基于HIRFL-CSR开展beta稳定线附近高电荷态离子的beta衰变性质研究

With the support of this application, beta decay properties of the highly charged ions will be studied systematically on the cooler storage ring at the Heavy Ion Research Facility in Lanzhou (HIRFL-CSR). Based on our research background, the current exeprimental condition of HIRFL-CSR, and the research frontiers in the highly charged ions, this applicaion focus on two related studies in the medium-mass nuclei in the neighboring of the beta-stability line as follows: 1)Study of the orbital electron-capture (EC) decays in hydrogenlike and heliumlike ions. The EC decay rates in these ions will be measured. Based on the experimental results and with the help of the theoretical calculations, the peculiarities found in the EC decay of few-electron ions will be probed intensively, such as the measured EC decay rates in some cases will disagree to the standard theory of the EC process in which the decay rates are assumed to be proportional to the number of orbital electrons. The dependence of EC decay rates of H-like ions on the nuclear spins, the ground-state nuclear magnetic moment, and the total angular momentum of the system involved will be discussed. 2)Study of the beta decay properties of the highly charged ions in the path of the astrophysical s-process in the 70 mass region. The half-lives of the nuclei of interest will be measured in highly charged states. These nuclear half-lives will contribute to our understanding of the s-process and the study could help to reproduce the true s-process path in the 70 mass region under the dense and hot stellar environment.

在本申请支持下，我们将利用兰州重离子加速器冷却储存环HIRFL-CSR所提供的先进实验平台对高电荷态离子的beta衰变性质进行系统性研究。基于我们以前的工作基础和HIRFL-CSR近期的实验条件并结合重要的研究前沿，本申请拟在靠近beta稳定线的中等质量核区重点开展以下两方面研究： 1）研究类氦和类氢离子的轨道电子俘获（EC）衰变，测量它们的EC衰变率；结合理论计算深入研究在极高离化态下EC衰变呈现的与传统理论不一致的反常现象，并探讨类氢离子的EC衰变率与核自旋、核基态磁矩以及系统总角动量的相关性。 2）研究70质量区与天体核合成慢中子俘获过程（慢过程）相关的高电荷态离子的beta衰变性质，获取它们的寿命信息，最终指定慢过程在该核区符合天体高温高密环境条件的真实反应路径。

RIBLL2放射性束线的束流传输性能和消色差能力对在兰州HIRFL-CSR大科学装置上开展高水平的核物理实验研究有着非常重要的影响。本课题围绕RIBLL2次级束流线的优化升级问题，结合重离子测量、探测器技术、和真空技术等学科，从束流如何实现优化、束线探测器的选用、和新实验终端等三个方面开展研究和相关建设。首先建立了一套精确高效的运用于RIBLL2的束流优化和光学性质测量方法；进而开展了基于LC延迟电路信号读出的多丝正比室（MWPC）气体探测器对入射位置响应性能的研究，最终研制出适合RIBLL2超高真空环境的高性能MWPC气体探测器并成功进行了测试；完成了RIBLL2终端的建设及相关真空系统的改造；另外，我们利用已有实验数据，通过半经验壳模型研究了A~90质量区核91Ru及其轻N=47同中子素的低位激发能级系统性。综合上述结果，本项目为最终实现RIBLl2的高传输效率，拓展CSR核物理实验研究奠定了坚实的工作基础。