  The dynamical scattering theory is developed for the Laue diffraction of the
M\"{o}ssbauer rays and x-rays, whose angular distribution is comparable with
the diffraction angular range. Both the Rayleigh and the resonant nuclear
scattering are taken into account.
  We consider typical case when incident radiation first passes through an
entrance slit and afterwards diffracts at the crystal planes within the
Borrmann triangle.
  In calculations of the wave function for $\gamma$-photons, refracted or
diffracted in such strongly absorbing crystal, we apply the saddle-point
method. The distribution of their intensities over the basis of the Borrmann
triangle is analyzed. In the spherical wave approximation of Kato, when
aperture of the incident beam much exceeds the diffraction interval, the
derived formulae well correlate with the familiar equations of the diffraction
theory of X-rays.

Optics;Materials Science