Nuclear Quadrupole Resonance
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Nuclear Quadrupole Resonance or NQR is a technique related to nuclear magnetic resonance (NMR) which is used to detect atoms whose nuclei have a nuclear quadrupole moment, such as 14N, 35Cl and 63Cu. Since unlike NMR, NQR is done in an environment without a static (or DC) magnetic field, it is sometimes called "zero-field NMR". Many NQR transition freqencies depend strongly upon temperature.
There are several research groups around the world currently working on ways to use NQR to detect explosives. Units designed to detect landmines and explosives concealed in luggage have been tested. A detection system consists of a radio frequency (RF) power source, a coil to produce the magnetic exictation field and a detector circuit which monitors for a RF NQR response coming from the explosive component of the mine.