重离子核反应与核物质状态方程

核物质状态方程描述核物质结合能、压强、密度和中子—质子数差异等宏观量之间的关系。核物质状态方程不仅仅与核力属性、核结构性质以及重离子核反应的动力学过程紧密相关，还与致密星体如中子星的结构、演化、辐射与并合等天体过程紧密相关。基于加速器装置的重离子核反应实验，是地面实验室模拟产生极端条件核物质的唯一手段，因而也成为研究核物质状态方程的有效途径。当核物质中的中子数远大于质子数时，例如中子星内部的情形，核物质状态方程中的主要贡献项是对称能项。迄今为止，对称能关于密度的函数是核物理和天体物理中一个未知而又非常重要的物理量。通过重离子核反应的实验和理论研究来确定对称能的密度依赖关系及其在核反应以及致密星天体事件中的物理效应，是当代核物理基础研究的重要前沿。文章介绍了中能重离子核反应和核物质状态方程的一些背景知识和研究方法，以及近年来的一些进展。

Heavy ion reactions and equation of state of nuclear matter

The nuclear equation of state describes the relationship among the macroscopic quantities including the binding energy, pressure, density and the density difference of neutrons and protons in bulk nuclear matter. It is not only relevant to the nuclear force properties, nuclear structure and dynamics of heavy ion reactions, but also related to the thermodynamic properties, structure, evolution and merging events of dense stellar objects like neutron stars. As a unique terrestrial way to produce nuclear matter in extreme conditions far away from saturation point, heavy ion reactions based on particle accelerators provide an effective tool to study the nuclear equation of state in a ground laboratory. When the neutron density is much higher than the proton density, as is the situation in an inner neutron star, the main contribution in the nuclear equation of state comes from the symmetry energy term, which is a function of density. This dependence is the most important yet so far unknown quantity in nuclear physics and astrophysics. Thus, it is now a foremost challenge of modern nuclear physics to determine, through experimental and theoretical research on the heavy ion reactions, the dependence of the symmetry energy on density as well as its effects on nuclear reactions and astrophysics events involving dense stellar objects. This paper presents the background and methods in the study of medium energy heavy ion reactions and the nuclear equations of state, followed by a brief introduction to some research progress in recent years.