Determination of the asymmetry parameter of EFG tensor from moments of NQRnutation spectra in powders

A never approach to determination of the asymmetry parameter of the EFG ten sor from zero-field nutation NQR spectra of the spin I= 3/2 nuclei in powde r samples is reported. The proposed theoretical treatment uses lineshape an alysis of the nutation NQR spectra by the method of line moments. The analy tical formulas for the lineshape of the powder nutation spectrum are given. It is shown that the asymmetry parameter can be determined from the second moment [omega(2)] and the frequency of only one singularity omega(2) of th e nutation spectrum. It is also shown that the asymmetry parameter can be d etermined from the second and fourth spectrum moments alone. The method is successfully demonstrated for the simulated nutation NQR spectra of the spi n I = 3/2 nuclei in powder samples.