丰中子核12-14Be的集团结构的实验研究

Cluster structure and valence neutron correlation seems enhanced at the drip-line area for neutron rich nuclei.This is an exhibition of the new structure degree of freedom of exotic nuclei. Based on the previous work for neutron drip-line nucleus 8He, we propose to study the cluster (molecular) structure and the valence neutron correlation of the 12-14Be isotopes. The main features of the experiment is the coincident measurement of two charged fragments and multi-neutrons,and the reconstruction of the excited states of the projectile.The experiment include three parts: calibration of the forward multi-neutron correlation spectrometer by using the 11Be beam; study of the cluster and valence neutron correlation structures for 12Be and for 14Be. An array of several charged particle telescopes, together with the specially designed neutron correlation spectrometer, will be used. From the reconstruction of the exicited states, which are to be compared with theoretical predictions, the cluter configurations of the 12Be will be extracted. For 14Be the cluster structure of its ground state will be obtained from the direct core knockout reaction. Neutron correlations will be investigated based on core excitation or knockout. The research group has been well experienced on performing breakup and knockout reaction experiments. The proposal is based on mature beam conditions and detection systems, except minor addition and replacement of some of the detector components.

丰中子核的集团结构和价中子关联，在滴线区有加强的趋势，体现了奇特原子核新的结构自由度。在此前研究丰中子滴线核8He的基础上，本项目提出研究12-14Be的集团（分子）结构和价中子关联形态。实验的特点是双带电碎片和多中子关联测量，并实现弹核激发态重建。主要内容包括利用11Be束流刻度前向多中子关联谱仪，12Be的集团结构和价中子关联形态研究，14Be基态的集团结构和价中子关联形态研究等三个部分。实验将采用多套带电粒子望远镜组合，以及专用的前向多中子关联谱仪。通过重建激发态能谱并和理论计算比较，获得12Be激发态和基态集团结构图像。通过直接敲出反应，获得14Be基态集团结构图像。在激发或敲出核芯条件下研究价中子关联组态。项目组具有在国内外长期开展非稳定核破碎和敲出反应实验的经验。本实验计划基于基本成熟的束流和探测设备条件，但部分探测器部件需要补充和更换。

项目按计划执行,研究目标圆满完成.有本项目标注的第一作者和通讯作者期刊论文21篇，会议邀请和口头报告38次，工作内容包含在“周培源物理学奖”和“何梁何利科学与技术进步奖”之中。本项目的核心成果是12Be的集团结构研究, 直接的核心文章是3篇，包括国内HIRFL-RIBLL装置上的首篇PRL文章；大型国际学术会议上讲述12Be集团结构的邀请和口头报告6次，包括在三年一轮的国际核物理大会（INPC）上报告两次。在12Be的研究中提出并完整测量了三个关键物理量来确认原子核内的集团结构，包括转动惯量（激发能-自旋依赖关系）、集团衰变分支宽度、以及特征跃迁模式。特别是首次在非稳定核中测定增强的单极跃迁强度，从而清楚识别了非稳定核12Be中10.3 MeV近阈激发态的分子集团结构。本项目相关工作培养毕业博士生5人。