氷床コアから復元される地磁気イベント時の宇宙線変動

概要

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Cosmogenic Radio Nuclides (CRNs) are produced by nuclear reactions induced by cosmic rays in the Earths atmosphere. The production rate of CRNs varies because changes in geomagnetic field intensity and solar activity strongly influence galactic cosmic rays, especially the lower part of energy. CRNs are produced in the upper atmosphere and are deposited on ice sheets in both Greenland and Antarctica, hence, ice cores in the polar regions provide excellent records of past histories of cosmic rays because of their continuous and relatively simple depositional processes. In recent studies, high-resolution records of 10Be flux from ice cores have been reported, and these revealed the continuity of 205-year solar cycles over the last glacial period. In particular, the changes induced in the production rate of CRNs by solar modulations increased during periods of low geomagnetic field intensity, such as the Laschamp geomagnetic excursion. The results obtained in this study suggest that it may be possible to obtain a better understanding of long-term solar activity through a high-resolution 36Cl analysis of the polar ice sheet.