First realization of Bonse-Hart angular profiles for multiple Bragg reflections

We have produced a monochromatic neutron beam with the sharpest yet angular profile. We evolved an optimal design for the geometry of a channel-cut perfect crystal effecting a multiple Bragg reflection. Using a pair of such channel-cut silicon crystals, we recorded rocking curves for a triple-triple symmetric {111} Bragg reflection of 5.229 A neutrons at the V12b Double Crystal Diffractometer in BENSC. The data agree with the theoretical Darwin reflection curves over an intensity range spanning five orders of magnitude. This constitutes the first realization of the proposal made by Bonse and Hart 35 years ago. Our results mark an order of magnitude improvement over the previous best USANS profiles.