms, and/or to obtain approximate eigenvalues. In this paper we review our recent efforts in obtaining approximate eigenvalues of the nuclear shell model Hamiltonian, with the focus on our semi-empirical approach and a number of extrapolation approaches towards predicting the lowest eigenvalue, as well as strong correlation between the sorted eigenvalues and the diagonal matrix elements, and so on.     

原子核体积效应对类锂离子体系基态能量的修正

用全实加关联的方法得到类锂离子1s22s（Z=21~30）波函数, 给出了原子核体积效应公式, 计算了原子核的体积效应及质量效应对类锂离子能级的修正. 结果显示, 在中等大小的核电核情形, 原子核体积效应对类锂离子能级的修正要比质量效应对类锂离子能级的修正要显著; 随着核电核数的增加, 原子核体积效应越来越重要.     

原子核体积效应对类锂离子体系基态能量的修正

用全实加关联的方法得到类锂离子15~22s(Z=21～30)波函数,给出了原子核体积效应公式,计算了原子核的体积效应及质量效应对类锂离子能级的修正.结果显示。在中等大小的核电核情形,原子核体积效应对类锂离子能级的修正要比质量效应对类锂离子能级的修正要显著;随着核电核数的增加,原子核体积效应越来越重要.     

Multiple parton scattering in nuclei: twist-four nuclear matrix elements and off-forward parton distributions

Multiple parton scatterings inside a large nucleus generally involve higher-twist nuclear parton matrix elements. The gluon bremsstrahlung induced by multiple scattering depends not only on direct parton matrix elements but also on momentum-crossed ones, due to the Landau–Pomeranchuk–Migdal interference effect. We show that both types of twist-four nuclear parton matrix elements can be factorized approximately into the product of twist-two nucleon matrix elements in the limit of extremely large nuclei, A→∞, as assumed in previous studies. Due to the correlative nature of the twist-four matrix elements under consideration, it is actually the off-forward parton distributions that appear naturally in this decomposition, rather than the ordinary diagonal distributions probed in deeply-inelastic scattering. However, we argue that the difference between these two distribution classes is small in certain kinematic regimes. In these regions, the twist-four nuclear parton matrix elements are evaluated numerically and compared to the factorized form for different nuclear sizes within a schematic model of the two-nucleon correlation function. The nuclear size dependence is found to be A^4/3 in the limit of large A, as expected. We find that the factorization is reasonably good when the momentum fraction carried by the gluon field is moderate. The deviation can be more than a factor of 2, however, for small gluon momentum fractions, where the gluon distribution is very large.