nuclear quadrupole resonance

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Nuclear quadrupole resonance

A selective absorption phenomenon observable in a wide variety of polycrystalline compounds containing nonspherical atomic nuclei when placed in a magnetic radio-frequency field. Nuclear quadrupole resonance (NQR) is very similar to nuclear magnetic resonance (NMR), and was originated as an inexpensive (no stable homogeneous large magnetic field is required) alternative way to study nuclear moments. It later gained a modest popularity. See Magnetic resonance

In the simplest case, for example, 35Cl in solid Cl2, NQR is associated with the precession of the angular momentum I (and the nuclear magnetic dipole moment μ) of the nucleus, depicted in the illustration as a flat ellipsoid of rotation, around the symmetry axis (taken as the z axis) of the Cl2 molecule fixed in the crystalline solid. The precession, with constant angle Θ between the nuclear axis and symmetry axis of the molecule, is due to the torque which the inhomogeneous molecular electric field exerts on the nucleus of electric quadrupole moment eQ. The absorption occurs classically when the frequency of the rf field and that of the precessing motion of the angular momentum coincide.

Interaction of 35 CI nucleus with the electric field of a Cl 2 moleculeenlarge picture
Interaction of 35CI nucleus with the electric field of a Cl2 molecule

NQR spectra have been observed in the approximate range 1–1000 MHz. Most of the NQR work has been on molecular crystals. For such crystals the coupling constants found do not differ very much from those measured for the isolated molecules in microwave spectroscopy. The most precise nuclear information which may be extracted from NQR data are quadrupole moment ratios of isotopes of the same element. If values for the axial gradient of the molecular electric field can be estimated from atomic fine structure data, then fair values of the quadrupole moment may be obtained. However, it has also proved very productive to use the quadrupole nucleus as a probe of bond character and orientation and crystalline electric fields and lattice sites, and extensive data have been accumulated in this area. See Microwave spectroscopy

McGraw-Hill Concise Encyclopedia of Physics. © 2002 by The McGraw-Hill Companies, Inc.

nuclear quadrupole resonance

[′nü·klē·ər ′kwäd·rə‚pōl ‚rez·ən·əns]
(physics)
The phenomenon in which certain nuclei in a static, inhomogeneous electric field absorb energy from a radio-frequency field.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
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InVision's wholly owned subsidiary Quantum Magnetics develops detection systems for weapons, narcotics, explosives and other threats based on quadrupole resonance and other proprietary magnetic sensing technologies.
The fluxional behavior of 2,6-dimethylphenyl(pentachlorocyclopentadienyl)mercury (II) has been examined in solution by variable temperature NMR spectroscopy and by Nuclear Quadrupole resonance (NQR) spectroscopy in the solid state.
It is shown that decreasing the shell layer thickness red-shifts the plasmon resonance and decreases the quadrupole resonance extinction [45,46].
Based on the Voshchinnikov and Farafonov (VF) code [57], it has been shown that in longitudinal polarization as the aspect-ratio of a nano-rod increases, the dipole plasmon resonance gradually is red-shifted and the quadrupole resonance peak, which is larger than the dipole peak in a nano-sphere, is further faded [29].
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In September of 1997, InVision Technologies purchased Quantum Magnetics, a company which uses quadrupole resonance to detect compounds found in sheet explosives, typically the most difficult type of explosive to detect.
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