B. Alefeld

High-resolution focusing SANS with a toroidal neutron mirror

Presently, high-resolution instruments for small-angle neutron scattering (SANS) use the conventional pinhole cameras. For high resolution they have to be extremely long (80 m for D11). Much shorter instruments can be built with focusing mirrors [1–3]. So far, however, this principle was not successful because of the insufficient quality of conventional optical mirrors. Recently, we succeeded in building a 20 m long focusing instrument at the NSE spectrometer IN15 in the ILL Grenoble. It uses a 4 m long, high-quality mirror as developed for X-ray telescopes. The image has a sufficiently low parasitic halo. Test experiments on polymeric precipitates down to Q=4×10−4 A−1 were successfully carried out. We expect that the Q-range can be extended to ≈10−4 A−1.

X-ray space technology for focusing small-angle neutron scattering and neutron reflectometry

Abstract In Julich, a small-angle neutron scattering instrument and neutron reflectometer will be built, both of them use a double-focusing mirror, which produces an one-to-one image of the entrance on the detector. This neutron focusing technique, known since 50 years, has become practicable only recently, since very smooth mirror surfaces were produced for X-ray space telescopes. The neutron mirrors are produced by the same technique. The focusing is especially good for high-resolution experiments (with the momentum transfer Q

The long-wavelength neutron spin-echo spectrometer IN15 at the Institut Laue-Langevin

Abstract A new ultra-high resolution neutron spin-echo spectrometer at the ILL (Grenoble) extends the time range for measurements of the intermediate scattering function S(Q,t) far beyond what has previously been possible. The spectrometer design is traditional, utilizing long neutron wavelengths (8–25 A) and large, homogeneous precession coils to reach Fourier times approaching the microsecond. The standard operational mode is currently functional, providing a Fourier time range of 0.03–180 ns, and a momentum transfer between 0.01 and 0.2 A−1. The other two operational modes (neutron optical focusing and time of flight) are also discussed.

KWS-3: The New (Very) Small-Angle Neutron Scattering Instrument Based on Focusing-Mirror Optics

Ultra-small angle (U-SANS) and small angle neutron scattering (SANS) experiments are performed by two different types of instruments to cover a combined Q-range from ≈10−5Å−1 up to ≈1Å−1. Bonse-Hart cameras (double crystal diffractometers) are used for U-SANS experiments, whereas the “standard” SANS experiment is performed using a pinhole camera. In principle, the Q-range of both instrument classes overlaps. Typical U-SANS instruments like S18 (ILL), PCD (NIST), or DKD (FZJ) may reach maximum Q-vectors of ≈5 × 10−3. The disadvantage of these instruments is that they do not allow taking a full area image on a 2D position sensitive detector. On the other hand, the well-known pinhole instrument D11 at Institut Laue-Langevin (France) reaches a minimum Q-vector of 5 × 10−4Å−1 by use of large wavelengths and sample-to-detector distances (≈40m).

Polarization analysis for the 2D position-sensitive detector of the HADAS reflectometer in Jülich

A neutron reflectometer with polarization analysis is being built on the basis of the HADAS spectrometer in the neutron guide hall at the research reactor FRJ-2 (DIDO) in Julich. The new instrument is optimized for reflectivity and diffuse scattering measurements under grazing incidence on layered magnetic structures with thicknesses in the nm range. In order to measure diffuse scattering with polarization analysis, the 2D position-sensitive detector has been equipped with a polarization analyser that consists of a stack of supermirrors parallel to the scattering plane. First tests have revealed that the resolution of the instrument is not reduced by the polarization analyser. A flipping ratio of 20 has been achieved already during the first experiment.

Structural and magnetic characterization of Fe/δ-Mn thin films

Abstract We report on a structural and magnetic investigation of Fe/δ-Mn multilayers. In situ LEED shows that Mn grows epitaxially on BCC Fe with a good crystallinity up to 30 A. Reflectivity and small-angle diffuse scattering of synchrotron radiation on Fe/Mn/Fe sandwiches reveal sharp interfaces with correlated roughness. From MOKE measurements, evidence for non-collinear coupling between the Fe layers was found for Mn spacer thicknesses below 13 A. With polarized neutron reflectometry and high-angle neutron diffraction we could not detect any sign of magnetic order inside the Mn layers.

Recent developments in neutron optics, in particular for neutron small angle scattering

Abstract Diferent types of SANS instruments are compared, in particular dealing with instruments using a focussing mirror. Studies concerning the quality of Ni-coated glass mirrors are presented, and a neutron lens consisting of micro guides is discussed.

Monochromator design for the HADAS reflectometer in Jülich

Abstract A reflectometer with polarization analysis is being built on the basis of the HADAS spectrometer in the neutron guide hall at the research reactor FRJ-2 (DIDO) in Julich. For obtaining the optimal flux at the sample position, the performances of several monochromator designs have been calculated, e.g. focusing mirrors, mosaic monochromator crystals and bent perfect crystal monochromators. Under the given geometrical limitations a double monochromator with bent perfect Si crystals and vertical focusing has the best performance.

High precision lattice parameter measurements on galliumarsenid by neutronbackscattering

Abstract A new four-counter-method was developed for lattice parameter measurements on GaAs-LEC-crystals reaching an accuracy of Δa a≈10 -7 . A linear decrease of Δa a=2x10 -6 was obtained with increasing stoichiometry in a region ranging from a composition XAs = 0.49665 (Ga-rich) to XAs=0 .50155 (As-rich). For the first time crystal instead of melt stoichiometry was investigated.