12/29/2023 0 Comments Powder diffractometerThe mail-in service is offered to everyone but is aimed at those with relatively 'basic' needs. ![]() ![]() Thus, use of the Ge(733) monochromator is restricted to those applications where highest resolution is clearly needed and where samples are available in sufficient quality and quantity.įor collaborative access to the diffractometer, please contact an instrument scientist or craig.brown (subject: Beam%20TIme%20Request, body: Dear%20Craig%2C%0A%0AI%20would%20like%20to%20know%20more%20details%20about%20accessing%20the%20BT1%20instrument%20for%20powder%20diffraction%20data%20collection.%20%0A%28please%20add%20as%20many%20details%20as%20possible.%29) (Craig Brown). With 7' collimation, gaussian line shapes with widths (FWHM) as small as 10' (delta d/d = 8 x 10 -4) are observed but for most samples the intrinsic sample broadening exceeds the instrumental resolution. 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.
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