原子核链式α结团结构及其动力学的协变密度泛函理论研究  

Structure and dynamics of linear-chain α cluster in covariant density functional theory

作　　者：张丹丹 任政学 赵鹏巍[1] ZHANG DanDan;REN Zheng Xue;ZHAO PengWei(State Key Laboratory of Nuclear Physics and Technology,School of Physics,Peking University,Beijing 100871,China;Instut furKephysik,InstituteforAdvanced Simulation and JulichCenterforHadronPhysics,Forschungszentrum JulichJulich D-52425,Germany;Helmholtz-Institut fur Strahlen-und Kernphysik and Bethe Centerfor Theoretical Physics,Universitat Bonn,Bonn D-53115,Germany)

机构地区：[1]北京大学物理学院,核物理与核技术国家重点实验室,北京100871 [2]于利希研究中心,原子核物理所和高等计算所,德国于利希D-52425 [3]波恩大学,亥姆霍兹辐射与核物理研究所,德国波恩D-53115

出　　处：《中国科学：物理学、力学、天文学》2024年第9期46-56,共11页Scientia Sinica Physica,Mechanica & Astronomica

基　　金：国家自然科学基金(编号:11935003,11975031,12070131001,12141501);北京大学核物理与核技术国家重点实验室(编号:NPT2020ZZ01);科技部高端外国专家引进计划和北京大学高性能计算平台资助项目。

摘　　要：本文回顾了基于协变密度泛函理论研究原子核链式α结团结构及其动力学的现状.协变密度泛函理论以核子为基本自由度,可以自洽地给出具有α结团现象的原子核链式结团结构.结合推转平均场方法,相关研究揭示了碳同位素链式结团结构中自旋和同位旋的相干效应.随着转动频率的增加,中子的σ轨道(平行于对称轴的轨道)的能量在科氏力作用下降低,进而被价中子占据,预示着链式结构更容易在丰中子原子核的高角动量态中发现.类似的现象同样出现在丰质子的3α和4α链式结团结构中,并且价质子能在更低的角动量下占据质子的σ轨道.三维格点空间的协变密度泛函理论研究表明:转动频率在2.0–3.5 MeV区间内,12C中的链式结团结构是位能面上的极小,表现出对弯曲运动和裂变的稳定性.进一步,含时协变密度泛函理论给出了^(4)He+^(8)Be和^(4)He+^(10)Be共振散射形成^(12)C和^(14)C链式结团结构的动力学过程,并发现价中子的动力学同位旋效应减缓了结团的纵向振荡,使得形成的^(14)C链式结团结构有更长的寿命.Recent progress in the structure and dynamics of nuclear linear-chain α clusters within the framework of covariant density functional theory is reviewed. The covariant density functional theory does not a priori assume the existence of α clusters and provides a microscopic and self-consistent description of the corresponding linear-chain cluster structure. By combining the covariant density functional theory with the cranking model, the coherent effects of nuclear spin and isospin on the linear-chain cluster structure of carbon isotopes are revealed. Owing to the effects of the Coriolis term in the cranking covariant density functional theory, σ orbitals show a reduction in energy with the rotational frequency and are occupied by valence neutrons, indicating that the linear-chain cluster structures are more feasible in fast-rotating neutron-rich nuclei. A similar mechanism exists for the 3α and 4α linear-chain cluster structures in proton-rich nuclei, wherein protons occupy σ orbitals at lower angular momenta than those observed for neutrons. Based on the calculations of the covariant density functional theory in a three-dimensional lattice space, the linear-chain cluster configuration in ^(12)C is shown as a state with the minimum energy on the potential energy surface for rotational frequencies of 2.0–3.5 Me V, thereby demonstrating the stability of the linear-chain cluster structure against nuclear bending motion and fission. Furthermore,the development of the time-dependent covariant density functional theory enables the dynamical study of the linear-chain cluster structure. Investigations of the microscopic dynamics of the linear-chain cluster states for ^(12)C and ^(14)C isotopes in the reactions ^(4)He+^(8)Be and ^(4)He +^(10)Be show that the dynamical isospin effects by the valence neutrons impede the longitudinal oscillations of clusters, thereby prolonging the lifetime of the linear-chain cluster states.

关 键 词：协变密度泛函理论 原子核结团 链式结团结构 原子核转动 共振散射 

分 类 号：O571[理学—粒子物理与原子核物理]