NMR

1. NUCLEAR
MAGNETIC
RESONANCE

2. CONTENT
 History
 Definition
 Principles of NMR
 NMR Spectroscopy
 Applications of NMR
 Advantages of NMR
 Disadvantages of NMR

3. HISTORY
Nuclear magnetic resonance was first described and
measured in molecular beams by Isidor Rabi in 1938
and in 1944. In 1946,FelixBloch and Edward Mills
Purcell expanded the technique for use on liquids
and solids. Purcell had worked on the development of
radar and detection of radio frequency power and on the
absorption of such RF power by matter laid the
background for Rabi's discovery of NMR.
The develpoment of NMR as a technique in analytical
chemistry and biochemistry parallels the development of
EM technologies.

4. DEFINITION
Nuclear Magnetic Resonance (NMR) is the phenomenon
whereby a magnetic nuclei absorbs and emits energy in
the presence of a magnetic field.
This energy is at a specific resonance frequency which
depends on the strength of the magnetic field and the
magnetic properties of the isotope of the atoms.
The principle of NMR usually involves two sequential
Steps:
 The alignment (polarization) of the magnetic nuclear spins in
an applied, constant magnetic field H0.

5. DEFINITION
 The perturbation of this alignment of the nuclear spins by
employing an electro-magnetic, usually radio frequency (RF)
pulse. The required perturbing frequency is dependent upon
the static magnetic field (H0) and the nuclei of observation.
The two fields are usually chosen to be perpendicular to
each other as this maximizes the NMR signal strength. The
resulting response by the total magnetization (M) of the
nuclear spins is the phenomenon that is exploited in NMR
spectroscopy and magnetic resonance imaging.

7. PRINCIPLES of NMR
 All subatomic particles (neutrons, protons, electrons) have the
intrinsic property of spin
 This spin corresponds to a small magnetic moment
 In the absence of a magnetic field the moments are randomly
aligned
 When a static magnetic field, Bo is applied this field acts as a
turning force that aligns the nuclear spin axis of magnetic
nuclei with the direction of the applied field

9. PRINCIPLES OF NMR
 When a torque is applied to a spinning object, the axis of
the object moves perpendicularly to the applied torque in
motion called precession
 So the nucleus will precesses around Bo with a frequency
called the Lamour frequency
 This proton can be in 2 energy states depending on the
orientation of the axis
 The difference between the number of protons in each
state gives the bulk magnetization which provides the
signal measured by NMR devices

10. PRINCIPLES OF NMR
 The alignment of these protons is called polarization but this does not
happen immediately it grows with a time constant called longitudinal
relaxation time T1
 After T1 an oscillating magnetic field is applied, sending pulses of
radio-frequency energy into the formation
 The initial pulse is perpendicular to Bo and aligns the spins in the
transverse direction in phase with one another
 As the pulse dies, the magnetisation caused buy the
precession decreases as the spins return out of phase and the
signal seen in the receiver decays
 This very rapid decay is referred to as free induction decay
(FID)

11. NMR SPECTROSCOPY
 NMR spectroscopy is one of the principal techniques used to
obtain physical, chemical, electronic and structural
information about molecules due to either the chemical
shift, Zeeman effect, or the Knight shift effect, or a
combination of both, on the resonant frequencies of the
nuclei present in the sample.
 It is a powerful technique that can provide detailed
information on the topology, dynamics and three-
dimensional structure of molecules in solution and the solid
state.

12. Types of NMR spectroscopy
 Continuous wave (CW) spectroscopy
The Continuous Wave Spectroscopy laboratory is specialized
in the observation of equilibrium states in semiconductor
nanostructures.
 Fourier transform spectroscopy
Fourier transform spectroscopy is a measurement technique
whereby spectra are collected based on measurements of
the coherence of a radiative source, using time-domain or
space-domain measurements of the electromagnetic radiation or
other type of radiation.

13. Types of NMR spectroscopy
 Multi-dimensional NMR Spectroscopy
 Multi-dimensional nuclear magnetic resonance spectroscopy
is a kind of FT NMR in which there are at least two pulses
and, as the experiment is repeated, the pulse sequence is
systematically varied
 In multidimensional nuclear magnetic resonance there will
be a sequence of pulses and, at least, one variable time
period. In three dimensions, two time sequences will be
varied. In four dimensions, three will be varied.

14. Types of NMR spectroscopy
 Solid-state NMR spectroscopy
This technique complements X-ray crystallography in that it
is frequently applicable to molecules in a liquid or liquid
crystal phase, whereas crystallography, as the name implies,
is performed on molecules in a solid phase.

15. APPLICATIONS OF NMR
 MEDICINE
 The application of nuclear magnetic resonance best known to the
general public is magnetic resonance imaging for medical
diagnosis magnetic resonance microscopy in research settings.
 NMR is used to generate metabolic fingerprints from biological
fluids to obtain information about disease states or toxic insults.
 Biochemical information can also be obtained from living tissue (e.g.
human brain tumors) with the technique known as in vivo magnetic
resonance spectroscopy or chemical shift NMR Microscopy.

17. APPLICATIONS OF NMR
 CHEMISTRY
 By studying the peaks of nuclear magnetic resonance
spectra, chemists can determine the structure of many
compounds.
 NMR spectroscopy is used to unambiguously identify known
and novel compounds, and as such, is usually required by
scientific journals for identity confirmation of synthesized
new compounds.
 A chemist can determine the identity of a compound by
comparing the observed nuclear precession frequencies to
known frequencies.

18. APPLICATIONS OF NMR
 PETROLEUM INDUSTRY
 Another use for nuclear magnetic resonance is data
acquisition in the petroleum industry for petroleum
and natural gas exploration and recovery.
 A borehole is drilled into rock and sedimentary strata into
which nuclear magnetic resonance logging equipment is
lowered.
 Nuclear magnetic resonance analysis of these boreholes is
used to measure rock porosity, estimate permeability from
pore size distribution and identify pore fluids (water, oil and
gas).

19. ADVANTAGES OF NMR
 Only fluids are visible to NMR technology so porosity
measurement is independent of the lithology.
 Producible zones with high percentage of clay-bound water
can be identified.
 A better measurement of permeability is possible than
traditional plots.
 In-situ measurement of oil viscosity
 Differentiation of oil/gas zones

20. DISADVANTAGES OF NMR
 Any diamagnetic or paramagnetic ions present in the
formation can affect the tool response.
 Expensive
 Slower logging speeds
 Slimhole tools are not available
 Shallow depth of penetration
 Permeability measurement is actually an empirical
measurement and should only be used to compare to
permeabilities