Résonance quadrupolaire de l'azote-14 : amélioration de la qualité spectrale et effet d'un champ magnétique statique de faible amplitude

Abstract : Nuclear quadrupole resonance (NQR) is a solid-state spectroscopic technique which doesn't require a static magnetic field in contrast to Nuclear Magnetic Resonance (NMR). It is used to detect molecules containing quadrupole nuclei (such as nitrogen-14). Nitrogen-14 quadrupole resonance is of particular interest because it is useful in the detection of drugs and explosives, which contain mostly of nitrogen molecules. In this thesis we have primarily focused on improving the spectral quality in nitrogen-14 quadrupole resonance (NQR) . Thus, we were concerned with the transient signals ( ringing ) following the radiofrequency (rf) pulse and which partly overwhelm the NQR signal. First, we demonstrated by theoretical and experimental study that low power measurements (< 3Watts ) were possible, allowing us to reduce the ringing amplitude. In addition, through this mode ( low power ), we have proposed an original quality factor switching circuit (Q -switch ) based on rf CMOS switch and which has reduced the ringing duration. The second part deals with the effect of a weak static magnetic field and various experimental parameters in nitrogen-14 quadrupole resonance. In the case of an axially symmetric electric field gradient tensor, we observed broadening or Zeeman doublets. By contrast, in the general case (no symmetry), we demonstrated the possibility to define the electric field gradient tensor from the line shape of a single transition instead of two transitions ( without static magnetic field ). This result reduces by half the time required for the characterization of a new nitrogen molecule.
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Sarra Aissani. Résonance quadrupolaire de l'azote-14 : amélioration de la qualité spectrale et effet d'un champ magnétique statique de faible amplitude. Autre. Université de Lorraine, 2014. Français. ⟨NNT : 2014LORR0069⟩. ⟨tel-01750792⟩

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