2026-04-14 理化学研究所,筑波大学,大阪大学,東北大学,高エネルギー加速器研究機構
電子架橋遷移の概要
＜関連情報＞
- https://www.riken.jp/press/2026/20260414_3/index.html
- https://www.nature.com/articles/s41567-026-03251-1
Lifetime of the singly charged 229Th nuclear isomer
Y. Shigekawa,A. Yamaguchi,K. Tokoi,N. Sato,H. Kikunaga,K. Shirasaki,Y. Kasamatsu,M. Wada & H. Haba
Nature Physics Published:14 April 2026
DOI:https://doi.org/10.1038/s41567-026-03251-1
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.
