Attempt to Photo-Excitation of Ultra-Low-Energy Excited Nuclei Th-229

• Project/Area Number: 18K18759
• Research Category: Grant-in-Aid for Challenging Research (Exploratory)
• Allocation Type: Multi-year Fund
• Review Section: Medium-sized Section 15:Particle-, nuclear-, astro-physics, and related fields
• Research Institution: Tohoku University
• Principal Investigator: KIKUNAGA Hidetoshi 東北大学, 電子光理学研究センター, 准教授 (00435645)
• Project Period (FY): 2018-06-29 – 2022-03-31
• Project Status: Completed (Fiscal Year 2021)
• Budget Amount: ¥6,240,000 (Direct Cost: ¥4,800,000、Indirect Cost: ¥1,440,000); Fiscal Year 2020: ¥910,000 (Direct Cost: ¥700,000、Indirect Cost: ¥210,000); Fiscal Year 2019: ¥1,170,000 (Direct Cost: ¥900,000、Indirect Cost: ¥270,000); Fiscal Year 2018: ¥4,160,000 (Direct Cost: ¥3,200,000、Indirect Cost: ¥960,000)
• Keywords: 核異性体 / トリウム / 核励起 / Th-229

Outline of Final Research Achievements

Thorium with a mass number of 229, has a metastable state (Th-229m) with the lowest excitation energy of any nucleus known to date. The energy is reported to be 7.8 eV, which is about 1/1000 of the excitation energies of other nuclei. Our research is exploring the possibility of direct excitation of Th-229 using electron beams or lasers. In this study, we isolated Th-229 from several U-233 samples and investigated the possibility of using them for Th-229 excitation studies. In addition, we developed an apparatus to measure absorption spectra in the vacuum ultraviolet region and attempted to prepare samples for direct excitation experiments.

Academic Significance and Societal Importance of the Research Achievements

本研究には，数eVの励起エネルギーを持つ特異な原子核状態であるTh-229mの直接励起の観測を目指すという基礎科学的な意義がある。今回，新たに入手することができたTh-229試料は原子核時計を含むTh-229研究に用いられるだけで無く，娘核種に核医学分野で注目されるAc-225など有用RIを含むため，本研究以外にも利用価値は大きい。また，本研究で開発された真空紫外照射・測定装置は，固体試料の真空紫外領域の吸光を簡便に測定することができ，今後目指していくTh-229直接励起研究のための基礎データ取得に役立つ。

Research Products

• [Journal Article] Estimation of radiative half-life of 229mTh by half-life measurement of other nuclear excited states in 229Th (2021)
  • Author(s): Shigekawa Y.、Yamaguchi A.、Suzuki K.、Haba H.、Hiraki T.、Kikunaga H.、Masuda T.、Nishimura S.、Sasao N.、Yoshimi A.、Yoshimura K.
  • Journal Title: Physical Review C Volume: 104 Issue: 2 Pages: 024306-024306
  • DOI: 10.1103/physrevc.104.024306
  • Peer Reviewed
• [Journal Article] Energy of the 229 Th Nuclear Clock Isomer Determined by Absolute γ -ray Energy Difference (2019)
  • Author(s): A. Yamaguchi, H. Muramatsu, T. Hayashi, N. Yuasa, K. Nakamura, M. Takimoto, H. Haba, K. Konashi, M. Watanabe, H. Kikunaga, K. Maehata, N.Y. Yamasaki, and K. Mitsuda
  • Journal Title: PHYSICAL REVIEW LETTERS Volume: 123 Issue: 22 Pages: 222501-222501
  • DOI: 10.1103/physrevlett.123.222501
  • Peer Reviewed
• [Presentation] 原子・原子核励起のための電子線照射装置の開発 (2019)
  • Author(s): 菊永英寿，南部健一
  • Organizer: 日本放射化学会第63回討論会(2019)
• [Presentation] U-233線源の利用 (2019)
  • Author(s): 菊永英寿
  • Organizer: 2019重元素核化学ワークショップ