处于力学不稳定条件下的受激有限核的动力学演化与确定论混沌  

Dynamic Evolution of Excited Finite Nuclei under Mechanical Instability and Deterministic Chaos

作　　者：邢永忠[1] 方玉田[1] 刘晓斌[1] 郑玉明[1,2] XING Yongzhong;FANG Yutian;LIU Xiaobin;ZHENG Yuming(Institute of fundamental Physics of Tianshui Normal University,Tianshui 741000,Gansu,China;China Institute of Atomic Energy,Beijing 102413,China)

机构地区：[1]天水师范学院基础物理研究所,甘肃天水741000 [2]中国原子能科学研究院,北京102413

出　　处：《原子核物理评论》2020年第1期34-39,共6页Nuclear Physics Review

基　　金：国家自然科学基金资助项目(11665019,11764035,11265013)。

摘　　要：以208Pb为例,研究了不同热力学稳定条件下有限核体系单体耗散的非线性特征。首先,给出了该原子核在不同温度下的压强密度相图以及相图中的力学不稳定区(Spinodal region),在相图中属于不同稳定性区域的温度和密度值下,抽取了208Pb中各核子的坐标和动量,然后,将其作为量子分子动力学(QMD)模型的初始值,模拟受激有限原子核体系仅在平均场作用下的时空演化,分析不同初始分布所对应的系统在时空演化过程中核子的空间分布、密度涨落等随时间的演化特征,重点对比分析了对应于相图中不同区域的初始208Pb原子核在演化过程中的不同表现特征;通过对定义在事件空间和定义在相空间的准Lyapunov指数的计算,清楚地显示,在力学不稳定的条件下,平均场动力学对于核子空间分布的敏感依赖性,定量地揭示了反应动力学中单体耗散的非线性混沌特征,进一步证实了中能重离子碰撞中多重碎裂的混沌机制。In the present paper the nonlinear characteristics of one-body dissipative of an excited finite nucleus has been studied by simulating the evolution of the nucleus 208Pb within the Quantum Molecular Dynamics(QMD)model. First, the phase diagram of the nucleus and the spinodal region were determined by computing the single particle energy and chemical potential. Then the position and momentum of each nucleons in the 208Pb were sampled according to uniform and fermi distribution respectively. After such preparation, taking these distributions as initial sates of QMD model, we simulated the evolution of the system in the action of the mean field with no collision term. The variation of the density and the fluctuation of the nucleons distribution have been analyzed.Our main attention paid on the comparison of the behavior of such quantities for the system started from 208Pb with different initial states. The sensitivity of the mean field dynamics on the initial space distribution of nucleons are demonstrated by calculating the Lyapunov exponents defined respectively in events space and phase space. The nonlinear dynamical mechanism of the one-body dissipation, and thus the multifragmentation of heavy-ion collisions at intermediate energy have been confirmed further. The conclusion is helpful for us both to understand the dynamical mechanism of the heavy-ion reactions and to extend our knowledge about the nonlinear dynamics.

关 键 词：有限核 力学不稳定性 多重碎裂 确定论混沌 

分 类 号：O562.5[理学—原子与分子物理]