[ Identification | Description | Input parameters | Links ]

# 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

## Links

- 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 ]