名古屋大学タンデトロンAMS14Cシステムの現状と利用(2013) [in Japanese] Status and Applications of a Tandetron AMS System at Nagoya University in 2013 [in Japanese]
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An AMS system (Model 4130-AMS) dedicated to 14C measurements, built by High Voltage Engineering Europe (HVEE), B.V., The Netherlands, was delivered to Nagoya University in 1996/97. Acceptance tests of its performance on carbon isotope measurements were completed in January of 1999, and routine measurements began in mid-2000. Since completion of the acceptance tests in early 1999, we have encountered a lot of troubles with the machine, particulayly in 2002. Since the end of 2002, the machine has worked relatively well, expect for minor problems. The standard deviation (one sigma) of the 14C/12C ratio is around ±0.3% to ±0.4% (a bit larger than the uncertainty of about ±0.3% calculated from 14C counting statistics) and that of the corresponding 13C/12C ratio is ±0.03% to ±0.07%, as are tested for HOxII targets. The number of targets measured was 330, 1430, 2077, 1003, 1,979, 1679, 1772, 1115, 1339, 866, 1300, 1701, 1449, 1634, 1351 in each year from 1999 to 2013, respectively, and total number of targets measured by the end of 2013 is 21,024. We briefly describe the maintenance processes and application results of the AMS system in 2013. The Tandetron AMS system at Nagoya University worked well in the early four months of 2013, with only minor failures. On 10th May, a noise from the accelerator tank became large, almost similar to the large noise generated on 24th October in 2012. The noise in 2012 was generated from the broken bearing mounted in the power generator that supplied electric power to a terminal turbo-pump mounted inside the tank. It took almost one month to replace it to a new one. So, this time soon opened the tank and checked inside the tank, but could find no special objects that might have generated the noise. Since we could not find the source of the noise, and the noise generated in the normal atmospheric pressure was not so large, we have decided to operate the machine under the small but explicitly existing noise. However, at a pressure of 6.5 bar by SF6 gas, the noise became far bigger and we could not operate the machine. We opened the tank again checked every parts inside the tank more carefully, and finally found out that the noise is generated from the timing belt connecting the power motor at the high-energy end and rotating rod which is transferring mechanical power to the generator used for turbo-molecular pomp operation. The belt was a bit too lose and swinging between the two gear wheels during transferring mechanical power. We tightened the belt and the noise disappeared. It took totally two month to notice the source of the noise. On 22nd October, a big noise was generated again from the tank. This time, we also noticed that the terminal voltage was not stable. At the same condition of high-energy power supply, the terminal voltage readout was a bit low than the normal condition, and the readout decreased with time. We considered that the generating voltmeter (GVM) for measuring the high voltage of the accelerator is in the wrong, and decided to replace it to a new one. We replace it and readout of the high voltage became perfect. Owing to these difficulties with the machine, the total number of graphite targets measured was 1351 in 2013, about 300 smaller in number than that in 2012 (1634).
名古屋大学加速器質量分析計業績報告書 (25), 30-39, 2014-03