Energy of the Th 229 Nuclear Clock Isomer Determined by Absolute γ -ray Energy Difference

A. Yamaguchi, H. Muramatsu, T. Hayashi, N. Yuasa, K. Nakamura, M. Takimoto, H. Haba, K. Konashi, M. Watanabe, H. Kikunaga, K. Maehata, N. Y. Yamasaki, K. Mitsuda

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10 Citations (Scopus)


The low-lying isomeric state of Th229 provides unique opportunities for high-resolution laser spectroscopy of the atomic nucleus. We determine the energy of this isomeric state by taking the absolute energy difference between the excitation energy required to populate the 29.2-keV state from the ground state and the energy emitted in its decay to the isomeric excited state. A transition-edge sensor microcalorimeter was used to measure the absolute energy of the 29.2-keV γ ray. Together with the cross-band transition energy (29.2 keV→ground) and the branching ratio of the 29.2-keV state measured in a recent study, the isomer energy was determined to be 8.30±0.92 eV. Our result is in agreement with the latest measurements based on different experimental techniques, which further confirms that the isomeric state of Th229 is in the laser-accessible vacuum ultraviolet range.

Original languageEnglish
Article number222501
JournalPhysical review letters
Issue number22
Publication statusPublished - 2019 Nov 26

ASJC Scopus subject areas

  • Physics and Astronomy(all)

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