RESUMO
Pulsed field gradient NMR diffusion experiments can, in principle, lead to the "diffusive diffraction" phenomenon. In practice, its observation by gradients of the static magnetic field is difficult in real systems because they involve internal gradients due to the static magnetic field (necessary for polarizing nuclear spins). This latter drawback can be circumvented by using gradients of the radio-frequency (rf) field (the other magnetic field used in any NMR experiment). For the first time, by means of rf gradients, a so-called diffusive diffraction peak has been observed in a real porous system and its position provides a value of the mean distance between pores; this can be further complemented by the mean pore size determined from the dependence of the apparent diffusion coefficient with respect to the diffusion interval.
