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

A preliminary study of small-mass radiocarbon samplemeasurement at Xi’an-AMS

To meet the measurement demands on small-mass radiocarbon (carbon content at 10&minus;6 g level) which are becoming increasingly significant, Xi&rsquo;an-AMS has made improvements to the existing method of sample loading and has upgraded the Cs sputter ion source from the original SO-110 model. In order to study the feasibility of small-mass samples in Xi&rsquo;an-AMS and evaluate the radiocarbon sample preparation ability using existing routine systems of H2/Fe and Zn/Fe, the small-mass samples prepared by four different methods are tested. They are the mass division method, mass dilution method, H2/Fe reduction method and Zn/Fe reduction method. The results show that carbon mass above 25 &micro;g can be prepared using the existing Zn/Fe system, but no less than 100 &micro;g is required using the existing H2/Fe system, which can be improved. This indicates Xi&rsquo;an-AMS are now able to analyze small-mass radiocarbon samples.</p

HIGH-LEVEL (14)C CONTAMINATION AND RECOVERY AT XI'AN AMS CENTER

A sample with a radiocarbon concentration estimated to be greater than 10(5) times Modern was inadvertently graphitized and measured in the Xi&#39;an AMS system last year. Both the sample preparation lines and the ion source system were seriously contaminated and a series of cleaning procedures were carried out to remove the contamination from them. After repeated and careful cleaning as well as continuous flushing with dead CO(2) gas, both systems have recovered from the contamination event. The machine background is back to 2.0 x 10(-16) and the chemical blank is beyond 50 kyr.</p