Basic NMR Principles
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Basic NMR Principles
NMR (Nuclear Magnetic Resonance) is made possible by the properties possessed by some
atoms that cause their nuclei (part of every atom) to have a magnetic moment. The atom
most commonly investigated by NMR is Hydrogen (
1
H), the nucleus of which is composed of
a single proton. Hydrogen is present in many natural and synthetic substances like oil, water,
polymers, pharmaceutics and foodstuffs. In a strong external magnetic field (called polarizing
field) produced by the permanent magnets in the Magnet Unit, the magnetic moments can be
oriented, and the vector sum of all moments results in a macroscopic magnetization. The
amount of magnetization depends on the strength of the external magnetic field and the
temperature.
Pulses of radio frequency (RF) at a suitable frequency can influence the magnetization in the
sample. In NMR this resonance frequency, called Larmor frequency, depends on the field
strength of the external magnetic field and the nucleus investigated. For example, at a field
strength of 0.47 Tesla, protons (
1
H) have a resonance frequency of 20 MHz. The orientation
of the magnetic field generated by the RF pulse is perpendicular to the static external
polarizing field.
When, for example, a sample containing NMR-active nuclei is exposed to a strong external
magnetic field by inserting a sample into the sample orifice of the magnet, the process of
buildup of macroscopic magnetization will start immediately, but it takes some time until the
equilibrium is reached. The time constant of this built-up process is called longitudinal
relaxation time
T
1
(see figure).
Figure 7.1: Increase of the NMR Signal Due to Longitudinal Relaxation
With skillful sequences of RF-pulses (generated by the minispec electronics and transmitted
to the sample via the probe) the macroscopic magnetization can be influenced. One
possibility is the generation of so-called transverse magnetization. This is not an equilibrium
state, and therefore different relaxation processes arise. The transverse magnetization is still
the vector sum of discrete atomic magnetic moments. Each one of these moments underlies
a specific time evolution, and a loss of phase coherence results. The time scale of this
magnetization loss is described by the transverse relaxation time
T
2
(see figure) in the easiest
case.
Summary of Contents for minispec LF Series
Page 1: ...minispec minispec LF series User Manual Version 002 Innovation with Integrity AIC...
Page 8: ...Introduction 8 72 E164809_2_002...
Page 13: ...Safety E164809_2_002 13 72 Figure 2 2 Example of a Stray Field Plot for the LF90 Top View...
Page 14: ...Safety 14 72 E164809_2_002...
Page 18: ...Transport Packaging and Storage 18 72 E164809_2_002...
Page 50: ...Operation 50 72 E164809_2_002...
Page 56: ...Maintenance 56 72 E164809_2_002...
Page 58: ...Replacement of Parts 58 72 E164809_2_002...
Page 64: ...Technical Data 64 72 E164809_2_002 Figure 12 1 An Example of a minispec Rating Plate...
Page 66: ...Contact 66 72 E164809_2_002...
Page 68: ...List of Figures 68 72 E164809_2_002...
Page 71: ...E164809_2_002 71 72...
Page 72: ...Bruker Corporation info bruker com www bruker com Order No E164809...
