²⁶Al interferences in accelerator mass spectrometry measurements

Highlights: •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. -- Abstract: 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