原子核裂变动力学的协变密度泛函理论研究

Nuclear fission plays crucial roles in the energy application, military, industry, agriculture, medical, and other fields. Fission presents a unique example of a non-equilibrium large-amplitude collective motion in a multi-dimensional space where all nucleons participate with complex correlation effects. Therefore, fission is considered as one of the most complex processes in nuclear physics. . The main objective of this project is to develop a microscopic theory of nuclear fission, based on covariant density functional theory (CDFT), that will enable a quantitative description of the fission mechanism and accurate predictions for fission observables. The specific goals, applications and expected results can be summarized as follows: .1. Development of a CDFT code that can describe the nuclear deformed states with both large quadrupole and octupole deformations by introducing a two-center harmonic oscillator basis in cylindrical coordinate. Calculate the multi-dimensional potential energy surface, collective masses and so on for nuclear fission, and then predict the fission barriers and life times for spontaneous fission of heavy and superheavy nuclei based on WKB approximation. .2. Development of a time-dependent generator-coordinate method in the Gaussian overlap approximation (TDGCM+GOA) based on the framework of CDFT, for the description of induced fission dynamics. This novel approach should enable precise and accurate microscopic calculations of relevant observables: charge and mass distributions of the fragments; their total kinetic and excitation energy distributions, the average number of neutrons emitted and the average neutron energy, etc. .3. A particularly important topic of investigation will be the effect of coupling between shape and pairing degrees of freedom on fission dynamics. Finally, a systematic study on induced fission dynamics and related observables of actinides will be performed by the TDGCM+GOA with pairing degrees of freedom.. Through this study, we will achieve more physical insights and deeper understandings on nuclear fission mechanism. We expect to reproduce the measured observables and provide reliable unmeasured ones.

核裂变在能源、国防、工农医及基础物理研究等领域扮演着至关重要的角色。裂变是核多体系统在多维空间中的一个非平衡、大振幅集体运动过程，存在复杂的关联效应和断点效应，是核物理中极具挑战性的课题。本项目拟基于协变密度泛函理论，发展描述核裂变动力学的微观模型，具体开展如下研究工作：1.引入双中心谐振子基，发展适用于描述大形变组态的协变密度泛函理论，计算裂变多维位能曲面、质量参数等，系统研究重核和超重核裂变位垒及自发裂变寿命等；2.发展多维空间含时生成坐标方法，描述诱发裂变动力学，并计算裂变碎片的质量和电荷分布、总动能和激发能分布、平均发射中子数和平均中子能量等重要观测量；3.引入对振动激发自由度，探讨裂变非绝热效应，并系统研究锕系原子核诱发裂变动力学及相关物理观测量。通过本项目的实施，深化对核裂变微观机制的认识和理解，实现对裂变观测量的再现和预言。

核裂变是核多体系统在多维空间中的一个非平衡、大振幅集体运动过程，存在复杂的关联效应和断点效应，是核物理中极具挑战性的课题。本项目首先发展了适用于描述裂变的协变密度泛函理论，基于此在含时生成坐标方法框架下构建了核裂变动力学微观模型，实现了对多个裂变观测量的自洽描述，最后详细分析了缺中子Hg区及锕系区的非对称裂变及微观机制。具体开展如下研究工作：. 1. 引入双中心谐振子基，发展了适用于描述大形变组态的协变密度泛函理论CDFT-TCHO，更精确高效地获取多维裂变位能面信息；. 2. 在四极-八极(β2-β3)约束的基础上增加了脖子处粒子数约束及密度约束，完成了多维裂变位能面的计算，获得了更合理的组态信息，包含了更多的裂变通道，提取了裂变剪裂面，揭示了新自由度对总动能分布及碎片分布的影响；. 3. 采用含时生成坐标方法(TDGCM)对缺中子180Hg进行了裂变动力学研究，再现了其新型非对称裂变模式，并揭示了其微观机制：非对称断点处的碎片100Ru等存在“八极幻数”N=56，使其能量比对称裂变道更低；. 4. 基于多维约束协变密度泛函理论，计算了锕系区有限温度下的势能面和质量张量，并用TDGCM进一步研究了其裂变动力学过程，理论结果很好的再现了实验，揭示了有限温度激发的重要性；. 5. 利用微观集体哈密顿量方法研究了超重核裂变位垒及谱学结构，揭示了动力学关联能对计算具有软势能面的超重核裂变内垒的重要性。