Analysis and environmental application of ¹²⁹I at the Xi'an Accelerator Mass Spectrometry Center

The newly established 3 MV Accelerator Mass Spectrometry (AMS) facility in Xi'an, with an instrument background of 2 × 10^-14 for ¹²⁹I/¹²⁷I ratio, provides efficient analytical capability to carry out ¹²⁹I environmental tracing studies. Chemical separation methods of iodine from different types of samples have been established at the Xi'an AMS Center, including solvent extraction and combustion followed by extraction or coprecipitation depending on sample types. A carrier free method for iodine separation and AMS measurement of ultra low level ¹²⁹I in samples with low total iodine concentration has been established, which can be used for analysis of geological samples for ¹²⁹I dating. Some environmental samples collected in China have been analyzed using the developed methods. The analytical results show ¹²⁹I/¹²⁷I ratios of (0.9-1.1) × 10^-10 for seawater collected adjacent to a nuclear power plant, and (3.02-5.43) × 10^-10 for soil samples collected in a less than 10 km area surrounding the NPP. These values are not significantly different from those measured in remote areas, reflecting a safe nuclear environment in terms of ¹²⁹I level.