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A National Network Of Accelerators Dedicated To Material Irradiation (EMIR)
Hosting Legal Entity
Lujan Neutron Scattering Center at Los Alamos Neutron Science Center (LANSCE) of Los Alamos National Laboratory
Coordinating Country
United States
RI Keywords
neutron, position-sensitive detector (PSD), time-of-flight (TOF) Laue technique
Lujan Center, Group Office TA-53, Bldg. 622, Rm. 220, LANSCE, Los Alamos National Lab, Los Alamos, NM 87545 USA
The SCD is used to determine the crystal and magnetic structures of a wide variety of materials. Neutrons are scattered from the crystalline sample onto a 3He gas-filled area detector that is position sensitive and measures 25 centimeters on each side. The wavelengths of the neutrons are determined by their time-of-flight from the source to the detector. To cover all of the reciprocal space for a particular crystal, the sample is mounted on a goniometer. For most crystals, about 10 to 15 histograms will provide a full data set./p>

SCD can be used to study the structure of organometallic molecules, crystal-structure changes at solid-solid phase transitions, magnetic spin structures, twinned or multiple crystals, texture in polycrystalline materials, and structural or magnetic modifications of materials under pressures up to 20,000 atmospheres. The instrument measures a large fraction of reciprocal space at one time and therefore can be used for studies of unknown incommensurate structures and diffuse scattering.
Application Area
The Single Crystal Diffractometer (SCD) is based on the time-of-flight (TOF) Laue technique, which combines the use of two large-area positionsensitive
detectors (PSD) with a range of incident neutron wavelengths available from the pulsed neutron source.
With a stationary sample and detector, a threedimensional sampling of reciprocal space is obtained that may contain hundreds of Bragg reflections. Simultaneously, all of the reciprocal space between the peaks is measured, making this technique highly advantageous for studying pressure- and temperature-dependent phase transitions. Measurements can be performed in the temperature range from 4 - 900 K and under pressures from 0 - 5 kbar. Typical sample volumes are of the order of 1 mm3, but smaller crystals will suffice for strong neutron scatterers. SCD implements the Integrated Spectral Analysis Workbench (ISAW) for data visualization, reduction, and analysis. The Java based software was written and develooped by Dennis and Ruth Mikkelson of the University of Wisconsin-Stout in collaboration with Argonne National Laboratory. Shown is a room temperature sample of CePb3. Specifications: - Wavelength range: 0.5 - 10 ? - Beam diameter at sample: 1 - 5 mm - Time resolution: 1% - Maximum lattice constant: 20 ? - Detector: 1 multiwire proportional counter (25 cm x 25 cm) at 90° - Detector resolution: 2.5 mm - Moderator: Chilled water at 283 K - Sample environment: 10 - 300 K - Sample size: 0.5 - 10 cm3 - Experiment duration: 2 to 4 days per octant of reciprocal space