Quasi-specular reflection of cold neutrons from nano-dispersed media at above-critical angles

We have predicted and observed for the first time a new phenomenon of quasi-specular reflection of cold neutrons at small incidence angles from nano-dispersed media. this is due to multiple small-angle scattering of neutrons from nano-sized inhomogeneities in the scattering potential. The reflection angle as well as the half-width of angular distribution of diffusively reflected neutrons is approximately equal to the incidence angle. For the powder of diamond nanoparticles used, the reflection probability was equal to ∼30% within the detector angular size, which corresponds to 40-50% of total probability (albedo) of quasi-specular reflection. The tangential velocity component of incident neutrons was up to an order of magnitude larger than the critical velocity for pure diamond. We provide an example of potential application of the discovered phenomenon for increasing cold neutron fluxes available for experiments.