【摘要】 利用同位旋相关的量子分子动力学理论 ,研究了中能重离子碰撞中同位旋分馏强度 (N Z) n (N Z) frag对于碰撞系统质量和能量的依赖关系 .这里 (N Z) n 和 (N Z) frag分别是核子发射 (气相 )和碎片发射多重性 (液相 )的中子 质子比 .研究结果表明同位旋分馏强度是反应系统质量和能量的灵敏函数 .当系统同位旋 (中子 质子比 )入射能量和碰撞参数都固定时 ,同位旋分馏强度随系统质量的增加而减少 .因为随系统质量的增加与较轻系统比较 .重系统具有大的压缩能 ,小的热能和大的液 气相变的临界温度 .故核子输运过程和同位旋分馏过程减弱 .但在确定系统质量条件下 ,同位旋分馏强度随系统同位旋的增加而增加 .即丰中子系统同位旋分馏比缺中子系统强得多 .故中能重离子碰撞系统丰中子系统的同位旋分馏强度是提取同位旋相关平均场的好的物理观测量更多还原

【Abstract】 Based on the isospin-dependent quantum molecular dynamics model, we have investigated the dependences of isospin fractionation degree （N/Z）_n/（N/Z）_frag on the mass and the beam energy of colliding system. The （N/Z）_n and （N/Z）_frag are the neutron proton ratio of the nucleon emission （gas phase） and that of the fragment emission （liquid phase） respectively. The isospin fractionation degree is a sensitive function to the mass and beam energy of the colliding system. The （N/Z）_n/（N/Z）_frag reduces with increasing mass of the colliding system when the beam energy and neutron proton ratio of the colliding system are fixed. This is due to the larger compression, small heating energy and larger critical temperature of the gas-liquid phase transition for the heavy colliding system, compared to those of the light colliding system. We also found that （N/Z）_n/（N/Z）_frag enhances with increasing beam energy due to the increase of excitation energy of the colliding system which leads to larger nucleon transport and isospin fractionation. But the isospin fractionation only occurr in the energy region for producing the liquid-gas phase transition. In this case, we propose that （N/Z）_n/（N/Z）_frag can be directly compared with the experimental data to get the information about symmetry potential.更多还原