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McStas: ILL_D2B

[ Identification | Description | Input parameters | Links ]

The ILL_D2B Instrument

Simple monochromator Diffractometer for powders


  • Site: ILL
  • Author: C. M. I Enrique, K. Lieutenant, E. Farhi and L. Cussen
  • Origin: ILL
  • 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

Input parameters

Parameters in boldface are required; the others are optional.
lambdaAngsWavelength at monochromator, computed from DM and THETA_M if left as 0.1.594
DMAngsd-spacing of monochromator, computed from lambda and THETA_M if left as 0.0
PowderstrFile name for powder description"Na2Ca3Al2F14.laz"
RVmMonochromator vertical curvature, 0 for flat, -1 for automatic setting-1
L1mSource-Monochromator distance16.05
L2mMonochromator-Sample distance2.645
L3mSample-Detector distance1.3
verbose1Print DIF configuration. 0 to be quiet1
ALPHA1minHorizontal collimator divergence for L1 arm (before monochromator)18
ALPHA2minHorizontal collimator divergence for L2 arm (monochromator-sample)11
ALPHA3minHorizontal collimator divergence for L3 arm (sample-detector)5
ETAminMonochromator horizontal mosaic (gaussian)12
THETA_MdegMonochromator take-off angle, computed from lambda and DM if left as 0.67.5
TILTdegMonochromator additional tilt, for rocking curves0
SM1Scattering sense of beam from Monochromator. 1:left, -1:right1
DheightmBanana detector height0.3
coating1Super-mirror in-beam tube guide coating0


  • Source code for ILL_D2B.instr.
  • G. Caglioti, A. Paoletti, F.P. Ricci, Nucl. Instr. and. Meth. 3 (1958) 223
  • L.D. Cussen, Nucl. Instr. and. Meth. A 554 (2005) 406
  • M. Morhac, NIM A 600 (2009) 478

[ Identification | Description | Input parameters | Links ]

Generated on 2023-09-19 20:01:36

Last Modified: Wednesday, 03-Jan-2024 19:59:10 CET
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