
Figure 1
Geometry of a plane intersecting a cone, representing a twodimensional detector intersecting a diffraction cone. (a) A single elliptical conic section cannot define the cone from which it came. (b) Plan view showing the geometry of a plane (thick line) intersecting a cone of opening angle , where is equivalent to Bragg's angle in the context of a powder sample diffracting to produce a diffraction cone. The projection of the resulting elliptical conic section is shown. (Diagrams are not drawn to scale.) 