Development of the ultrasensitive detection method for hard-to-measure nuclides by means of accelerator mass spectrometry

Accelerator mass spectrometry (AMS) is a mass analysis technique making use of tandem accelerators for determination of ultra-low isotopic ratios from 10^-10 to 10^-15. The AMS technique takes advantage of the high ion energies and negative ion interferential instabilities to enable extremely low backgrounds to be achieved. In the case of ¹⁴C which has a half-life of 5,730 years and an abundance in living organisms of 10^-12 relative to stable ¹²C, small tandem or single end type accelerators are mainly used for ¹⁴C-AMS. However, the utility of AMS is not only limited to ¹⁴C, but many other hard-to-measure nuclides such as ¹⁰Be, ²⁶Al, ³⁶Cl and ¹²⁹I are suitable to analyze. At present, five new generation 6 MV tandem accelerators were installed in the world for multi-nuclide AMS. In 2016, the 6 MV AMS system was designed and constructed for the high-sensitivity multi-nuclide AMS at the University of Tsukuba. We have developed ⁴¹Ca and ⁹⁰Sr AMS methods by using the 6 MV AMS system. Future prospects of the ultrasensitive detection method for hard-to-measure nuclides by means of the most-advanced AMS system are reported in this paper. (author)