A Versatile Bragg-Brentano/Seeman-Bohlin Powder Diffractometer

Abstract

An interchangeable Bragg-Brentano:Seeman-Bohlin diffractometer, with variable specimen setting, has been constructed. A study of the influence of the geometry on the resolution, angular displacement and intensity of diffraction profiles clearly demonstrates that the standard Bragg-Brentano method is to be preferred when recording Bragg reflections below 40°,2θ. At higher Bragg angles, which permit the specimen to be set further away from the X-ray source, it is demonstrated that the diffracted intensity of the Seeman-Bohlin method can be increased above that of the Bragg- Brentano because the use of an increased divergent angle does not reduce the resolution. A study of the effect of specimen setting on the systematic errors associated with the Seeman- Bohlin geometry indicates that a setting of 60° (half-angle from the X-ray source) gives optimum resolution with minimum displacement error.