名古屋大学タンデトロン2号機の性能と運用

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  • Performance of the Second-Generation Tandetron AMS and Its Usage for Researches

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We have introduced a second-generation Tandetron (carbon dating system, Model 4130-AMS) which was manufactured by High Voltage Engineering Europe (HVEE) BV, the Netherlands. Two sets of the similar HVEE AMS system have been installed successfully at University of Groningen, Holland, and at University of Christian-Albrechts, Kiel, Germany. They have already proved excellent performances in carbon-isotope-ratio measurements : reproducibility of ^<13>C/^<12>C ratio as ±0.1% ; error and reproducibility of ^<14>C/^<12>C ratio as ±0.15-0.22% and ±0.3%, respectively. Main improvements of the 2nd-generation Tandetron compared with the old Tandetron are : (1) a high intensity cesium sputter ion source is equipped with the new system, so that the ^<14> counting rate is almost one order higher than that for the old system. In addition, since up to 59 targets can be loaded at a time, measurements can be conducted more efficiently. (2) carbon isotopes ^<12>C^-, ^<13>C^- and ^<14>C^- can be injected into a tandem accelerator simultaneously, by using a recombinator system, which will archive high accuracy measurements of the carbon isotope ratio. (3) the terminal voltage of the accelerator is 2.5MV, which gives the maximum yield in producing C^<3+> from C^- in the charge exchange process of the tandem accelerator. In addition, a slit feedback system with a position sensitive Faraday cup to monitor the energy of accelerated ^<13>C^<3+> ions stabilizes terminal voltage, which provides us highly stable isotope-ratio measurement. (4) a heavy ion detector measures E and E_<residual> of incoming ions, to separate ^<14>C^<3+> ions from various background ions. Provided that the background ions are rejected efficiently, ^<14>C ages older than 60,000 will be measurable with this system. (5) A computer program is equipped with the system which controls the carbon-isotope-ratio measurement for multi-samples automatically. This provides us a high-efficient measurement without any hard works of operation staff. As the results of those improvements stated above, the highest performances is the ^<14>C measurements with the new Tandetron is : (1) a measurement error of ^<14>C age can be as small as ±20 years with a measurement time of a few tens of minutes for a carbon sample of less than 1mg ; (2) a full automatic measurement can be routinely performed ; (3) more than 3,000 samples can be measured annually. The new system will be used efficiently and speedy by many domestic researchers as well as by those outside of the university, if graphite targets are provided to us which are prepared from raw carbonaceous materials by researchers themselves.

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