  Scattering cold particles on an $N$-slit grating is shown to reproduce an
interference pattern, that manifests itself in the near-field region as the
fractal Talbot carpet. In the far-field region the pattern is transformed to an
ordinary diffraction, where principal beams are partitioned from each other by
($N-2$) weak ones. A probability density plot of the wave function, to be
represented by a gaussian wavepacket, is calculated both in the near-field
region and in the far-field one. Bohmian (geodesic) trajectories, to be
calculated by a guidance equation, are superimposed on the probability density
plot well enough. It means, that a particle, moving from a source to a
detector, passes across the grating along a single bohmian trajectory
through-passing one and only one slit.
  Keywords: Gaussian wavepacket, neutron scattering, guidance equation, bohmian
trajectory, near-field interference, far-field diffraction, Talbot carpet,
fractal
