Techniques for detecting explosives and contraband

Because terrorism continues to be a societal threat, scientists are still searching for ways to identify concealed weapons that can be used in terrorist attacks. Explosives are singled out for particular attention because they can easily be shaped to look innocuous, and are still hard to detect. At present, there are three methods under development for the detection of explosives: X-ray imaging, vapour detection and nuclear techniques, and this article will concentrate on the latter. Since there is no single technology that can address all the questions concerning the detection of explosives and other illicit contraband, the philosophy that emerges is that of an integral system combining methodologies. Such a system could contain a nuclear technology device, a vapour detector, and an X-ray imaging device, all backed by an intelligence gathering system. In this paper methods are suggested for identifying explosives which may be used in terrorist attacks and for detecting concealed drugs. Techniques discussed are X-ray imaging, combining high and low energy x-ray machines, vapour detection using a ''sniffer'' to collect vapour samples then analysing the vapour by gas chromatography, chemiluminescence and mass spectroscopy and nuclear techniques. Nuclear techniques, such as neutron activation analysis, are discussed in detail but it is stressed that they need to be carried out at speed to eliminate disruption and delay at airports etc. (UK)