The `ILL_D2B` Instrument

Simple monochromator Diffractometer for powders

Identification

Site: ILL
Author: C. M. I Enrique, K. Lieutenant, E. Farhi and L. Cussen
Origin: ILL
Date: 13 Apr 2006

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	min	Horizontal collimator divergence for L1 arm (before monochromator)	18
ALPHA2	min	Horizontal collimator divergence for L2 arm (monochromator-sample)	11
ALPHA3	min	Horizontal collimator divergence for L3 arm (sample-detector)	5
ETA	min	Monochromator horizontal mosaic (gaussian)	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

The ILL_D2B Instrument

Identification

Description

Input parameters

Links

The `ILL_D2B` Instrument