抄録
The technical details of accelerator mass spectrometry (AMS) developed at the University of Tokyo tandem facility are described for 10Be and 26Al measurements. Using a unique techique called the “internal beam monitor method”, isotopic ratios of 10Be/9Be and 26Al/27Al are determined without sequentially accelerating each isotope. 10Be and 26Al are injected to the accelerator in forms of negative ions, 10Be16O- and 26Al-, accompanied by the pilot beams of 9Be17O- and 10B16O-, respectively. The accelerated negative ions are converted to positively charged atomic ions by passing through a thin Ar gas in the stripping canal at the high voltage terminal of the accelerator. The triply charged ions, 10Be3+ and 26Al3+, are selected and counted by a heavy ion detector, while the currents of 9Be3+ and 16O2+, decomposed ions from the pilot beams, are simultaneously monitored with Faraday cups at the focal plane of the magnetic analyzer. The monitor beam currents allow the determination of the beam transmission efficiency through the accelerator. The data are presented to show an ability of precise measurement. The reproducibilities for repeated measurements in 24 hours were 1~3% and 2~5% and the sensitivities were 5×10-14 and 1×10-13, for 10Be and 26Al, respectively.
