We have produced a monochromatic neutron beam with the sharpest angular pro
file to date. Multiple Bragg reflections from optimally designed channel-cu
t silicon single crystals have produced neutron beams with theoretical Darw
in angular profiles. This experiment constitutes the first realization of t
he proposal made by Bonse and Hart 35 years ago and opens up avenues for ul
trasmall angle neutron scattering studies down to wave vector transfers of
10(-5) Angstrom (-1).