Deposition of vaporized species onto glassy fallout from a near-surface nuclear test
Deposition of vaporized species onto glassy fallout from a near-surface nuclear test
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DOI：
10.1016/j.gca.2016.10.036
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发表时间：
2017-03-15
影响因子：
5
通讯作者：
Hutcheon, Ian D.
中科院分区：
文献类型：
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作者：
Weisz, David G.;Jacobsen, Benjamin;Hutcheon, Ian D.
在近地表核爆炸中，所产生的火球可以与地表相互作用，来自核装置的蒸发材料可以被并入来自该表面的熔融土壤和其他载体材料中。这种混合材料在淬火时成为玻璃状沉降物的来源，并局部沉积。已经提出了沉降物形成模型;然而，土壤和其他载体材料在火球中相互作用的具体机制和物理条件，以及随后将装置材料与载体材料结合起来，并没有受到很好的限制。我们观察到一个表面沉积层保存在界面处，两个空气动力学的沉降物玻璃聚集和融合，其特征在于11个这样的边界，使用空间分析，以更好地了解在火球中的物种的蒸发和冷凝行为。使用纳米级二次离子质谱法（NanoSIMS），我们在8个界面层中识别出来自装置的更高浓度的铀（U-235/U-238比率>7.5）。界面的主要元素分析表明，沉积层富含Fe、Ca、Mg、Mn和Na物种，而贫含Ti和Al物种。最值得注意的是，相对于在沉降玻璃内测量的平均浓度，Fe和Ca-轴承物种在界面层处富集约50%，而Ti和Al-轴承物种被耗尽约20%。发现SiO2在样品和界面上相对不变（类似于3%的标准偏差）。铝，难熔氧化物丰富的土壤中，连同丰富的U-235和Fe的显着的枯竭，建议富集物种的人为来源或意想不到的蒸发/冷凝行为。两种难治性（例如，Ca和U）和挥发性（例如，Na）物种大致共位在大多数观察到的层（1.5 μ m内）表明，一个连续的冷凝过程也可能发生。这些沉降物的形成过程偏离了沉降物形成的历史模式，以前在文献中没有得到承认。（C 2016 Elsevier Ltd.保留所有权利。
In a near-surface nuclear explosion where the resultant fireball can interact with the surface, vaporized materials from the nuclear device can be incorporated into molten soil and other carrier materials from that surface. This mixed material becomes a source of glassy fallout upon quenching and is locally deposited. Fallout formation models have been proposed; however, the specific mechanisms and physical conditions by which soil and other carrier materials interact in the fireball, as well as the subsequent incorporation of device materials with carrier materials, are not well constrained. We observe a surface deposition layer preserved at interfaces where two aerodynamic fallout glasses agglomerated and fused, and characterized 11 such boundaries using spatial analyses to better understand the vaporization and condensation behavior of species in the fireball. Using nanoscale secondary ion mass spectrometry (NanoSIMS), we identify higher enrichments of uranium from the device (U-235/U-238 ratio >7.5) in 8 of the interface layers. Major element analysis of the interfaces reveals the deposition layer to be enriched in Fe, Ca, Mg, Mn, and Na-bearing species and depleted in Ti and Al-bearing species. Most notably, the Fe and Ca-bearing species are enriched approximately 50% at the interface layer relative to the average concentrations measured within the fallout glasses, while Ti and Al-bearing species are depleted by approximately 20%. SiO2 is found to be relatively invariable across the samples and interfaces (similar to 3% standard deviation). The notable depletion of Al, a refractory oxide abundant in the soil, together with the enrichment of U-235 and Fe, suggests an anthropogenic source of the enriched species or an unexpected vaporization/condensation behavior. The presence of both refractory (e.g., Ca and U) and volatile (e.g., Na) species approximately co-located in most of the observed layers (within 1.5 mu m) suggests a continuous condensation process may also be occurring. These fallout formation processes deviate from historical models of fallout formation, and have not been previously recognized in the literature. (C 2016 Elsevier Ltd. All rights reserved.