Development of 41Ca-AMS at MALT, The University of Tokyo

Mr Takeyasu Yamagata1, Mr. Hironori Tokuyama1, Ms. Miwako Toya1, Mr Lezhi Wang1, Mr Li Zheng1, Prof Hiroyuki Matsuzaki1

1MALT, The University Of Tokyo, Yayoi 2-11-16, Bunkyo-ku, Japan

The long-lived radionuclide ⁴¹Ca (half-life 1.03 x 10⁵ y) is important for the environmental assessment of nuclear waste from decommissioning of nuclear facilities. Currently, Femto-isotopes such as ¹⁰Be, ²⁶Al, ³⁶Cl, and ¹²⁹I are measured using the 5UD Pelletron accelerator, National Electrostatics Corp., at MALT, The University of Tokyo. In this study, we developed a new AMS system of ⁴¹Ca at MALT.
We chose CaF₂ for the chemical composition of the ⁴¹Ca-AMS target, and the dried CaF₂ precipitation ware packed in a cathode with a 1.5 mm diameter. The 300nA of CaF₃- beam was extracted from the MC-SNICS ion source. ⁴¹CaF₃- (m.w.98) and ⁴⁰CaF₃- (m.w.97) were injected sequentially into the accelerator by the jumping method. We selected the charge state of 5+, which has a high charge fraction (3%) and a relatively low ⁴¹Ca/⁴⁰Ca background. The counts of ⁴¹Ca⁵+ were measured by the 2 plates gas ionization chamber. From the spectrum from the GIC, no significant interference of isobar as ⁴⁰K was investigated, although it might be only measured the standard sample and the reagent blank before, several unknown signals were investigated. The calibration curve was obtained from 10-¹² to 10-¹⁰ with good linearity. The background of ⁴¹Ca/⁴⁰Ca in our system was obtained 2 x 10-¹³. The background was increased by the scattering component from unknown ions.


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Nov 15 2021


11:00 am - 11:45 am