Neutron holography of metal-hydrogen systems

Neutron holography constitutes a novel technique to obtain structural information on an atomic scale. It is based on the recording of the interference pattern of neutron waves coherently scattered by atomic nuclei located on a crystal lattice with an appropriate reference wave. The technique is particularly well suited to obtain holograms of metal-hydrogen systems. In one approach, a point-like source of spherical neutron waves is realized inside a single-crystalline sample by making use of the large incoherent neutron scattering cross section of hydrogen nuclei, i.e. protons. Alternatively, strongly neutron-absorbing nuclei can be used as point-like detectors within a sample. Various features of the method are explained referring to a recent holographic reconstruction of the positions of the metal atoms around hydrogen on octahedral interstitial sites in a palladium-hydrogen single crystal. Further, the potential of the method for the investigation of metal-hydrogen systems, in general, is discussed.