中子诱发重核裂变后产物的演化规律及定量描述

Developing the scientific fission model is key to studying on the evolution rule and quantitative description of post-fission phenomenon for neutron-induced heavy nuclei fission. Firstly, based on five-dimensional deformation space, we develop post-fission theory for neutron-induced fission to quantitatively describe the potential energy distribution before the breakpoint, and describe potential energy along with the evolution of the deformation. Secondly, we establish a phenomenological model to precisely calculate the driving potential distribution and pre-neutron-emission mass distributions for neutron-induced heavy nuclei fission. Thirdly, phenomenological model is implanted on Geant4, Geant4 code simulates physical process of neutron-induced actinide nuclei post-fission, which contributes to further research on scientificity and universality, and also break out the limitation for computer capacity. Based on potential-driving model, Geant4 code studies and calculates the mass or charge distributions for independent yields and cumulative yields, kinetic energy distribution and fission neutron spectrum. Ultimately, we develop TFGIC detector to experimental research on mass distribution and kinetic energy distribution for neutron-induced heavy nuclei post-fission. Compared between experimental measurement data and theoretical data, we evaluate and provide the mass distribution and kinetic energy distribution for neutron-induced heavy nuclei post-fission, which will provide reliable data for the developments of nuclear device and new nuclear power system. It is help to provide solutions for all-round fission theory for neutron-induced heavy nuclei fission, meanwhile, it is help to train more young talent for national defendant science and technology.

中子诱发重核裂变后产物的演化规律及定量描述研究，重在建立科学的裂变模型。本项目一方面开展五维位能面模型研究，发展中子诱发重核裂变后现象的理论，定量描述裂变核在断点前的势能分布及势能随形变的演化；另一方面，建立唯象模型研究复合核在断裂点时刻的驱动势分布，评价计算中子诱发锕系重核裂变后，发射中子前裂变碎片的质量分布数据；第三，将唯象模型植入Geant4程序，Geant4调用该模型模拟中子诱发重核裂变过程，进一步研究唯象模型对裂变后物理描述的科学性和普适性，定量研究裂变碎片质量分布、电荷分布、平均总动能分布的特性和物理机制；最终，将实验测量数据与理论计算数据对比分析，系统地评价给出不同能量中子诱发不同重核裂变后裂变碎片质量分布、电荷分布和动能分布数据。为核装置研究、新型核能利用系统的研发提供可靠的数据支持，对全方位裂变后理论研究提供方案，同时为培养国防科技领域青年科技人才提供帮助。

随着第四代核反应堆和新型核能、核动力系统的快速发展，以及超重核熔合机制和天体核物理中的快中子俘获反应等领域的研究进展，使得中子诱发重核裂变机制研究及裂变数据测量成为国际上核物理研究的新热点。中子诱发重核裂变后产物的演化规律及定量描述研究，重在建立科学的裂变模型。理论方面：本工作发展完成了宏观-微观的五维势能曲面模型、唯象的Potential-driving裂变模型、基于双核理论的断点统计模型、基于Potential-driving模型的Monte Carlo方法等4种裂变物理模型，系统地开展了中子诱发重核裂变后产物的演化规律及定量描述。宏观-微观的五维势能曲面模型将裂变看成是核形状随时间演化的过程来处理，计算裂变性质和产额分布的规律，能够较好的描述实验测量的质量和电荷分布特征。唯象的Potential-driving裂变模型能够较高精度地计算、预测发射中子前裂变碎片质量分布，入射中子能量达到160 MeV，计算结果能够很好地与实验数据符合，明显优于其它程序计算结果。基于Potential-driving模型的Monte Carlo方法描述中子诱发锕系重核裂变物理过程，模拟计算裂变碎片独立产额、累积产额、动能分布、裂变中子谱分布，以及衰变γ谱分布，计算结果能够很好地与实验数据符合，该方法预测并解释了中子诱发重核裂变碎片质量分布、电荷分布、平均总动能分布的特性和物理机制。基于双核理论的断点统计模型考虑了壳修正和八级形变修正，能够较好地计算中子诱发重核裂变质量分布、电荷分布和动能分布，计算结果能够较好地与实验数据符合，该模型能够较好地解释180Hg非对称裂变的物理机制。实验方面：本工作研制完成了双屏栅裂变电离室(TFGIC)探测器，开展中子诱发natU裂变碎片质量分布实验测量工作，实现了2.45 MeV中子诱发natU裂变碎片质量分布数据实验测量工作。本工作从理论研究和实验研究同时开展，相互验证，相互支撑，将实验测量数据与理论计算数据对比分析，评价裂变模型的科学性与适用性，完成了中子诱发重核裂变后产物的演化规律及定量描述的研究内容，为核装置、新型核能系统和核动力系统的物理设计提供可靠的数据支持。