Progress made by the Precision Measurement Institute in Thorium Ion Trapping Research

Recently, the Cold Molecular Ion Research Group of the Institute of Precision Measurement has made significant progress in the loading, trapping, and recognition of thorium ions. The related research results have been published as cover and selected articles in the international physics journal Journal of Applied Physics, titled "Loading and identifying variable charged thorium ions in a linear ion trap with a time of flight mass spectrometer".

In recent years, the measurement of the first excited state energy of thorium-229 atomic nuclei has become a frontier and hotspot in precision measurement physics research. The energy of the first excited state of thorium-229 atomic nucleus is only about 8.3 eV higher than that of the ground state, and the corresponding radiation transition line width is about 10-4? Hz。 At present, thorium-229 is the only nuclide confirmed to be capable of using laser to regulate nuclear energy levels and achieve nuclear clocks.

The research team successfully trapped and accumulated thorium ions in an ion trap using a dynamic loading combined with buffer gas collision cooling method [2]. Meanwhile, the self-developed ion trap time-of-flight mass spectrometry combined system was used to analyze the quantity, velocity distribution, and trapping lifetime of thorium ions. The relevant achievements have laid the technical foundation for further exciting thorium-229 nuclear transitions through electron bridge processes [3].

PhD students Li Lin and Li Zi from the Institute of Precision Measurement are the co first authors of this article, Associate Researcher Hua Xia is the co author, and Researcher Tong Xin is the corresponding author.

This work has been supported by the National Natural Science Foundation of China and the National Key Research and Development Program.

［1］ Zi Li，Lin Li，Xia Hua，and Xin Tong，Loading and identifying various charged thorium ions in a linear ion trap with a time－of－flight mass spectrometer，J． Appl． Phys． 135，144402 （2024）．

［2］ Lin Li，Zi Li，Xia Hua，and Xin Tong，Dynamic laser ablation loading of a linear Paul trap，arXiv：2402．17981，J． Phys． D accepted （2024）．

［3］ Lin Li，Zi Li，Chen Wang，Wen－Ting Gan，Xia Hua，and Xin Tong，Scheme for the excitation of thorium－229 nuclei based on electronic bridge excitation，Nucl． Sci． Tech． 34，24 （2023）．

Cover and Selected Articles of the International Journal of Applied Physics

Source: Institute of Precision Measurement Science and Technology Innovation, Chinese Academy of Sciences