[ Identification | Description | Input parameters | Output parameters | Links ]

The ILL_D2B Instrument

Simple monochromator Diffractometer for powders

Identification

Description

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
wavelengths.

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


Input parameters

Parameters in boldface are required; the others are optional.
Name Unit Description Default
lambda Angs Wavelength at monochromator, computed from DM and THETA_M if left as 0. 1.594
DM Angs d-spacing of monochromator, computed from lambda and THETA_M if left as 0. 0
Powder str File name for powder description "Na2Ca3Al2F14.laz"
RV m Monochromator vertical curvature, 0 for flat, -1 for automatic setting -1
L1 m Source-Monochromator distance 16.05
L2 m Monochromator-Sample distance 2.645
L3 m Sample-Detector distance 1.3
verbose 1 Print DIF configuration. 0 to be quiet 1
ALPHA1 before monochromator [min] Horizontal collimator divergence for L1 arm 18
ALPHA2 monochromator-sample [min] Horizontal collimator divergence for L2 arm 11
ALPHA3 sample-detector [min] Horizontal collimator divergence for L3 arm 5
ETA gaussian [min] Monochromator horizontal mosaic 12
THETA_M deg Monochromator take-off angle, computed from lambda and DM if left as 0. 67.5
TILT deg Monochromator additional tilt, for rocking curves 0
SM 1 Scattering sense of beam from Monochromator. 1:left, -1:right 1
Dheight m Banana detector height 0.3
coating 1 Super-mirror in-beam tube guide coating 0

Links


[ Identification | Description | Input parameters | Output parameters | Links ]

Generated automatically by McDoc, Peter Willendrup <peter.willendrup@risoe.dk> / Wed Sep 5 11:20:18 2018