Exotic structure of very neutron-rich nuclei --- Search for shape coexistence and clarifying its mechanism

• Project/Area Number: 17H02891
• Research Category: Grant-in-Aid for Scientific Research (B)
• Allocation Type: Single-year Grants
• Section: 一般
• Research Field: Particle/Nuclear/Cosmic ray/Astro physics
• Research Institution: Osaka University
• Principal Investigator: Shimoda Tadashi 大阪大学, その他部局等, 名誉教授 (70135656)
• Co-Investigator(Kenkyū-buntansha): 小田原 厚子 大阪大学, 理学研究科, 准教授 (30264013)
• Project Period (FY): 2017-04-01 – 2020-03-31
• Project Status: Completed (Fiscal Year 2019)
• Budget Amount: ¥20,020,000 (Direct Cost: ¥15,400,000、Indirect Cost: ¥4,620,000); Fiscal Year 2019: ¥520,000 (Direct Cost: ¥400,000、Indirect Cost: ¥120,000); Fiscal Year 2018: ¥3,250,000 (Direct Cost: ¥2,500,000、Indirect Cost: ¥750,000); Fiscal Year 2017: ¥16,250,000 (Direct Cost: ¥12,500,000、Indirect Cost: ¥3,750,000)
• Keywords: 中性子超過剰核 / 中性子魔法数20 / 変形共存 / 平均場と核子間相関の競争 / ベータ・ガンマ・中性子核分光法 / 31Al,33Al核の構造 / 不安定核ビーム31Mg,33Mg / カナダTRIUMF研究所 / 31Al, 33Al 核の構造 / 不安定核ビーム31Mg, 33Mg / 中性子過剰核の構造 / ベータ遅発中性子崩壊 / 超微細構造 / レーザー分光 / island of inversion / 核スピン偏極 / ベータ遅発崩壊 / 32Mgと33Alの構造 / レーザー光ポンピング / 中性子検出器 / 原子核実験 / 中性子過剰核

Outline of Final Research Achievements

The exotic structures of very neutron-rich nuclei have been attracting much attention. One of the highlights is the discovery of “shape coexistence” in 31Mg by our group in 2017. It was found that the coexistence of various structures is realized as a result of competition between the spherical mean field which favors spherical shapes and the nuclear correlation which favors deformed shapes.
To investigate the shape coexistence in more neutron-rich nuclei, it is essential to detect the beta-delayed neutrons because of less neuron threshold. We have developed a new neutron detector system to investigate the shape coexistence phenomena in wide region of nuclear chart. In fall of 2019 we have successfully performed the beta-decay spectroscopy experiment with the radioactive nuclear beam of 33Mg at TRIUMF. The preliminary results show, for the first time, the excited states in 33Al above the neutron threshold. The detailed analyses are in progress to reveal the exotic structure of 33Al.

Academic Significance and Societal Importance of the Research Achievements

中性子の数が極端に多い不安定核（超非対称核子系）は、宇宙における元素合成の過程で重要な役割を果たしているはずだが、それらの核構造はほとんど未知であり、元素合成への寄与を定量的に評価し難い状況にあった。
我々のグループは、これらの不安定核を二次ビームとして生成し、そのスピンの向きを偏らせ、ベータ崩壊を詳細に調べるという独自の手法を用いることによって、超非対称核子系では様々な形に変形した状態が励起エネルギーの狭い領域に出現していること（変形共存）を初めて明らかにした。本研究では、それに続く系統的研究を行うための中性子検出器系の開発に成功した。喫緊の課題となっている不安定核の構造が解明される日は近い。

Research Products

• [Int'l Joint Research] TRIUMF(カナダ)
• [Int'l Joint Research] TRIUMF(カナダ)
• [Journal Article] Resonance width for a particle-core coupling model with a square-well potential (2020)
  • Author(s): K. Hagino, H. Sagawa, S. Kanaya, A. Odahara
  • Journal Title: Prog. Theor. Exp. Phys. Volume: 2020 Issue: 2
  • DOI: 10.1093/ptep/ptz163
  • Peer Reviewed / Open Access
• [Journal Article] Structure of Mg31: Shape coexistence revealed by β-γ spectroscopy with spin-polarized Na31 (2019)
  • Author(s): Nishibata H.、Kanaya S.、Shimoda T.、Odahara A.、Morimoto S.、Yagi A.、Kanaoka H.、Pearson M. R.、Levy C. D. P.、Kimura M.、Tsunoda N.、Otsuka T.
  • Journal Title: Physical Review C Volume: 99 Issue: 2 Pages: 024322-024322
  • DOI: 10.1103/physrevc.99.024322
  • Peer Reviewed / Open Access / Int'l Joint Research
• [Journal Article] スピン偏極したNa原子核のベータ崩壊を用いた中性子過剰Mg同位体の特異な核構造の研究 (2018)
  • Author(s): 西畑洸希
  • Journal Title: 原子核研究 Volume: 63 Pages: 35-44
• [Journal Article] Shape coexistence in the N=19 neutron-rich nucleus 31Mg explored by β-γ spectroscopy of spin-polarized 31Na (2017)
  • Author(s): H.Nishibata, T.Shimoda, A.Odahara, S.Morimoto, S.Kanaya, A.Yagi, H.Kanaoka, M.R.Pearson, C.D.P.Levy, M.Kimura
  • Journal Title: Physics Letters Volume: B767 Pages: 81-85
  • DOI: 10.1016/j.physletb.2017.01.049
  • Peer Reviewed / Open Access / Int'l Joint Research / Acknowledgement Compliant
• [Journal Article] Shape coexistence in the N=19 neutron-rich nucleus 31Mg explored by β-γ spectroscopy of spinpolarized 31Na (2017)
  • Author(s): H. Nishibata, T. Shimoda, A. Odahara, S. Morimoto, S. Kanaya, A. Yagi, H. Kanaoka, M.R. Pearson, C.D.P. Levy, and M. Kimura
  • Journal Title: RIKEN Accel. Prog. Rep. Volume: 50 Pages: 82-82
  • Peer Reviewed / Open Access / Int'l Joint Research
• [Presentation] Structure of neutron-rich Al investigated by spin-polarized Mg (2020)
  • Author(s): Y. Hamano, H. Nishibata, T. Wakasa, A. Odahara, T. Shimoda, D. Maejima, Y. Okami, Y. Otani, S. Iimura, S. Kanaya, A. Hatakeyama,K.Asakawa, N.Sekiguchi, Y.Hirayama, C.D.P Levy, M.R. Pearson,J. Lassen, R. Li
  • Organizer: International symposium on Clustering as a Window on the Hierarchical Structure of Quantum Systems (CLUSHIQ2020), Beppu, Jan. 2020
  • Int'l Joint Research
• [Presentation] スピン偏極Mgのベータ崩壊を用いた中性子過剰なAl同位体の構造研究 (2020)
  • Author(s): 西畑洸希, 浜野友哉, 小田原厚子, 下田正, 前島大樹, 大上能弘, 大谷優里花, 金谷晋之介, 飯村俊, 関口直太, 浅川寛太,畠山温, 平山賀一, 若狭智嗣, C.D.P Levy, M.R. Pearson, J. Lassen, R. Li
  • Organizer: 日本物理学会, 名古屋大学, 2020年 3月
• [Presentation] スピン偏極Mgビームを用いた中性子過剰Alの構造研究 (2019)
  • Author(s): 濵野友哉, 西畑洸希, 小田原厚子, 下田正, 前島大樹, 大上能弘, 大谷優里花, 飯村俊, 金谷 晋之介, 畠山温, 浅川寛太, 関口直太,平山賀一, 若狭智嗣, C.D.P. Levy, M.R. Pearson, J. Lassen, R. Li
  • Organizer: 日本物理学会 九州支部例会, 佐賀大学, 2019年 11月
• [Presentation] 偏極Naビームで探る中性子過剰原子核30Mg, 31Mgの多様な原子核構造 (2019)
  • Author(s): 西畑洸希
  • Organizer: 日本物理学会、九州大学、2019年3月
  • Invited
• [Presentation] Shape coexistence in 31Mg revealed by beta-gamma and n-gamma spectroscopy with spin-polarized 31Na (2018)
  • Author(s): H. Nishibata, T. Shimoda, A. Odahara, S. Morimoto, S. Kanaya, A. Yagi, H. Kanaoka, M.R. Pearson, C.D.P. Levy, and M. Kimura
  • Organizer: The IX International Symposium on Exotic Nuclei, EXON2018, Petrozavodsk, Russia, Sep. 10-15, 2018
  • Int'l Joint Research / Invited
• [Presentation] Structure of neutron-rich 31Mg by beta-decay spectroscopy of spin-polarized 31Na (2018)
  • Author(s): H. Nishibata, T. Shimoda, A. Odahara, S. Morimoto, S. Kanaya, A. Yagi, H. Kanaoka, M.R. Pearson, C.D.P. Levy, M. Kimura, N. Tsunoda, and T. Otsuka
  • Organizer: 5th Joint Meeting of the APS Division of Nuclear Physics and the Physical Society of Japan Waikoloa, Hawaii, USA, Oct. 23-27, 2018
  • Int'l Joint Research
• [Presentation] Shape coexistence in neutron-rich 31Mg investigated by beta-gamma spectroscopy of spin-polarized 31Na (2017)
  • Author(s): H. Nishibata, T. Shimoda, A. Odahara, S. Morimoto, S. Kanaya, A. Yagi, H. Kanaoka, M.R. Pearson, C.D.P. Levy, and M. Kimura
  • Organizer: The third International Conference on Advances in Radioactive Isotope Science (ARIS2017), May 28- June 2 (2017) Colorado, USA
  • Int'l Joint Research / Invited
• [Presentation] Spectroscopy of neutron unbound states in 31Mg and shape coexistence in low excitation energy region (2017)
  • Author(s): S. Kanaya, T. Shimoda, A. Odahara, H. Nishibata, S. Morimoto, A. Yagi, H. Kanaoka, T. Kawamura, M. Pearson, and C.D.P. Levy
  • Organizer: Ito International Research Center (IIRC) Symposium 'Perspectives of the Physics of Nuclear Structure', July 1-4 (2017) Tokyo, Japan
  • Int'l Joint Research
• [Presentation] 中性子過剰核31Mgの中性子非束縛状態における変形共存探索 (2017)
  • Author(s): 金谷晋之介，下田正，小田原厚子，西畑洸希，森本翔太，八木彩祐未，金岡裕志，河村嵩之，M. Pearson，C.D.P. Levy
  • Organizer: 日本物理学会 秋季大会、宇都宮大学、2017年9月
• [Remarks] 大阪大学大学院理学研究科物理学専攻原子核構造グループホームぺージ
  • URL: http://adam.phys.sci.osaka-u.ac.jp/