已有 2272 次阅读 2019-12-30 14:27 |系统分类:科研笔记

Review Article

Bo Zhou, Yasuro Funaki, Hisashi Horiuchi, and Akihiro Tohsaki, Nonlocalized clustering and evolution of cluster structure in nuclei, Front. Phys. 15(1), 14401 (2020), arXiv: 1905.00788 

(64 pages)

原子核轻重核中普遍存在着丰富的结团结构，原子核结团理论物理的一个中心任务就是建立起更精确的微观结团模型来探索这种新颖的量子多体关联，研究其形成机理，同时也为实验和核天体理论提供可靠的参考和输入量。传统的微观结团模型是基于原子核结团具有良好的几何局域化结构的假设。为了得到较为精确的多体波函数，往往需要考虑数量巨大的不同结团空间，数值计算难度较大，而且并没有清晰的图像来阐释结团之间的运动关联。 

周波等人与合作者通过发展一种新的α凝聚THSR(Tohsaki-Horiuchi-Schuck-Röpke)波函数，提出了一种具有非局域化结团特点的微观波函数，并对具有20个核子，结构复杂的20Ne(α+16O)的结团结构进行了理论研究。通过完全的变分计算，20Ne的基态能量、基态宇称反转双重转动带结构等可观测量都在理论上得到了精确描述。结果表明,原子核结团在原子核内做相对自由的非局域化运动，而非传统意义上的局域化运动。作者进一步提出了容器模型来描述原子核结团的非局域化运动，这种新的理论框架超越了传统的微观结团模型。如下图所示，它将不同的α和16O结团限制在一个尺寸为β的容器中，来描述复杂的结团运动。为了得到相同的描述效果，在传统的模型中，需要使用结团间距参数{R1, R2, …}，并叠加数目巨大的不同局域化波函数才能得以近似的描述。这样，作者提出了原子核结团运动关联的新理解，同时发展了一个更有效的描述原子核结团结构的理论工具。

近五年来，周波等人与合作者将新提出的容器模型成功应用到了12C(3α)、16O(4α)等Nα原子核系统中，并进一步推广到了一些不稳定的丰中子核、超核等系统。容器模型提供了一个更为统一的理论框架来描述原子核结团的演化过程，如下图中12C丰富的0+态在容器模型中得到了很自然的描述。尤其是对于处理结团阈值之上的类气态(gas-like)结团结构，更是具有突出的优势。作者通过新的容器模型研究和解决了一系列传统模型很难处理的多结团结构问题，为实验提供了大量的原子核结构结团信息。在本综述文章中，作者详细讨论了从非局域化结团运动概念到容器模型这一理论的发展过程和应用。

Nonlocalized clustering and evolution of cluster structure in nuclei 

Bo Zhou1,2, Yasuro Funaki3, Hisashi Horiuchi4, Akihiro Tohsaki4

1 Institute for the Advancement of Higher Education, Hokkaido University, Sapporo 060-0817, Japan

2 Department of Physics, Hokkaido University, Sapporo 060-0810, Japan

3 College of Science and Engineering, Kanto Gakuin University, Yokohama 236-8501, Japan

4 Research Center for Nuclear Physics (RCNP), Osaka University, Osaka 567-0047, Japan

E-mail: [email protected], [email protected], [email protected], [email protected]

Contents

1  Introduction

2  Hoyle state and gas-like structure of clusters

2.1  3α condensate-like structure of the Hoyle state

2.1.1  Reduced α-decay width and S-wave dominant structure of the Hoyle state

2.1.2  α-condensate-like character and the THSR wave function of Hoyle state

2.1.3  Equivalence of the 3α THSR wave function to 3α RGM/GCM wave functions

2.1.4  Quantum Monte Carlo calculation of the Hoyle state

2.1.5  Breathing-like excitation of the Hoyle state

2.2  4α condensate-like state in 16O

2.2.1  4α OCM calculation

2.2.2  4α THSR calculation

3  Characters of the THSR wave function

3.1  Shell-model limit of the THSR wave function

3.2  Equivalence of projected prolate and oblate THSR wave functions

3.3  Negative-parity THSR wave function

3.4  Single-particle property of the THSR wave function of 13C

4  Localized vs. nonlocalized clustering

4.1  Inversion-doublet bands in 20Ne and their description by the THSR wave function

4.1.1  Energy curve by the hybrid-Brink–THSR wave function

4.1.2  Equivalence between the 16O+α THSR wave function and 16O+α RGM/GCM wave functions

4.2  Localized clustering from the inter-cluster Pauli principle

5  Container model of cluster dynamics

5.1  Nuclear size as the generator coordinate for the evolution of cluster structure and extension of the THSR wave function

5.2  One-dimensional gas of α clusters – α-linear-chain structure

5.3  Rich spectra of 3α states above the Hoyle state in 12C

5.3.1  Positive-parity states in 12C

5.3.2  Container picture for the 3- and 4- states in 12C

5.4  Variety of cluster states in 16O

5.5  Application to other nuclear systems

5.5.1  Neutron-rich isotopes of beryllium

5.5.2  Λ-hypernuclei

5.6  More generalization and manipulation of the THSR wave function

5.6.1  Two-center THSR wave function

5.6.2  Cluster systems with different size variables

5.6.3  Monte Carlo integration in the THSR wave function

5.6.4  New development of analytical treatment of the THSR wave function

6  Evolution of cluster structure

6.1  Duality property of mean-field states and formation of cluster states

6.1.1  Duality property of shell-model states with good SU(3) symmetry

6.1.2  Formation of cluster states from mean-field state with duality property

6.1.3  Observed large monopole transition strengths between ground state and cluster states

6.2  Pauli-allowed states of many-cluster systems

6.2.1  Two-cluster Pauli-forbidden states and many-cluster Pauli-allowed states

6.2.2  Many-cluster Pauli-allowed state and evolution of cluster structure

6.3  Container model and evolution of cluster structure

7  Summary