VERIFICATION OF THE COSMIC-RAY EVENT IN AD 993-994 BY USING A JAPANESE HINOKI TREE

A rapid yearly increase in the radiocarbon content has been detected for the period from AD 993 to 994. However, this event is supported by the C-14 measurements of only one cedar tree sample, and verification is necessary to confirm this event more reliably. For this purpose, this study measured the C-14 content in Japanese Hinoki tree rings corresponding to the period from AD 988 to 997 using the accelerator mass spectrometry system at Yamagata University (YU-AMS). The result shows a significant C-14 increase from AD 993 to 994, and is consistent with the previously measured data for the Japanese cedar tree. This marks the second case detecting an increased C-14 level corresponding to the AD 994 event.