2023 Fiscal Year Final Research Report

Search for secular variations of in cosmic rays over the past 10 million years using muon-induced cosmogenic nuclides in deep underground granite rocks

Research Project

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Project/Area Number	19K03882
Research Category	Grant-in-Aid for Scientific Research (C)
Allocation Type	Multi-year Fund
Section	一般
Review Section	Basic Section 15020:Experimental studies related to particle-, nuclear-, cosmic ray and astro-physics
Research Institution	Yamagata University
Principal Investigator	Sakurai Hirohisa 山形大学, 理学部, 客員教授 (60150265)
Co-Investigator(Kenkyū-buntansha)	堀内一穂弘前大学, 理工学研究科, 准教授 (00344614) 湯口貴史熊本大学, 大学院先端科学研究部(理), 教授 (00516859)
Project Period (FY)	2019-04-01 – 2024-03-31
Keywords	宇宙線 / 宇宙線生成核種 / ミューオン / 宇宙線永年変化 / 花崗岩 / AMS分析
Outline of Final Research Achievements	We have measured the Be-10 and Al-26 (with respective half-lives of 1.36 × 10^6 yr and 7.2 × 10^5 yr) concentrations in boring core samples from the Toki Granite down to a depth of 100 m, using AMS analysis. We, also, have determined the production cross-sections of Be-10 and Al-26 in the granite quartz by a 160 GeV muon beam exposure experiment, compared with a detailed simulation. Additionally, the depth profiles of Be-10 and Al-26 concentrations in rocks estimated from the known total muon flux deep underground and this study’s cross sections were comparable to those of the concentrations measured at depths greater than 5 m. Overall, our study showed that these cross sections revealed by the high-energy muon beam experiment are a valuable tool for estimating variations in high-energy galactic cosmic rays over a few million years using in situ rocks and simulators.
Free Research Field	宇宙線物理学
Academic Significance and Societal Importance of the Research Achievements	本研究の100 mの深度での実験データは、国際的に見ても1例程度の先行研究しかない。さらに世界的にみても例をみない３次元的岩石情報を取得している土岐花崗岩体からの単一ボーリングコア試料による系統的分析測定結果は本研究が唯一のものである。本実験研究で導出した生成断面積は、世界に先駆けたデータであり学術的に大きな意義がある。また、高エネルギー宇宙線により過去１千万年の銀河の様子を調べることは社会文化的貢献でもある。