2018 Fiscal Year Final Research Report
Search for cosmic rays related to supernova remnants in the past of 3 million years using muon induced cosmogenic nuclides in granite rocks at a deep underground
| Project/Area Number |
15K05097
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Multi-year Fund |
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| Section | 一般 |
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| Research Field |
Particle/Nuclear/Cosmic ray/Astro physics
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| Research Institution | Yamagata University |
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Principal Investigator |
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| Co-Investigator(Kenkyū-buntansha) |
堀内 一穂 弘前大学, 理工学研究科, 助教 (00344614)
中島 和夫 山形大学, 理学部, 教授 (70159060)
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| Research Collaborator |
IWATA naoyoshi
SUZUKI soichiro
TOKANAI fuyuki
MATSUZAKI hiroyuki
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| Project Period (FY) |
2015-04-01 – 2019-03-31
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| 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 |
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| Outline of Final Research Achievements |
Secular variations of galactic cosmic rays (GCRs) are associated with the occurrence of supernova explosions, the confinement of cosmic rays in supernova remnants, and the propagation of cosmic rays in the galaxy. The high-energy muons produced in the atmosphere by high-energy GCRs can penetrate deep underground. Since rocks deep underground have been exposed to high-energy muons over a long period of time, the muon-induced radioisotope Be-10 with the half-life of 1.36×10^6 yrs have been accumulating there. In rocks more than 50 m underground, these nuclides are mainly produced by muons with energies above 100 GeV, corresponding to GCRs of a few TeV. We have measured the Be-10 concentrations at the depths of 5m,20m, and 50m by AMS, employing Toki granite boring core sample. There are a few publications containing data on the Be-10 concentrations in rocks at depths. The results play an important role to discuss experimentally the spectral variability of GCRs over a few million years.
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| Free Research Field |
宇宙線物理学
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| Academic Significance and Societal Importance of the Research Achievements |
国際的に見ても50mの深度での実験データは、2例程度の先行研究しかない。且つ、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。
本研究の結果は、現代の高エネルギー宇宙線ミューオンスペクトルから推定されるBe-10濃度に比べ高エネルギー側で変化している可能性を示唆しており過去の高エネルギー宇宙線スペクトルを調べる上で重要な研究成果である。
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