利用电子散射方法研究Sn同位素链上放射性核素的电荷分布

Electron scattering is one of the best tools to measure the size and shape of the charge distributions of atomic nuclei, with the advantages of a point like particle, and probes nuclei through the fairly weak and well-understood electromagnetic interaction. In the middle of last century, this method had already been used to precisely determine the charge density distributions of most stable nuclei, which has greatly contributed to establish the current nuclear model. With the development of accelerator, some nuclei near the drip line were found to have peculiar structures in 1980s. The charge distributions of those nuclei have never been studied by electron scattering due to short lifetime and low production rates. A novel internal target method was developed to realize the experiment of electron scattering off short-lived nuclei. The method was based on the well-known “ion trapping” phenomenon in electron storage rings. With the understanding of this phenomenon, short-lived nuclei ions, which are injected from external ion source, can be trapped by electron beam itself to form a “target” in the electron storage ring and scattered with circulating electron beam at the same time. The information about the charge density distribution of short-lived nuclei can be obtained from the measurement of those scattered electrons. A large facility for electron and short-lived nuclei scattering experiment had been constructed since the year of 2009 in RIKEN and the first experiment will be done in 2015. The applicant worked for the development of this novel method from 2005 to 2013 and plan to do the measurement about the charge density distribution of 128Sn and 130Sn.

原子核内部的电荷分布一直是核物理领域研究的重点问题之一，电子散射是研究电荷分布最为有效的方法。利用该方法已经获得了稳定原子核的电荷分布信息，为原子核模型的建立提供了实验依据。随着加速器技术的发展，短寿命的放射性核素成为核物理领域的研究热点。由于寿命与产额的限制，电子散射一直没能应用到放射性核素的研究中。日本理化所基于电子束对离子的俘获现象，成功在电子储存环中形成放射性核素靶，为实现电子与放射性核素散射实验奠定了基础。申请人作为探测器方面负责人之一，全程参与了该方法的研制。一台大型电子与放射性核素散射装置已于日本理化所建造完成，计划于2015年起开展电子与Sn同位素链上放射性核素散射实验研究，双幻核132Sn将作为首个目标核。申请人拟计划对放射性核素128,130Sn进行研究，并基于已知稳定核素的电荷分布，揭示该同位素链上电荷分布的变化规律，对研究奇特原子核电荷分布的同位旋依赖性有重要意义。

本项目原计划与日本理化学研究所SCRIT研究组合作，利用世界上唯一的一台电子与放射性核素散射装置，对Sn同位素链上的放射性核素的电荷分布进行系统研究。由于日本政府削减科研经费以及在制作铀靶等工艺方面的问题，导致该装置的升级改造进度严重放缓，一直无法产生足够数量的132Sn、130Sn及128Sn离子来进行电子散射实验。因此项目负责人不得不对原实验内容进行更改，在继续跟进电子与放射性散射实验进展的基础上，增加了核天体物理方向的研究工作，主要内容为中国锦屏深地核天体物理实验项目（JUNA）的顺利开展，进行前期实验与技术方面的准备。.项目组与中科院近代物理研究所和中国原子能研究院的核天体组合作，利用中科院近代物理研究所320 kV高压平台，对12C(p,γ)13N、27Al(p,γ)28Si、24Mg(p, γ)25Al等关键核反应进行了细致的研究，并对320 kV高压平台质子束流的能量进行了刻度，对束流能量展宽、及长期稳定性进行了测量。系统地掌握了利用非共振反应及共振反应，对加速器的束流性质进行测量的方法，为精确测量新建的JUNA 400kV强流加速器的束流性质下了基础。项目执行期间发表基金标注的期刊论文4篇，另有1篇会议文章已接收还未发表，还有3篇文章正在筹备中，受邀赴日本东北大学进行专题讲座1次，国际会议口头报告3次，参与本项目相关工作的博士研究生3人，硕士研究生3人。