A signature of cosmic-ray increase in ad 774-775 from tree rings in Japan

摘要

树木年轮中的碳-14可用作宇宙射线活动的—rn个指标-~(14)C是由大气中的氮与宇宙射线中rn的中子相互作用产生的。现在，对两个日本雪rn松的年轮中~(14)C含量所做的一项高分辨率分析，rn显示了在公元774年和公元775年间~(14)C含量增rn加约12‰的证据，比按太阳的普通调制效应rn所预期的数值大约20倍。本文作者得出的结论rn是，在公元775年前后，在我们的空间环境中rn发生了一次能量极高的事件，其原因目前尚不rn知道，因为没有当时发生一次超新星事件或一rn次大型太阳耀斑事件的支持证据。%Increases in ~(14)C concentrations in tree rings could be attributed to cosmic-ray events, as have increases in ~(10)Be and nitrate in ice cores. The record of the past 3,000 years in the IntCal09 data set10, which is a time series at 5-year intervals describing the ~(14)C content of trees over a period of approximately 10,000 years, shows three periods during which ~(14)C increased at a rate greater than 3%o over 10 years. Two of these periods have been measured at high time resolution, but neither showed increases on a timescale of about 1 year (refs 11 and 12). Here we report ~((14)C measurements in annual rings of Japanese cedar trees from ad 750 to ad 820 (the remaining period), with 1- and 2-year resolution. We find a rapid increase of about 12%o in the ~(14)C content from AD 774 to 775, which is about 20 times larger than the change attributed to ordinary solar modulation. When averaged over 10 years, the data are consistent with the decadal IntCal ~(14)C data from North American and European trees. We argue that neither a solar flare nor a local supernova is likely to have been responsible.