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

A rapid yearly increase in the radiocarbon content has been detected for the period from AD 993 to 994. How- ever, this event is supported by the 14C measurements of only one cedar tree sample, and verification is necessary to confirm this event more reliably. For this purpose, this study measured the 14 C 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 re- sult shows a significant 14 C 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 14 C level corresponding to the AD 994 event.