Level and source of 129I of environmental samples in Xi'an region, China

Iodine-129 is widely used as a tracer in various environmental practices such as monitoring of nuclear environmental safety, seawater exchange and transport, geochemical cycle of stable iodine and dating of geological events. The spatial distribution of (129)I concentration varies significantly on global scale because of anthropogenic input from nuclear activities coupled with scarcity of data on environmental (129)I variability in many parts of the world including Asia. Here we report new data on (129)I and (127)I concentrations in soil, vegetation, river water and precipitation collected from Xi&#39;an area, China. The results indicate values for environmental (129)I/(127)I ratios in the investigated area range from 1.1 x 10(-10) to 43.5 x 10(-10) with a mean of 20.6 x 10(-10), which is 1-3 orders of magnitude lower than the ratios observed in Europe, but comparable with those observed in the locations far from direct effect of point release sources and at similar latitude. The main source of (129)I in the investigated area is attributed to the global fallout of both atmospheric nuclear weapons testing and long distance dispersion of fuel reprocessing releases. (C) 2011 Elsevier B.V. All rights reserved.</p

Be-10 signature of the Matuyama-Brunhes transition from the Heqing paleolake basin

We present a new 10Be record spanning the Matuyama-Brunhes (M-B) reversal from the Heqing paleolake basin in southern China. It provides a robust proxy for past geomagnetic variations that can be compared with paleomagnetic records. The M-B transition is identified as a pronounced maximum of authigenic 10Be/9Be ratio between 768.6 and 778.5 ka, that is consistent with all other available 10Be-proxy records from marine, ice and loess archives. However, it is offset by approximately 0–60 cm depth from the magnetic signature of the polarity transition recorded in the same sediments. We attribute this offset to the lock-in effect of the remanence acquisition process, which is similar to the phenomenon that exists in marine sediments. We suggest that after eliminating the climatic-hydrological signal, the Heqing sediments may be used as an archive for atmospheric 10Be production rate changes. The combination of magnetic remanence measurements and the cosmogenic 10Be allows for a more precise geochronology of geomagnetic polarity reversals

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