Nuclear quadrupole resonance
spectroscopy or NQR is a chemical analysis technique related to nuclear magnetic resonance (NMR
Nuclear magnetic resonance is a physical phenomenon in which magnetic nuclei in a magnetic field absorb and re-emit electromagnetic radiation...
In NMR, nuclei with spin
In quantum mechanics and particle physics, spin is a fundamental characteristic property of elementary particles, composite particles , and atomic nuclei.It is worth noting that the intrinsic property of subatomic particles called spin and discussed in this article, is related in some small ways,...
≥ 1/2 have a magnetic dipole moment so that their energies are split by a magnetic field, allowing resonance absorption of energy related to the difference between the ground state energy and the excited state. In NQR, on the other hand, nuclei with spin ≥ 1 , such as 14N
Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...
Chlorine is the chemical element with atomic number 17 and symbol Cl. It is the second lightest halogen, found in the periodic table in group 17. The element forms diatomic molecules under standard conditions, called dichlorine...
Copper is a chemical element with the symbol Cu and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish...
, also have an electric quadrupole
A quadrupole or quadrapole is one of a sequence of configurations of—for example—electric charge or current, or gravitational mass that can exist in ideal form, but it is usually just part of a multipole expansion of a more complex structure reflecting various orders of complexity.-Mathematical...
moment so that their energies are split by an electric field gradient, created by the electronic bonds in the local environment. Since unlike NMR, NQR is done in an environment without a static (or DC) magnetic field, it is sometimes called "zero field NMR
Zero field NMR is the NMR spectrum analysis of certain substances in an environment carefully screened from magnetic fields. It is useful for studying nuclei with spins greater than 1/2, and for studying molecular dynamics ....
". Many NQR transition frequencies depend strongly upon temperature.
Any nucleus with more than one unpaired nuclear particle (protons or neutrons) will have a charge distribution which results in an electric quadrupole moment.
Allowed nuclear energy levels are shifted unequally due to the interaction of the nuclear charge with an electric field gradient supplied by the non-uniform distribution electron density (e.g. from bonding
electrons) and/or surrounding ions. The NQR effect results when transitions are induced
between these nuclear levels by an externally applied radio frequency
Radio frequency is a rate of oscillation in the range of about 3 kHz to 300 GHz, which corresponds to the frequency of radio waves, and the alternating currents which carry radio signals...
(RF) magnetic field.
The technique is very sensitive to the nature and symmetry of the bonding around the nucleus.
The energy level shifts are much larger than the chemical shifts measured in NMR. Due to symmetry,
the shifts become averaged to zero in the liquid phase, so NQR spectra can only be measured
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 excitation field and a detector circuit which monitors for a RF NQR response coming from the explosive component of the object.
Another practical use for NQR is measuring the water/gas/oil coming out of an oil well
An oil well is a general term for any boring through the earth's surface that is designed to find and acquire petroleum oil hydrocarbons. Usually some natural gas is produced along with the oil. A well that is designed to produce mainly or only gas may be termed a gas well.-History:The earliest...
This particular technique allows local or remote monitoring of the extraction process, calculation of the well's remaining capacity and the water/detergents ratio the input pump must send to efficiently extract oil.
The strong temperature dependance of NQR's frequency allows to make a precise temperature sensor with resolution 10-4