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

The accurate determination of ultra low level I-129 in sample is critical and essential for the application of natural I-129 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. I-129 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 I-129 in soil sample with low iodine content. A I-129/I-127 atomic ratio as low as 10(-11) in the deep soil has been determined. The determination of I-129/I-127 was ratio down to 10(-12) in solid samples.