| In three dimensions the Ewald circle becomes a sphere and
can intersect relpoints anywhere in the reciprocal lattice. However, it is unlikely to
intersect with more than 3 or 4 lattice points at the same time.  The
diffraction pattern which can be recorded for any particular k
vector and lattice orientation is usually seen as a projection onto a 2-D film. Click on
the animation opposite to show this.
Since very few relpoints are intersected, very few sets of planes give rise to
diffracted beams. In general, from a single crystal, only a few diffraction spots are
recorded.
Put another way: in a single crystal only a few sets of planes are orientated at
their Bragg
angle at any one time. |
