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D20

High-intensity two-axis diffractometer with variable resolution

Manual

This manual is an introduction to the use of the two-axis diffractometer D20 at the ILL. It first describes the general features of the instrument and try to provide the minimum information needed to prepare, run an experiment and analyse the data.

Experiments on D20 fall basically in two categories :

  • Crystallographic-type experiments, i.e. measurements of BRAGG reflections. Depending on sample and/or purpose, this kind of experiment will be somewhat similar to what is done routinely either on D1B (fixed detector mode) or on D1A / D2B (scanning detector mode).
  • Liquid & amorphous-type experiments (say, D4-type experiments)

D20 - USERS MANUAL

This manual is an introduction to the use of the two-axis diffractometer D20 at the ILL. It first describes the general features of the instrument and try to provide the minimum information needed to prepare, run an experiment and analyse the data.

Experiments on D20 fall basically in two categories :

  • Crystallographic-type experiments, i.e. measurements of BRAGG reflections. Depending on sample and/or purpose, this kind of experiment will be somewhat similar to what is done routinely either on D1B (fixed detector mode) or on D1A / D2B (scanning detector mode).
  • Liquid & amorphous-type experiments (say D4-type experiments).

1 - General Description

You will find a schema of D20 in the chapter "Neutron Optics"

1.1 Location of the diffractometer

The PSD powder diffractometer D20 shares the beam tube H11 in the reactor (level C) with two other instruments: the PSD single crystal diffractometer D19 and the high resolution powder diffractometer D2B. D20 has the end-position of this tube. The 'bouchon' H11 has to be open in order to provide neutrons for all three instruments, the 'obsturateur' B2 has to be open for D2B and D20 and only the third and last shutter is exclusively for D20.

1.2 Neutron optics

In this paragraph the instrument 'geometry' from the reactor via the monochromators up to the sample is described. A monochromator may be choosen by turning the changer in the protected monochromator and beam tube housing, muliple take-off angles are choosen by deplacing the whole platform with goniometer detector etc. Collimation may be controlled by the collimator before the monochromators, the slits after the monochromators and before the sample.

1.3 Goniometer

The goniometer allows an omega-rotation of the sample of up to 360°. The available space for the sample environment has a diameter of 790 mm. The maximum weight is in the order of 100 kg.

1.4 Detector

The diffractometer was up to 1996 equipped with a 126 cell curved position sensitive detector (PSD) filled with a mixture of 3He (4 bars) and propane (1bar).

  • Height : 150 mm, Radius 1455 mm
  • Angular aperture : horizontal = 12.6°
  • Vertical = 11.8°

Today, D20 is equiped with a 1600 cell (1997/98), respectiveley a 1536 cell (since 2000) curved position sensitive detector (PSD) filled with a mixture of 3He (3.1 bars) and CF4 (0.8 bar). Microstrip plates (invented by Anton Oed) replace the conventional wires in this new PSD technology (see Poster at ECNS96). They allow an extremely high counting rate, an exact definition of detection cells and high stability of counting rate and definition.

  • Height : 150 mm, Radius 1471 mm
  • Angular aperture : horizontal = 160°
  • Detection gap 50 mm
  • Definition: 0.1° in 2Theta (2.568 mm) per cell

1.5 Electronics

Motor control
The motor controls are situated in the rack outside the wall and are largely controled by the instrument control program MAD (on the Linux workstation D20 near the instrument zone and the electronics rack). The sample slits are controlled and read manually on the instrument zone itself.

Data acquisition

Standard data acquisition
There is the standard data acquisition of all 1600 detector channels as for other instruments, but only time-controlled, not monitor-controlled. You may perform a simple acquisition, a scan or a coupled scan (moving one or two motors between the steps of a multiple acquisition) with a preset time in seconds. These acquisitions are controlled by the instrument control program MAD, turning on the Linux workstation on the protection wall (see below).

Stroboscopic measurements
This is a feature of D20 which allows experiments up to now impossible on other diffraction instruments in order to obtain a time resolution in the scale of microseconds. These acquisitions may be coupled with a motor scan. As for normal acquisitions, these measurements are only time-controlled and may be performed via the instrument control program MAD turning on the Linux workstation beside the instrument.

1.6 Computer

Computer
D20 is equipped with a Linux workstation for instrument control and with another Linux workstation, as well as a Windows-PC and a Macintosh for data treatment. The instrument control workstation is called d20.ill.fr and is situated at the ground level just behind the protection wall of the instrument. From this computer you may run the instrument control program MAD and the live display to visualize data during its acquisition.

1.7 Auxilliary equipement

Click here for a general view of ILL's standard sample environments!

In addition to that, D20 disposes of its own dedicated sample environments:
Vacuum vessel

This is the standard room temperature environment. It allows you to push down the background due to air scattering.

D20 orange standard Cryostat

For temperatures down to 1.7 K (exceptionally 1.2 K with roots vacuum pump after discussion with the instrument responsibles) you may use the dedicated cryostat of D20 (and D4) which will give a reduced background contribution due to Cadmium shielding and beam-stop inside.

  • cryostat alignment
  • liquid N2 refill
  • liquid He refill
  • liquid He gauge
  • sample change and cooling
  • temperature regulation

Furnances

D20 Furnace
D20 has its own dedicated furnace with Vanadium heating element which was former on D1B. It will work under vacuum up to 800°C. For low temperatures or higher ones you should discuss with local contact and instrument responsibles.

Very high temperature furnaces
In the pool of ILL furnaces you may find furnaces adapted to more than 800°C. There are conventional furnaces with Niobium heating element which will give a higher background contribution not only due to the Niobium but also because they are not adapted to D20 (beamstop and flags, as D20 has not yet a radial collimator).
If you want to work at air up to 1600°C you may choose the mirror furnace. There is even a furnace for up to 3000 K but this is still under development and it demands electrical alimentation and water cooling facilities that are not available in the reactor yet.

Eulerian cradle (chi, phi rotations)
An Eulerian cradle is part of D20's standard equippment for texture measurements, strain scanning experiments etc. Coupled scans of chi and phi are possible.

Translations (sample changer)
Two microcontrol translators of 250 mm, normally mounted perpendicular to each other allow you to scan your sample in the space or to change your samples on a sample holder mounted on one of these translations.

Dilution cryostats
For temperatures below 1.2 K you will need either a 3He (>500 mK) or a dilution-cryostat that is available in the pool - with the drawback of some background contribution.

Cryomagnets
Cryomagnets are available in the ILL pool.

High pressure
High pressure cells are available in the ILL pool.

1.8 Safety

From the ILL reception you should have been sent to the Health Physics service if it is you first stay at ILL where you obtain general information, follow a security video and obtain at least two informative brochures. Before entering the reactor level C (the ground level with the diffraction instruments on beam tubes) you have to pass the reactor guardian in order to obtain your dosimeters.

Withthe invitation for your experiment you obtain an authorization form which you have to send back to ILL signed with all the names of the members of your experiment team. You will get it back at the site entrance signed by the local contact as well. This paper, indicating the concerned persons and the participants of an experiment has to be exposed at the instrument during the experiment.

Experimentators and local contact should know at any time what sample is in the beam. After changing the sample you should check the radioactive activation of your sample with the 'babyline' of the instrument. Remember that Vanadium is activated but its radioactivity will decrease rapidly in a few minutes. Everything that was in the beam during an experiment should additionally be checked by the radioprotection before leaving the reactor level C.

The 'dossier de sécurité' (in French) is disposed at the instrument site. It contains all security relevant descriptions of the instrument D20.

2 - Instrument Calibration

Instrument Calibration
A very simple detector efficiency calibration consists simply in measuring a vanadium or a plexiglass sample to obtain a nearly flat background. A Two-Theta scan has to be performed to obtain a the correct efficiency corrections.

3 - Performing an Experiment

Performing an Experiment
Here you will be informed how to set up a typical experiment, using the standard cryostat and some commands under MAD.

4 - Workstations

Workstations
Instrument Control

5 - Data Treatment

Data Treatment
Data Pre-Treatment
Crystallographic-type programs
Liquid & amorphous-type programs

6 - Information for local contacts

Information for local contacts
Have a look for helpfull informations ... otherwise, refer to the phone numbers below ...

Neutron scattering lengths

General Neutron Scattering Information 
List of neutron scattering lengths 
Activation of elements 
Periodic Table of the Elements 
Neutron Scattering Conversion Factors

Restaurants

Personally tested and recommended (Thomas Hansen) :

Le Pudding, Le Sappey en Chartreuse, 1014 m high, 0476888466
Even mentionned in the Michelin (XX, "Good meal at moderate price"), not really cheap, but really good ...

Café des Alpes, Corenc (Col de Vence - Chartreuse)
Cuisine Dauphinoise, traditional ...

A Confesse, Grenoble (St Laurent)
Cuisine Savoiarde, traditional and student's budget ...

Le Mal Assis, Grenoble (City)
Candlelight Dinners ...

Le Canard Laque, Grenoble (City)
Chinese food ...


Recommended by the "Michelin" (number of forks):

Auberge Napoléon XXX, Grenoble, 7 rue Montorge, 0476875364

L'Escalier XX, Grenoble, 6 place Lavalette, 0476546616

Brasserie de Strasbourg XX, 11 avenue Alsace-Lorraine, 0476461803

A ma Table XX, 92 cours Jean Jaurès, 0476967704

La Table d'Ernest XX, 2 rue Doudart de Lagrée, 0476431956

La Madelon XX, 55 rue Alsace-Lorraine, 0476463690

L'Arche X, 4 rue P. Duclot, 0476442262

Bistrot Lyonnais X, 168 cours Berriat, 0476219533