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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．

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 routine measurements began in mid-2000. The number of targets measured was 330, 1430, 2077, 1003, 1,979, 1679, 1772, 1115, 1339, 866, 1300, 1701, 1449, 1634, 1351, 1741, 1156, 466 and 900 in each year from 1999 to 2017, respectively, and total number of targets measured by the end of December 2017 is 25,287. We briefly describe the maintenance processes of the AMS system in the year of 2017. The Tandetron AMS system at Nagoya University has encountered several problems in 2017. They are; (1) two big sparks seriously damaged the solid state RF driver for the high voltage generation, and the AMS system could not supply the high voltage of 2.5 MV used for 14C measurements. We replaced a damaged coil at the final part of the high-voltage power supply unit with a new coil; (2) a power supply unit for loading electrical current to correctly adjust the current for the recombinator magnet was in trouble. A resistance unit located at the end of current supply circuit was burnt out. We replaced it to a new one; (3) 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 electrical board B-5-41-205-0001 was out of work. We replace the board to one repaired previously; (4) During the usual measurement of a graphite target, 12C3+, 13C3+ and 14C3+ decreased gradually in the last half of its measurement time of 30 minutes. The plus ion beam intensity of 13C3+ decreased from 200nA to 5nA in ten minutes, without any changes on its target current (corresponding to 13C- current). We first checked all the parameter values of the power supplies to the AMS system, but we could not find any changes from their nominal values. We finally concluded that something wrong has happened inside the accelerator tank, and decided to open the tank after 5 years of previously opening the tank. Owing to these problems, we can process only 900 graphite targets in 2017. In 2017, we also have carried out some application programs of 14C measurements at Nagoya University. Some of the results are included in this Proceedings volume.

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．

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 on its performance on carbonisotope- ratio measurements were completed in January of 1999 and routine measurements began in mid-2000. The numbers of targets measured from 1999 to 2016 were: 330, 1430, 2077, 1003, 1,979, 1679, 1772, 1115, 1339, 866, 1300, 1701, 1449, 1634, 1351, 1741, 1156, and 466, respectively (24,387 were measured by the end of June 2016). We briefly describe the maintenance processes for the AMS system in 2016. The Tandetron AMS system at Nagoya University encountered several serious problems in 2016. First, the high voltage of the accelerator broke down frequently for no clear reasons. Any sparks happened before these voltage downs. Second, a compressor for the cryo-pumping system stopped suddenly. Parts for maintaining the pump system are no longer supplied by the manufacturer, leaving us no choice but to replace the cryo-pumping system with a turbomolecular pumping system. Third, ion source cleaning had to be conducted due to a shortage of Cs in the container. Fourth, the excessively high temperature of the circulating water used to cool down the power supply system for two high-energy mass-analyzing magnets forced us to replace the system with a magnet power supply system cooled by air. Fifth, a power supply unit for the servo-amplifier controlling the motor for target exchanging function was found to be out of order. Replacement with a spare unit corrected the problem. Six, two big sparks seriously damaged the solid state RF driver for the high-voltage generation, rendering the AMS system incapable of applying the high voltage of 2.5 MV used for 14C measurements. We replaced a damaged coil at the final part of high-voltage power supply for the repair. As a consequence of these numerous problems, were only able to process 466 graphite targets in 2016. We also carried out a number of application programs for 14C measurements at Nagoya University in 2016. Some of the results are reported in these Proceedings.

著者人数: 30名, Accepted: 2017-06-19, 資料番号: SA1170078000

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

From July 31, 2013 through August 1, we held a workshop of the dendrochronology for primary and secondary students in Center for Chronological Research, Nagoya University. Ten children and two protectors participated in this workshop. They experienced fundamental experiment of the dendrochronology. In addition, they attended various lectures about the tree ring. They were able to decide the date of the experiment samples. They appreciated these experiments and lectures., 2013年7月31日-8月1日に，名古屋大学年代測定総合研究センターは，小中学生のための「年輪年代法体験学習」を開催した.この体験学習には10名の小中学生と2名の保護者が参加した.参加者は，年輪年代法の基礎実験を体験し，あわせて樹木年輪に関する様々な講義を受講した.全ての参加者が，実験試料の年代決定を成功させた.参加者はこの体験学習の内容を高く評価した., 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

Variation of the sunspot number, which reflects solar activity, has shown the periodicity of around 11-year since the early 18th century. However, in the period of 1645 to 1715 AD sunspots were almost absent, and this period is called the Maunder Minimum, one of grand solar minima implying weak solar activity. Variation of solar activity in grand solar minima can be investigated by determining the concentration of cosmogenic isotope ^C in annual tree rings. We previously obtained the ^C records of1413 to 1745 AD including the Spoerer Minimum (1416-1534 AD) and the Maunder Minimum with annual time resolution. As a result of frequency analysis of these ^C records, we found that the cycle length of the "11-year cycle" during the Maunder Minimum was around 14 years while that during the Spoerer Minimum was modulating slightly from 11 years. This result suggests that a pattern of the "11-year" cycle length variation depends on a type of minima classified by their duration of estimated sunspot absence. In order to verify this hypothesis, we have measured ^C contents in Japanese camphor tree rings during a possible grand solar minimum in the 4th century B.C. Preliminary result shows the solar cycle length was several years longer than 11 years, as in the Maunder Minimum.

The sunspot number, which is a typical index of solar activity, shows a clear 11-year periodicity called the Schwabe cycle. However, in the period around 1645 to 1715 AD the sunspots were almost absent on the solar surface. This is considered to be due to extraordinary weakening of solar activity and this period is called the Maunder minimum. We cannot know from the sunspot record if the Schwabe cycle continued or not in the Maunder minimum. Also we cannot know the periodicity of solar activity without sunspot observation as in pre-telescope era. So we use carbon 14, which is one of cosmogenic nuclides as an indirect index of solar activity with inverse correlation, in order to study 11-year periodicity during grand solar minima like the Maunder minimum. Stuiver classified grand solar minima into two types by duration of minima. The Maunder-type minima have a duration of 〜80yr whereas the Spoerer-type minima last 〜120yr. We previously measured carbon 14 content in Japanese tree for the Maunder minimum (the Maunder type), the Spoerer minimum (the Spoerer type) and the 4^-century-BC minimum (the Maunder type) and a periodicity of 14 yr was obtained for the Maunder-type minima. But we have not finished measuring the carbon 14 content around a leading edge of the Spoerer minimum. This year we measured carbon 14 content in tree rings of 80 years for the pre-Spoerer minimum (1346 to 1425 AD). As a result of frequency analysis we obtained a periodicity signal of 13yr, but only with small significance. A limit of measurement error to get significant signal of 11-year periodicity is discussed., 第20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19(2007)年度報告 Proceedings of the 20th symposiumon on Chronological Studies at the Nagoya University Center for Chronological Research in 2007 日時:平成20 (2008)年1月10日(木)～11日(金) 会場:名古屋大学野依記念学術交流館 Date:January10th-11th, 2008 Venue:Nagoya Uhiversity Noyori Conference Hall

Sunspot numbers, which reflect solar activity, have presented clear 11-year periodicity since the beginning of the 18^ century. But in the period around 1645 to 1715 AD sunspots were nearly absent, so we can not know if 11-year periodicity of solar activity was continued or not during the period by the records of sunspot numbers. This period is called as the Maunder Minimum. Radiocarbon ^C, which is one of cosmogenic radioisotopes, is a good indicator of solar activity too. By determining the concentration of the ^C in each tree ring, we can get information on the change of solar activity in grand solar minima like Maunder Minimum. Variation of decadal ^C content measured by Stuiver et al. shows that grand solar minima, a period solar activity was extremely weak for decades or more, occurred several times in the last 10000 years. Stuiver classifies grand solar minima into 3 categories depending on the length of their durations. The Maunder type minima have a period of 〜80 yr and the Sporer type minima last 〜40 yr longer. We have already obtained the records of ^C content in Japanese cedar tree rings of 1413 to 1745 AD including the Spoerer Minimum and the Maunder Minimum with annual time resolution. As a result of frequency analysis of these ^C records, we found that the Sun maintained its periodic activity even if during the minima. We found, however, the cycle length of the "11-year cycle" during the Maunder Minimum was around 14 years and that during the Spoerer Minimum was around 11 years. This suggests that a pattern of the "11-year cycle" cycle length variation depends on a type of minima. In order to verify this hypothesis, we have measured ^C content in Japanese camphor tree rings of 431 to 323 BC. The age, when this tree was growing has been determined by comparing ^C records measured by us with world typical ^C records called as the IntCal04. The period 431 to 323 BC covers start of ^C increase to around its peak in the 4^ century BC solar minimum. We will measure and analyze the ^C content during the last half of the 4^ century BC solar minimum and find out the actual cycle length of the "11-year cycle"., 第19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18(2006)年度報告 Proceedings of the 19th symposiumon on Chronological Studies at the Nagoya University Center for Chronological Research in 2006 日時:平成19 (2007)年1月15日(月)～17日(水) 会場:名古屋大学シンポジオン Date:January15th-17th, 2007 Venue:Nagoya Uhiversity Symposion Hall

Radiocarbon is mainly produced by the incoming galactic cosmic rays modulated by solar wind and the interplanetary magnetic field, and thus its production rate and its content in the atmosphere and in the tree-rings reflect the state of solar magnetic activity. By measuring the radiocarbon contents in annual tree-rings, we can trace back the characteristics of the eleven-year solar cycles during the pre-historical periods. The Sun holds several long-term cyclic variations in addition to the 11-year sunspot activity cycle and the 22-year cycle in the polarity reversals. The 88-year and the 208-year quasi cyclic variations of the Sun have caused several long-lasting sunspot minima such as the Maunder Minimum (1645-1715 AD), and have brought cold spells as referred as the Little Ice Age. However, not only the mechanisms of the solar influence on climate but also the mechanism of such long-term variations in solar activity is not clarified yet. In order to obtain the clues for the mechanisms of the long-term solar variations, we investigated the change of the characteristics of the eleven-year solar cycle during the last 1200 years, including the grand solar activity maxima around the 9-10^ century, the Spoerer Minimum (1415-1534 AD) and the Maunder Minimum. The spectral analyses of our radiocarbon data have indicated the suppression of the eleven-year variations and the slight stretching of the cycle lengths during the grand activity minima. On the other hand, slight shortening of the eleven-year cycle has been found around the grand solar activity maxima. The variability of the "11-year" solar cycle during the last 1200 years seems to be 9-15years., 第19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18(2006)年度報告 Proceedings of the 19th symposiumon on Chronological Studies at the Nagoya University Center for Chronological Research in 2006 日時:平成19 (2007)年1月15日(月)～17日(水) 会場:名古屋大学シンポジオン Date:January15th-17th, 2007 Venue:Nagoya Uhiversity Symposion Hall

Radiocarbon ^C, which is one of cosmogenic radioisotopes, is a good index of solar activity. Investigation of the ^C content in each tree ring gives information on the change of solar activity in the past. Variation of the ^C content shows that grand solar minima, when the solar activity was extremely weak for several ten years or more, occurred many times in the past. The Maunder Minimum (1645-1720 AD), one of the grand solar minima in the last millennium, is well known to have had almost no sunspots, and then periodicity of solar activity cannot be seen. Therefore, we have investigated the periodicity of radiocarbon content in tree rings in order to clarify the characteristics of variation of solar activity during the grand solar minima. We have already obtained the ^C records for 1413-1554 AD including the Spoerer Minimum and for 1617-1745 AD including the Maunder Minimum with annual time resolution by using Japanese cedar trees. As a result of frequency analysis of these radiocarbon records, we found that the Sun maintained periodic variation even if the minima. We found, however, the length of the "eleven-year" cycle during the Maunder Minimum was around 14 years and that during the Spoerer Minimum was around 11 years. This suggests that the cycle length is related to solar activity, and that the pattern of periodicity of solar activity for the type of grand solar minimum. In order to clarify these possibilities, we have investigated periodicity of solar activity in periods other than the grand solar minimum by measuring the ^C content in the period between the Maunder Minimum and the Spoerer Minimum (1555-1615 AD) and 9^-10^ centuries (880-964AD). As a result, we found that the length of the "eleven-year" cycle during the normal period was around 11 years, which was expected from the modern solar activity. This result supports the difference in the cycle length in each solar minimum mentioned above. Furthermore, inverse correlation of the strength of solar activity and the cycle length is suggested. Our results should be a great clue as to the mechanism to which solar activity becomes weak and bases for studies of long-term solar periodic variations., 第18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17(2005)年度報告 Proceedings of the 18th symposiumon on Chronological Studies at the Nagoya University Center for Chronological Research\ in 2005 日時:平成18 (2006)年1月17日(火)､18日(水) 会場:名古屋大学シンポジオン Date:Januaryl7th and 18th, 2006 Venue:Nagoya Uhiversity Symposion Hall

It was suggested by Konstantinov and Kocharov that gamma ray emission from a supernova explosion produces detectable amount of ^C in atmosphere of the earth. According to the idea, Damon et al. measured the ^C content in tree rings from AD 998 to AD 1025 and detected Δ^C increase of about 6‰ in AD 1010, which corresponds to an appearance of SN1006 (the supernova explosion that occurred in AD 1006). If the Δ^C increase is really due to the gamma-ray emission by SN1006, the result must be important for the study of cosmic ray acceleration by supernova explosions. However, it is not clear if the Δ^C increase in AD 1010 is caused by SN1006, because Δ^C variation caused by solar activity is not considered. To test the possibility of solar activity, we extended the duration of measurement of tree ring samples. We have measured tree rings of Yaku cedar from AD 992 to AD 1028 and determined Δ^C with the precision of ±2.8‰ by the accelerator mass spectrometry (AMS). Our result agrees with Damon's within the measurement error. Comparison of the 5 years before AD 1011 with the 5 years after shows an average increase of 4.1±1.7‰, which is similar to that of Damon. However, we can see the cyclic feature in the variation, which is similar to the 11-year cycle variation by solar activity as to a cycle length and the amplitude. Therefore, most part of Δ^C increase in AD 1012 is considered to be the variation caused by solar activity. We plan the measurement intended for SN1054, which is a type II supernova. Kinetic energy of type II supernovae is evaluated to be larger than that of type I supernovae (ex : SN1006). So, SN1054 would be more detectable., 第17回名古屋大学タンデトロン加速器質量分析計シンポジウム平成16(2004)年度報告 Proceedings of the 17th symposiumon Researches Using the Tandetron AMS System at Nagoya University in 2004\ 日時:平成17 (2005)年1月24日(月)､25日(火) 会場:名古屋大学シンポジオン Date:January 24th and 25th, 2005 Place:Nagoya University Symposion Hall

This paper presents the variation of solar activity during the Maunder Minimum (1645-1715 AD) deducted from radiocarbon content in tree-rings. Radiocarbon is produced by the galactic cosmic rays, which are modulated by the solar wind and the interplanetary magnetic field in the heliosphere. The production rate of radiocarbon, therefore, reflects the state of solar magnetic activity. Most distinct index of solar magnetic activity it the group sunspot number. The variations of sunspot number have shown clear cyclicity since the 18^ century with average length being about eleven years. The sunspots, however, have once almost disappeared during the period of 1645-1715 AD due to extraordinary weakening of solar activity. This period has been called as the Maunder Minimum. There is no remarkable cyclicity in the sunspot variations. We, therefore, investigated the cyclicity of radiocarbon content in tree rings from the Maunder Minimum in order to clarify the characteristics of solar activity during this period. We compared two radiocarbon records obtained newly by our group and by Stuiver et al. The results of frequency analyses have shown that solar magnetic reversals had maintained through the Maunder Minimum and that the length of the "eleven-year" cycle was stretched to 13-15 years., 第17回名古屋大学タンデトロン加速器質量分析計シンポジウム平成16(2004)年度報告 Proceedings of the 17th symposiumon Researches Using the Tandetron AMS System at Nagoya University in 2004\ 日時:平成17 (2005)年1月24日(月)､25日(火) 会場:名古屋大学シンポジオン Date:January 24th and 25th, 2005 Place:Nagoya University Symposion Hall

Radiocarbon ^C, which is one of cosmogenic radioisotopes, is a good index of change in the solar activity. Investigation of the ^C content in each tree ring gives information on the change of solar activity in the past. Variation of the ^C content shows that five grand minima, when the solar activity was extremely weak, existed in the last millennium. The Maunder Minimum(1645-1720 AD), one of the grand minima in the last millennium, is well known to have had almost no sunspots. To clarify the characteristics of solar activity during the grand minima, we have investigated the solar activity during the Sporer Minimum(1415-1534 AD) and Maunder Minimum. We mesured the ^C content in the 714-year-old Yaku ceder tree from Sporer Minimum and the 392-year-old Murou-ji ceder tree from Maunder Minimum by the accelerator mass spectrometry(AMS). The time series of the ^C data for the Sporer Minimum was analyzed by Fourie Analysis. The power spectrum shows peaks in the periodicity at 11.9yr and 28.6yr. The amplitude of 11.9yr period was stronger than that of 28.6yr. The 11-year cycle was extracted from the time series of the data by using band-pass filter. The 11-year cycle was suppressed during the 50 years of the mid Sporer Minimum. In Fourie Analysis of the ^C data for the Maunder Minimum, the power spectrum shows no significant peak. We continue this study to get more detail characteristics of the solar activity during the grand minima., 第16回名古屋大学タンデトロン加速器質量分析計シンポジウム(平成15年(2003年度)報告 Proceedings of the 16th Symposium on Researches Using the Tandetron AMS System at Nagoya University in 2003 日時:平成16(2004)年1月22日(木)､23日(金) 会場:名古屋大学シンポジオン Date:January 22nd and 23rd,2004 Place:Nagoya University Symposion Hall

Radiocarbon ^C, which is one of cosmogenic radioisotopes, is a good index of change in the solar activity. Investigation of the ^C contents in each tree ring gives information on the change of solar activity in the past. We have focused on the solar variation during the grand minima, when the solar activity was extremely weak and almost no sunspot appeared. In some prior studies, the existence of the 22-year periodicity during the Maunder Minimum (1645-1720 AD) was suggested. To clarify whether the 22-year periodicity is common in the grand minima, we have investigated the solar activity during the Spoerer Minimum (1514-1534 AD). We measured the ^C contents in the 714-year-old Japanese cedar tree by the accelerator mass spectrometry (AMS). Time series of the data were examined by Fourier analysis and by the band pass filtering. They showed the following periods; 7.4yr, 10.8yr and 23.3yr. The amplitude of 10.8yr period was stronger than that of 23.3yr, though the feature of amplitude variation of them differed. The periodicity of 22 years showed constant amplitude, however 11-year cycle was attenuated during the mid 40 years of the Spoerer Minimum. During the mid 40 years, the amplitude of 11-year cycle and 22-year cycle were equivalent. Thus, It is possible to say that the 22-year periodicity can be observed when the solar activity is quite weakened. We continue this study to get more detailed characteristics of the solar activity during the grand minima., 第15回名古屋大学タンデトロン加速器質量分析計シンポジウム(平成14年(2002年度)報告 Proceedings of the 15th Symposium on Researches Using the Tandetron AMS System at Nagoya University in 2002 日時:平成15 (2003)年1月30日(木)､31日(金) 会場:名古屋大学シンポジオン Date:January 30th and 31st,2003 Place:Nagoya University Symposion Hall

It is known that the periods when solar activity was extremely weak (so-called grand minima) existed several times in the last 1000 years. It is reported by Kocharov et al. that the solar activity periodicity during the Maunder minimum was not the 11 year variation but the 22 year variation. What does the cycle of 22 years mean? Does the periodicity of 22 years exist also in the minima other than the Maunder minimum? We have investigated the solar activity of the Sporer minimum, which preceded the Maunder minimum, in order to understand the periodicity of solar activity during the minima. Both the liquid scintillation method and the accelerator mass spectrometry method (AMS method) were used for measuring the ^C concentration in annual tree rings., 第14回名古屋大学タンデトロン加速器質量分析計シンポジウム(平成13 (2001)年度)報告

著者人数: 41名, Accepted: 2017-09-25, 資料番号: SA1170174000

Production rate of radiocarbon ^C in upper atmosphere depends on the solar activity through its modulation effect on the intensity of galactic cosmic ray on the earth. Tree rings record radiocarbon contents in the past because they take atmospheric carbon dioxide including radiocarbon by photosynthesis year by year. We are investigating radiocarbon contents in Yaku cedar to understand the variability of the solar activity in the last millennium and also the relation between the solar activity and the global climate change. Our recent measurement of ^C contents in tree ring sampls of the Yaku cedar from the Spoerer minimum shows a large dip in the period between 1470 and 1550 AD while the data for the period between 1410 and 1470 AD are rather constant. The reason for this large varuation of ^C contents is not known at present. Further measurements are necessary., 第13回名古屋大学タンデトロン加速器質量分析計シンポジウム(平成12 (2000)年度)報告 名古屋大学タンデトロン加速器質量分析計第2号機の研究成果と利用計画

The purpose of our investigation is to measure ^C concentration in the tree rings, in the period of a minimum of the solar activity, called as the Sporer Minimum (AD1416〜AD1534). In order to accomplish this purpose, we must know the absolute ages of the samples. Dendrochronology is one of the methods with which we determine absolute ages, if tree rings have concentric circles. But in case of Yaku ceder rings, dendrochronology is usually difficult to be applied, because of deformation of tree rings. In case of deformed tree rings, it seems to be useful to measure ^C concentration, using the fact that the peak of bomb effect is AD1964. In this study, we confirmed the validity of this method, using another Yaku ceder trees of which the absolute ages were measured by dendrochronology., 第11回名古屋大学タンデトロン加速器質量分析計シンポジウム(平成10 (1998)年度)報告 名古屋大学タンデトロン加速器質量分析計第1号機の研究実績と1号機,2号磯の利用計画