The Ge(733) monochromator is used for study of materials such as perovskites where a subtle lowering of the unit cell symmetry requires separation of reflections at high angles or where precise determination of oxygen vacancies is desired. Diffraction intensities are approximately 25% of what is obtained with the Cu(311) monochromator. This monochromator has a takeoff angle of 120 o and produces neutrons with wavelength 1.197 Å. The Ge(733) monochromator provides the best resolution at high scattering angles, but longer data collection times are needed, often from 4 to 24 h.The Cu(311) monochromator has been used with 15' collimation to collect data for Rietveld refinement of the structures of a wide variety of materials, including high T c superconductors, fullerenes, ceramics, and intermetallics, as well as for determining phase fractions in multiphase powders. Typical data collection times range from 1 to 12 h, averaging 3-4 h. This monochromator has a takeoff angle of 90 o and produces neutrons with a wavelength 1.540 Å.

The Cu(311) monochromator is appropriate for the majority of samples, offering an optimal balance between intensity and resolution and a perfect gaussian line shape.It is also useful for studies of magnetic ordering and phase changes. The Ge(311) monochromator has been used for zeolite materials where high-angle diffraction measurements are not needed. Typical data collection times range from 15 minutes to a few hours, depending on sample size and diffraction properties. Diffraction intensities are approximately three times that obtained with the Cu(311) monochromator. This monochromator has a takeoff angle of 75 o and produces neutrons with wavelength 2.079 Å. The Ge(311) monochromator yields the highest neutron intensity and best resolution at low scattering angles.All monochromators give data up to 165 degrees in 2 theta range. The choice of three focusing monochromators, Ge(311), Cu(311), and Ge(733), and either a 60', 15' or a 7' in-pile Soller collimator allows optimization of the instrument's resolution minimum versus relative diffraction intensities.

Neutron powder