The isotope 229Th is the only nucleus known to possess an excited state 229mTh in the energy range of a few electronvolts—a transition energy typical for electrons in the valence shell of atoms, but about four orders of magnitude lower than typical nuclear excitation energies. Of the many applications that have been proposed for this nuclear system, which is accessible by optical methods, the most promising is a highly precise nuclear clock that outperforms existing atomic timekeepers. Here we present the laser spectroscopic investigation of the hyperfine structure of the doubly charged 229mTh ion and the determination of the fundamental nuclear properties of the isomer, namely, its magnetic dipole and electric quadrupole moments, as well as its nuclear charge radius. Following the recent direct detection of this long-sought isomer, we provide detailed insight into its nuclear structure and present a method for its non-destructive optical detection.Laser spectroscopy is used to investigate the hyperfine structure and determine the fundamental nuclear properties of the isomer 229mTh, the strongest candidate for the realization of a nuclear clock.

中文翻译：

---

核钟异构体 229mTh 的激光光谱表征

同位素 229Th 是已知的唯一在几个电子伏特的能量范围内具有激发态 229mTh 的原子核——这是原子价壳中电子的典型跃迁能，但比典型的核激发能低约四个数量级。在为这种可通过光学方法访问的核系统提出的许多应用中，最有前途的是一种高精度的核时钟，其性能优于现有的原子计时器。在这里，我们介绍了双电荷 229mTh 离子的超精细结构的激光光谱研究，并确定了异构体的基本核性质，即磁偶极子和电四极矩，以及其核电荷半径。在最近直接检测到这种长期寻找的异构体之后，