  A simple model of X-Ray standing waves (XSW) formation in the slit of a
planar waveguide of X-Ray radiation beam for the angle area restricted by the
critical total reflection angle is developed. It is shown that the model is
true for a case of the Bragg reflection. The conditions required for XSW to
appear in the space between two polished parallel plane plates are formulated
and a slit size interval conforming to these conditions is evaluated. A
mechanism of a XSW intensity decrease in a planar waveguide is proposed. This
mechanism explains a high efficiency of slitless collimator application for the
transportation of narrow X-Ray beams.
  Some recommendations on the application of the planar X-Ray waveguide in
X-Ray structural and spectral studies of surface are presented.
