Cosmic ray event of AD 774-775 shown in quasi-annual 10Be data from the Antarctic Dome Fuji ice core

C-14 content in tree rings and Be-10 concentration records in polar ice core provide information about past cosmic ray intensities. The A.D. 774-775 cosmic ray event has been identified by C-14 measurement in several tree rings from all over the world. Although the quasi-decadal Be-10 Dome Fuji data in the Antarctic ice core also shows a sharp peak around A.D. 775, annual Be-10 variations in the Dome Fuji core or in other cores have not been revealed. We have measured quasi-annual Be-10 concentrations from approximately A.D. 763-794 in the Dome Fuji ice core, and detected a clear increase (80% above the baseline) in Be-10 concentration around A.D. 775. However, an accurate height of this increase is not straightforwardly estimated due to the background variation in Be-10 concentration. The Be-10 increase can be due to the same cosmic ray event as shown in the C-14 content in A.D. 774-775.