Mine detection by nuclear quadrupole resonance

Nuclear quadrupole resonance (NQR) methods of mine detection rely on the observation of radiofrequency (RF) signals from the ¹⁴N nuclei present in the explosive. The frequencies of these signals lie between 0.5 and 6 MHz; they are characteristic of a given explosive and provide not only a positive identification but also an estimate of quantity or depth. Unlike the better known technique of nuclear magnetic resonance (NMR), no static magnetic field is needed, so that portable probes can be used. Furthermore, signals are only seen in solids or solid-like materials, and because of the highly compound-specific nature of NQR frequencies, there is little, if any interference from other nitrogen-containing materials which may be present in the mine casing or the surrounding terrain. The paper discusses the principles of NQR and experimental methods, and its application to mine detection