Identification of 129I interferences in accelerator mass spectrometry

Abstract The identification of interferences to 129 I n+ (n = 3–6) was conducted with a 5 MV tandem accelerator mass spectrometer at SUERC. In addition to 128 Te, the detectable interferences to 12 MeV 129 I 3+ ions include 43 Ca 1+ and 86 Sr 2+ which are likely injected as 43 Ca 86 Sr − , 43 Ca 32 S 18 O 3 − , etc. whereas those to 15 MeV 129 I 4+ ions include 32 S 1+ injected as 43 Ca 32 S 18 O 3 − , 65 Cu 2+ as 63 Cu 65 Cu 1 H − , 97 Mo 3+ as 97 Mo 16 O 2 − . The 18 MeV 129 I 5+ ions might be interfered by 77 Se 3+ and 104 Pd 4+ (or 104 Ru 4+ ) and the 21 MeV 129 I 6+ ions by 43 Ca 2+ , 65 Cu 3+ , 86 Sr 4+ and 108 Pd 5+ (or 107 Ag 5+ , 108 Cd 5+ ). Apart from 128 Te, these ions can be fully separated from 129 I in the gas ionization detector equipped with a thin SiN membrane window and propane gas, which contributes negligibly to the 129 I-AMS detection for samples after careful chemical preparation. Although the 129 I background is mainly controlled by Te content and the source memory, the rareness of Te in natural environmental samples results in our routine background 129 I/ 127 I level in range of ∼10 −14 . The precision and accuracy of 3% can be routinely achieved at 129 I/ 127 I > 10 −12 level at SUERC.