Explosive detection machines on the basis of quadrupole resonance (QR) technology are under development for land reine detection and other antiterro¡ applications. The QR machines ate optimized to detect the actual explosive ingredient in a detonable formulation and to ignore signals from other, benign materials. This presents a safety and logistical challenge for QR land mine detector testing and calibration because of the hazards involved when handling even small amounts of a detonable explosive. The detonation hazard can be mitigated by adding inert mate¡ (desensitizers) to coat the crystalline explosive. The effect on the QR signal of various types of inert mate-¡ is examined, with a view to developing a safe QR land reine target.
I Introduction
Quadrupole Resonance Explosive DetectionQuadrupole resonance (QR) is a radio-frequency spectroscopic method. The signal detected by a QR explosive detection machine originates from the interaction between quadrupolar nuclei and microscopic electric field gradients created by the local electron environment [1]. This makes the QR signal very sensitive to small changes in the crystal lattice. The resonance refers to the fact that the nuclear system absorbs and reemits energy preferentially at specific frequencies.For the application of QR to land mine detection the resonance results from the 14N nuclei, typically found in the range of 500 kHz to 5 MHz. The exact QR frequency is very sensitive to the molecular environment and is therefore unique to each explosive chemical. The uniqueness of the QR signal also means that other nitrogen-containing materials do not interfere with the QR measurement.
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