中能重离子碰撞中同位旋分馏的同位旋效应

Isospin Effects in the Isospin Fractionation Process in Intermediate Energy HeavyIon Collisions

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 .

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.