Isobar suppression for 36Cl accelerator mass spectrometry at the University of Tsukuba

Abstract

A 6 MV tandem accelerator at the University of Tsukuba, Japan, has been working on multi-nuclide (10Be, 14C, 26Al, 36Cl, 41Ca, and 129I) accelerator mass spectrometry (AMS) since 2016. This paper reports improvement of isobar suppression techniques for 36Cl AMS. Previous studies have shown that a Cu sample holder with AgBr backing is the most suitable for 36Cl AMS to decrease isobaric 36S interference. Therefore, the method of AgBr preparation was considered, and we found that preparation under acidic conditions was most appropriate to reduce 36S in 36Cl AMS. Cl charge states and their analysis method were considered to improve peak separation. 36Cl8+ was chosen for detection because it allows clear separation of 36S from the 36Cl spectrum. Furthermore, 36S spectrum tails could be removed using a third anode (dE3) signal. As a result, a 36Cl/Cl background of ∼3×10-15 was achieved.