Introduction:
Some nuclei, such as nitrogen-14, possess electric quadrupole moments.
When compounds with such nuclei are probed with radio-frequency signals,
they give rise to unique signals defined by the specific nucleus and its
chemical
environment.
An NQR mine detector has the big advantage in that the NQR technique
can detect many of the high explosives commonly used in small, anti-personnel
mines. Since it is the explosive that is being detected rather than an
object buried in the ground, the
number of "false positive" indications is drastically reduced.
Nuclear Quadrupole Resonance (NQR) provides an unprecedented degree
of
accuracy in the detection of plastic explosives and illegal drugs.
It works by using
low-intensity radio waves to probe the molecular structure of the substance
under
test. Nuclei rotating within the substance are momentarily tipped out
of alignment due
to the excitation from the incident radio waves.
As the nuclei attempt to right themselves, they produce a characteristic
signal of their own. This signal is picked up by a special receiver, and
is analyzed by a computer. Each type of explosive material has a unique
NQR "fingerprint" that can be readily distinguished from harmless materials.
NQR signature for RDX
explosive.
NQR signature
for PETN explosive.
The peaks occur at frequencies unique to the substance under test.
NQR has a better than 99% compound-specific detection rate and less
than 1% false
positive rate for very small amounts of plastic explosives. This makes
it an ideal
candidate technology for detecting many of the small, non-metallic
land mines that
cannot be detected using conventional methods.
Research studies:
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