Speciation and migration of 129I in soil profiles

A method has been developed for speciation analysis of ultra low level I-129 in soil using sequential extraction combined with coprecipitation for separation of carrier free iodine and AMS measurement of I-129. Two loess profiles collected from northwest China were analyzed for species of I-129 and I-127. Similar partitioning of I-129 and I-122 was observed in the loess profiles, the distribution of iodine isotopes followed an order of organic &gt; leachable &gt; reducible &gt; residue. The I-129 concentrations and I-129/I-127 ratios decreased exponentially with the depth, and 2 orders of magnitude lower in the deepest layer (60 and 90 cm) compared with the top layer, indicating a significant contribution of anthropogenic input in the upper layer, and high retention of I-129 in soil. The mobility of I-129 in different fractions decreased in an order of leachable &gt; organic &gt; oxides &gt; residue. The results suggest that migration of iodine downwards in the soil profile is a slow process; the oxides and residue are the less mobile fractions of iodine.</p

Performance of Accelerator Mass Spectrometry for I-129 using AgI-AgCl carrier-free coprecipitation

I-129 has been successfully applied as tracer in environmental, geological, and oceanographic research. For samples with low stable iodine concentration and ultra low level I-129, the sample preparation technique to separate iodine prior to AMS measurement has been a bottleneck, limiting the applicability of I-129 We have reported a carrier-free method, using coprecipitation, to avoid the potential introduction of I-129 through the use of stable iodine carrier iodine. In this work, the detection limit and the analytical uncertainty of this method are investigated and minimum sample amount required to obtain reliable analytical results are estimated. The method is validated with a series of samples in ranges of known iodine concentrations and I-129/I-127 ratios. The results confirm our previous conclusion that an AMS target containing 5.0 mu g iodine can be used for analyzing samples with I-129/I-127 &gt; 10(-12), and that for samples with I-129/I-127 &lt; 10(-13) more than 25 mu g iodine is necessary.</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