X-ray pumping of the 229Th nuclear clock isomer
X-ray pumping of the 229Th nuclear clock isomer
复制标题
DOI：
10.1038/s41586-019-1542-3
复制
发表时间：
2019-09-12
期刊：
影响因子：
64.8
通讯作者：
Yoshimura, Koji
中科院分区：
文献类型：
--
作者：
Masuda, Takahiko;Yoshimi, Akihiro;Yoshimura, Koji
钍-229的亚稳态第一激发态，Th-229 m，仅比原子核基态（1-4）高出几个电子伏特，并且可以通过真空紫外激光获得。以原子激光光谱学的精度操纵Th-229核态的能力（5）开辟了几个前景（6），从物理学中基本相互作用的研究（7，8）到紧凑和强大的核钟等应用（5，9，10）。然而，异构体的直接光激发及其辐射衰减到基态尚未被观察到，并且几个关键的核结构参数-例如Th-229的低核能级的确切能量和半衰期-仍然未知（11）。在这里，我们提出了积极的光泵浦到Th-229 m，实现使用窄带29 kiloelectronvolt同步辐射共振激发Th-229的第二激发态，然后主要衰变成异构体。我们确定的共振能量的准确度为0.07电子伏特，测量的半衰期为82.2皮秒和1.70 nanoelectronvolts的激发线宽，并提取的分支比的第二激发态到地面和异构状态。这些测量使我们能够通过将它们与过去40年收集的伽马光谱数据相结合来限制Th-229 m异构体的能量。
The metastable first excited state of thorium-229, Th-229m, is just a few electronvolts above the nuclear ground state(1-4) and is accessible by vacuum ultraviolet lasers. The ability to manipulate the Th-229 nuclear states with the precision of atomic laser spectroscopy(5) opens up several prospects(6), from studies of fundamental interactions in physics(7,8) to applications such as a compact and robust nuclear clock(5,9,10). However, direct optical excitation of the isomer and its radiative decay to the ground state have not yet been observed, and several key nuclear structure parameters-such as the exact energies and half-lives of the low-lying nuclear levels of Th-229-remain unknown(11). Here we present active optical pumping into Th-229m, achieved using narrow-band 29-kiloelectronvolt synchrotron radiation to resonantly excite the second excited state of Th-229, which then decays predominantly into the isomer. We determine the resonance energy with an accuracy of 0.07 electronvolts, measure a half-life of 82.2 picoseconds and an excitation linewidth of 1.70 nanoelectronvolts, and extract the branching ratio of the second excited state into the ground and isomeric state. These measurements allow us to constrain the Th-229m isomer energy by combining them with gamma-spectroscopy data collected over the past 40 years.