弱束缚核的新形态与连续谱效应的研究

With the development of Radioactiv Nuclear Beam (RNB) facilities in the world, the research on rare isotopes far from stabilty has been the frontier of nuclear physics. These extremely unstable nuclei are very weakly-bound, having significant continuum contributions, and exotic properties are expected compared to stable nuclei. To describe the continuum exactly is difficult, especially difficult for deformed nuclei and self-consistent calculations in this respect are still missing. On the other hand, we have developed a coordinate-space Skyrme Hartree-Fock-Bogoliubov solver, which has been demonstrated to be able to precisely treat the quasiparticle continuum and resonances in deformed nuclei. Based on this model, we prediced new exotic halo structures. Furthermore, we proposed to develop a deformed HFB+FAM-QRPA model, to study the continuum effects and electromagnetic transitions in excited states of weakly-bound nuclei，particularly the pygmy dipole resonance. Compared to the conventional QRPA which is computationally very expensive, FAM-QRPA is a very efficient new method solving QRPA equations. This means that systematical calculations and physics analysis become possible. Furthermore, the FAM-QRPA is a promising method to realize deformed continuum QRPA calculations which are too difficult for conventional QRPA method. Actually the HFB solver we developed has used MPI+OpenMP programming, to enable large-scale parallel calculations in Tianhe-1A supercomputer. This is essential for the description of surface diffuse structures of drip-line nuclei involving large boxes. In summary, by looking for exotic structures and continuum effects based on the coordinate-space HFB method and the FAM-QRPA method, our study of ground states and excited states of weakly bound nuclei can provide important information for experiments.

随着国际上放射性核束装置的进展，远离稳定线直至滴线的原子核的研究是核物理一个前沿课题。这些核极不稳定，束缚很弱，连续态的贡献很重要，已呈现与稳定核很不一样的奇特性质。然而对于形变核来说，严格求解连续谱非常困难。我们通过坐标空间求解Skyrme Hartree-Fock-Bogoliubov（HFB）方程可以精确的处理连续态和表面弥散，对形变弱束缚核的描述具有独特优势, 可能会发现一些新形态。 我们将进一步发展HFB模型，结合FAM-QRPA模型来研究弱束缚形变核的激发态的连续谱效应和电磁跃迁, 特别是Pygmy共振态。FAM－QRPA是一种求解准粒子无规位相近似（QRPA）方程的有效方法，如果用通常的QRPA求解方法，则形变核的连续谱QRPA因为计算量巨大而很难实现。这项研究可以为实验观测提供直接可靠的理论支持。

本项目为弱束缚核新形态与连续谱效应的研究。目前国际上正在发展大型放射性核束物理实验装置，如美国的FRIB，中国的HIAF等，这些装置可以产生极其远离稳定线的同位素。研究极不稳定核的新物理已经成为核物理的前沿方向。 极不稳定核非常弱束缚，表面密度分布有很大弥散，形成晕结构，从而有新的激发模式。比较感兴趣的是形变晕核基态和软共振激发。 本项目主要目的是发展先进格点空间连续谱密度泛函模型研究形变弱束缚核的基态，激发模式和背后的物理，从这一点来说，我们很好的完成了项目的预设目标。 我们的主要成果是完成了格点空间的连续谱形变FAM-QRPA的计算程序，研究了软单极和软偶极共振模式的精细结构，发表了3篇Phys.Rev. C的Rapid Communication, 在这一领域形成了独特的国际领先优势。 通过软共振的物理机制的研究，特别是反常形变分裂和表面的量子拓扑流，刷新了人们对弱束缚核的重新认识，这也主要归结于我们的精确的大尺度格点空间模型计算。