  NMR spectra of 73 Ge (nuclear spin I = 9/2) in germanium single crystals with
different isotopic compositions have been measured at the frequency of 17.4 MHz
at room temperature. Due to the small concentration (~0.1%) of the magnetic (73
Ge) isotope, the magnetic dipole-dipole interaction is negligible in the
samples studied, and the observed specific features of the resonance lineshapes
(a narrow central peak and a wide plateau) are determined mainly by the
quadrupole interaction of magnetic nuclei with the random electric field
gradient (EFG) induced by the isotopic disorder. The second and fourth moments
of the distribution function of the EFG are calculated taking into account
local lattice deformations due to mass defects in the close neighborhood of the
magnetic nuclei, as well as charge density redistributions and lattice strains
induced by distant impurity isotopes. The simulated lineshapes, represented by
a superposition of Gaussians corresponding to individual transitions between
nuclear Zeeman sublevels, agree reasonably well with the measured spectra.
