It is demonstrated experimentally that the well known spin-selective deflection of neutrons transmitted through a static magnetic field region with triangular geometric boundaries combined with the high angular resolution of a non-dispersive double-crystal arrangement can be used to polarize a thermal neutron beam to a degree close to unity at reasonably low laboratory fields of 1.0 to 1.5 T.

A new type of crystal monochromator is presented which facilitates the selection of a precisely fixed wavelength λ₀ from a continuum at an intermediate bandwidth Δλ/λ of typically 10⁻³. Its essential feature is consecutive Bragg reflections from two crystals with slightly different Bragg-plane spacings glued rigidly together at near-parallel orientation. The bicrystal effectively manifests a wavelength standard the exact value of which is determined by the angle β of misorientation of the two crystals. The application of a germanium–silicon version of the new device to neutron interferometry is described. The influence of ray geometry on the values of λ₀ and Δλ is discussed.

Amplitude and intensity distributions within the outgoing beams of the triple-Laue-case (LLL) interferometer have been calculated for the case of zero absorption, which in practice is predominantly encountered with thermal neutrons. The type-1 wavefield with antinodes on the atomic sites, which with X-rays is quite frequently anomalously attenuated in the lattice, is here fully taken into account together with the type-2 wavefield of anomalous low absorption. After the combined diffraction by beam splitter, mirror, and analyser crystal of the interferometer for an incident plane wave has been solved, the solution for an incident spherical wave is developed by Fourier expansion, by a similar method to that first given by Kato [Acta Cryst. (1961), 14, 526-532] for just one diffracting crystal plate. In order to optimize the interferometer geometry spatial intensity profiles as functions of the geometric dimensions of the interferometer and of the phase shift between the interfering beams are calculated. The influence of deviations from the ideal geometry is investigated. Deviations of the order of the extinction length can result in a drastic reduction of interference contrast. Very good energy-converging and contrast properties are found if tM = 2t_S= 2t_A where t_M, t_S, t_A are the thicknesses of mirror, beam splitter, and analyser respectively. The calculated intensity profiles are in agreement with preliminary experimental profiles obtained recently with a silicon interferometer at the HFR in Grenoble.

An experimental method is described for the determination of crystallite dimensions in polycrystalline materials. It is based on studying the geometry of streaks that appear in powder photographs taken with white X-ray radiation. A detailed analysis is presented that includes a differentiation between these streaks and somewhat similar streaks due to asterism. Results by synchrotron radiation from powder samples of various materials are discussed and compared with the crystallite dimensions obtained by other methods. It is demonstrated that the method is largely complementary to measurements by electron microscopy and that it is particularly useful for the determination of the thickness distribution of thin (0.005–0.5 μm) platelets, oriented parallel to the substrate.