ON THE RECONSTRUCTION OF NQR NUTATION SPECTRA IN SOLIDS WITH POWDER GEOMETRY

In single crystals the NQR nutation frequency depends on the relative orientation of the coil and the quadrupole axes. In powders the nutati on lineshape is a superposition of spectra from the randomly oriented single crystals, so that powder patterns appear in such experiments if the reconstruction is performed by the Fourier transform method. In t his paper an alternative reconstruction method of nutation spectra is suggested making use of the Hankel Transform. In this way the nutation spectra are simplified. Singularities arising with experiments for th e determination of the asymmetry parameter eta can easily be resolved. In the particular case of an axially symmetric quadrupolar tensor and a homogeneous radiofrequency field one can reduce the powder pattern to a single line without heterogeneous broadening with respect to orie ntation. Further improvement of the nutation spectra can be achieved b y taking advantage of the maximum entropy method, which strongly reduc es apodisation and noise problems. Applications of the new data manipu lation techniques to NQR imaging methods published elsewhere and 2D ze ro-field NQR spectroscopy are reported.