NMR Imaging of Materials (Monographs on the Physics and by Bernhard Blumich

By Bernhard Blumich

This booklet presents an creation to NMR imaging of fabrics protecting solid-state NMR spectroscopy, imaging tools for liquid and good samples, and weird NMR when it comes to unique methods to spatial answer like an NMR floor scanner. certain realization is dedicated to the big number of how you can generate photograph distinction in order that beneficial properties invisible through different equipment should be detected by means of NMR. It comprises large references to trendy literature and addresses staff in a variety of fields of imaging purposes in addition to scholars.

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By Bernhard Blumich

This booklet presents an creation to NMR imaging of fabrics protecting solid-state NMR spectroscopy, imaging tools for liquid and good samples, and weird NMR when it comes to unique methods to spatial answer like an NMR floor scanner. certain realization is dedicated to the big number of how you can generate photograph distinction in order that beneficial properties invisible through different equipment should be detected by means of NMR. It comprises large references to trendy literature and addresses staff in a variety of fields of imaging purposes in addition to scholars.

Show description

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1 Magnetic fields used in NMR spectroscopy and imaging. A strong magnetic field B0 is oriented along the z-direction of the laboratory frame, and a weak field Brf is oscillating perpendicular to it in the rf regime. When the weak field Brf(t) oscillates with the nuclear resonance frequency, energy can be transferred from the oscillating field to the nuclei and vice versa. Typical NMR frequencies are in the rf regime between 10 and 900 MHz. The strength of the excitation field is of the order of 1 mT and less.

From this the population difference An = nm — n m _1 is calculated. 6-10- 5 . 7) can be expanded, and the expansion can be truncated after the second term. This so-called high- temperature approximation can be used down to rather low temperatures. In this limit the population difference corresponding to the magnitude of the magnetization is proportional to the strength of the magnetic field. 5). 6 • 1015 of them make up for the nuclear magnetization. For this reason NMR spectroscopy is a method insensitive compared to infrared and optical spectroscopy with respect to the amount of sample needed.

For convenience, space-invariant or constant magnetic-field gradients are generally used (Fig. 5). A field gradient is the spatial derivative of the field. A constant gradient denotes a linear variation of the field with space. In a space-dependent magnetic field, the Larmor frequency depends on position. A sufficiently weak space dependence of the magnetic field can be expanded into a Taylor series. For example, a variation along the x coordinate is described by In most imaging experiments, the second and higher order derivatives in this expansion are small and negligible.

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