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Explosives Detection with Nuclear Quadrupole Resonance

An emerging technology will help to uncover land mines and terrorist bombs

Joel Miller, Geoffrey Barrall

Hidden bombs pose an enormous menace. Some are responsible for such well-publicized atrocities as the downing of two Russian jetliners on the same day last August. Those in the many millions of land mines that now litter the globe garner fewer headlines on any particular day but do far more damage overall, killing or injuring more than 10,000 people each year. How can civilized society rid itself of such threats? Clearly, the answer is complicated, but one component of the solution is to devise equipment that can reliably uncover concealed explosives before they do harm.

Figure 1. Artificial legs await fitting...Click to Enlarge Image

We have been focused on that task for many years now. Specifically, we and our many government, academic and industry colleagues are trying to develop the means for detecting explosive chemicals based on a phenomenon called nuclear quadrupole resonance (NQR). This approach offers some distinct advantages over the other options available. For example, the ability of bomb-sniffing dogs and vapor detectors to sense explosives is influenced by environmental factors such as wind and ground moisture; also, these approaches can fail with an explosive that is hermetically sealed, as is the case for some types of land mines and could readily be arranged in a terrorist bomb. And one of the most high-tech tactics tried so far—sensing the nitrogen in explosives using thermal-neutron analysis—has proved to have inadequate sensitivity and specificity. Detection through NQR does not face these difficulties. To understand why not, it is helpful to review the basic physics behind this promising technique.

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