Development of a method evaluating the surface roughness of neutron guides for a measurement of the permanent electric dipole moment of the neutron

2023 Fiscal Year Final Research Report

• Project/Area Number: 21K13940
• 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: Osaka University
• Principal Investigator: Imajo Sohei 大阪大学, 核物理研究センター, 特任研究員 (10796486)
• Project Period (FY): 2021-04-01 – 2024-03-31
• Keywords: 超冷中性子 / 中性子光学 / 中性子ガイド管 / 反射モデル / 表面粗さ / 装置開発 / シミュレーション / BRDF

Outline of Final Research Achievements

We have studied the development of guide tubes for transporting ultracold neutrons (UCN) used in fundamental physics experiments such as neutron electric dipole moment measurements. Then, we have succeeded in developing a new method to evaluate the UCN transport efficiency and surface roughness of the inner surface of the guide tube. We have also demonstrated that the reflection of UCN on a relatively large surface roughness with a period of several tens of nanometers can be described using a diffuse reflection model of visible light by comparing experiments and simulations. In order to verify the reflection model in more detail, we performed experiments in which flat samples with surface irregularities of a few to several tens of nanometers were irradiated with a UCN beam with limited divergence, and we have successfully observed the diffusion of reflected UCN using a two-dimensional detector.

Free Research Field

原子核物理実験

Academic Significance and Societal Importance of the Research Achievements

粗い表面に対する量子力学的な中性子反射モデルの適用範囲はこれまで数ナノメートルサイズの凹凸に制限されており、研磨された金属表面のような比較的大きな粗さを取り扱えるものが存在しなかった。この研究では中性子と光とのアナロジーに基づいて、古典的な光学からアプローチすることで中性子光学が取り扱える表面粗さの範囲を拡大することができた。中性子輸送ガイド管は超冷中性子だけでなく低速中性子を利用する実験全般で用いられている。我々が検証した反射モデルを用いることでそれらの中性子輸送の理解がより正確になり、より輸送効率の高いガイド管の作成が実現すると思われる。