For the geometry of the proposed experiment the main contributions to the relative energy resolution are:

1. Intrinsic width of the crystal (rocking curve width of a plane crystal,see
10.4)

2. Finite width of crystal, where
.
The maximum energy shift along the coordinate ** x** is given by:

3. Height of source

The need to avoid small Bragg angles again becomes obvious. With and being of the order of the influence of these quantities has to be optimized during preparation experiments. The influence of the finite vertical extensions, however, disappears in this order because we measure the geometrical distribution of the reflection in the detector plane (curvature correction).