Neutron Screening for Airborne Cargo.

目前，政治和科学方面都非常重视开发新的爆炸物和违禁品探测技术的必要性。最近的恐怖主义袭击，特别是2001年9月11日的恐怖主义袭击，已经发现了漏洞，并刺激了加强航空和其他运输工业安全的活动。目前，侦测航空货物中的隐藏违禁品主要是利用x射线成像技术。生产和检测技术成熟，机器相对便宜，操作简单。然而，x射线的缺点是与组成有机材料的低电子密度元素的相互作用概率很小。大多数违禁品，如炸药和非法药物，都是有机的，因此具有无法区分的x射线吸收或非相干散射特性。此外，虽然一些x射线扫描仪可以产生清晰的图像以及被检查对象的密度依赖阴影，但爆炸物和非法药物可以被塑造或包装成任何形式。这使得通过简单的形状识别来检测它们非常困难。这些限制刺激了替代方法的发展，包括基于中子的方法。虽然爆炸物和非法药物种类繁多，但大多数在一个或多个基本特征上很容易与普通材料区分开来。炸药的特点是氮和氧的比例相对较高，而碳和氢的比例相对较低，而非法药物通常富含氢和碳而缺乏氮和氧。由于中子不受电磁力的影响，它们可以深入物质内部，只与原子核相互作用。当中子相互作用时，核素以一种独特的方式反应，这取决于中子的入射能量和目标核素的种类。大多数核素在其散射截面上表现出独特的结构，这增加了特定入射中子能量和散射角下某些中子相互作用发生的概率。特别是，麻醉品和爆炸性物质的主要元素成分在与中子的相互作用方面彼此差别很大，因此可以通过这些差别来加以表征。我们将建立一个中子筛选装置的原型，该装置将整合来自发生器伽马闪光和发射中子的射线照相信息以及扫描材料中中子吸收产生的激活特征。这种信息融合将提供图像信息以及扫描货物的元素组成细节。

There is currently a massive political and scientific focus on the need to develop new explosive and contraband detection technologies. Recent terrorist attacks, especially those of 11 September 2001, have identified vulnerabilities and stimulated activities to improve security in aviation and other transport industries.At present, the detection of concealed contraband in air cargo is based mainly on the use of X-ray imaging. The production and detection technologies are mature, while the machines are relatively inexpensive and simple to operate. However, X-rays suffer from the disadvantage of having a small interaction probability with the low electron density elements from which organic materials are composed. Most contraband, such as explosives and illicit drugs, are organic and consequently have undistinguishable X-ray absorption or incoherent scattering characteristics. In addition, although some X-ray scanners can produce a sharp image as well as a density-dependent shading of the interrogated object, explosives and illicit drugs and can be moulded or packed into any form. This makes their detection very difficult through simple shape recognition. Such limitations have stimulated the development of alternative methods, including those based on neutrons. Although there are many types of explosives and illicit drugs, most are easily distinguished from common materials in one or more elemental features. Explosives are distinguished by relatively high proportions of nitrogen and oxygen and relatively low proportions of carbon and hydrogen whilst illicit drugs are generally rich in hydrogen and carbon and poor in nitrogen and oxygen.Since neutrons are unaffected by electromagnetic forces they can penetrate deeply into matter, interacting only with nuclei. When a neutron interacts, the nuclide reacts in a unique way that depends on the incident energy of the neutron and the species of the target nuclide. Most nuclides exhibit distinctive structure in their scattering cross sections which enhances the probability of certain neutron interactions occurring at specific incident neutron energies and scattering angles. In particular, the principal elemental constituents of narcotic and explosive substances differ strongly from one-another in their interactions with neutrons and can therefore be characterized via these differences.We will build a build a cut down prototype of a neutron screening device that will integrate radiographic information from the generator gamma flash and the transmitted neutrons with the activation signatures resulting from neutron absorption in the scanned material. This fusion of information will provide image information as well as details of the elemental composition of the scanned cargo.