Development of Measurement system for Branching Ratios of Superallowed Pure Fermi-Type Beta Decays

Research Project

Project/Area Number	17K14299
Research Category	Grant-in-Aid for Young Scientists (B)
Allocation Type	Multi-year Fund
Research Field	Particle/Nuclear/Cosmic ray/Astro physics
Research Institution	Tokyo City University
Principal Investigator	Daiki Nishimura 東京都市大学, 理工学部, 准教授 (30612147)
Project Period (FY)	2017-04-01 – 2022-03-31
Project Status	Completed (Fiscal Year 2021)
Budget Amount *help	¥4,550,000 (Direct Cost: ¥3,500,000、Indirect Cost: ¥1,050,000) Fiscal Year 2019: ¥650,000 (Direct Cost: ¥500,000、Indirect Cost: ¥150,000) Fiscal Year 2018: ¥520,000 (Direct Cost: ¥400,000、Indirect Cost: ¥120,000) Fiscal Year 2017: ¥3,380,000 (Direct Cost: ¥2,600,000、Indirect Cost: ¥780,000)
Keywords	ベータ崩壊 / 実験核物理
Outline of Final Research Achievements	The unitarity of the Cabibbo-Kobayashi-Maskawa (CKM) matrix and the inclusion of right-handedness into the weak interaction have been actively verified by precisely determining the ft value corresponding to the beta decay strength of the super-allowed pure Fermi type beta decay. However, the ft values of 18Ne and 30S have so far deviated from the average ft values of other nuclides, albeit with poor precision, in a direction that cannot be explained by anomalies in the nuclear structure. In order to elucidate this discrepancy, we have developed a general system to measure β-decay branching ratios with a high precision of 0.3%.
Academic Significance and Societal Importance of the Research Achievements	本研究が完成すれば、これまでに測定が困難とされていた基底状態への崩壊を含むベータ崩壊核種の「分岐比」を絶対測定できるようになり、不安定原子核における魔法数の消失や新魔法数の発現といった原子核構造の解明、まだその起原が明らかになっていない速い中性子捕獲過程（r-process)などの宇宙元素合成にとって重要な原子核のベータ崩壊の研究に対しての道が開けると期待される。