2020 Fiscal Year Final Research Report

Weak Transition in Nuclei Studied by Means of Strong Transition

Research Project

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Project/Area Number	15K05104
Research Category	Grant-in-Aid for Scientific Research (C)
Allocation Type	Multi-year Fund
Section	一般
Research Field	Particle/Nuclear/Cosmic ray/Astro physics
Research Institution	Osaka University
Principal Investigator	Fujita Yoshitaka 大阪大学, 核物理研究センター, 招へい教授 (60093457)
Co-Investigator(Kenkyū-buntansha)	民井淳大阪大学, 核物理研究センター, 准教授 (20302804)
Project Period (FY)	2015-04-01 – 2021-03-31
Keywords	ガモフ・テラー遷移 / スピン・アイソスピン励起 / 弱い相互作用 / 強い相互作用 / 原子核アイソスピン構造 / 低励起スーパーGT状態 / Gamow-Teller Resonance / Isoscalar Interaction
Outline of Final Research Achievements	Gamow-Teller (GT) transitions, like Fermi transition, are the most common weak interaction of spin-isospin type in atomic nuclei. The direct study of them by the weak decay processes, however, gives relatively limited information; note that β decay can access states only lower than the decay Q-value. However, one should note that β decay has a direct access to the absolute GT transition strengths B(GT). In contrast, the charge-exchange (CE) reactions, in our case (3He, t) reaction at 420 MeV and 0°, can selectively excite GT states up to high excitation energies in final nuclei. In addition, it has been found that there is a close proportionality between the cross-sections at 0° and the B(GT) values. In addition, in Osaka, a high-resolution of 30 keV has been achieved. Therefore, (3He, t) reaction became a useful tools to study the B(GT) strengths up to high excitation energies. We derived B(GT) strength distributions for many nuclei including those of astro-physics interest.
Free Research Field	Gamow-Teller 遷移による原子核構造の研究
Academic Significance and Societal Importance of the Research Achievements	スピンσ及びアイソスピンτは、原子核状態の性質を示す重要な量子数である。σ・τ演算子により起こるガモフ・テラー（GT）遷移は許容遷移と呼ばれ、原子核毎に異なる構造を端的に反映する。カーボン年代測定に使われる14C→14N の基底状態間のベータ崩壊はGT許容遷移で起こり、短い半減期を持つはずである。しかし実際には許容遷移では最長の5,700年もの長さを持つ。この事実は1950 年代からの疑問であった。 2020年夏、我々はこの疑問に「シーソー機構」を提唱して終止符を打った。この遷移では、量子力学的に可能な2種類の遷移行列が、打消しあっていた (EPJA '20 56:138 参照）。