Use of atomic and molecular probes in NMR studies of materials and construction of a xenon-129 hyperpolarizer
1University of Oulu, Faculty of Science, Department of Physical Sciences
|Online Access:||PDF Full Text (PDF, 1 MB)|
|Persistent link:|| http://urn.fi/urn:isbn:9789514291043
|Publish Date:|| 2009-08-27
|Thesis type:||Doctoral Dissertation
|Defence Note:||Academic dissertation to be presented, with the permission of the Faculty of
Science of the University of Oulu, for public discussion in the Auditorium L10, Linnanmaa, on June 5<sup>th</sup>, 2009, at 12 o’clock noon.
Professor Clifford R. Bowers
Doctor Christopher I. Ratcliffe
Xenon atoms and sulfur hexafluoride (SF6) molecules can be dissolved in liquids and liquid crystals or adsorbed in porous materials. Nuclear magnetic resonance (NMR) spectra of 129Xe or 19F nuclei reveal information about their surroundings. This means that xenon atoms and SF6 molecules can be used as probes to indirectly study materials by NMR spectroscopy. The change in the spectra arises from a NMR interaction called shielding. Especially in the case of xenon, shielding reveals even the slightest changes, for example, in the density of a liquid it is dissolved in. Because a change in temperature leads to a change in the density of the liquid as well, temperature change is observed as a shift of the resonance line in the 129Xe NMR spectrum. This property can be utilized in the accurate determination of the sample temperature. Self-diffusion measurements of the gases provide additional information on a larger scale rather than just the immediate surroundings of atoms or molecules. Various liquid crystals were studied using xenon and SF6 as probes proving their applicability.
It is often considered that the signal observed in NMR experiments is very weak and limits the full potential of the method. This is true especially with the samples in gaseous form. The Spin-Exchange Optical Pumping (SEOP) hyperpolarization method solves this problem in the case of xenon. A 129Xe NMR signal can be enhanced by a factor of 104–105 by SEOP and this opens access to techniques that are not otherwise possible. The remote detection technique, which separates the encoding and detection steps of the typical NMR experiment both temporally and spatially, is one of these techniques. The potential of the combination of SEOP and remote detection techniques was shown in studies of thermally modified Pinus Sylvestris.
Report series in physical sciences
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