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Energy of the $$^{229}$$Th nuclear clock isomer determined by absolute $$gamma$$-ray energy difference

Yamaguchi, Atsushi*; Muramatsu, Haruka*; Hayashi, Tasuku*; Yuasa, Naoki*; Nakamura, Keisuke ; Takimoto, Misaki ; Haba, Hiromitsu*; Konashi, Kenji*; Watanabe, Makoto*; Kikunaga, Hidetoshi*; Maehata, Keisuke*; Yamasaki, Noriko*; Mitsuda, Kazuhisa*

The low-lying isomeric state of $$^{229}$$Th provides unique opportunities for high-resolution laser spectroscopy of the atomic nucleus. We determine the energy of this isomeric state by measuring the absolute energy difference between two $$gamma$$-decays from the 29.2-keV second-excited state. A transition-edge sensor microcalorimeter was used to measure the absolute energy of the 29.2-keV $$gamma$$-ray with improved precision. Together with the cross-band transition energy (29.2 keV$$rightarrow$$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$$pm$$0.88 eV. Our result is in agreement with latest measurements based on different experimental techniques, which further confirms that the isomeric state of $$^{229}$$Th is in the laser-accessible vacuum ultraviolet range.



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Category:Physics, Multidisciplinary



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