Determination of Low Level 129I in Soil Samples Using Coprecipitation Separation of Carrier Free Iodine and Accelerator Mass Spectrometry Measurement
Abstract The accurate determination of 129 I in samples at ultralow level is critical and essential for the application of natural 129 I in geological dating and environmental tracer studies. In this study, iodine is first separated from soil through combustion at high temperature; the released iodine is collected in an alkali trap solution. AgI-AgCl coprecipitation is used to separate carrier-free iodine from the trap solution and to prepare 129 I target. 129 I is then measured using a 3.0-MV accelerator mass spectrometry (AMS) in the Xi'an Accelerator Mass Spectrometry Center. The recovery of iodine is higher than 95%, during combustion. An iodine recovery of about 75%–85% is obtained through coprecipitation separation method, and the total recovery of iodine is above 70%. The developed method has been successfully used to determine 129 I in soil samples with low iodine content. An atomic ratio of 129 I/ 127 I as low as 10 −11 in deep soil has been determined. With this method, the ratio of 129 I/ 127 I down to 10 −12 can be determined in solid samples with low level of iodine.