Observing the electron bridge process of the Th-229 isomer utilizing ion-molecule reactions

• Project/Area Number: 20K14500
• 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: Institute of Physical and Chemical Research
• Principal Investigator: Shigekawa Yudai 国立研究開発法人理化学研究所, 仁科加速器科学研究センター, 特別研究員 (60845626)
• Project Period (FY): 2020-04-01 – 2023-03-31
• Project Status: Completed (Fiscal Year 2022)
• Budget Amount: ¥4,160,000 (Direct Cost: ¥3,200,000、Indirect Cost: ¥960,000); Fiscal Year 2022: ¥1,300,000 (Direct Cost: ¥1,000,000、Indirect Cost: ¥300,000); Fiscal Year 2021: ¥1,300,000 (Direct Cost: ¥1,000,000、Indirect Cost: ¥300,000); Fiscal Year 2020: ¥1,560,000 (Direct Cost: ¥1,200,000、Indirect Cost: ¥360,000)
• Keywords: トリウム229 / 電子架橋遷移 / 核異性体 / イオントラップ / RFカーペット / ガスセル / イオン分子反応 / 原子核時計 / 電子架橋

Outline of Research at the Start

Th-229m（Th-229原子核の第一励起準位）は8.3 eV程度の極端に低い励起エネルギーを持つため，「電子架橋遷移」という特異な過程により脱励起する可能性が予測されている．電子架橋遷移では，原子核の励起エネルギーの一部が軌道殻電子の電子遷移に費やされ，余剰分のエネルギーが光子として放出される．本研究では，世界で初めて電子架橋遷移を明確に観測し，電子架橋遷移の性質を解明することを目指す．そのために様々な電子状態のTh-229mイオンをイオンー分子反応によりイオントラップ中で生成・制御する技術を開発し，電子架橋遷移由来の光子を放出するTh-229mイオンを探索する．

Outline of Final Research Achievements

The first excited state of the Th-229 nucleus, Th-229m, has an excitation energy of 8.3 eV. This extremely low isomeric energy would allow the deexcitation by the electronic bridge process, which is a higher order process than the gamma-ray emission and the internal conversion process. In this project, we aim to observe the electronic bridge process for the first time using singly charged Th-229m ions produced by the reaction between doubly charged Th-229m ions and reactive gaseous molecules. We first developed an ion-extraction and ion-trap apparatus, and then we successfully extracted and trapped doubly charged Th-229m ions recoiling out of a U-233 source. Moreover, we were able to produce singly charged Th-229m ions by the chemical reaction in the ion trap.

Academic Significance and Societal Importance of the Research Achievements

本研究課題では、2価や3価のTh-229mイオンの引き出しと、イオン分子反応を利用した1価のTh-229mイオンの生成に成功した。1価のTh-229mイオンでは電子架橋遷移によって壊変する可能性が高いと理論的に予測されているため、本研究で開発した装置を用いることで、近日中に新規の核現象である電子架橋遷移を世界で初めて観測できる期待が高まる。一方、本研究で開発された多価のTh-229イオン引き出し技術は、超高精密なTh-229原子核時計の実現に極めて重要である。本技術を利用して原子核時計を開発できれば、基礎物理学や測地学などの発展に大きく貢献できると期待される。

Research Products

• [Journal Article] Tumor Targeting of 211At-Labeled Antibody under Sodium Ascorbate Protection against Radiolysis (2023)
  • Author(s): Takashima Hiroki、Ohnuki Kazunobu、Manabe Shino、Koga Yoshikatsu、Tsumura Ryo、Anzai Takahiro、Wang Yang、Yin Xiaojie、Sato Nozomi、Shigekawa Yudai、Nambu Akihiro、Usuda Sachiko、Haba Hiromitsu、Fujii Hirofumi、Yasunaga Masahiro
  • Journal Title: Molecular Pharmaceutics Volume: 20 Issue: 2 Pages: 1156-1167
  • DOI: 10.1021/acs.molpharmaceut.2c00869
  • Peer Reviewed / Open Access
• [Journal Article] Estimation of radiative half-life of 229mTh by half-life measurement of other nuclear excited states in 229Th (2022)
  • Author(s): Y. Shigekawa, A. Yamaguchi, K. Suzuki, H. Haba, T. Hiraki, H. Kikunaga, T. Masuda, S. Nishimura, N. Sasao, A. Yoshimi, and K. Yoshimura
  • Journal Title: RIKEN Accel. Prog. Rep. Volume: 55
  • Peer Reviewed / Open Access
• [Journal Article] Development of RF carpet gas cell for extracting 229mTh ions (2022)
  • Author(s): Y. Shigekawa, K. Tokoi, A. Yamaguchi, N. Sato, M. Wada, and H. Haba
  • Journal Title: RIKEN Accel. Prog. Rep. Volume: 55 Pages: 127-127
  • Peer Reviewed / Open Access
• [Journal Article] Development of a photon measurement apparatus for observing the radiative decay of 229mTh produced from 229Pa (2022)
  • Author(s): Y. Shigekawa, Y. Wang, X. Yin, A. Nambu, T. Yokokita, and H. Haba
  • Journal Title: RIKEN Accel. Prog. Rep. Volume: 55 Pages: 124-124
  • Peer Reviewed / Open Access
• [Journal Article] Surface ionization of protactinium toward implanting 229Pa into a CaF2 crystal (2022)
  • Author(s): Y. Shigekawa, and H. Haba
  • Journal Title: RIKEN Accel. Prog. Rep. Volume: 55 Pages: 126-126
  • Peer Reviewed / Open Access
• [Journal Article] Probing Optimal Reaction Energy for Synthesis of Element 119 from ⁵¹V+²⁴⁸Cm Reaction with Quasielastic Barrier Distribution Measurement (2022)
  • Author(s): M. Tanaka and Y. Shigekawa (34人中29番目) et al.
  • Journal Title: Journal of the Physical Society of Japan Volume: 91 Issue: 8 Pages: 084201-084201
  • DOI: 10.7566/jpsj.91.084201
  • Peer Reviewed / Open Access / Int'l Joint Research
• [Journal Article] Coprecipitation with samarium hydroxide using multitracer produced through neutron-induced fission of 235U toward chemical study of heavy elements (2022)
  • Author(s): Kasamatsu Yoshitaka、Nagase Masahiro、Ninomiya Hidemi、Watanabe Eisuke、Shigekawa Yudai、Kondo Narumi、Takamiya Koichi、Ohtsuki Tsutomu、Shiohara Naoya、Shinohara Atsushi
  • Journal Title: Applied Radiation and Isotopes Volume: 179 Pages: 110006-110006
  • DOI: 10.1016/j.apradiso.2021.110006
  • Peer Reviewed / Open Access
• [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] Production and photon measurement of 229Pa toward the observation of radiative decay of 229mTh (2021)
  • Author(s): Y. Shigekawa, T. Yokokita, Y. Komori, and H. Haba
  • Journal Title: RIKEN Accel. Prog. Rep. Volume: 54 Pages: 143-144
  • Peer Reviewed
• [Journal Article] Measurement of Extraction Time and Efficiency of 220Rn Ions Using a Cryogenic RF-Carpet Gas Cell for the Chemistry of Superheavy Elements (2021)
  • Author(s): Y. Shigekawa, A. Yamaguchi, N. Sato, A. Takamine, M. Wada, and H. Haba
  • Journal Title: RIKEN Accel. Prog. Rep. Volume: 54 Pages: 145-146
  • Peer Reviewed
• [Journal Article] Anion- and cation-exchange studies of Zr, Hf, and Th using ion-exchange resin and fiber in H2SO4 media for chemical characterization of sulfate complex of Rf (2021)
  • Author(s): E. Watanabe, Y. Kasamatsu, T. Yokokita, S. Hayami, K. Tonai, H. Ninomiya, N. Kondo, Y. Shigekawa, H. Haba, Y. Kitagawa, M. Nakano, and A. Shinohara
  • Journal Title: Solvent Extr. Ion Exch. Volume: 未定 Issue: 6 Pages: 1-16
  • DOI: 10.1080/07366299.2021.2020956
  • Peer Reviewed
• [Journal Article] Co-precipitation behaviour of single atoms of rutherfordium in basic solutions (2021)
  • Author(s): Y. Kasamatsu, K. Toyomura, H. Haba, T. Yokokita, A. Kino, Y. Yasuda, Y. Komori, J. Kanaya, M.H. Huang, M. Murakami, H. Kikunaga, E. Watanabe, T. Yoshimura, K. Morita, T. Mitsugashira, K. Takamiya, T. Ohtsuki, A. Shinohara
  • Journal Title: NATURE CHEMISTRY Volume: 13 Issue: 3 Pages: 226-230
  • DOI: 10.1038/s41557-020-00634-6
  • Peer Reviewed
• [Journal Article] Absolute X-ray energy measurement using a high-accuracy angle encoder (2021)
  • Author(s): Masuda Takahiko、Watanabe Tsukasa、Beeks Kjeld、Fujimoto Hiroyuki、Hiraki Takahiro、Kaino Hiroyuki、Kitao Shinji、Miyamoto Yuki、Okai Koichi、Sasao Noboru、Seto Makoto、Schumm Thorsten、Shigekawa Yudai、Tamasaku Kenji、Uetake Satoshi、Yamaguchi Atsushi、Yoda Yoshitaka、Yoshimi Akihiro、Yoshimura Koji
  • Journal Title: Journal of Synchrotron Radiation Volume: 28 Issue: 1 Pages: 111-119
  • DOI: 10.1107/s1600577520014526
  • NAID: 120006956810
  • Peer Reviewed / Open Access / Int'l Joint Research
• [Journal Article] Development of a retarding-field type magnetic bottle spectrometer for studying the internal-conversion process of 235mU (2020)
  • Author(s): Shigekawa Y.、Kasamatsu Y.、Yamakita Y.、Yasuda Y.、Watanabe E.、Kondo N.、Haba H.、Shinohara A.
  • Journal Title: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment Volume: 976 Pages: 164207-164207
  • DOI: 10.1016/j.nima.2020.164207
  • Peer Reviewed
• [Journal Article] Half-life determination of nuclear excited states of 229Th by the coincidence measurement between α particles and γ rays from 233U (2020)
  • Author(s): Y. Shigekawa, A. Yamaguchi, K. Suzuki, H. Haba, T. Hiraki, H. Kikunaga, T. Masuda, S. Nishimura, N. Sasao, A. Yoshimi, and K. Yoshimura
  • Journal Title: RIKEN Accel. Prog. Rep. Volume: 53 Pages: 51-51
  • Peer Reviewed
• [Journal Article] Development of an RF-carpet gas cell for the chemistry of superheavy elements (2020)
  • Author(s): Y. Shigekawa, A. Yamaguchi, N. Sato, A. Takamine, M. Wada, and H. Haba
  • Journal Title: RIKEN Accel. Prog. Rep. Volume: 53 Pages: 168-168
  • Peer Reviewed
• [Journal Article] Solvent Extraction of Zr and Hf from HCl by Aliquat 336 using a Flow-Type Extraction Apparatus Toward Online Chemical Studies of Element 104, Rutherfordium (2020)
  • Author(s): Kasamatsu Yoshitaka、Kondo Narumi、Nakamura Kouhei、Kuboki Yuki、Ninomiya Hidemi、Shigekawa Yudai、Watanabe Eisuke、Yasuda Yuki、Toyomura Keigo、Nagase Masahiro、Yokokita Takuya、Komori Yukiko、Haba Hiromitsu、Yoshimura Takashi、Itabashi Hideyuki、Shinohara Atsushi
  • Journal Title: Solvent Extraction and Ion Exchange Volume: 38 Issue: 3 Pages: 318-327
  • DOI: 10.1080/07366299.2020.1726075
  • Peer Reviewed
• [Journal Article] Production of Bh266 in the Cm248(Na23,5n)Bh266 reaction and its decay properties (2020)
  • Author(s): Haba H.他（Shigekawa Y. 19番目）
  • Journal Title: Physical Review C Volume: 102 Issue: 2 Pages: 024625-024625
  • DOI: 10.1103/physrevc.102.024625
  • Peer Reviewed / Int'l Joint Research
• [Presentation] Progress toward observing γ-rays emitted from 229mTh by doping fluoride crystals with 229Pa (2023)
  • Author(s): Yudai Shigekawa, Wang Yang, Yin Xiaojie, Akihiro Nambu, Hiromitsu Haba
  • Organizer: 5th International Conference on Application of RadiotraCers and Energetic Beams in Sciences (ARCEBS 2023)
  • Int'l Joint Research
• [Presentation] トリウム229アイソマー状態からの脱励起真空紫外光の探索 (2023)
  • Author(s): 平木貴宏, Kjeld Beeks, 藤本弘之, 福永優太, 管明, 羽場宏光, 笠松良崇, 北尾真司, 小無健司, 増田孝彦, 永澤延元, 岡井晃一, 笹尾登, Fabian Schaden, Thorsten Schumm, 瀬戸誠, 重河優大, 高取沙悠理, 玉作賢治, 植竹智, 渡部司, 渡部信, 山口敦史, 安田勇輝, 依田芳卓, 吉見彰洋, 吉村浩司, 吉村太彦
  • Organizer: 日本物理学会2023年春季大会
• [Presentation] 固体原子核時計の実現へ向けた放射光X線を用いたトリウム229結晶の特性評価 (2023)
  • Author(s): 高取沙悠理, Kjeld Beeks, 藤本弘之, 福永優太, 管明, 羽場宏光, 平木貴宏, 笠松良崇, 北尾真司, 小無健司, 増田孝彦, 永澤延元, 岡井晃一, 笹尾登, Fabian Schaden, Thorsten Schumm, 瀬戸誠, 重河優大, 玉作賢治, 植竹智, 渡部司, 渡部信, 山口敦史, 安田勇輝, 依田芳卓, 吉見彰洋, 吉村浩司, 吉村太彦
  • Organizer: 日本物理学会2023年春季大会
• [Presentation] トリウム229アイソマー準位探索のための核共鳴散乱標的の開発 (2023)
  • Author(s): 福永優太, Kjeld Beeks, 藤本弘之, 平木貴宏, 管明, 羽場宏光, 笠松良崇, 北尾真司, 小無健司, 増田孝彦, 永澤延元, 岡井晃一, 笹尾登, Fabian Schaden, Thorsten Schumm, 瀬戸誠, 重河優大, 高取沙悠理, 玉作賢治, 植竹智, 渡部司, 渡部信, 山口敦史, 安田勇輝, 依田芳卓, 吉見彰洋, 吉村浩司, 吉村太彦
  • Organizer: 日本物理学会2023年春季大会
• [Presentation] 原子核時計実現にむけたトリウムイオンのトラップとレーザー分光 (2023)
  • Author(s): 山口敦史, 重河優大, 羽場宏光, 和田道治, 香取秀俊
  • Organizer: レーザー学会学術講演会第43回年次大会
  • Invited
• [Presentation] 超低エネルギー励起核U-235mとTh-229mの核壊変特性に関する研究 (2022)
  • Author(s): 重河優大
  • Organizer: 電気学会2022年度第1回調査専門委員会
  • Invited
• [Presentation] Th-229mのγ線観測に向けたPa-229のフッ化物結晶への導入法及び光子測定装置の開発 (2022)
  • Author(s): 重河優大, Wang Yang, Yin Xiaojie, 南部明弘, 羽場宏光
  • Organizer: 日本放射化学会第66回討論会(2022)
• [Presentation] Laser spectroscopy of triply charged thorium ions towards a nuclear clock (2022)
  • Author(s): A. Yamaguchi, Y. Shigekawa, H. Haba, M. Wada, H. Katori
  • Organizer: URSI-JRSM2022
  • Int'l Joint Research / Invited
• [Presentation] Development of an RF-carpet gas cell to obtain a low-energy thorium ion beam (2022)
  • Author(s): A. Yamaguchi, Y. Shigekawa, H. Haba, M. Wada, H. Katori
  • Organizer: Second Workshop of the Center for Time, Constants and Fundamental Symmetries
  • Int'l Joint Research
• [Presentation] 229mThのγ線測定に向けた希ガスマトリックス単離装置の開発 (2022)
  • Author(s): 益田遼太郎, 安田勇輝, 澤村慶, 重河優大, 宮本祐樹, 吉村浩司, 篠原厚, 笠松 良崇
  • Organizer: 日本放射化学会第66回討論会(2022)
• [Presentation] トリウム229アイソマー状態からの脱励起に伴う真空紫外光の探索 (2022)
  • Author(s): 岡井晃一, Kjeld Beeks, 藤本弘之, 福永優太, 管明, 羽場宏光, 原秀明, 平木貴宏, 稲垣新, 小早川大貴, 笠松良崇, 北尾真司, 小無健司, 増田孝彦, 宮本祐樹, 笹尾登, Thorsten Schumm, 瀬戸誠, 重河優大, 高取沙悠理, 玉作賢治, 植竹智, 渡部司, 渡部信, 山口敦史, 安田勇輝, 依田芳卓, 吉見彰洋, 吉村浩司, 吉村太彦
  • Organizer: 日本物理学会 2022年秋季大会
• [Presentation] 原子核時計実現にむけたトリウムイオントラップ装置の開発 (2022)
  • Author(s): 山口敦史, 重河優大, 羽場宏光, 和田道治, 香取秀俊
  • Organizer: 日本物理学会2022年秋季大会
• [Presentation] Th-229mの壊変特性の解明に向けた高周波イオン収集・質量分離装置の開発 (2021)
  • Author(s): 重河優大, 床井健運, 山口敦史, Wang Yang, Yin Xiaojie, 南部明弘, 佐藤望, 和田道治, 羽場宏光
  • Organizer: 日本放射化学会第65回討論会(2021)
• [Presentation] U-233のα-γ同時計数測定によるTh-229の原子核励起状態の半減期の決定 (2020)
  • Author(s): 重河優大, 山口敦史, 鈴木健太, 羽場宏光, 平木貴宏, 菊永英寿, 西村俊二, 笹尾登, 吉見彰洋, 吉村浩司
  • Organizer: 日本放射化学会第64回討論会(2020)
• [Presentation] 核化学研究用高周波イオン収集システムの開発 (2020)
  • Author(s): 重河優大, 山口敦史, 佐藤望, 高峰愛子, 和田道治, 羽場宏光
  • Organizer: 日本放射化学会第64回討論会(2020)