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Theoretical evaluation of decay mode of Th229m in solid samples

Ryotaro Masuda (益田遼太郎)1,*, Tomoya Naito (内藤智也)2,3,4,†, Masashi Kaneko (金子政志)1, Hiroyuki Kazama (風間裕行)1, So Hashiba (橋場奏)1, Kosuke Misawa (三澤宏介)1, and Yoshitaka Kasamatsu (笠松良崇)1

  • *Contact author: masudar21@chem.sci.osaka-u.ac.jp
  • †Contact author: tnaito@ribf.riken.jp
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Phys. Rev. Research 7, 043217 – Published 24 November, 2025

DOI: https://doi.org/10.1103/hn1b-51yx

Abstract

The excitation energy of Th229m is extremely low at 8.4eV; thus, this isotope exhibits changes in its decay modes depending on the chemical state, specifically the outermost electronic states. However, the reported half-lives of the γ-ray transition are not consistent among the previous experiments. In this study, we investigate the chemical states of Th229m by density functional theory calculations. Based on these results, we evaluate the relationship between the experimental half-life of each sample and the electronic state of Th. The calculation results indicate that ion trap method, CaF2 model, and MgF2 one decay only via the γ-ray transition, whereas LiSrAlF6 one decays via the γ-ray transition and has a possibility of decay via internal conversion and electron bridge.

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Phys. Rev. Research 7, 043217– Published 24 November, 2025
  • Received 18 July 2025
  • Accepted 3 October 2025
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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

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