Elucidation of origin of unexpected nuclear-radius growth probed by neutron skin thickness of Sn isotopes

2023 Fiscal Year Final Research Report

• Project/Area Number: 21K13947
• Research Category: Grant-in-Aid for Early-Career Scientists
• Allocation Type: Multi-year Fund
• Review Section: Basic Section 15020:Experimental studies related to particle-, nuclear-, cosmic ray and astro-physics
• Research Institution: Kyushu University (2023); Institute of Physical and Chemical Research (2021-2022)
• Principal Investigator: Tanaka Masaomi 九州大学, 基幹教育院, 助教 (70838143)
• Project Period (FY): 2021-04-01 – 2024-03-31
• Keywords: 不安定原子核 / 中性子スキン

Outline of Final Research Achievements

This study aims to measure the neutron skin thickness of Sn isotopes across the double magic number nucleus 132Sn to elucidate the origin of the unexpected nuclear-radius enhancement occuring across the magic number. The neutron skin thickness can be extracted from the difference between the matter and point-proton radius. In Sn isotopes, the point-proton radii of 135-137Sn has not been measured yet due to their
extremely low experimental yield. In this study, we established a new method to derive point-proton radii from charge change cross sections, and verified its validity by the test experiment in neighboring Te isotopes. Unfortunately, the experiment for Sn isotopes could not be performed because the machine time was not allocated at the accelerator facility during the period of this project, but we prepared experimental equipments and are ready to perform.

Free Research Field

原子核物理実験

Academic Significance and Societal Importance of the Research Achievements

陽子分布半径は原子核の基本的な物理量であり、不安定原子核に対する測定はレーザー分光法が主に行われてきた。しかし、適したビーム生成の収量の観点や適用核種の化学的性質に依存することから、極めて中性子過剰な原子核の適用は容易ではなかった。本研究で確立した荷電変化断面積を利用した陽子分布半径導出法は収量が乏しい核種にも適用可能であるため、超中性子過剰核に対する測定が本研究成果によって切り開かれる。このことにより、超中性子過剰核の中性子スキン厚の実験的決定にも取り組むことができ、原子核構造の議論や元素合成過程に必要不可欠な核物質の状態方程式の理解への貢献が期待される。