Author: C. M. I Enrique, K. Lieutenant, E. Farhi and L. Cussen
Date: 13 Apr 2006
The diffractometer D2B is characterised by the very high take-off angle (135 deg)
for the monochromator, which has a relatively large mosaic spread of 20' to
compensate for the corresponding intensity (dl/l) loss. It is 300 mm high,
focusing vertically onto about 50 mm; this large incident vertical divergence
is matched by 200 mm high detectors and collimators. A complete diffraction
pattern is obtained after about 100 steps of 0.025 deg in 2theta, since the 64
detectors are spaced at 2.5 deg intervals. Such scans take typically 30 minutes;
they are repeated to improve statistics.
D2B was designed for work on samples and high resolution of very large
d-spacings using wavelengths of between 2.4 Å and 6 Å. Wavelengths can easily be
changed under computer control, since they are all obtained by a simple rotation
within the Ge[hhl] plane. A large graphite filter can be switched in to provide
a very clean beam at 2.4 Angs, and a cold Be-filter can be used for longer
This model implements as well the Caglioti UVW equations, that give estimates
of the instrument resolution.
Monochromator lattice parameter
Ge 111 DM=3.266 AA
Ge 311 DM=1.714 AA
Ge 511 DM=1.089 AA
Ge 533 DM=0.863 AA
Parameters in boldface are required;
the others are optional.
Wavelength at monochromator, computed from DM and THETA_M if left as 0.
d-spacing of monochromator, computed from lambda and THETA_M if left as 0.
File name for powder description
Monochromator vertical curvature, 0 for flat, -1 for automatic setting
Print DIF configuration. 0 to be quiet
[min] Horizontal collimator divergence for L1 arm
[min] Horizontal collimator divergence for L2 arm
[min] Horizontal collimator divergence for L3 arm
[min] Monochromator horizontal mosaic
Monochromator take-off angle, computed from lambda and DM if left as 0.
Monochromator additional tilt, for rocking curves
Scattering sense of beam from Monochromator. 1:left, -1:right