核物质的对称能与中子皮厚度(英文)

在现有的平均场模型中引入同位旋相关的高阶修正项．研究了核物质对称能的密度依赖性和。^208Pb的中子皮厚度。采用新提出的PK1相互作用以及NL3．S271和Z271相互作用．得到核物质饱和点对称能的范围为29-38MeV以及相应的^208Pb中子皮厚度为0．17—0.28fm．在所有相互作用中，核物质饱和点的对称能与^208Pb的中子皮厚度近似呈线性关系。After adding isospin dependent high order correction terms to existing relativistic mean field models (RMF), the density dependence of symmetry energy and the neutron skin thickness S for 208Pb are studied. Using the new effective interaction PK1, together with NL3, S271 and Z271, a range of 29—38 MeV for the symmetry energy for nuclear matter at saturation point and the corresponding neutron skin thickness S = 0.14—0.28 fm for 208Pb are obtained. For all effective interactions, a linear relation between the symmetry energy at saturation point and the neutron skin thickness for 208Pb is observed.     

A new probe of neutron skin thickness

The correlation between neutron-to-proton yield ratio (R_np) and neutron skin thickness (δ_np) in neutron-rich projectile induced reactions is investigated within the framework of the Isospin-Dependent Quantum Molecular Dynamics (IQMD) model. The density distribution of the Droplet model is embedded in the initialization of the neutron and proton densities in the present IQMD model. By adjusting the diffuseness parameter of neutron density in the Droplet model for the projectile, the relationship between the neutron skin thickness and the corresponding R_np is obtained. The results show strong linear correlation between R_np and δ_np for neutron-rich Ca and Ni isotopes. It is suggested that R_np may be used as an experimental observable to extract δ_np for neutron-rich nuclei, which is very interesting in the study of the nuclear structure of exotic nuclei, the equation of state (EOS) of asymmetric nuclear matter and neutron-rich matter in astrophysics, etc.     

Symmetry energy at subsaturation densities and the neutron skin thickness of ~(208)Pb

The mass-dependent symmetry energy coefficients asym(A) has been extracted by analysing the heavy nuclear mass differences reducing the uncertainties as far as possible in our previous work.Taking advantage of the obtained symmetry energy coefficient asym(A) and the density profiles obtained by switching off the Coulomb interaction in208 Pb,we calculated the slope parameter L0.11 of the symmetry energy at the density of 0.11 fm-3.The calculated L0.11 ranges from 40.5 Me V to 60.3 Me V.The slope parameter L0.11 of the symmetry energy at the density of 0.11 fm-3is also calculated directly with Skyrme interactions for nuclear matter and is found to have a fine linear relation with the neutron skin thickness of208 Pb,which is the difference of the neutron and proton rms radii of the nucleus.With the linear relation the neutron skin thickness Rn pof208 Pb is predicted to be 0.15–0.21 fm.     

中子皮厚度与中子星半径

在相对论平均场理论框架下在拉氏量密度中引入同位旋相关的高阶修正项, 研究了中子皮厚度和中子星半径的关系. 利用有效相互作用PK1得到208Pb的中子皮厚度最小可达0.17 fm, 这与近期Skyrme HF模型得到的结果一致. 随着同位旋相关的高阶修正项系数的变化, 208Pb的中子皮厚度和中子星半径的变化趋势相同. By adding isospin dependent high order correction ferms to existing relativistic mean field models．tlle thickness of neuron．skin in 208Pb and the radius of 1.4 solar mass neutron star are studied．The effecfive interaction PK1 would lead the thickness of neutron-skin to a minimum of 0.17 fm which agrees with the analysis from Skyrme‘HF models． The coupling constants of the isospin dependent high order corection terms tend to change，the thickness of neutron-skin and the radius of neutron stars chan ge simultaneously.     

原子核放射性对核对称能的约束（英文）

核对称能的密度依赖性对于原子核物理和天体物理中的许多问题很重要。基于密度依赖的结团模型,奇特的结团放射性被用来约束核对称能及其斜率的大小。在密度依赖的结团模型中,清楚地给出了结团放射性子核208Pb的中子皮大小与对称能的斜率参数L（ρ0） 之间的关联。发现从M3Y核子-核子相互作用得到的结团-208Pb 同位旋矢量势对于对称能的斜率参数L（ρ0） 非常重要。基于结团放射性实验数据和新的208Pb 的中子皮大小实验数据,成功得到对称能的斜率参数L（ρ0） 的大小。也讨论了利用质子放射性数据提取的斜率参数L（ρ0）。The density-dependence of symmetry energy is of particular importance to many problems in nuclear physics and astrophysics. Exotic cluster radioactivity is proposed to constrain the density slope of symmetry energy L(ρ0) by using the density-dependent cluster model (DDCM) where the cluster radioactivity serves as a link between the neutron skin thickness of 208Pb and the density slope L(ρ0). The isovector part of cluster-208Pb potential constructed from the M3Y nucleon-nucleon interaction is found to be very important in determining the density slope parameter L(ρ0). The correlation between the neutron skin thickness of 208Pb and the density slope parameter are obtained from cluster radioactivities around 208Pb with measured data. The constraint of L(ρ0) from proton radioactivity is also discussed.     

用中子晕弹核探寻同位旋非对称核物质状态方程

总结和评述了用中子晕弹核探寻同位旋非对称核物质状态方程。 在具有同位旋和动量依赖的同位旋相关量子分子动力学框架内, 采用对比中子晕弹核和相等质量稳定弹核在完全相同入射道条件下物理观测量的差别, 来突出中子晕核明显的同位旋效应和加强物理观测量对于同位旋的灵敏性, 从而提取核物质状态方程。 例如, 与稳定弹核碰撞系统相比, 中子晕弹核明显提高了发射核子的中子\|质子比和增加了它对于对称势的灵敏性, 这两点特征非常有利于提取对称势。 同样, 由于中子晕弹核碰撞系统在低能区（E<60 MeV）由于内部松散结构减弱了核子碰撞力度和动量耗散, 与稳定核碰撞系统相比, 明显提高了原子核阻止; 而在高能区由于两体碰撞同位旋效应的增加, 从而明显提高了原子核阻止。 利用这些特征可以提取核子\|核子碰撞截面的介质效应和同位旋依赖性。 Based on the isospin and momentum dependent quantum molecular dynamics, we use the comparison for the differences between observables in the reactions induced by the halo\|neutron projectile and stable projectile with the same mass under complete same incident channel condition to protrude the isospin effect of halo\|neutron projectile and strengthen the sensitivity of observable on the isospin for extracting the information for the equation of state. For example, the halo\|neutron projectile increases the emitted neutron\|proton ratio and then enhances its sensitivity on the symmetrical potential. Two points above are more favorable than the normal neutron\|rich and neutron\|poor projectiles for extracting the symmetry potential. We also found that the neutron\|halo projectile induces the decrease of nuclear stopping in lower beam energy region and the increase in higher beam energy region, compared to corresponding same mass stable projectile under the same incident channel condition, so that we can use these properties to extract the information for the medium effect and isospin effect of in\|medium nucleon\|nucleon cross section.     

Constraints on neutron skin thickness and symmetry energy of 208Pb through Skyrme forces and cluster model

We used the cluster structure properties of the 212Po to estimate the neutron skin thickness of 208Pb.For this purpose,we considered two important components:(a)alpha decay is a low energy phenomenon;therefore,one can expect that the mean-field,which can explain the ground state properties of 212Po,does not change during the alpha decay process.(b)212Po has a high alpha cluster-like structure,two protons and two neutrons outside its core nucleus with a double magic closed-shell,and the cluster model is a powerful formalism for the estimation of alpha decay preformation factor of such nuclei.The slope of the symmetry energy of 208Pb is estimated to be 75±25 MeV within the selected same mean-fields and Skyrme forces,which can simultaneously satisfy the ground-state properties of parent and daughter nuclei,as their neutron skin thicknesses are consistent with experimental data.     

Influence of the nuclear equation of state on the hadron-quark phase transition in neutron stars

We study the hadron-quark phase transition in the interior of neutron stars, and examine the influence of the nuclear equation of state on the phase transition and neutron star properties. The relativistic mean field theory with several parameter sets is used to construct the nuclear equation of state, while the     

Exploring nuclear symmetry energy with isospin dependence in neutron skin thickness of nuclei

We propose an alternative way to constrain the density dependence of the symmetry energy from the neutron skin thickness of nuclei which shows a linear relation to both the isospin asymmetry and the nuclear charge with a form of Z^2/3. The relation of the neutron skin thickness to the nuclear charge and isospin asymmetry is systematically studied with the data from antiprotonic atom measurement, and with the extended Thomas-Fermi approach incorporating the Skyrme energy density functional. An obviously linear relationship between the slope parameter L of the nuclear symmetry energy and the isospin asymmetry dependent parameter of the neutron skin thickness can be found, by adopting 70 Skyrme interactions in the calculations. Combining the available experimental data, the constraint of -20 MeV L 82 MeV on the slope parameter of the symmetry energy is obtained. The Skyrme interactions satisfying the constraint are selected.     

A new probe of neutron skin thickness

The correlation between neutron-to-proton yield ratio (R<,n p>) and neutron skin thickness (δ<,n p>) in neutron-rich projectile induced reactions is investigated within the framework of the Isospin-Dependent Quantum Molecular Dynamics (IQMD) model. The density distribution of the Droplet model is embedded in the initialization of the neutron and proton densities in the present IQMD model. By adjusting the diffuseness parameter of neutron density in the Droplet model for the projectile, the relationship between the neutron skin thickness and the corresponding R<,n p> is obtained. The results show strong linear correlation between R<,n p> and δ<,n p> for neutron-rich Ca and Ni isotopes. It is suggested that R<,n p> may be used as an experimental observable to extract δ<,n p> for neutron-rich nuclei, which is very interesting in the study of the nuclear structure of exotic nuclei, the equation of state (EOS) of asymmetric nuclear matter and neutron-rich matter in astrophysics, etc.     

Neutron skin thickness and nuclear matter properties

Linear correlations are found among the isovector nuclear matter properties in both the Skyrme-Hartree-Fock (SHF) and the relativistic mean-field (RMF) models. In addition, we found a kind of correlation between the isovector nuclear matter properties and the incompressibility in the SHF model. The Skyrme parameters are related analytically to nuclear matter properties with the Thomas—Fermi approximation. By using a linear correlation between the neutron skin thickness and the pressure of the neutron matter in the SHF model, we show that the neutron skin thickness of ²⁰⁸Pb gives crucial information about not only the neutron equation of state but also the isovector nuclear matter properties and the parametrization of Skyrme interaction. The text was submitted by the authors in English.     

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.     

The lead nucleus as a miniature surrogate for a neutron star

The nucleus of ²⁰⁸Pb, a system 18 orders of magnitude smaller and 55 orders of magnitude lighter than a neutron star, may be used as a miniature surrogate to establish important correlations between its neutron skin and several neutron-star properties. Indeed, models with a thicker neutron skin in ²⁰⁸Pb generate larger neutron stars that have a lower liquid-to-solid transition density. Further, we illustrate how the correlation between the neutron skin in ²⁰⁸Pb and the radius of a 1.4 solar-mass neutron star may be used to place important constraints on the equation of state of neutron-rich matter and how it may help elucidate the existence of a phase transition at the core of the star.     

Isospin and symmetry energy study in nuclear EOS

This paper summarizes the isoscaling and isospin related studies in asymmetry nuclear reactions by different dynamic and statistical models. Isospin dependent quantum molecular dynamics model (IQMD) and lattice gas model (LGM) are used to study the isoscaling properties and isoscaling parameters dependence on incident energies, impact parameters, temperature and other parameters. In the LGM model, the signal of phase transition has been found in free neutron (proton) chemical potential difference Δµ_n or Δµ_p as a function of temperature, or in free neutron and proton chemical potential difference Δµ_n−Δµ_p. Density dependence of symmetry energy coefficient C _sym(ρ/ρ ₀) is also studied in the frame of LGM, with the potential parameters which can reproduce the nuclear ground state property, soft density dependence of symmetry energy is deduced from the simulation results. Giant dipole resonance (GDR) induced by isospin asymmetry in entrance channel is also studied via IQMD model, and the dynamic dipole resonance shows isospin sensitivity on the isospin asymmetry of entrance channel and symmetry energy of the nuclear equation of state (EOS). GDR can also be regarded as a possible isospin sensitive signature.

     

Neutron Skin Thickness of Nuclei and Effective Nucleon-Nucleon Interactions

The Skyrme energy density functional is applied to study the ground state properties of a series of finite nuclei. The charge rms radii, neutron rms radii, and the neutron skin thickness for some nuclei are calculated and compared with the experimental data. The constraint on the effective interactions, especially, the density dependence of the isospin-dependent. part of Skyrme interactions is extracted by the data of neutron skin thicknesses of ^208Pb and isotopes of Sn.     

Theoretical study on neutron distribution of ~(208)Pb by parity-violating electron scattering

The precise determination of neutron distribution has important implications for both nuclear structure and nuclear astrophysics. The purpose of this paper is to study the characteristics of neutron distribution of~(208) Pb by parity-violating electron scattering(PVS). Parity-violating asymmetries of~(208) Pb with different types of neutron skins are systematically calculated and compared with the experimental data of PREx. The results indicate that the PVS experiments are very sensitive to the nuclear neutron distributions. From further PVS measurements, detailed information on nuclear neutron distributions can be extracted.