相对论和非相对论理论模型研究奇异核的性质

采用相对论和非相对论理论模型可描述奇异核的性质 .相对论平均场理论预言了2 6,2 7,2 8P存在一个质子晕 ,而27,28,29S存在两个质子晕 .最近 ,MSU的最新的实验发现了2 6,2 7,2 8P核存在一个质子晕.采用相对论 Hartree- Fock理论研究了 Fock项和矢量介子对奇异核性质的贡献,研究表明交换项和矢量介子对非常丰中子核性质的影响非常不同于对稳定线附近核性质的影响.同时,采用形变的Hartree- Fock- Bogoliubov理论研究了某些轻核同位素链的性质和形变.     

稳定和不稳定核巨共振性质的相对论研究

在相对论平均场的基态上自洽的相对论无规位相近似(RRPA)理论框架下,研究稳定核和不稳定核的巨共振性质.研究了稳定核²⁰⁸Pb,¹⁴⁴Sm,¹¹⁶Sn,⁹⁰Zr,⁴⁰Ca,¹⁶O和不稳定核Ca同位素链同位旋标量和同位旋矢量集体巨共振激发,并讨论了Dirac海负能核子态和矢量介子空间分量对核的巨共振性质的影响.研究的结果表明,Dirac海负能核子态和矢量介子空间分量对同位旋标量激发有贡献,特别是对重核,而对轻核它的贡献减弱,对于同位旋矢量激发的贡献可忽略.几组常用的相对论平均场非线性模型参量,不仅能成功的描述有限核的基态性质,也能很好地描述核的巨共振激发.对于N/Z极端情况下,同位旋矢量巨偶极激发模式存在低能集体激发,它是由于费密面附近弱束缚核子的激发和同位旋混杂效应 关键词： 相对论无规位相近似 核巨共振     

基于相对论Hartree-Fock理论的原子核壳结构性质研究

一直以来，原子核壳结构是原子核物理研究的重点关注内容。特别是随着近年来新一代放射性核束装置和探测技术的蓬勃发展，丰中子原子核中新的壳结构及其演化与形成机制等成为核物理关注的热点之一。在基于核力介子交换图像建立的相对论Hartree-Fock 理论框架下，本工作以Ca同位素、双幻核 208Pb、超重核以及极端丰中子核为例，综述丰中子原子核中新的壳结构形成机制，高角动量态赝自旋对称性恢复与介质中核力吸引-排斥平衡，赝自旋对称性恢复/破缺与原子核壳结构、新奇现象等研究工作，并着重关注了与原子核新壳结构形成、赝自旋对称性恢复以及新奇现象等密切相关的交换(Fock)项效应。     

等效的DBHF方法研究有限核性质

利用等效的Dirac Brueckner Hartree-Fock(DBHF)方法,即用密度相关的核子–介子耦合常数在相对论平均场近似下,考虑了重排列项,研究了有限核的性质.介子–核子耦合常数的密度相关性是由考虑了核子短程关联的DBHF方法来确定的,要求在每个密度下用相对论平均场方法得到的核子自能与用DBHF得到的自能一致.计算了核物质性质及有限核基态性质,并着重讨论了重排列项对Ca及Pb同位素链结果的影响.考虑重排列项作用后使计算的核电荷均方根半径增大,更好地符合实验值.     

复动量表象方法对丰中子Cr同位素奇特结构的研究

奇特核的研究是核物理中最有趣的前沿课题之一。中等质量核中是否存在晕现象,目前的研究相对较少。复动量表象(CMR)方法可以用来探索原子核中的奇特结构。连续谱阈值附近的共振态在奇特现象的形成中起着重要的作用。利用相对论点耦合框架下的复动量表象(RMFPC-CMR)方法研究了丰中子Cr同位素中的奇特结构,得到的非常接近于零的双中子分离能和迅速增大的中子均方根半径表明在靠近中子滴线的Cr同位素中存在晕结构。从获得的单粒子能级、费米面附近价核子占据几率、中子和质子密度分布以及各能级对原子核密度的贡献可以发现3s_1/2和2d_3/2能级的占据有利于中子晕的形成。研究发现,低角动量弱束缚能级对异常增大的半径和弥散密度分布有显著的贡献,这导致靠近中子滴线的^76-82Cr是中子晕核。这一预测结果对在实验中探索中等质量区的晕核具有一定的参考价值。     

对关联对核基态和集体激发态性质的影响

基于相对论平均场和BCS理论,研究了共振连续对奇特核对关联性质的影响. 利用S矩阵方法，通过设定合理的散射态边界条件来得到单粒子共振态的能量和宽度. 通过引入连续态能级密度的方法来处理共振态宽度对核对关联的贡献. 计算结果显示合理地处理共振态对对关联性质的贡献在研究滴线附近核性质时很重要. 它可以影响中子的对隙、费米能级、对关联能以及总结合能. 其次,基于RMF+BCS基态,采用线性响应理论给出了描述开壳核集体激发态性质的准粒子相对论无规位相近似理论. 并且将该方法应用于开壳核120Sn的各种同位旋标量集体激发态性质的研究中. 研究表明：对关联对核的集体激发性质的影响主要表现在低能集体激发态上,考虑对关联后的相对论无规位相近似理论能够很好地再现低能集体激发的实验结果.     

温度相关的核子相对论微观光学势

本文将Walecka模型和热场动力学理论应用在核物质和有限核中,研究了核子在各种温度下的相对论微观光学势以及相应的薛定谔等效势和平均自由程.对于核物质,取核子的Hartree-Fock自能为光学势的实部,交换σ和ω介子的极化图为光学势的虚部.对于有限核的微观光学势通过定域密度近似获得.     

推广的介子云口袋模型和核力

利用介子云口袋模型, 本文计算了π场对核子-核子间相互作用势的贡献. 本文证明, 在核子之间距离较大的条件下由介子云口袋模型给出的结果与单π交换势相符. 此外, 为考虑矢量介子对核力的贡献, 我们推广了介子云口袋模型使包含矢量介子和夸克的相互作用. 利用这个推广的介子云口袋模型和两核子体系的Breit-Fermi方程, 通过Foldy-Wouthuysen变换, 在非相对论近似下, 本文计算的核子间相互作用势与通常核理论的结果相符, 但本文考虑了核子体积大小(形式因子)对核力的影响.     

原子核中新的有效相互作用、新对称性及奇特核态

总结了近年来对奇特核和极端条件下核物质的研究结果,包括原子核的新有效相互作用、新对称性及奇特性质.在相对论平均场理论中,发现了反核子谱中的自旋对称性,提出了包含微观质心修正的新相互作用PK1,PK1r和PKDD?.这些新相互作用不但可以很好地描述核物质与中子星,还可以很好地给出靠近或远离β稳定线的原子核性质,包括中子滴线核与超核中的晕和巨晕现象.     

适用于轻核区的相对论平均场理论新参数

考虑对关联和微观质心修正效应, 适用于轻核区的两组相对论平均场理论新参数被提出:包含σ, ω介子非线性自耦合项的NLLN和包含密度依赖的介子-核子耦合项的DDLN. 对于Z≤8轻核区β稳定线附近以及远离β稳定线的原子核, 新参数对结合能等基态性质给出了比已有参数更好的描述. 同时, 新参数给出O同位素的中子滴线核为²⁶O, ²⁴O中新幻数N=16的出现也能够被合理解释.     

基于相对论Hartree-Fock-Bogoliubov近似的新幻数研究（英文）

基于相对论Hartree-Fock-Bogoliubov （RHFB） 近似分别探索了质量-电荷极限下的超重元素与极端中质比下的奇特原子核中的新幻数问题。研究结果表明,赝自旋对称性的守恒和破缺与超重核区球形幻数结构的形成密切相关,并分别决定了中子与质子的新幻数结构。同时,理论模型之间的差异也与之密切相关。在中重奇特核区,RHFB近似很好地再现了Ca 同位素中的新幻数N = 32,34,其中同位旋矢量道中洛伦兹张量耦合扮演了较为关键的角色。以此为例,研究证明了显式考虑交换（Fock） 项的RHFB 近似的可靠性。Recent applications of the relativistic Hartree-Fock-Bogoliubov (RHFB) approach in exploring the new magicities under extreme conditions are presented for the superheavy elements with the limits of mass and charge and for the exotic nuclei with extreme neutron-to-proton ratios. It is found that the emergence of new magic shells in superheavy region is tightly related to the restoration and violation of pseudo-spin symmetry, respectively for the neutron and proton ones, in which the model deviations are indicated and discussed. In medium-heavy exotic nuclei, the occurrence of new magicity N = 32, 34 in Ca isotopes is well reproduced by the RHFB approach, in which the isovector Lorentz tensor couplings are found to play an essential role. The results exemplify that the RHFB approach, which considers the exchange (Fock) terms explicitly, furnishes a new theoretical instrument for advancing relativistic nuclear mean-field approaches.     

Ground-State Properties of Ca Isotopes and the Density Dependence of the Symmetry Energy

A relativistic mean field model is used to study the ground-state properties of neutron-rich nuclei in Ca isotopes. An additional isoscalar and isovector nonlinear coupling has been introduced in the relativistic mean field model, which could soften the symmetry energy, while keep the agreement with the experimental data. The sensitivity of proton and neutron density distributions and single particle states in Ca isotopes to the additional isoscalarisovector nonlinear coupling term is investigated. We found that the binding energies, the density distributions of single particle levels are strongly correlated with the density dependence of the symmetric energy in nuclear matter.     

Soft Giant Dipole Modes in Ca Isotopes in the Relativistic RPA

The isovector giant dipole resonance in Ca isotopes is investigated in the framework of the fully consistent relativistic random phase approximation.The calculations are performed in an effective Lagrangian with a parameter set NL3,which was proposed for satisfactorily describing nuclear ground state properties.It is found that a soft isovector dipole mode for Ca isotopes near drip lines exists at energy around 6-7MeV.The soft dipole states are mainly due to the excitation of the weakly bound and pure neutron (proton)states near Fermi surface as well as the correlation of isoscalar and isovector operators.For nuclei with the extreme value of N/Z,the contributions of isoscalar mesons in the isovector mode play a non-negligible role.     

Self-consistent hartree description of finite nuclei in a relativistic quantum field theory

Relativistic Hartree equations for spherical nuclei are derived from a relativistic nuclear quantum field theory using a coordinate-space Green function approach. The renormalizable field theory lagrangian includes the interaction of nucleons with σ, ω, ρ and π mesons and the photon. The Hartree equations represent the “mean-field” approximation for a finite nuclear system. Coupling constants and the σ-meson mass are determined from the properties of nuclear matter and the rms charge radius in ⁴⁰Ca, and pionic contributions are absent for static, closed-shell nuclei. Calculated charge densities, neutron densities, rms radii, and single-nucleon energy levels throughout the periodic table are compared with data and with results of non-relativistic calculations. Relativistic Hartree results agree with experiment at a level comparable to that of the most sophisticated non-relativistic calculations to date. It is shown that the Lorentz covariance of the relativistic formalism leads naturally to density-dependent interactions between nucleons. Furthermore, non-relativistic reduction reveals non-central and non-local aspects inherent in the Hartree formalism. The success of this simple relativistic Hartree approach is attributed to these features of the interaction.     

Ground-state properties of neutron magic nuclei

A systematic study of the ground-state properties of the entire chains of even–even neutron magic nuclei represented by isotones of traditional neutron magic numbers N = 8, 20, 40, 50, 82, and 126 has been carried out using relativistic mean-field plus Bardeen–Cooper–Schrieffer approach. Our present investigation includes deformation, binding energy, two-proton separation energy, single-particle energy, rms radii along with proton and neutron density profiles, etc. Several of these results are compared with the results calculated using nonrelativistic approach (Skyrme–Hartree–Fock method) along with available experimental data and indeed they are found with excellent agreement. In addition, the possible locations of the proton and neutron drip-lines, the (Z, N) values for the new shell closures, disappearance of traditional shell closures as suggested by the detailed analyzes of results are also discussed in detail.     

Isoscalar and isovector nuclear matter properties and neutron skin thickness

Isoscalar and isovector nuclear matter properties are investigated in the Skyrme Hartree-Fock (SHF) and the relativistic mean field (RMF) models. The Skyrme parameters are related analytically to the isoscalar and the isovector nuclear matter properties of the Hamiltonian density. Linear correlations are found among the isovector nuclear matter properties of the Hamiltonian density in both the SHF and the RMF models. We also discovered that the correlations between the isovector properties and the incompressibility K show a singularity at the critical incompressibility K_c=306 MeV. It is shown that the neutron skin thickness gives crucial information about not only for the neutron EOS but also about the isovector nuclear matter properties and about the parameterization of Skyrme interaction. Charge exchange spin-dipole (SD) excitations are proposed to determine the neutron skin thickness model independently.     

Ground-state properties of light kaonic nuclei signaling symmetry energy at high densities

A sensitive correlation between the ground-state properties of light kaonic nuclei and the symmetry energy at high densities is constructed under the framework of relativistic mean-field theory. Taking oxygen isotopes as an example, we see that a high-density core is produced in kaonic oxygen nuclei, due to the strongly attractive antikaonnucleon interaction. It is found that the 1 S_(1/2) state energy in the high-density core of kaonic nuclei can directly probe the variation of the symmetry energy at supranormal nuclear density, and a sensitive correlation between the neutron skin thickness and the symmetry energy at supranormal density is established directly. Meanwhile, the sensitivity of the neutron skin thickness to the low-density slope of the symmetry energy is greatly increased in the corresponding kaonic nuclei. These sensitive relationships are established upon the fact that the isovector potential in the central region of kaonic nuclei becomes very sensitive to the variation of the symmetry energy. These findings might provide another perspective to constrain high-density symmetry energy, and await experimental verification in the future.     

Nuclear symmetry energy effects in finite nuclei and neutron star

Within a relativistic mean-field model with nonlinear isoscalar–isovector coupling, we explore the possibility of constraining the density dependence of nuclear symmetry energy from a systematic study of the neutron skin thickness of finite nuclei and neutron star properties. We find the present skin data supports a rather stiff symmetry energy at subsaturation densities that corresponds to a soft symmetry energy at supranormal densities. Correlation between the skin of ²⁰⁸Pb and the neutron star masses and radii with kaon condensation has been studied. We find that ²⁰⁸Pb skin estimate suggest star radii that reveals considerable model dependence. Thus precise measurements of neutron star radii in conjunction with skin thickness of heavy nuclei could provide significant constraint on the density dependence of symmetry energy.