Article title: Commissioning of a high-resolution collinear laser spectroscopy apparatus with a laser ablation ion source

新发展的高分辨共线激光谱系统投入运行

DOI: https://doi.org/10.1007/s41365-022-00992-5

One sentence summary:

一句话概要：

Advanced studies of short-lived exotic nuclei at the domestic RIB facilities can now be supported by a newly commissioned collinear laser spectroscopy (CLS) apparatus in Peking University.

北京大学新建成的共线激光核谱仪(CLS)将为在我国放射性核束装置上开展不稳定核性质和结构研究开辟新的机遇。

http://www.nst.sinap.ac.cn/newsDetails/112/26477/en/

The Novelty (What)

创新性（主要内容）

As an initial step to fully leverage the available radioactive ion beam facilities and resources, this study developed a collinear laser spectroscopy (CLS) apparatus combined with an offline laser ablation ion source at Peking University. The CLS was commissioned using a bunched stable calcium ion beam being accelerated up to 20 keV, with a pulse width of approximately 10 μs. This CLS, integrated with the ion source and an anti-collinear laser system, has enabled high-resolution measurements of the hyperfine structure spectra of stable ^40,42,44,48Ca isotopes. With its successful commissioning, the CLS is ready for laser spectroscopy measurement of unstable nuclei at radioactive ion beam (RIB) facilities in China, paving the way for further developing higher-sensitivity collinear resonance ionization spectroscopy techniques.

作为利用放射性束测量不稳定核基本性质的第一步，首先在北京大学利用激光溅射离子源产生的稳定脉冲离子束对共线激光谱系统进行了完整测试。 基于离子束与激光束反共线的方法实现了对稳定的^{40、42、44、48}Ca同位素的超精细结构光谱的高分辨率测量。 此共线激光谱系统将被应用到国内的放射性核束装置，用于不稳定核素的基本性质和结构研究。此工作也为后续继续发展更高灵敏度的共线共振电离谱技术奠定基础。

The Background (Why)

研究背景（主要原因）

The fundamental properties of atomic nuclei, such as nuclear spins, magnetic dipole moments, electric quadrupole moments, and mean-squared charge radii, are the essential experimental observables in studying the exotic nuclear structure and nucleon-nucleon interactions. Despite having various experimental methods to measure these nuclear properties, CLS is one of the most sophisticated experimental techniques available to simultaneously measure these properties in a nuclear-model independent way. This is realized by probing the subtle hyperfine effects, only as small as one part in a million compared with the total atomic transition frequency, resulting from the interaction between the atomic nucleus and surrounding electrons. CLS system has been set up in various RIB facilities worldwide to explore the exotic structure of radioactive isotopes. Lanzhou's HIRFL-RIBLL and Beijing's BRIF are among the uprising RIB facilities with short-lived isotopes ready for in-depth nuclear structure studies. The CLS, however, has not yet been involved in nuclear physics research at the domestic RIB facilities so far. The CLS apparatus developed by this study thus represents new opportunities for advanced studies of the nuclear properties of unstable nuclei at the RIB facilities in China.

不稳定原子核的基本性质（例如自旋、磁矩、电四极矩和均方电荷半径）是研究原子核奇特结构和核子-核子相互作用的重要实验观测量。共线激光谱技术是能够有效测量不稳定核多个基本性质的关键技术，在确定不稳定核基本性质方面有独特和显著的优势。这种技术通过探测不稳定原子核外电子能级的超精细分裂和移位来提取原子核的多个基本性质。共线激光谱技术近年来在国际核物理大科学装置上快速发展和广泛部署。我国已有中国科学院近代物理研究所 (兰州) 的HIRFL-RIBLL和中国原子能科学研究院的BRIF等放射性核束装置，但在这些装置上还未建立用于不稳定核性质研究的共线激光谱实验平台。 因此，本工作中发展的共线激光谱系统将为在中国放射性核束装置上开展不稳定核基本性质和奇特结构的研究提供了新的机遇。

The SDG impact (Big Why)

SDG影响力（研究意义）

The unexpected new phenomena of unstable nuclei have been continuously unveiled when the study reaches the exotic isotopes far from the beta-stability line. By exploring short-lived nuclei produced artificially at RIB facilities, this study helps scientists understand the rich, complex, and even unexplored exotic structure of atomic nuclei and the nucleon-nucleon interactions. Ultimately, this would unveil the puzzle: where and how heavy matter forms in the universe (UNSDG 9: Industry, Innovation & Infrastructure).

远离β稳定线的不稳定原子核中不断展现出新的物理规律和奇特结构。 实验上，不断探索放射性核束装置上产生的短寿命原子核的性质，将有助于科学家更深入地理解核子核子间相互作用和弱束缚核中丰富且复杂的奇特结构。 最终，这些不稳定原子核的研究也将有助于解开“宇宙中重元素在何处以及如何形成的？”等谜团（联合国可持续发展目标9：工业、创新和基础设施）

研究课题组：

北京大学物理学院和核物理与核技术国家重点实验室-激光核谱与核性质课题组（课题组负责人杨晓菲）。本课题组于2018年组建，主要工作是在国内发展先进激光核谱技术，并依托国内外大科学装置开展不稳定核性质和奇特结构研究。目前主要成员包括1位PI，2位教师，6名博士研究生和若干本科生等。