Determination of Low Level 129I in Soil Samples Using Coprecipitation Separation of Carrier Free Iodine and Accelerator Mass Spectrometry Measurement

The accurate determination of ultra low level (129)I in sample is critical and essential for the application of natural (129)I in geological dating and environmental tracer studies. In this work, iodine was first separated from soil by combustion at high temperature; the released iodine was collected in an alkali trap solution. AgI-AgCl coprecipitaiton was used to separate carrier free iodine from the trap solution and to prepare target. (129)I in the target was then measured using a 3. 0 MV accelerator mass spectrometer. The recovery of iodine during the combustion is higher than 95%. An iodine recovery of about 75%-85% was obtained in the coprecipitation and the total recovery of iodine is above 70%. The developed method has been successfully used to determine (129)I in soil sample with low iodine content. A (129)I/(127)I atomic ratio as low as 10(-11) in the deep soil has been determined. The determination of (129)I/(127)I was ratio down to 10(-12) in solid samples.</p

I-129 level in seawater near a nuclear power plant determined by accelerator mass spectrometer

(129)I concentration in the seawater samples near a nuclear power plant was determined in the Xi&#39;an Accelerator Mass Spectrometer (AMS) Center. Isotope dilution method was used via addition of excessive amount of stable iodine ((127)I) in the sample before separation, and iodine in the seawater was separated by solvent extraction, and the back extracted iodine in iodide form was precipitated as Agl, which was used as AMS target for (129)I measurement. (125)I tracer was added to monitor the recovery of iodine in the whole separation process. (129)I/(127)I ratios in the prepared target were determined by AMS. The concentration of (127)I in seawater samples was determined by inductively coupled plasma mass spectrometry. The results show that the (129)I/(127)I atomic ratios in the seawater range from 8.29 x 10(-11) to 9.45 x 10(-10), approximately one order of magnitude higher than that in seaweed collected in the pre-nuclear era, but fall in the environmental level of global fallout.</p

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

The newly established 3 MV Accelerator Mass Spectrometry (AMS) facility in Xi&#39;an, with an instrument background of 2 x 10(-14) for I-129/I-127 ratio, provides efficient analytical capability to carry out I-129 environmental tracing studies. Chemical separation methods of iodine from different types of samples have been established at the Xi&#39;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 I-129 in samples with low total iodine concentration has been established, which can be used for analysis of geological samples for I-129 dating. Some environmental samples collected in China have been analyzed using the developed methods. The analytical results show I-129/I-127 ratios of (0.9-1.1) x 10(-10) for seawater collected adjacent to a nuclear power plant, and (3.02 similar to 5.43) x 10(-19) 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 I-129 level.</p