X-ray pumping of the 229Th nuclear clock isomer

Takahiko Masuda, Akihiro Yoshimi, Akira Fujieda, Hiroyuki Fujimoto, Hiromitsu Haba, Hideaki Hara, Takahiro Hiraki, Hiroyuki Kaino, Yoshitaka Kasamatsu, Shinji Kitao, Kenji Konashi, Yuki Miyamoto, Koichi Okai, Sho Okubo, Noboru Sasao (), Makoto Seto, Thorsten Schumm, Yudai Shigekawa, Kenta Suzuki, Simon Stellmer, Kenji Tamasaku, Satoshi Uetake, Makoto Watanabe, Tsukasa Watanabe, Yuki Yasuda, Atsushi Yamaguchi, Yoshitaka Yoda, Takuya Yokokita, Motohiko Yoshimura and Koji Yoshimura ()
Additional contact information
Takahiko Masuda: Okayama University
Akihiro Yoshimi: Okayama University
Akira Fujieda: Okayama University
Hiroyuki Fujimoto: National Institute of Advanced Industrial Science and Technology (AIST)
Hiromitsu Haba: RIKEN
Hideaki Hara: Okayama University
Takahiro Hiraki: Okayama University
Hiroyuki Kaino: Okayama University
Yoshitaka Kasamatsu: Osaka University
Shinji Kitao: Kyoto University
Kenji Konashi: Tohoku University
Yuki Miyamoto: Okayama University
Koichi Okai: Okayama University
Sho Okubo: Okayama University
Noboru Sasao: Okayama University
Makoto Seto: Kyoto University
Thorsten Schumm: Institute for Atomic and Subatomic Physics
Yudai Shigekawa: Osaka University
Kenta Suzuki: Okayama University
Simon Stellmer: Institute for Atomic and Subatomic Physics
Kenji Tamasaku: RIKEN SPring-8 Center
Satoshi Uetake: Okayama University
Makoto Watanabe: Tohoku University
Tsukasa Watanabe: National Institute of Advanced Industrial Science and Technology (AIST)
Yuki Yasuda: Osaka University
Atsushi Yamaguchi: RIKEN
Yoshitaka Yoda: Japan Synchrotron Radiation Research Institute
Takuya Yokokita: RIKEN
Motohiko Yoshimura: Okayama University
Koji Yoshimura: Okayama University

Nature, 2019, vol. 573, issue 7773, 238-242

Abstract: Abstract The metastable first excited state of thorium-229, 229mTh, is just a few electronvolts above the nuclear ground state1–4 and is accessible by vacuum ultraviolet lasers. The ability to manipulate the 229Th nuclear states with the precision of atomic laser spectroscopy5 opens up several prospects6, from studies of fundamental interactions in physics7,8 to applications such as a compact and robust nuclear clock5,9,10. 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 229Th—remain unknown11. Here we present active optical pumping into 229mTh, achieved using narrow-band 29-kiloelectronvolt synchrotron radiation to resonantly excite the second excited state of 229Th, 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 229mTh isomer energy by combining them with γ-spectroscopy data collected over the past 40 years.

Date: 2019
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DOI: 10.1038/s41586-019-1542-3

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