关键词: 核裂变, 协变密度泛函理论, 含时生成坐标方法, 裂变碎片质量分布

Abstract: Nuclear fission is an import object in nuclear physics and engineering due to its crucial role in the military, energy application and industry, agriculture, medical and other fields. In recent years, nuclear fission attracts more attention due to the following reasons: Nuclear fission plays a crucial role in determining the stability of superheavy elements, and is one of the primary mechanisms that terminate nucleosynthesis and determine the abundance of the synthesized nuclides; It is also an important mechanism used to produce shortlived exotic nuclides and fission of exotic nuclei far from stability also provides a new and effective way to study exotic nuclei. Generally, heavy nucleus contains hundreds of nucleons which are coupling with each other by nucleonnucleon manybody interaction. Due to the complication of lowenergy heavy nuclear fission, it is out of reach for ab initio calculation or interacting shellmodel. Modern microscopic approaches are based on the framework of nuclear energy density functionals(NEDFs) which consider the Pauli exclusion principle and nucleon-nucleon interaction simultaneously and include the shell effect and quantum manybody effect selfconsistent. In our previous work, the timedependent generator coordinator method plus Gaussian overlap approximation (TDGCM+GOA) has been implemented based on the covariant density functional theory (CDFT) and applied to describe the fission dynamics of 226Th where three peaks were observed in the fragment yield distribution. In this work, the dynamics of lowenergy induced fission of 258Fm was analyzed by using the TDGCM+GOA based on CDFT, mainly focusing on the potential energy surface(PES), total kinetic energies (TKE) of the fragments, and fragment mass yields. A remarkable symmetric fission valley is found in the potential energy surface, and thus both the TKE distribution and fragment mass yields present a single symmetric peak structure. The scission lines show an obvious separation between the number of the nucleons in the neck Qn=4,3,2, and an almost coincidence between Qn=2,1. The evolution of wave function probability distribution with time was presented, and the results show that most of the wave function flow through the scission line along the symmetric fission path, while a negligible part of the wave function flow through the scission line along the cluster emission path. The TKE distribution and fragments mass yields distribution were analyzed with the variance of the number of nucleons in the neck. As the number of nucleons in the neck decreases from 4 to 1, the peak of TKE distribution becomes narrow and the maximum of mass yield increases from 988% to 1028%. In addition, the influence of initial excitation energy on the fragments mass distribution was analyzed, and the results show that the peak of mass yield becomes lower, i.e., from 988% to 855%, as the excitation energy of the initial state increases from 83 MeV to 173 MeV.

Key words: nuclear fission, covariant density functional theory, time-dependent generator coordinate method, fragment mass yield