Quasi-specular albedo of cold neutrons from powder of nanoparticles

We predicted and observed for the first time the quasi-specular albedo of cold neutrons at small incidence angles from a powder of nanoparticles. This albedo (reflection) is due to multiple neutron small-angle scattering. The reflection angle as well as the half-width of angular distribution of reflected neutrons is approximately equal to the incidence angle. The measured reflection probability was equal to ~30% within the detector angular size that corresponds to 40 − 50% total calculated probability of quasi-specular reflection. Coherent scattering of ultracold (UCN), very cold (VCN) and cold (CN) neutrons on nanoparticles could be used (1), (2) in fundamental and applied low-energy neutron physics (3), (4), (5), (6). A theoretical analysis of such scattering could be found, for instance, in (7). In the first Born approximation, the scattering amplitude equals f θ = − 2mU0 ħ2 r sin qr qr 3 − cos qr qr 2 , q = 2ksin θ