Improved BCS-type pairing for the relativistic mean-field theory

A density-dependent delta interaction (DDDI) is proposed in the formalism of BCS-type pairing correlations for exotic nuclei whose Fermi surfaces are close to the threshold of the unbound state. It provides the possibility to pick up those states whose wave functions are concentrated in the nuclear region by making the pairing matrix elements state dependent. On this basis, the energy level distributions, occupations, and ground-state properties are self-consistently studied in the RMF theory with deformation. Calculations are performed for the Sr isotopic chain. A good description of the total energy per nucleon, deformations, two-neutron separation energies and isotope shift from the proton drip line to the neutron drip line is found. Especially, by comparing the single-particle structure from the DDDI pairing interaction with that from the constant pairing interaction for a very neutron-rich nucleus it is demonstrated that the DDDI pairing method improves the treatment of the pairing in the continuum.

Properties of proto-neutron star and effect of three-body forces

Within the Brueckner-Hartree-Fock framework, the equation of state and the properties of newborn neutron stars are investigated by adopting a realistic nucleon-nucleon interaction AV(18) supplemented with a microscopic three-body force or a phenomenological three-body force. The maximum mass of newborn neutron star and the proton fraction in the newborn beta-stable neutron-star matter are calculated. The neutrino-trapping and the three-body force effects are discussed, and the interplay between the effects of the trapped neutrino and the three-body force are especially explored. It is shown that neutrino trapping considerably affects the proton abundance and the equation of state of the newborn neutron star in both cases with and without the three-body forces. The effect of neutrino trapping remarkably enhances the proton abundance, and the contribution of the three-body force makes the equation of state of the newborn neutron star much stiffer at high densities and consequently increases the proton abundance strongly. The trapped neutrinos significantly reduce the influence of the three-body force on the proton abundance in newborn neutron stars.

NUCLEON-NUCLEON CROSS SECTIONS IN ISOSPIN ASYMMETRIC NUCLEAR MATTER

The in medium nucleon-nucleon (N N) cross sections in isospin asymmetric nuclear matter at various densities are investigated in the frame work of Brueckner-Hartree-Fock theory with the Bonn B two-body nucleon-nucleon inter action supplemented with a new version microscopic three-body force (TBF). The TBF depresses the amplitude of cross sections at high density region. At low densities, the proton-proton and neutron-neutron cross sections decrease while the proton-neutron one increases as the asymmetry increases. But the sensitivity of the N N cross sections to the isospin a symmetry are reduced with the increasing density.

中子及中子星物质中的3PF2态超流性和微观三体核力效力效应

本论文介绍了当前中子及中子星物质中超流性研究的背景及现状、核多体理论Brueckner-Hartree-Fock及同位旋相关的Brueckner-Hartree-Fock方法，以及利用BHF和BCS理论计算中子及中子星物质中的对关联能隙方法。系统计算并描述了中子及中子星物质中子的3PF2态超流性，并重点考虑了利用介子交换流方法建立的微观三体核力所产生的影响。 我们的研究结果表明：三体核力对中子物质中3PF2态中子超流性有强烈的增强效应。 当在BCS能隙方程中采用自由粒子能谱近似时，三体核力使相应的对关联能隙峰值增加了77%(由0.64MeV增大到1.13MeV)；当采用自洽BHF单粒子能谱时，三体核力导致相应的对关联能隙峰值由0.22MeV增大到0.50MeV，增加了约127%。 三体核力使中子星物质中3PF2态中子超流能隙随着密度的增大而单调递增。当采用自洽BHF单粒子能谱时不考虑三体核力时，对关联能隙峰值在密度约1.9fm-3时有峰值0.19MeV。而在这个两体力导致的能隙的峰值密度，三体核力导致相应的对关联能隙由0.19MeV增大到0.36MeV

Mode softening in charge-density excitations of a two-dimensional electron gas driven by Rashba spin-orbit interaction

The electron density response of a uniform two-dimensional (2D) electron gas is investigated in the presence of a perpendicular magnetic field and Rashba spin-orbit interaction (SOI). It is found that, within the Hartree-Fock approximation, a charge density excitation mode below the cyclotron resonance frequency shows a mode softening behavior, when the spin-orbit coupling strength falls into a certain interval. This mode softening indicates that the ground state of an interacting uniform 2D electron gas may be driven by the Rashba SOI to undergo a phase transition to a nonuniform charge density wave state.

Electronic states of a two-dimensional electron system in a lateral superlattice and a perpendicular magnetic field

The electronic state of a two-dimensional electron system (2DES) in the presence of a perpendicular uniform magnetic field and a lateral superlattice (LS) is investigated theoretically. A comparative study is made between a LS induced by a spatial electrostatic potential modulation (referred to as a PMLS) and that induced by a spatial magnetic-field modulation (referred ro asa MMLS). By utilizing a finite-temperature self-consistent Hartree-Fock approximation scheme; the dependence of the electronic state on different system parameters (e.g., the modulation period, the modulation strength, the effective electron-electron interaction strength, the averaged electron density, and the system temperature) is studied in detail. The inclusion of exchange effect is found to bring qualitative changes to the electronic state of a PMLS, leading generally to a nonuniform spin splitting, and consequently the behavior of the electronic state becomes similar to that of a MMLS. The Landau-level coupling is taken into account, and is found to introduce some interesting features not observed before. It is also found that, even in the regime of intermediate modulation strength, the density dependence of the spin splitting of energy levels, either for a PMLS or a MMLS, can be qualitatively understood within the picture of a 2DES in a perpendicular magnetic field with the modulation viewed as a perturbation. [S0163-1829(97)02248-0].

笼内金属富勒烯Gd@C_(82)的分离和质谱研究

由于其独特的电子结构，笼内金属富勒烯（碳笼内包容金属原子）的研究一直吸引着人们极大的兴趣，目前已经合成并分离出的笼内金属富勒烯主要包括碳笼内包容铱、钪、镧系原子等。在本论文中我们利用质谱技术对笼内金属富勒烯Gd_2@C_(82)气相离子行为和C_(60)与丙烯酸甲酯气相离子反应进行研究，X光电子能谱对碳笼内轧原子的价态进行研究。笼内金属富勒烯Gd_2@C_(82)是利用电弧放电法合成的。将碳份与三氧化二钆 （C：Gd=1：100, 摩尔比）灌入碳棒，将为棒前处理后，在氦气份保护下进行放电。通过对空心富勒烯在不同沸点的溶解情况进行了研究，发现大碳数的空心富勒烯在高沸点容剂中有较大的溶解度。利用两步高温高压法，既先利用1，2，4－三甲2基苯对大碳数的空心富勒烯进行分离，然后利用吡啶对笼内金属富勒烯进行提取。利用三种不同的质谱电离方式：电喷雾 （ESI），激光解析飞行时间（LDI-TOF），共振电子捕获技术（REC）来研究笼内金属富勒烯的气相离子特征。实验结果表明LDI-TOF和REC电离技术得到的质谱谱图中，笼内金属富勒烯和空心富勒烯均出现分子离子峰，但在电喷雾质谱谱图中只有笼内金属富勒烯出现分子离子峰。结合这一实验结果和理论分析说明碳笼内钆离子偏离碳中心位置。通过对比笼内金属富勒烯Gd@C_(82)和三氧化二钆中钆离子的光电子能谱谱图，Gd@C_(82)的电子结构应表示为Gd~(3+)@C_(82)~(3-)。利用四极杆质谱仪对C_(60)分子[C_(60)H]~+和加成产物为[C_(60)C_4H_3O]~+，后者是丙烯酸甲酯分子经过α短裂后与质子化[C_(60)H]~+ 发生加成反应所得的产物，在限制性Hartree-Fock条件下，采用AM1半经验量子化学计算方法对加成产[C_(60)C_3H_3O]~+八种可能结构的产物进行计算，得出了三种可能的最稳定的环加成同分异构体。

84.5MeV~(12)C~(4+)离子诱发金属靶原子发射的Kβ与Kα-X射线强度比值的研究

本实验是在中国科学院兰州近代物理研究所,国家实验室的重离子加速器上完成的.实验用OR-TEC公司生产的HPGe X射线探测器测量了84.5 MeV的12C4+离子轰击Cu,Mo,Ag,Cd,In,Sn,W和Au金属靶产生的K壳层特征X射线谱,计算了Kβ与Kα-X射线强度的比值,并将结果与Scofield用Hartree-Fock-Slater模型计算出的理论值与用其它方法(如:衰变幅射,用光子,电子,质子等粒子与靶相互作用)得到的实验值进行了比较.比较结果表明用84.5 MeV的12C4+离子轰击Cu,Mo,Ag,Cd,In,Sn,W和Au金属靶产生的Kβ与K-αX射线强度比值比理论值和其它实验值要大许多.

丰中子核中的中子势能特性

利用Skyrme Hartree Fock势和Woods Saxon势 ,选取稳定核4 8Ca和丰中子核60 Ca ,对中子平均场势能进行了研究 ,并给出了其特性 .发现丰中子核60 Ca的SHF势与Woods Saxon势在核表面区域相当符合 ,但在核表面以外有相当大的差距 .SHF势在表面以外部分比表面区域呈现出更大的弥散度 ,而原有的Woods Saxon势不能描述这一特征 .为此 ,对Woods Saxon势形式进行了修正 ,经过验证 ,修正的Woods Saxon势能正确地描述丰中子核的中子晕特性 .

自旋极化的对称核物质和中子物质的性质

利用Skyrme有效相互作用对自旋极化的同位旋对称核物质和中子物质的特性进行了研究 .用 4种核子 -核子相互作用参数SⅢ ,SKM ,SLy2 30a和SLy2 30b ,分别描绘了核物质状态方程曲线 .可以发现不论使用哪一种参数 ,在自旋极化的同位旋对称核物质和中子物质中都存在着磁化相变转换点 .另外还对磁化系数进行了计算 ,给出了磁化系数比率随密度的变化关系 ,由于无限不连续点的存在 ,进一步肯定了在Skyrme Hartree Fock理论框架内两种物质会出现磁化相变转换点

溴的类镁离子跃迁谱线和能级扩展分析

用中国原子能科学研究院HI 13串列加速器提供的 90和 130MeV的Br离子和束箔技术 ,研究了波长在 13— 2 9nm范围内Br的类Mg离子的光谱 .识别出 2 4条属于BrXXIV的“3,3”跃迁 ,即 3s2 ,3s3p ,3p2 ,3s3d和 3p3d组态之间的跃迁谱线 ,其中 19条以前未见报道 .基于实验跃迁谱线 ,19个观测能级得以确立 ,其中有 14个能级此前未见报道 .相对论Hartree Fock(HFR)方法的计算结果对所观测的能级进行了解释 .

非对称核物质的化学不稳定性与力学不稳定性

基于扩展的Skyrme有效相互作用 ,在Hartree Fock近似下对非对称核物质的化学不稳定性与力学不稳定性进行了研究 ,并与简单的三参数势 ,即所谓的软势与硬势的计算结果进行了比较 .结果发现两种模型给出的非对称核物质化学不稳定性与力学不稳定性之间的关系是完全不同的 .通过研究化学不稳定性在临界温度附近的行为发现 ,对软势与硬势 ,化学不稳定性可能出现在温度高于临界温度的气化 (全爆炸 )机制中 .而对于SKM势参数 ,化学不稳定性不会出现在温度高于临界温度的气化 (全爆炸 )机制中 .这种差别也反映在压强 密度平面上力学不稳定区与化学不稳定区的位置关系上 .进一步的计算表明 ,这种差别是由于两种模型给出的单粒子势的密度依赖形式的不同而导致的 ,这必将体现在重离子碰撞的现象中 ,从而可以作为提取核物质状态方程密度依赖形式的探针

中子星中质子比例的密度依赖

利用Hartree Fock理论 ,基于扩展的Skyrme有效相互作用 ,采用抛物线近似下对称能的密度相关形式以及 β平衡和电中性条件 ,给出了中子星中质子比例的密度依赖关系 .通过比较不同的势参数SII,SIII,SKM和SKI5下对称能强度系数的密度依赖关系研究了中子星中的质子比例 ,发现在高密时势参数SII,SIII和SKM能够给出中子星中质子消失的结果 ,这预示着致密核物质可能存在纯中子物质的基态 .同时计算表明 ,考虑中子星中 μ- 子的贡献后使质子比例增加 .

同位旋激发能研究

在扩展的Skyrme有效相互作用下 ,利用Hartree Fock理论研究了同位旋激发能与温度、密度的关系 .结果表明同位旋激发能随密度的降低以及温度的增加而降低 .同时研究了对称能与同位旋激发能的关系 ,指出对称能是同位旋激发能的一部分 ,且占相当大的比重 .最后研究了不同的势参数下 ,同位旋激发能随相对中子过剩的变化关系 ,发现同位旋激发能较强地依赖于对称能强度系数 ,而对不可压缩系数以及有效质量不太敏感 .从而为实验上通过研究同位旋激发能来提取核物质状态方程中的对称能部分指出了一条途径