名古屋大学に設置されているGIC社およびHVEE社製の2台のタンデトロン加速器質量分析計の現状

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  • Present Status of the GIC-and HVEE-Tandetron AMS Systems of the DMRC, Nagoya University

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In the financial years of 1995-1996,we introduced a second-generation Tandetron (a carbon dating system, Model 4130-AMS) which was manufactured by High Voltage Engineering Europe (HVEE) BV, the Netherlands. Main improvements of the 2nd-generation Tandetron compared with the old GIC(General Ionex Corporation)-Tandetron are : (1) a high intensity cesium sputter ion source is equipped with the new system, so that the ^<14>C 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- are 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 gas ionization 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. These improvements are discussed here in detail. As the results of those improvements stated above, the highest performances in 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 1 mg ; (2) a full automatic measurement can be routinely performed ; (3) more than 3,000 samples can be measured annually.

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