Srncik M, Tims S G, De Cesare M, Fifield L K
Department of Nuclear Physics, Research School of Physics and Engineering, Australian National University, Canberra, ACT 0200, Australia.
Department of Nuclear Physics, Research School of Physics and Engineering, Australian National University, Canberra, ACT 0200, Australia.
J Environ Radioact. 2014 Jun;132:108-14. doi: 10.1016/j.jenvrad.2014.02.022. Epub 2014 Mar 12.
The variation of the (236)U and (239)Pu concentrations as a function of depth has been studied in a soil profile at a site in the Southern Hemisphere well removed from nuclear weapon test sites. Total inventories of (236)U and (239)Pu as well as the (236)U/(239)Pu isotopic ratio were derived. For this investigation a soil core from an undisturbed forest area in the Herbert River catchment (17°30' - 19°S) which is located in north-eastern Queensland (Australia) was chosen. The chemical separation of U and Pu was carried out with a double column which has the advantage of the extraction of both elements from a relatively large soil sample (∼20 g) within a day. The samples were measured by Accelerator Mass Spectrometry using the 14UD pelletron accelerator at the Australian National University. The highest atom concentrations of both (236)U and (239)Pu were found at a depth of 2-3 cm. The (236)U/(239)Pu isotopic ratio in fallout at this site, as deduced from the ratio of the (236)U and (239)Pu inventories, is 0.085 ± 0.003 which is clearly lower than the Northern Hemisphere value of ∼0.2. The (236)U inventory of (8.4 ± 0.3) × 10(11) at/m(2) was more than an order of magnitude lower than values reported for the Northern Hemisphere. The (239)Pu activity concentrations are in excellent agreement with a previous study and the (239+240)Pu inventory was (13.85 ± 0.29) Bq/m(2). The weighted mean (240)Pu/(239)Pu isotopic ratio of 0.142 ± 0.005 is slightly lower than the value for global fallout, but our results are consistent with the average ratio of 0.173 ± 0.027 for the southern equatorial region (0-30°S).
在南半球一个远离核武器试验场的地点，研究了土壤剖面中（236）U和（239）Pu浓度随深度的变化。得出了（236）U和（239）Pu的总存量以及（236）U/（239）Pu同位素比值。为了这项研究，选取了位于澳大利亚昆士兰州东北部赫伯特河流域（南纬17°30′ - 19°）一片未受干扰的森林地区的土壤岩心。U和Pu的化学分离通过双柱进行，其优点是能在一天内从相对较大的土壤样品（约20克）中提取这两种元素。样品在澳大利亚国立大学使用14UD串列加速器通过加速器质谱法进行测量。（236）U和（239）Pu的最高原子浓度出现在2 - 3厘米深度处。根据（236）U和（239）Pu存量的比值推断，该地点沉降物中的（236）U/（239）Pu同位素比值为0.085±0.003，明显低于北半球约0.2的值。（8.4±0.3）×10^11 原子/平方米的（236）U存量比北半球报道的值低一个多数量级。（239）Pu活度浓度与先前的一项研究结果高度一致，（239 + 240）Pu存量为（13.85±0.29）贝可/平方米。加权平均（240）Pu/（239）Pu同位素比值为0.142±0.005，略低于全球沉降物的值，但我们的结果与赤道南部地区（南纬0 - 30°）的平均比值0.173±0.027一致。
