形变奇特核单粒子共振密度泛函研究及对恒星爆炸影响

Nuclei synthesized along pathways of the rapid proton capture process (rp-process) or rapid neutron capture process (r-process) in stellar explosions are among the most exotic nuclei found in nature. Due to their large number and experimental inaccessibility, an improved understanding of stellar explosions relies on improved models of these important nuclei. Often having deformed shapes and Fermi surfaces close to or even embedded in the continuum, these nuclei are often loosely bound or unbound, and they often exhibit resonances with a pronounced single-particle character. In some, valence nucleons can be easily scattered into the long-lived or quasi-stationary single-particle (s.p.) resonant states (or Gamow states) with certain decay widths in the continuum. Single particle resonant states must therefore be considered in models of these nuclei. For this reason, the structures of low-energy near-threshold resonant states in exotic nuclei are the focus of significant international efforts. We propose to develop a new density functional approach to modeling these nuclei that fully includes deformation effects, pairing correlations, and resonant continuum effects. We will determine the properties of s.p. resonant states in these deformed exotic nuclei, comparing our results when possible to experiments. We will additionally adopt a new isospin-density dependent effective pairing interaction to quantitatively analyze the contributions from the s.p. resonant states with low angular momentum to deformed nuclear halos. Finally, we will utilize our level information to generate new resonant capture cross sections, and investigate their impact on nucleosynthesis pathways and abundances synthesized in stellar explosions.

恒星爆炸过程沿快质子/中子俘获路径，核合成自然界大部分奇特核。由于核质量数大，实验很难到达，对于恒星爆炸过程探索，依赖描述关键核素的理论模型。这些核大多具有形变，弱束缚或非束缚，费米面接近/嵌入连续谱，具有明显单粒子特性，故价核子易被散射到连续谱中有一定宽度和单粒子特性的共振态上。鉴于重要的核天体物理应用前景，奇特核阈值附近低能共振态结构的理论和实验研究备受国际瞩目，是兰州 CSR 大科学装置物理研究目标之一。 本项目将紧密结合国内外放射性核束大科学装置的相关实验研究，发展含形变、对关联及共振连续谱的密度泛函理论。拟开展工作：1）研究形变奇特核单粒子共振态性质，同可能的实验结果比较，确认核素能级性质；2）对关联采用同位旋－密度依赖有效对相互作用新形式，定量分析低角动量的共振态对形变晕贡献；3）利用新能级和波函数信息，计算新的共振反应截面，研究共振反应率对恒星爆炸核合成路径及元素丰度的影响

恒星爆炸过程沿快质子/中子俘获路径，核合成自然界大部分奇特核。由于奇特核远离稳定线，实验上很难测得包括质量、寿命、低能核反应截面等决定演化路径的重要物理量。理论模型预言有八千多个核素，现有实验涉及到的非常有限，大概几百个。对于恒星爆炸过程的全面探索，无疑需要依赖核结构的理论模型。奇特核大多具有形变，对于弱束缚或非束缚不稳定核素，费米面接近/嵌入连续谱，低能区的能级分布具有明显单粒子特性，导致价核子容易被散射到连续谱中有一定宽度和单粒子特性的共振态上，尤其影响质子俘获截面及反应率。鉴于重要的核天体物理应用前景，奇特核阈值附近低能共振态结构的理论和实验研究备受关注。本项目紧密结合国内外放射性核束大科学装置的相关实验研究，发展考虑形变、对关联及共振连续谱的密度泛函理论。主要体现在：.1）采用协变密度泛函理论，研究形变奇特核单粒子共振态性质；同实验结果比较，以确认核素能级性质；相关的研究成果发表在 2014 PLB，2015 PRC，2017 PRC上。.2）考虑介质极化效应，从不对称核物质中提取诱发相互作用，约束有限核同位旋－密度依赖有效对相互作用新形式。相关的研究成果发表在 2016 PRC 上。.3）将协变密度泛函理论给出的奇特核结构信息，用于低能中（质）子俘获反应截面和反应率的计算；研究反应率对恒星爆炸核合成路径及元素丰度的影响。相关的研究成果发表在 2015 PRC 上。