Lifetime of the singly charged 229Th nuclear isomer
Abstract
The nucleus of thorium-229 (229Th) has an exceptionally low-energy isomeric state (229mTh). Because its excitation energy is close to the energy levels of valence electrons, the lifetime of 229mTh varies substantially depending on its electronic state. Although internal conversion and radiative decay were recently observed, the electronic bridge decay of 229mTh, a higher-order decay process through an electronic transition, has not yet been confirmed. A promising candidate to search for this decay channel is singly charged 229mTh+ in the electronic ground state. Here we produce 229mTh+ by a charge exchange reaction in an ion trap and detect the isomers through measuring the electrons emitted from internal conversion processes. We determined the half-life of 229mTh+ to be 0.46(8) s. Our result differs by several orders of magnitude from the half-lives of internal conversion and radiative decay, indirectly suggesting the existence of the electronic bridge decay of 229mTh. This will enable the direct observation and further investigation of the electronic bridge process, which will contribute to understanding nuclear-electron interactions and accelerating nuclear deexcitation in the operation of a thorium-based nuclear clock.
Versions
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BibTeX
@misc{shigekawa2026lifetime,
title = {{Lifetime of the singly charged $^229$Th nuclear isomer}},
author = {Y. Shigekawa and A. Yamaguchi and K. Tokoi and N. Sato and H. Kikunaga and K. Shirasaki and Y. Kasamatsu and M. Wada and H. Haba},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.31009},
eprint = {2610.31009},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.31009},
}
RIS
TY - UNPB
TI - Lifetime of the singly charged ^229Th nuclear isomer
AU - Y. Shigekawa
AU - A. Yamaguchi
AU - K. Tokoi
AU - N. Sato
AU - H. Kikunaga
AU - K. Shirasaki
AU - Y. Kasamatsu
AU - M. Wada
AU - H. Haba
PY - 2026
DA - 2026/10/22
PB - arXiv
DO - 10.48550/arxiv.2610.31009
UR - https://arxiv.org/abs/2610.31009
AB - The nucleus of thorium-229 (^229Th) has an exceptionally low-energy isomeric state (^229mTh). Because its excitation energy is close to the energy levels of valence electrons, the lifetime of ^229mTh varies substantially depending on its electronic state. Although internal conversion and radiative decay were recently observed, the electronic bridge decay of ^229mTh, a higher-order decay process through an electronic transition, has not yet been confirmed. A promising candidate to search for this decay channel is singly charged ^229mTh^+ in the electronic ground state. Here we produce ^229mTh^+ by a charge exchange reaction in an ion trap and detect the isomers through measuring the electrons emitted from internal conversion processes. We determined the half-life of ^229mTh^+ to be 0.46(8) s. Our result differs by several orders of magnitude from the half-lives of internal conversion and radiative decay, indirectly suggesting the existence of the electronic bridge decay of ^229mTh. This will enable the direct observation and further investigation of the electronic bridge process, which will contribute to understanding nuclear-electron interactions and accelerating nuclear deexcitation in the operation of a thorium-based nuclear clock.
ER -