Search

An AMS system (Model 4130-AMS) dedicated to 14C measurements, built by High Voltage Engineering (HVE), B.V., the Netherlands, was delivered to Nagoya University in 1996/97. Acceptance tests of its performance on carbon-isotope-ratio measurements were completed in January of 1999, and a routine measurement started in mid-2000. The number of targets measured was 330, 1430, 2077, 1003, 1979, 1679, 1772, 1115, 1339, 866, 1300, 1701, 1449, 1634, 1351, 1741, 1156, 466, 900, and 1345 in each year from 1999 to 2018, respectively, and total number of targets measured by the end of December 2018 is 26,632. We briefly describe the maintenance processes of the Nagoya AMS system in the year of 2018. After suffering from severe machine problems in the last two years, the Tandetron AMS system at Nagoya University has also encountered a few problems in 2018. They are; (1) During the usual measurement of a graphite target, 12C^3+, 13C^3+ and 14C^3+ decreased gradually in the last half of its measurement time of 30 minutes. The plus-ion-beam intensity of 13C^3+ decreased from 200 nA to 5 nA in ten minutes, without any changes on its target current (corresponding to 13C^- injection current). We first checked all the parameter values of the power supplies to the AMS system, but we could not find any suspicious changes from their normal values. We finally concluded that something wrong has happened inside the accelerator tank, and decided to open the tank in 5 years after previously opening the tank. A timing belt to drive the power generator that supplies power to a turbomolecular pump was completely broken, and was dropped down to the bottom. The turbo molecular pump is important to keep good transmission from C^- to C^3+. We replaced the broken belt to a new one, and recovered a good transmission; (2) After a high-voltage spark, we could not apply high voltage to the accelerator. A control circuit board of supplying high voltage was checked and it was found out that the IC (IC3-AD669-BN) mounted on the electrical board B-5-41-205-0001 was out of work. We replace the board to a new one; (3) Carbon-ion current decreased as the result of full exhaustion of Cs in the ionizer system. Cleaning of whole ion source parts, and 1 g of Cs was filled to the reservoir tank of Cs sputtering ion source; (4) An air compressor was damaged after a long-term usage. We replace it to a new one; (5) A Faraday cup in front of the heavy ion detector was out of order and cannot be controlled to load in and put out from the beam line. We have checked the Faraday cup system and found out that the cup was disconnected from the pneumatic cylinder for controlling the cup position. We tighten the screw connecting the cup and air cylinder; (6) A computer system for controlling the AMS apparatus cannot work well, maybe by a heat problem. We re-greased the connecting area of CPU and the heat- sink unit for a better thermal conduction. We also replaced the hard disk presently used to the one of heavy-duty option. In spite of these problems, we can process totally 1345 graphite targets in 2018., 名古屋大学宇宙地球環境研究所では，1997年3月に完置されたHigh Voltage Engineering(HVE)社製Tandetron (Model4130-AMS)が放射性炭素（14C）測定に運用されている．イオン入射部にリコンビネーターを備えて，炭素の3種の同位体が同時に測定でき，導入された当時は14C測定において高性能を誇っていた．しかし，今になるとる14Cしか測定できない事が利用拡張の妨げになっている．同研究所は，2016年度から，「全国共同利用・共同研究拠点」に認定されており，「拠点」の重責を担っていくうえで，本装置は，特色のある，非常に重要な装置の一つと位置付けられている．2015年10月に年代測定総合研究センターから宇宙地球環境研究所へと組織改編された後，この装置のさまざまな故障が一挙に吹き出したが，これらの問題は，新研究所の理解と支援によりほぼ解決できた．2018年の1年間に発生した主な故障や保守作業を以下に示す．(1)試料の測定中に加速器から出力される炭素正イオン強度が次第に低くなった．5年ぶりに加速器タンクをオープンして点検したところ，加速器のターミナル部に設置されているターボ分子真空ポンプを駆動する発電機にメカニカルに動力を伝えるタイミングベルトが破断しているのが確認された（2018年1-2月）．(2)イオン源の分解洗浄，アイオナイザーの交換，Cs1gを充填（2018年6月末）．(3)エアコンプレッサーの故障と交換（2018年7月末）．(4)14C測定のルーティンの立ち上げにおいて，12C^3+,13C^3+は通常どおりの電流値を示すが，重イオン検出器での14C^3+の計数が全く無くなった．その原因として，検出器の直前にあるファラディ・カップをビームラインに出し入れするエアシリンダーの軸とファラディ・カップの軸受けのネジが緩んでおり，ファラディ・カップがビームラインに挿入されたままになっていた．（2018年8月初旬）．(5)装置制御用のプログラムがときおり停止し，またパソコンがフリーズするようになった．ハードディスクをサーバー用の製品に交換した（2018年8月末）．このような故障にもかかわらず，2018年には1345個のターゲットの測定を実施できた．

The annual C-14 data in tree rings is an outstanding proxy for uncovering extreme solar energetic particle (SEP) events in the past. Signatures of extreme SEP events have been reported in 774/775 CE, 992/993 CE, and similar to 660 BCE. Here, we report another rapid increase of C-14 concentration in tree rings from California, Switzerland, and Finland around 5410 BCE. These C-14 data series show a significant increase of similar to 6 parts per thousand in 5411-5410 BCE. The signature of C-14 variation is very similar to the confirmed three SEP events and points to an extreme short-term flux of cosmic ray radiation into the atmosphere. The rapid C-14 increase in 5411/5410 BCE rings occurred during a period of high solar activity and 60 years after a grand C-14 excursion during 5481-5471 BCE. The similarity of our C-14 data to previous events suggests that the origin of the 5410 BCE event is an extreme SEP event.

The annual 14C data in tree rings is an outstanding proxy for uncovering extreme solar energetic particle (SEP) events in the past. Signatures of extreme SEP events have been reported in 774/775 CE, 992/993 CE, and ∼660 BCE. Here, we report another rapid increase of 14C concentration in tree rings from California, Switzerland, and Finland around 5410 BCE. These 14C data series show a significant increase of ∼6‰ in 5411–5410 BCE. The signature of 14C variation is very similar to the confirmed three SEP events and points to an extreme short-term flux of cosmic ray radiation into the atmosphere. The rapid 14C increase in 5411/5410 BCE rings occurred during a period of high solar activity and 60 years after a grand 14C excursion during 5481–5471 BCE. The similarity of our 14C data to previous events suggests that the origin of the 5410 BCE event is an extreme SEP event., Geophysical Research Letters, 48 (11), ISSN:0094-8276, ISSN:1944-8007

Radiocarbon (14C) ages cannot provide absolutely dated chronologies for archaeological or paleoenvironmental studies directly but must be converted to calendar age equivalents using a calibration curve compensating for fluctuations in atmospheric 14C concentration. Although calibration curves are constructed from independently dated archives, they invariably require revision as new data become available and our understanding of the Earth system improves. In this volume the international 14C calibration curves for both the Northern and Southern Hemispheres, as well as for the ocean surface layer, have been updated to include a wealth of new data and extended to 55,000 cal BP. Based on tree rings, IntCal20 now extends as a fully atmospheric record to ca. 13,900 cal BP. For the older part of the timescale, IntCal20 comprises statistically integrated evidence from floating tree-ring chronologies, lacustrine and marine sediments, speleothems, and corals. We utilized improved evaluation of the timescales and location variable 14C offsets from the atmosphere (reservoir age, dead carbon fraction) for each dataset. New statistical methods have refined the structure of the calibration curves while maintaining a robust treatment of uncertainties in the 14C ages, the calendar ages and other corrections. The inclusion of modeled marine reservoir ages derived from a three-dimensional ocean circulation model has allowed us to apply more appropriate reservoir corrections to the marine 14C data rather than the previous use of constant regional offsets from the atmosphere. Here we provide an overview of the new and revised datasets and the associated methods used for the construction of the IntCal20 curve and explore potential regional offsets for tree-ring data. We discuss the main differences with respect to the previous calibration curve, IntCal13, and some of the implications for archaeology and geosciences ranging from the recent past to the time of the extinction of the Neanderthals.

To investigate the 14C concentration of atmospheric CO2 over the past few millennia in Japan, we measured the 14C age of annual rings from several Japanese trees with calendar dates ranging from ca. 2000 yr old to present, and we compared the tree-ring 14C age with the corresponding 14C age of IntCal13. It was revealed that the 14C age of the annual rings of Japanese trees are not consistent with IntCal13 datasets in some instances. Many cases of 14C age of tree rings are older than those of IntCal13, but younger than those of SHCal13 datasets. The average shift in Nagoya 14C age from IntCal13 datasets and one-sigma errors were obtained to be +26±36, +24±30, +16±22, +5±21, and +14±22 14C yr for the intervals AD72-382, AD589-1072, AD1413-1615, AD1617-1739, and AD1790-1860, respectively. In addition, a wood sample collected from northern end of the mainland of Japan also showed a value of +35±22 14C yr shifted older than IntCal13. We also analyzed 14C age data obtained for trees grown up in Korea, and yielded the values of +17±35 and +6±35 14C yr for the intervals AD1250-1650 and AD 1650-1850, respectively. The Japanese archipelago is situated near the boundary of the inter-tropical convergence zone in summer, and the 14C concentration of atmospheric CO2 over Japan can be influenced by air masses of the Southern Hemisphere with lower 14C concentrations during periods of higher solar activity and heightened East Asian summer monsoons. Korean Peninsula is also influenced by air masses of the Southern Hemisphere. Present results suggest that the southeast end of Eurasian Continent is located in the critical zone from where it is difficult to calibrate the 14C age of tree ring samples using existing calibration datasets. At the moment, it should be noted that calibration of the 14C dates of Japanese samples with IntCal13 induces additional systematic shifts of calibrated ages toward older ages by about 10-30 yr compared with the sample optimum calendar ages., 本研究の遂行において，科学研究費補助金基盤研究（B）代表者：中村俊夫，課題番号：26284120を用いた．また，本研究の一部は，文科省の共同利用・共同研究拠点プログラムとして行われたものである．

We, the members of the Division for Chronological Research at the Institute for Space-Earth Environmental Research at Nagoya University, held a regional contribution program for elementary and junior high school students on August 4–5, 2016: “Investigation of past solar activity and the paeloclimate change from tree annual rings and varved lake sediments.” Thirty-five students and six of their parents observed natural samples to experience earth and archaeological sciences. The first day began with a lecture on how tree annual rings and varved lake sediments can be used to reveal the paleoclimate. After the lecture, the students took part in several hands-on experiments on sedimentology. On the second day they travelled to the Wakasa area by bus and visited the Wakasa-Mikata Jomon Museum to learn about the pre-historic Jomon lifestyle and culture by observing remains from the Jomon Period excavated from the Torihama shell mound. Later in the day they took a cruising observation expedition across Suigetsu Lake, Mikatagoko to observe unique varved sediment layers on a lakebed revealing paleoclimate change dating back 70,000 years. Finally, they observed genuine sediment cores at the Fukui Prefectural Satoyama-Satoumi Research Institute. The program ended a success. The post-program questionnaire shows that the participants enjoyed the program and learned many new things., 年代測定研究部においては、平成28年度総長裁量経費地域貢献事業として、平成28年8月4日（木）と5日（金）の2日間に亘り、小学5年生から中学3年生まで35名を対象とした体験学習「樹木年輪・年縞堆積物から過去の太陽活動、地球の古気候を探る」を実施した。初日は名古屋大学で講義・実習を、2日目はバスで福井県若狭三方五湖に出向き、若狭三方縄文博物館の見学、水月湖の野外調査、ならびに福井県里山里海湖研究所において年縞堆積物の見学を行った。全体的に内容を詰めすぎた感はあるが、参加者は楽しみながら体験学習には取り組んでいた。アンケート結果が示すように、本事業の目的である“小・中学生に自然科学・地球科学・文化財科学等の面白さを伝える”ことは十分に果たされ、地域社会へ貢献できたと考えられる。

Although some candidates for the cause of the mysterious cosmic ray event in AD 774-775 have been reported we were not able to specify. In order to investigate the occurrence rate of the 14C increase event like the AD 775 one, we measured 14C content in Japanese tree-rings during an extended periods. As a result，we detected the second 14C increase by significant amount from AD 993 to AD 994. From the occurrence rate (one 14C event/800 years)，it was revealed that a large-scale SPE is the most plausible explanation for the 14C event., 775年の宇宙線イベントの原因について、いくつかの候補が挙がっていたが特定するのは難しい状況であった。本研究の年代を拡張した14C濃度測定により、993-994年にかけても似たような14C急増を発見した。また、994年イベントは日本産の2個体の樹木から存在を確認した。14Cイベントの発生頻度から、その原因として大規模SPEが妥当であると考えられる。見つかった14Cイベントの14C増加量は、観測史上最大のSPEの1O～数10倍に相当する。このような規模のSPEが仮に今日発生した場合、現代社会へ深刻な被害を及ぼすと想定される。今回の発見はこうした大SPEが将来において発生する可能性を示したものである。, 名古屋大学年代測定総合研究センターシンポジウム報告

Radiocarbon (14C) is produced in the upper atmosphere by galactic cosmic rays, which are modulated by solar magnetic activity. Its content in tree rings is retained and provides a record of past cosmic ray intensity and solar activity. We have measured the 14C content in Japanese cedar tree rings from AD 600 to 760, a time interval that includes a grand solar minimum in the 7th century, with a resolution of 2 year. Periodicity analysis of the 14C data shows that there is a component in the frequency band of the Schwabe cycle, with a period of 12-13 years continuing throughout the minimum. This is the fourth case in which an increase in the length of the Schwabe cycle has been observed in a grand solar minimum, after the Maunder Minimum, the Spörer Minimum，and the 4th century BC Minimum. In addition to the increase in the cycle length, it was also found that short frequency components appear in preceding and the beginning of the minimum. It is possible that this short component is related to the solar dynamo., 名古屋大学年代測定総合研究センターシンポジウム報告

We report an event of rapid increase in cosmic ray intensity, which occurred 1,200 years ago, by the measurements of radiocarbon concentration in tree rings in STEL, Nagoya University. The details of this event are described and high energy cosmological phenomena causing the event are discussed., 名古屋大学太陽地球環境研究所における炭素14測定によって最近得られた1200年前に起きた急激な宇宙線増加事象について報告する。この事象の詳細を述べるとともに，原因となる高エネルギー宇宙現象について議論する。, 名古屋大学年代測定総合研究センターシンポジウム報告

Radiocarbon 14C is produced in the upper atmosphere by the galactic cosmic rays which are modulated by solar magnetic activity. Its content in tree-rings is retained for record of the past cosmic ray intensity and the solar activity. We have measured the 14C content in Japanese cedar tree rings from 602 AD to 1072 AD with 2-year resolution. The 13-year periodicity was detected by the periodic analysis on the 14C content data in a grand solar minimum from 650 to 720 AD (Maunder-type minimum). This periodicity may come from the solar cycle (Schwabe cycle). It is the third case of the increasing of Schwabe cycle length in the Maunder type solar minimum, after the Maunder minimum and the BC4 minimum., 名古屋大学年代測定総合研究センターシンポジウム報告

In establishing the accurate chronology of any archeological events in Holocene, in particular, Yayoi, Kofun and younger periods in Japan by 14C dating, a proper calibration method of 14C age to calendar date is required. The calibration data, IntCal04/Intcal09, that are normally applied to 14C ages of terrestrial plant materials produced in the northern hemisphere, were tested for their consistency with the relevant relations between 14C age and dendro-age for tree-ring samples formed in the Japanese Archipelago. Some parts of dendro-dated tree-rings, formed from the 10th century BC to the AD 18th century, have been analyzed for 14C ages, and the resulting relations were almost consistent with those of IntCal04/IntCal09, except for a clear discrepancy at around AD50 to AD250; 14C ages for the tree ring samples formed in Japan were older than those of IntCal04/IntCal09 by about 50-80 14C years. In addition, more frequent periods in which such discrepancies had occurred were observed in the last two millennia for Yaku-sugi trees, grown in the southern part of Japan. The present status in the studies of the 14C-age-calibration issues for Japanese samples is discussed., 名古屋大学年代測定総合研究センターシンポジウム報告

Radiocarbon 14C is produced by the galactic cosmic rays which are modulated by solar magnetic activity because most cosmic rays are charged particles. 14C is oxidized to form 14CO2 and taken by trees during the carbon cycle. So 14C content in tree-rings is retained for record of the past cosmic ray intensity and the solar activity. We have measured the 14C content in Japanese cedar tree rings from 602 to 1072 AD with 2-year resolution, and found a rapid increase in 14C content at 775 AD. This 775 AD peak is consistent with the decadal IntCal data and the 10Be record from the Antarctic ice core. Therefore, it is highly possible that this peak was recorded all over the world and it was due to the increase in the cosmic ray intensity in 775 AD. The 11-year and 14-year periodicities are detected by the Fourier analysis on the 14C content data from 602 to 1072 AD. These periodicities may come from the solar cycle (Schwabe cycle)., 第23回名古屋大学年代測定総合研究センターシンポジウム平成22(2010)年度報告

主論文ファイル公開2014年11月20日