Fermi能区周边碰撞中的破裂与耗散过程的竞争
Competition of breakup and dissipative processes in peripheral collisions at Fermi energies
摘要：
费米能区的重离子碰撞可能同时表现出直接过程和耗散过程的特征。为了研究这种行为的细节，我们研究了在反应$^{18}$ O（35 $A\cdot$ MeV）+ $^9$ Be（$^{181}$ Ta）在前进角的弹丸状碎片的同位素和速度分布。我们分解的实验速度分布经验分为两个贡献：一个直接的，“分裂”的组件集中在光束速度和耗散组件在较低的速度导致尾部的速度分布。在Goldhaber模型中解释了直接分量，并提取了速度分布的宽度。耗散组件，然后成功地描述了运输计算。直接贡献和耗散贡献的产率之比可以从偏转函数的行为来理解。耗散分量的同位素分布与数据定性一致，但由于二次去激发的修改需要考虑。这些反应对研究重离子碰撞中的平衡机制是有意义的。
英文摘要：
Heavy ion collisions in the Fermi energy regime may simultaneously show features of direct and dissipative processes. To investigate this behavior in detail, we study isotope and velocity distributions of projectile-like fragments in the reactions $^{18}$O (35 $A\cdot$MeV) + $^9$Be($^{181}$Ta) at forward angles. We decompose the experimental velocity distributions empirically into two contributions: a direct, `breakup' component centered at beam velocity and a dissipative component at lower velocities leading to a tail of the velocity distributions. The direct component is interpreted in the Goldhaber model, and the widths of the velocity distributions are extracted. The dissipative component is then successfully described by transport calculations. The ratio of the yields of the direct and the dissipative contributions can be understood from the behavior of the deflection functions. The isotope distributions of the dissipative component agree qualitatively with the data, but the modification due to secondary de-excitation needs to be considered. We conclude, that such reactions are of interest to study the equilibration mechanism in heavy ion collisions.
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