3-DIMENSIONAL DIFFRACTION PHENOMENON AT A 90-DEGREES BRAGG REFLECTION

The experimental observation of a three-dimensional diffraction phenom enon at a 90 degrees Bragg reflection is reported and discussed. A ref ined experimental technique for the direct observation and accurate me asurement of scattered intensity profiles in the vicinity of a 90 degr ees Bragg reflection was proposed and implemented. The detector arrang ement allowed the scintillator detection of back-reflected beams via f luorescence scattering from an in-beam copper plate. A small hole in t he plate allowed free passage of the incident beam. This detector syst em has allowed a very high ratio, up to five orders of magnitude, of f luorescence back-reflection peak to the incident beam air scattering b ackground. Three-dimensional tracking of the reciprocal lattice point of the Si(800) Bragg reflection around the 90 degrees Bragg position w as studied over a range of tilt angles in a plane perpendicular to the diffraction plane.