2026-09-07 日本原子力研究開発機構
図１：変形したフェルミウム（252Fm）原子核の回転速度が増加する様子（左図）と、回転エネルギーの様子（中図）
回転運動の様子から、252Fmは、陽子数100、中性子数152の魔法数を有し、周囲の原子核と比べ、原子核がより強く結合している（右）
＜関連情報＞
- https://www.jaea.go.jp/02/press2026/p26090701/
- https://journals.aps.org/prl/abstract/10.1103/7gzt-ldn5
重アクチニドにおける変形と魔法性：基底状態回転バンドの最初の観測252Fm Deformation and Magicity in Heavy Actinides: First Observation of the Ground-State Rotational Band of 252Fm
R. Orlandi, M. Asai, H. Makii, K. Nishio, K. Hirose, K. Tsukada, T. K. Sato, Y. Ito, F. Suzaki et al.
Physical Review Letters Published :17 August, 2026
DOI: https://doi.org/10.1103/7gzt-ldn5
Abstract
The ground-state rotational band of 252Fm ( =100, =152) was investigated using two different experimental setups at the JAEA Tandem Accelerator Laboratory. The 2+→0+ and 4+ →2+ transitions were observed in the decay of 256No via − coincidence spectroscopy. The energies of the (6+)→(4+), (8+) →(6+), and (10+) →(8+) transitions were identified in the prompt -ray spectrum of 252Fm produced in the 18O+249Cf multinucleon transfer reaction. The new data reveal that, compared with neighboring fermium isotopes and =152 isotones in the region, 252Fm has the lowest first excited 2+-state energy, 41.88(16) keV, and the largest kinematic moment of inertia. These properties constitute new evidence for the deformed shell gaps at =100 and =152, supporting the understanding of 252Fm as a deformed doubly magic nucleus.
