同位旋非对称核物质性质的理论研究

Studying the properties of isospin asymmetric nuclear matter is among fundamental questions in nuclear physics. Knowledge on the properties of asymmetric nuclear matter is important for understanding not only the structure of radioactive nuclei and their nuclear reactions, but also many critical issues such as the properties of compact stars and their evolution in astrophysics. In the past decades, significant progress has been made both theoretically and experimentally in determining the properties of symmetric nuclear matter, e.g., its equation of state from subsaturation density to about 5 times normal nuclear matter density has been relatively well-known. On the other hand, the isospin dependent properties of asymmetric nuclear matter, especially the density dependence of the nuclear symmetry energy, are still largely uncertain. The present project aims to constrain the properties of asymmetric nuclear matter, especially the density dependence of the nuclear symmetry energy, by comparing the theoretical results with the experimental or observation data based on the structure properties of radioactive nuclei, isospin effects in heavy ion collisions and the properties of compact stars. In particular, we will focus on the following aspects: 1) to develop some nuclear structure models and methods, and study the correlations of the neutron-skin structure, neutron and proton drip lines and giant resonances of radioactive nuclei with the properties of asymmetric nuclear matter; 2) to develop modern isospin dependent microscopic transport models for heavy-ion collisions, and study isospin effects in heavy ion collisions and search for sensitive probes of the density dependence of the symmetry energy as well as explore their model dependences; 3) to study the properties of compact stars, especially neutron stars, and constrain the properties of asymmetric nuclear matter from astrophysical observations; 4) to explore the general structure and decomposition of the symmetry energy, and develop new approaches to calculate the symmetry energy. The above contents are hot topics in current research in nuclear physics and astrophysics, and they are of great importance for understanding the nuclear physics at extreme isospin condition and some critical issues in physics of compact stars. These studies are also very useful for exploring the isospin dependence of the QCD phase diagram of strongly interacting matter at low temperature.

同位旋非对称核物质的性质是核物理研究的基本问题之一,它不仅对于理解放射性核的结构及其引起的核反应有重要意义，而且对于研究致密星体的结构及其演化有决定性影响。在过去的几十年中，人们通过大量的实验和理论研究，对核物质对称部分的性质有了相对清楚的认识，然而关于核物质非对称部分的性质，尤其是对称能的密度相关性，还存在很大的不确定性。本项目拟从理论上通过研究放射性核的结构性质、重离子碰撞以及致密星体的结构等来约束非对称核物质的性质。发展建立相关的核结构模型和方法，研究丰中子核的中子皮结构、滴线性质和巨共振现象等与非对称核物质状态方程的关联；改进完善同位旋相关的重离子碰撞微观输运模型，研究重离子碰撞中的同位旋效应，探索敏感于非对称核物质状态方程的实验探针及其可能存在的模型依赖；研究致密星体尤其是中子星的性质，结合天文学观测来约束非对称核物质的性质；研究核物质对称能的一般结构，探索计算对称能的新方法。

探索同位旋非对称核物质的性质，尤其是核物质的对称能，是当前核物理研究前沿的一个核心内容。本项目主要从理论上研究放射性核的结构性质、重离子碰撞以及致密星体的结构，通过与相关实验数据或天文观测结果进行比较，约束非对称核物质的性质，尤其是提取关于核物质对称能密度相关性的信息。截至目前，已基本完成原计划的研究内容，部分成果还在整理之中。通过该项目的研究，我们取得了以下代表性成果：1) 基于Sn中子皮数据、一系列重核同位素结合能差数据以及208Pb电偶极极化率的数据，精确确定了亚饱和密度区核物质的对称能; 2) 基于不同的能量密度泛函，研究了核物质对称能密度相关性的系统学。基于系统学，利用亚饱和密度对称能的精确值约束了对称能的高密行为；3)在极端高重子数密度条件下，夸克物质的对称能将成为一个重要的物理量。假定最近观测到的重脉冲星为夸克星，我们首次提出了关于夸克物质对称能的一个约束; 4) 发现核素图上中子滴线位置和快中子俘获过程(r过程)路径与对称能亚饱和密度处的值存在强关联，并利用目前对称能的精确结果确定了相应的位置、路径和数目；5) 发现对于同位旋破缺的暗物质，对称能的不确定性可能显著影响地面直接探测实验关于暗物质粒子与质子散射截面的提取；6) 利用最新的核物质对称能给出的核物质状态方程计算了中子星的结构，并使用古老中子星约束了玻色暗物质粒子与质子散射截面，排除了所有声称发现了该类暗物质的实验报道。截至目前，已在国内外学术刊物上已正式发表40篇标注有本项目基金资助号码的学术论文，指导了8位博士生的学位论文工作和2位博士后的研究工作，其中4位同学已获得博士学位，1位博士后已出站。