Assessment of I-129 measurement at low MV tandem voltages

作者：Zhao X L^*; Litherland A E; Kieser W E; Soto C

来源：Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms , 2007, 259(1): 265-270.

DOI：10.1016/j.nimb.2007.01.170

• iodine 129
• AMS
• charge state 3+

Significantly higher efficiencies for I-129 measurement by Accelerator Mass Spectrometry (AMS) would be possible if I-129(3+) ions could be counted at terminal voltages as low as 1 MV. However, at M/Q = 3, the molecular interference was anticipated to be severe; this has prevented the use of charge 3+ from being adequately considered. Instead, charge 5+ has been used at higher terminal voltages because of the minimal interference. During a recent performance assessment with charge state 3+, a background of I-129/(127) approximate to 10(-14) was readily obtained and few Sr-86(2+) and Ca-43(1+) ions were encountered. This surprising result is possibly due to the very low binding energy and consequent poor stability of anions such as CaSr- and Ca-3(-). Some triply charged molecular ions were found in the energy spectrum at lower stripping gas pressure but their interference with the detection of I-129(3+) was readily suppressed with the Ar gas stripper operated at normal thickness. It now appears that as long as the prepared AMS samples are of good chemical purity, the molecular fragments can be expected to remain quite low in intensity and readily resolved by the final detector. As a result, charge state 3+ can be used for 1291 measurements at lower terminal voltages with higher overall efficiency.

• 出版日期2007-6
• 单位中国科学院地球环境研究所