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The phase-object approximation for neutron scattering based on a one-dimensional dynamic forward scattering theory is discussed and used to calculate the differential cross section of an object. It is shown that this approximation is valid in ultra-small-angle neutron scattering (USANS) and spin-echo small-angle neutron scattering (SESANS) experiments on silicon gratings. In the weak scattering limit, the phase-object approximation reduces to the kinematic or first Born approximation. The spatial coherence function is used to describe instrumental resolution effects. Measurements on three different instruments are in good agreement with calculation results. In the experiment with a time-of-flight SESANS instrument, the effect ofPendellösungwith object size is observed.

Bonse-Hart double-crystal diffractometers (DCDs) with multi-bounce channel-cut crystals show rocking curves that depart dramatically from dynamical diffraction theory in their wings. The intrinsic background is many orders of magnitude higher than the predictions of dynamical diffraction theory. This effect was studied at the ultra-small-angle neutron scattering facility at the Atominstitut in Wien and at facilities in Grenoble, Jülich and Villigen. The scattering intensity contains Bragg reflections from the front and the back faces, and thermal diffuse scattering from the internal volume. The aim of this study was to eliminate this contamination and develop a new crystal design which provides optimal resolution. Therefore different ways were tested. In the first step the contamination was eliminated by cutting a groove in the middle of the back plate of the channel-cut crystals and inserting a cadmium absorber in this groove. With this modification an additional suppression of the wings of the rocking curve of about one order of magnitude was achieved. After this, we developed a new design for a DCD. The concept for this new crystal design was to avoid the back reflection and the thermal diffuse scattering. The different steps on the way to produce these crystals are presented in a detailed way. The crystal preparation and the different instruments where these crystals have been tested are also described.

Ultra-small-angle neutron scattering (USANS) with the use of perfect silicon crystals provides a resolution of the order of 10−5 Å−1 in reciprocal space, which corresponds to μrad in scattering angles and μm structures in real space. From small-angle scattering by artificial lattices follows a unique test procedure for the related devices and techniques. Corresponding measurements were performed at the USANS facilities of the Atominstitut in Vienna and of the S18 instrument at the ILL. We observed diffraction patterns from samples being periodically structured in one and two dimensions. These measurements take advantage of the extended coherence function of the set-up and the high quality of the manufactured silicon sample lattices. Due to these characteristics up to 50 interference orders were obtained at the S18 instrument. Scattering from two-dimensional periodic structures was observed for different orientations of the sample which shows characteristic diffraction maps in reciprocal space.

In 1998, the combined Interferometer and Ultra Small Angle Neutron Scattering (USANS) instrument S18 at the 58 MW High Flux Reactor at the Institute Laue-Langevin in Grenoble (France) started operation. The instrument has been upgraded to allow more advanced neutron optics experiments for fundamental, nuclear and condensed matter physics. The new supermirror guide along with the two channel cut silicon perfect crystals, configured as an advanced high resolution Bonse-Hart camera, provides optimal intensity conditions. A large range of wavelengths is accessible by variations of the Bragg angle and by using different reflecting planes of a properly cut silicon monochromator block in combination with different channel-cut analyzer crystals. The fine adjustment analyzer system is achieved by an advanced piezo drive, which has an accuracy of 0.036 seconds of arc. The basic features of the USANS camera, which takes advantage of a new tail suppression method, and the results of various test measurements concerning intensities, long term stability and the accessible wavelength range will be presented. A high resolution position sensitive detector can either be used to analyze beam profiles or to perform neutron radiography experiments.

The use of a bent comb-shaped analyzer crystal in a perfect-crystal SANS instrument makes possible the simultaneous measurement of many points of the rocking curve by means of a one-dimensional position-sensitive detector. This design permits high-resolution measurements with much higher efficiency than standard techniques. Results from our prototype instrument, using seven reflecting plates, are in very good agreement with predictions based on the dynamic theory of neutron diffraction.

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.

Multiple Laue rocking curves of perfect crystals show a narrow central peak with a width of some 10-3s arc and an additional oscillatory structure. The finite structure of these curves is analyzed for two- and three-crystal Laue arrangements. These profiles can be used for precise determinations of structure factors and for an extension of small-angle scattering experiments to the extreme small-angle regime where large objects and long-range particle correlations become visible. An extremely high angular resolution can be achieved without significant reduction of the intensity, owing to a decoupling of the angular resolution from angular width of the beam. The analytically calculated rocking curves are compared to numerical results and to experimental results and show good agreement with both.