Development of Th-doped crystal for the study of the isomeric state of the 229Th

2020 Fiscal Year Final Research Report

• Project/Area Number: 19K14740
• Research Category: Grant-in-Aid for Early-Career Scientists
• Allocation Type: Multi-year Fund
• Review Section: Basic Section 15020:Experimental studies related to particle-, nuclear-, cosmic ray and astro-physics
• Research Institution: Okayama University
• Principal Investigator: Hiraki Takahiro 岡山大学, 異分野基礎科学研究所, 特任助教 (40791223)
• Project Period (FY): 2019-04-01 – 2021-03-31
• Keywords: 原子核実験 / トリウム229 / 放射光

Outline of Final Research Achievements

The nucleus of thorium-229 has the lowest first excitation level among all nuclei at about 8 eV. Therefore, it can be excited to this level by a vacuum ultraviolet laser, and various applications are expected. However, laser excitation has not yet been realized, and there are no reports of observation of de-excitation light from the first excited level. In this study, we generated the first excited level of thorium-229 by our original method using the synchrotron radiation facility, SPring-8, and attempted to observe the de-excitation light. We also evaluated the transmittance of a highly 232Th-doped CaF2 target and the degradation effect by X-ray beam irradiation.

Free Research Field

素粒子物理

Academic Significance and Societal Importance of the Research Achievements

現在周波数標準で最も精度が良いものは原子の電子遷移を用いた原子時計である。これに対し、トリウム(原子番号90)の同位体の１つであるトリウム229原子核を用いた「原子核時計」の開発に成功すれば、より高精度な時計（周波数標準）が実現できると期待されている。しかしそのために必要なトリウム229原子核の第一励起準位からの脱励起光の観測に成功した例は未だない。本研究では脱励起光探索を高感度で行うためのセットアップを構築し、脱励起光探索実験を遂行し、更に感度を向上させるための手法を研究した。