Hummel David, Ivan Lucian
Canadian Nuclear Laboratories, 286 Plant Road, Chalk River, Ontario, K0J 1J0, Canada.
J Environ Radioact. 2017 Jun;172:30-42. doi: 10.1016/j.jenvrad.2017.02.017. Epub 2017 Mar 17.
A "dirty bomb" is a type of radiological dispersal device (RDD) that has been the subject of significant safety and security concerns given the disruption that would result from a postulated terrorist attack. Assessing the risks of radioactive dose in a hypothetical scenario requires models that can accurately predict dispersion in a realistic environment. Modelling a RDD is complicated by the fact that the most important phenomena occur over vastly disparate spatial and temporal length scales. Particulate dispersion in the air is generally considered on scales of hundreds to thousands of meters, and over periods of minutes and hours. Dispersion models are extremely sensitive, however, to the particle size and source characterization, which are determined in distances measured in micrometers to meters, over milliseconds or less. This study examines the extent to which the explosive blast determines the transport of contaminant particles relative to the atmospheric wind over distances relevant to "near-field" dispersion problems (i.e., hundreds of meters), which are relevant to urban environments. Our results indicate that whether or not the effect of the blast should be included in a near-field dispersion model is largely dependent on the size of the contaminant particle. Relatively large particles (i.e., >40 μm in diameter), which are most likely to be produced by a RDD, penetrate the leading shock front, thereby avoiding the reverse blast wind. Consequently, they travel much farther than suspended aerosols (<10 μm) before approaching the ambient wind velocity. This suggests that, for these "near-field" dispersion problems in urban environments, the transport of contaminants from the blast wave may be integral to accurately predicting their dispersion.
“脏弹”是一种放射性散布装置（RDD），鉴于假定的恐怖袭击可能造成的破坏，它一直是重大安全问题的主题。评估假设场景中的放射性剂量风险需要能够准确预测现实环境中扩散情况的模型。对RDD进行建模很复杂，因为最重要的现象发生在空间和时间尺度差异极大的情况下。空气中的颗粒扩散通常在数百米到数千米的尺度上考虑，时间跨度为几分钟到几小时。然而，扩散模型对颗粒大小和源特征极其敏感，这些是在从微米到米的距离上、在毫秒或更短时间内确定的。本研究考察了在与“近场”扩散问题（即数百米）相关的距离上，爆炸冲击波相对于大气风对污染物颗粒传输的决定程度，这些距离与城市环境相关。我们的结果表明，近场扩散模型是否应包括爆炸的影响在很大程度上取决于污染物颗粒的大小。相对较大的颗粒（即直径>40μm）最有可能由RDD产生，它们穿透领先的冲击波前沿，从而避免了反向爆炸风。因此，在接近环境风速之前，它们比悬浮气溶胶（<10μm）传播得更远。这表明，对于城市环境中的这些“近场”扩散问题，爆炸波中污染物的传输可能是准确预测其扩散不可或缺的一部分。
