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

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