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The so-called Millennium Eruption of Baitoushan Volcano is one of the largest of the Common Era but its date has been uncertain. Recently, Oppenheimer et al. (2017) reported the eruptive year as late AD 946 using a new method called carbon-14 spike matching. However, it is necessary to verify their result to confirm the eruptive year, since only one wood sample was used in their study. We verified the eruptive year by measuring 14C contents in tree rings from another wood sample buried during the Baitoushan eruption. We succeeded in reproducing the AD 774–775 14C spike (Miyake et al. 2012), and counted the number of rings from the outermost ring accompanied by bark to the ring possessing the AD 774–775 14C spike. We found the outermost ring was formed in AD 946. Our study supported the result of Oppenheimer et al. (2017), which makes the eruptive year conclusive. Also, we suggest that the 14C spike-matching method can be a prominent dating tool applicable to ancient woods that are difficult to date using the usual dendrochronology techniques.
Two radiocarbon excursions (AD 774–775 and AD 993–994) occurred due to an increase of incoming cosmic rays on a short timescale. The most plausible cause of these events is considered to be extreme solar proton events (SPE). It is possible that there are other annual 14C excursions in the past that have yet to be confirmed. In order to detect more of these events, we measured the 14C contents in bristlecone pine tree-ring samples during the periods when the rate of 14C increase in the IntCal data is large. We analyzed four periods every other year (2479–2455 BC, 4055–4031 BC, 4465–4441 BC, and 4689–4681 BC), and found no anomalous 14C excursions during these periods. This study confirms that it is important to do continuous measurements to find annual cosmic-ray events at other locations in the tree-ring record.
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 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 14C 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 14C 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 14C level corresponding to the AD 994 event.
We performed accelerator mass spectrometry (AMS) radiocarbon dating and wiggle-matching of 2 wood samples from charred trunks of trees (samples A and B) collected from an ignimbrite deposit on the northeastern slope of the Baitoushan Volcano on the border of China and North Korea. The obtained calendar years for the eruption are cal AD 945–960 for sample A and cal AD 859–884 and cal AD 935–963 for sample B in the 2-σ range. These results are unable to determine the precise eruption age. The reason for the difference in reported ages may be due to volcanic gas emission prior to the huge eruption.
Alkaline earth and rare-earth fluoride thin films were prepared on silica glass substrates by a sol-gel process using trifluoroacetic acid (TFA) as a fluorine source. Homogeneous solutions were obtained by stirring a mixture of alkaline earth or rare-earth metal acetates, TFA and H2O, dissolved in isopropanol. The solutions were spin-coated and heated at 300–800 °C. The fluoride thin films were obtained by heat treatment around 400 °C in air. The crystallization behavior, the surface morphology, and the optical properties of the films depended on the heating temperature as well as the chemical species of the metal ions.
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