中能重离子碎裂反应的同位旋效应及其消失

Isospin Effect of Fragmentation Reaction and Its Disappearance in Intermediate Energy Heavy Ion Collisions

用修正的统计擦去模型计算了中能重离子碎裂反应产生的同位素分布的同位旋效应 ,发现随着 (Zproj-Z) /Zproj的增大 ,碎裂反应的同位旋效应将逐渐减小直到消失 .同时 ,研究表明碎裂反应的同位旋效应的消失主要是由擦去阶段的几何效应和随后的蒸发效应导致的 .

Isospin effect of fragmentation reaction on isotopic distribution was investigated by a modified statistical abrasion-ablation model. It is shown that the isotopic distribution shifts toward the neutron rich side for neutron rich projectile, but this isospin effect will decrease and disappear at last when ( Z pro j - Z)/Z pro j closes to 0.5 and becomes larger than 0.5 independent of the reaction systems, where Z and Z proj are the atomic numbers of the produced isotop and projectile, respectively. It is pointed out that the disappearance of isospin effect comes mainly from the geometry effect in abrasion stage and the evaporation process later.