基于傅里叶级数展开的裂变位能曲面与碎片质量分布计算

doi:10.7538/yzk.2021.youxian.0614

摘要/Abstract

摘要： 裂变位能曲面是裂变核结构性质和裂变动力学研究的基础。本文使用傅里叶级数展开方法描述裂变过程中原子核的形状，采用基于LublinStrasbourg Drop(LSD)宏观模型和YukawaFolded微观模型计算了236U多维裂变位能曲面，研究了位能曲面随不同集体自由度(原子核拉长形变、左右碎片质量不对称度以及颈部宽度)的变化情况以及温度对位能曲面的影响。在位能曲面基础上采用基于BornOppenheimer近似的三维集体模型描述原子核裂变过程，计算了236U裂变碎片质量分布，计算结果与实验数据符合较好，特别是质量分布的峰位，同时分析了核温度、零点能和颈部断裂概率半宽度对裂变碎片质量分布计算结果的影响。

关键词: 核裂变, 宏观-微观模型, 位能曲面, 碎片质量分布

Abstract: The fission potential energy surface is the basis of describing structural properties and dynamics of fission nuclei. The shape parameters constructed by Fourier series were used to describe the nuclear shape from ground state to the scission configuration in fission process. Multidimensional fission potential energy surfaces of 236U were calculated with the macroscopicmicroscopic method, in which the macroscopic energy part was obtained by the LublinStrasbourg Drop (LSD) model and the microscopic shell and pairing energy correction part were calculated based on the YukawaFolded (YF) single particle potential. The evolutions of the potential energy surface with different collective degrees of freedom (elongation of the nucleus, massasymmetry of leftright fragments and the neck thickness) were studied. The results show that the neck degree of freedom plays an important role in the evolution of nucleus from one fission path to two fission paths. With the calculated potential energy surface, the fission fragment mass distributions were obtained by using a three-dimensional collective model based on the BornOppenheimer approximation with two adjustable parameters zeropoint energy and half width of neck breaking probability. The calculated results are in good agreement with the experimental data, especially, the peak positions of the light and heavy fragments mass distribution are consistent with the experimental results. The effects of zeropoint energy and half width of neck breaking probability on fission fragment mass distributions also have been analyzed. The results show that zeropoint energy mainly affects the mass distribution width of fission fragment and the half width of neck breaking probability has an effect on the peak position of fragment mass distribution. The effect of temperature on potential energy surface of 236U has also been investigated in the Fourier nuclear shape parametrization framework. The height of the fission inner and outer barrier in symmetric fission path reduced with temperature increasing. The general topography of potential energy surface changes obviously as temperature increases and the main reason is the effect of microcorrection energy gradually decreases with the increasing of temperature. Finally, the higher temperature will lead to the disappearance of asymmetric fission valley on the potential energy surface. The dynamic calculated results based on the temperaturedependent potential energy surface show that the asymmetric fission contribution of fission fragment mass distribution gradually reduces and the symmetric fission contribution gradually dominates the fission fragment mass distribution with higher temperature, and these dynamic calculated results are consistent with the trend of temperaturedependent potential energy surface, as well as in accordance with the experimental observation.

Key words: nuclear fission, mac-mic model, potential energy surface, fragment mass distribution

宿阳, 刘丽乐, 陈永静, 葛智刚. 基于傅里叶级数展开的裂变位能曲面与碎片质量分布计算[J]. 原子能科学技术, 2021, 55(12): 2290-2299.

SU Yang, LIU Lile, CHEN Yongjing, GE Zhigang. Calculation of Fission Potential Energy Surface and Fragment Mass Distribution Based on Fourier Nuclear Shape Parametrization[J]. Atomic Energy Science and Technology, 2021, 55(12): 2290-2299.

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