Polished sapphire for ultracold-neutron guides

We show that polished sapphire allows one to efficiently reflect ultracold neutrons (UCN) at specular trajectories. The probability of specular UCN reflection at sapphire surface under typical experimental conditions was measured to be at least 99.8%. That could provide nearly loss-free transport of UCN between a source and an experimental installation at a distance of some 10 m. Polished sapphire can be used for specular neutron guides at steady and pulsed UCN sources. It can also be used in experimental installations, in particular, for building compact gravitational spectrometers and for study of the resonance transitions between neutron quantum states in the gravitational field.