基于微观核动力学研究光-核吸收截面

Photonuclear absorption cross-sections based on microscopic nuclear dynamics

目前国际上正在兴建一批光核反应的实验装置,如上海激光电子伽马源装置.光核反应正作为研究原子核结构的一种独特手段而受到很大关注.本文基于时间相关的微观核动力模型——Time-dependent Hartree-Fock+BCS研究了光核反应的截面.该方法包含了动力学对关联,并基于三维坐标空间求解,在动力学演化的基础上通过傅里叶变换可以得到集体共振的截面.该方法可以描述任意形状的原子核的光核反应.本文以形变核^(154)Sm为例,计算了不同极化光的光吸收截面的角分布,为研究共振机制提供了观测量.计算所得的^(154)Sm的巨偶极共振总吸收截面与实验值有很好的符合.对球形丰中子核^(132)Sn的巨偶极共振与矮偶极共振的计算也能较好地符合实验.本工作为后续更深入地开展光核反应研究提供了基础.

Currently, experiments on photonuclear reactions are being vigorously conducted worldwide, achieving significant results,and new photonuclear reaction facilities are continuously being designed, built, and operated. Thus, research on photonuclear reactions is highly important and meaningful. Giant dipole resonance(GDR) plays a dominant role in the photon absorption process of atomic nuclei, and can be described within the small amplitude limit of the time-dependent mean field combined with energy density functional. Typically, the quasiparticle random phase approximation(QRPA)method, an approximation of the time-dependent mean field in the small amplitude limit, is used to replace real-time calculations to study the collective excitation states of atomic nuclei. However, the QRPA method also faces some intractable problems. In recent years, with the advent of supercomputers, time-dependent mean-field calculations have developed. The time-dependent Hartree-Fock+BCS(TDHF+BCS) method consistently includes pairing correlations while keeping the computational resources required at an acceptable level. Our research group has recently developed a selfconsistent Skyrme TDHF+BCS model which solves in three-dimensional coordinate space and can describe atomic nuclei of any shape, making it a powerful tool for theoretical research on nuclear dynamics. Previous GDR studies within the mean field framework have mostly involved calculations of the total photon absorption cross-section, lacking a systematic study of photonuclear reactions. Such research can help us gain a deeper understanding of the photonuclear interaction process and reveal richer and more detailed information about the internal structure, energy levels, and dynamic effects of atomic nuclei.In this work, we developed the TDHF+BCS model for photonuclear reaction research, enabling it to calculate the absorption cross-sections and their angular distributions for atomic nuclei under different polarization of light. Calculations were conducted for the axially symmetric deformed nucleus154Sm. In intrinsic coordinate systems, the angular distribution of absorption cross-sections for different polarizations of light shows deformation effects, allowing for the selective excitation of K=0 and K=1 states through angular distributions. Subsequently, we calculated the absorption cross-sections in the laboratory system coordinate. The calculated total absorption cross-section values match well with experimental results.This work, as the initial step in employing the TDHF+BCS framework as a novel tool for photonuclear reaction research,validates the efficacy of this method for photonuclear reaction studies. It also establishes a foundation for more comprehensive and advanced research in photonuclear reactions based on this model in the future.