Extinction in Polycrystalline Materials

Abstract

An expression is given for an extinction factor appropriate to powders composed of spherical perfect crystal grains or subgrains. This factor extrapolates to the dynamical theory value for the plane parallel plate in the symmetric Bragg case. Experimental tests of the theory have been made by nelitron diffraction experiments on polycrystalline specimens of MgO of controlled grain size. Agreement is excellent to an extinction level of y = 0·60.