A preliminary study of direct 10Be2+ counting in AMS using the super-halogen anion BeF3−

The key to effective 10Be measurements by AMS is to efficiently suppress the interference of the isobar 10B and at the same time optimize 10Be transmission. In this work, a new approach of measuring 10Be by AMS has been studied. It uses the super-halogen anion of beryllium, BeF3−, which inherently suppresses 10B interference by nearly 5 orders of magnitude because the accompanying BF3− anion is rarely formed. The resulting 10B suppression factor is not as high as that achieved with energy degrader foils, but the 10B and 10Be separation in the final ionization detector was found to result in sufficient total 10B suppression for 10Be2+ to be counted directly at ∼6 MeV energies. Although the stripping yield from 10BeF3− to 10Be2+ is not as large as that from 10BeO−, this inefficiency is compensated by avoiding the reduction in transmission due to charge fraction splitting and optical transmission losses after the degrader foil. This paper summarizes our first observation of the direct 10Be2+ counting approach using the 3 MV multi-element system at the Xi'an AMS.