中能重离子碰撞中的同位旋分馏过程

利用同位旋相关的量子分子动力学模型研究了中能重离子碰撞中同位旋分馏过程.研究结果表明自由粒子中质比与碎片中质比的比值即同位旋分馏强度灵敏地依赖于对称势,而对同位旋相关核子–核子碰撞截面的依赖很弱.同位旋分馏对对称势的灵敏主要来自于气相部分,而液相部分对对称势不够灵敏.气相部分灵敏地依赖于对称势是直接造成同位旋分馏强度对对称势灵敏的主要原因.同时还讨论了各种液相部分的取法,其结果表明不同取法对以上结论的影响不大.因此理论结果与实验数据可以直接比较从而提取对称势的知识.并对引发同位旋分馏的动力学的起因进行了分析和讨论.

Isospin Fractionation Process in Intermediate Energy Heavy Ion Collisions

The isospin fractionation in intermediate energy heavy ion collisions is studied by using isospin dependence quantum molecular dynamics model. At first, the reaction productions in isospin fractionation process is separated into a gas phase and a liquid phase. The gas phase includes free neutrons and protons. But there are many choices for the liquid phase, we select the fragments from the region of 1 < Z < ( ZP + ZT)/2 as the liquid phase, here Z, ZP and ZT are charge of the fragment, projectile and target, respectively. For considering the influence of projectile-like and target-like , we choose the upper limit of charges to ( ZP + ZT )/2. We define the degree of isospin fractionation as a ratio of gas phase neutron-proton ratio (N/Z)gas to liquid phase neutron-proton ratio (N/Z)liq. The calculated results show that the degree of isospin fractionation is sensitive to the symmetry potential and insensitive to isospin dependent neucleon-neucle-on cross section. This sensitivity mainly comes from the gas part of the isospin fractionation. The liquid part is insensitive to the symmetry potential. So we may compare the theory calculation results with the experimental data directly to get the knowledge of symmetry potential. The calculated results also show that the ( N/Z) gas is larger than the (N/Z)sys of the colliding system but the (N/Z)liq is less than the ( N/Z)sys for the neutron-rich system. Finally, the isospin fractionation process is not sensitive to the choices for the fragments of liquid phase.