核熔合裂变反应机制中鞍点重要性的研究

We investigate both the key problem of fusion-fission mechanism and the difficulty problem of the calculation in the cross section of superheavy elements. New mechanism of diffusion help fusion should be established through improving the fusion probablity formula and considering neutron emission, and then the suggustion for experiment should be proposed. In order to solve the complex stochastic problems, we develop some new algorithms, for instance, the master-equation Monte-Carlo approach and the fast Fourier transform for producing time and spatial correlated noise with arbitrary correlation function. The results of this project have important significations to the intercross between nuclear physics and statistical physics, as well as a new direction for inverse Kramers problem might be opened. ... The about 10 Physical Review papers will be published, which include of 1 Physical Review Letter paper and a book for Langevin equation will also be published. An international conference for fusion-fission dynamics will be preformed in Beijing Normal University. By the way, the international collaboration will be formed.

超重核熔合裂变是核反应研究中的难点问题，而鞍点动力学是近垒熔合实验的关键问题。本申请拟在熔合形成复合核预平衡阶段，考虑中子发射效应；通过引入亚稳势反射边界的影响，给出修正的熔合概率公式；统一描述伴随中子发射的熔合裂变过程，增强理论计算的可靠性；发展数值求解量子朗之万方程的蒙特卡罗方法，为探究非线性量子随机过程提供算法。本项目成果将对实验合成超重核提供支撑，揭示近位垒熔合反应新机制，对探讨应用广泛的逆Kramers问题有启发。. . 预期发表10篇左右物理评论论文，力争发表1篇物理评论快报论文，出版论著1部，培养博士硕士研究生8~10名。

从重核及超重核的熔合与裂变反应机制中，提炼出破缺亚稳系统逃逸动力学，这是一个挑战性问题。考虑了原子核特有的对壳效应，进而对光滑的亚稳势的局部进行修正，即存在许多小陷阱和小势垒。所以，解决逃逸速率的复杂性，要突出鞍点及建立其上的回流的关键作用。主要内容包括：(a)提出平均最后离开最后一个鞍点时间的概念，计算裂变速率，考虑了随机关联涨落影响下的Kramers问题，研究反常扩散系统的位垒逃逸速率；(b)发展了一种反应流方法，对温度小于势垒高度的情况，给出了速率的解析表达式，即通过鞍点的概率速流积分与存活相的概率积分之比；(c )原子核对壳效应给出了势的微扰修正，一般来说，这对应于介质中存在局域破缺，我们提出快速傅立叶变换方法产生具有高斯关联的空间噪声，用蒙特卡罗方法模拟多维及广义朗之万方程，并建立了双平均技术，实现了复杂亚稳系统的逃逸速率的计算。(d)在偏压周期势中粒子的定向扩散，鞍点对于空间分布波包劈裂，进而放大有效扩散系数的研究；（e）研究了反常弛豫扩散过程，发现了一种自振荡现象。