これまで観測されていなかった2種類の原子核を創出（Chinese Scientists Create 2 Never-before-seen Atomic Nuclei）

2026-04-01 中国科学院（CAS）

A graphic showing Berkelium and Americium from the Periodic Table. Chinese scientists have recently synthesized brand-new isotopes of these two elements: Berkelium-235 and Americium-231. Gong Zhe/CGTN

＜関連情報＞

• https://english.cas.cn/newsroom/cas-in-media/202604/t20260401_1154974.shtml
• https://www.sciencedirect.com/science/article/pii/S0370269326002194

新同位体235Bkおよび231Amの崩壊特性 Decay properties of new isotopes 235Bk and 231Am

J.G. Wang, Z.C. Li, Z.Y. Zhang, Z.G. Gan, A.N. Andreyev, M.H. Huang, L. Ma, M.M. Zhang, H.B. Yang, C.L. Yang, Y.H. Qiang, Z.H. Li, X.Y. Huang, G. Xie, L. Zhu, H. Zhou, X. Zhang, J.H. Zhen, S.Y. Xu, Z. Zhao…A.N. Polyakov
Physics Letters B  Available online: 17 March 2026
DOI:https://doi.org/10.1016/j.physletb.2026.140365

Abstract

The new isotopes, ²³⁵Bk and its α-decay daughter ²³¹Am, were investigated using the gas-filled recoil separator SHANS2. They were identified by measuring radioactive decay chains originating from ²³⁵Bk, which was produced via the ¹⁹⁷Au(⁴⁰Ar, 2n)²³⁵Bk reaction. Three correlated α-decay chains were assigned to ²³⁵Bk, from which the α-particle energy of ²³⁵Bk was measured to be 7632(17) keV. For ²³¹Am, the α-particle energy and half-life were determined to be 7109(18) keV and 75⁺¹³⁷_-30 s, respectively. The α-decay branching ratio of ²³¹Am was evaluated as 17⁺⁶⁵_-15%. A systematic analysis reveals significant discrepancies between the experimental data and the WS4+RBF theoretical predictions for the isotopes of Bk and Am, which warrant further investigation.