中能重离子碰撞中同位旋分馏的同位旋效应

基于改进的同位旋相关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强度(N/Z)_气(N/Z)_液随着碰撞系统中子–质子比和碰撞参数的变化所呈现出的同位旋效应,得到了一些有兴趣的结果.如在碰撞系统质量、入射能量和碰撞参数固定的条件下,(N/Z)_气(N/Z)_液随碰撞系统中子–质子比的增加而增加.对于丰中子系统而言,(N/Z)_气(N/Z)_液灵敏地依赖于对称势而较弱地依赖于核子–核子碰撞截面;而缺中子系统,(N/Z)_气(N/Z)_液对于对称势和介质中核子–核子碰撞截面都不灵敏.对于造成这种现象的物理机制进行了分析和讨论.一般核反应中,碰撞参数是各种物理观测量的灵敏函数,但计算结果表明同位旋分馏强度对于碰撞参数并不灵敏,故对于丰中子系统而言,同位旋分馏强度是提取对称势知识的灵敏物理观测量.

Isospin Effects in the Isospin Fractionation Process in Intermediate Energy Heavy Ion Collisions

Based on the isospin dependent quantum molecular dynamics model we investigated the isospin effects of isospin fractionation (N/Z) gas/(N/Z) liq from the neutron-proton ratio of colliding system and impact parameter. Here (N/Z) gas and (N/Z) liq is the neutron-proton ratio of nucleon emission for gas phase and that of fragment emission for liquid phase, respectively. Our results show that the (N/Z) gas/(N/Z) liq increases with the neutron-proton ratio of colliding systems when the system mass, incident energy and impact parameters are fixed. For the neutron-rich systems, the (N/Z) gas/(N/Z) liq depends sensitively to the form of symmetry potential and weakly on the isospin effect of the in-medium nucleon-nucleon cross section; For the neutron-poor colliding system, however, the (N/Z) gas/(N/Z) liq is not sensitive to both the form of symmetry potential and the isospin effect of the in-medium nucleon-nucleon cross section. We also found that the dependence of (N/Z) gas/(N/Z) liq on the impact parameter is not obvious. Detailed discussion and explanation for leading to these results are presented in the paper. According to these results, we propose that (N/Z) gas/(N/Z) liq can be directly compared with the experimental data to get the information about symmetry potential.