Development of high-density and high-precision analytical method of cosmic-ray produced radionuclei in ice core samples

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In this study, development of analytical methods for cosmic ray-produced long-lived radionuclei in the ice core sample, i.e., ^<10>Be, ^<26>Al and ^<36>Cl, have been successfully conducted by modifying / developing ion sources and detectors of accelerator mass spectrometer (AMS) as well as improving sample preparation techniques. All these three radionuclei could be detected in the real ice core samples obtained at Dome Fuji in Antarctica. The effect of solar activity change during "little ice age" between 1500-1800 AD could be detected clearly in the ^<10>Be data obtained from ice core samples with less than 10 g weight. Another challenging topics of analyzing ^26<Al> in ice core samples were also succeeded, although further improvement of beam strength as well as ionization efficiency will be needed for decreasing necessary amount of precious ice core samples. ^<10>Be/^<36>Cl data, on the other hand, showed considerable deviation from the previous reports obtained in other places. This may suggest the variation of initial ^<10>Be/^<36>Cl values depending on the time/location, indicating difficulties to use ^<10>Be/^<36>Cl data for dating purposes. The techniques established in this study will be used for the analysis of these radionuclei in the 3,000 m ice core sample obtained from Dome Fuji in order to conduct supplemental dating as well as to elucidate solar climate change, geomagnetic change and global climate change in the last million years.