26Al interferences in accelerator mass spectrometry measurements

• We identified multi-interferences to 26Al3+, 26Al5+ and 26Al7+ with SUERC 5 MV accelerator mass spectrometer.
• 37Cl4+ as continuum events is the most significant interference to 26Al3+.
• The problem of interferences is generic in different charge states.

The identification of interferences to 26Al was conducted with a 5 MV tandem accelerator mass spectrometer. In addition to 9Be1+, 17O2+ and 35Cl4+ ions observed previously, this study confirmed existence of the most significant interference 37Cl4+ continuum ion to 16 MeV 26Al3+ by measuring primary standard mixed with Cl with various 37Cl/35Cl ratios. The 37Cl− ions were formed by 37Cl16O− molecular-dissociation before the injection magnet, resulting in −0.7% of 26Al− magnetic rigidity. Subsequently, the 37Cl4+ ions have ME/q2 value that differ from 26Al3+ by −0.1%. These allow the 37Cl− and 37Cl4+ to simultaneously pass through injection magnet, analytical magnet and high-energy analyser, and finally reach the detector with 26Al3+.Further investigations on high charge states (26Al5+ and 26Al7+) indicate that the problem of interferences is generic. That is, interferences closest to 24 MeV 26Al5+ ions include 10B2+, 16O3+, 35Cl7+ and 37Cl7+ ions, while 32 MeV 26Al7+ ions may be interfered by 7Li2+, 16O4+, 18O5+, 35Cl9+ and 37Cl9+. However, it remains unclear that 37Cl continuum events observed in 26Al3+-AMS do not exist in 26Al5+ and 26Al7+-AMS operations.