OrientExpress
Test Laue neutron-diffractometer
Instrument configuration and layout
Computers
OrientExpress requires two computers to run:
- A Windows 10 machine. This computer runs the detector software. It also has the data analysis software (Clip and OrientExpress)
- A Linux machine. This computer runs Nomad and is used to control the instrument, driving motors and collecting images.
Active accounts must be logged in to both computers to be able to collect data.
Instrument Zone
There is a monitor mirroring the Linux display mounted on the cage inside the zone. This is used when aligning the sample with the camera.
There is also a set of drawers with useful stuff. You are welcome to use the stuff, but anything used from these drawers goes back into the drawers at the end of the measurements.
The search button for the beam opening procedure is found on the back wall, next to the beam stop.
Detector
The Neutron Imaging Camera system consists of two high resolution intensified digital CCD cameras coupled to a high performance neutron scintillator screen.
The scintillator screen is fragile! Be very careful not to tap or bump it as it may become damaged.
The sample-detector distance is adjusted manually with a wheel located at the opposite end to the sample position. A ruler at the end closest to the detector shows the distance, and this distance is also read and stored by NOMAD.
The neutron beam size is set using a boron nitride aperture. OrientExpress has a selection of apertures with different sizes, and these may be interchanged manually.
The system is based upon two high-performance thermoelectrically cooled image-intensified CCD cameras that view a large area neutron scintillator via close-focus lenses. The exposure of the two cameras is synchronized to take place simultaneously, and a single stitched image is transferred to the Windows 10 computer. The active scintillator area of 252 x 198 mm2 is thus rendered as a single image of 1726 x 1320 pixels, each pixel 150 mm on edge. The cameras view the scintillator inside a sealed light-tight box. The incident neutrons pass through this box and the scintillator via a small-diameter light-tight tube that itself passes through the center of the scintillator which allows full backscattering geometry. The two cameras are positioned in such a way that their views overlap so the tube does not obscure any part of the scintillator.
The cameras view the scintillator via f0.95 lenses to give maximum sensitivity.
The neutron scintillator is an AST ND screen based on 6LiF with ZnS:Ag added to provide high neutron capture efficiency.
Integration periods of 1 ms to many minutes are possible, and on-chip binning option is available independently in both X and Y. The intensifier gain is fully adjustable via software. The cameras were upgraded recently with new faster color ships with larger dynamic range (16-bit).
More informationmay be found in the reference "OrientExpress: A new system for Laue neutron diffraction ", Ouladdiaf B. , Archer J. , McIntyre G.J. , Hewat A.W. , Brau D. , York S., Physica B 385-386, 1052-1054 (2006).
Camera
The camera shows the sample position and is used to align the sample in the beam
Do not touch the camera. You may misalign it for others
Make sure that the lens cap is off. You won't see much if the lens cap is left on!
Sample Position
The sample position has a series of manual and motorised stages to adjust the sample position and alignment.
Position adjustments (manual):
The sample position may be adjusted using the two horizontal (X and Y) position stages and one height (Z) stage.
These stages may be used to align the sample with the cross on the camera, which will correctly align the sample in the beam.
The Z stage has a locking nut - ensure that it is loosened before trying to adjust the height.
The sample support-to-beam axis distance is adjustable between 40 - 70 mm. Any samples with mounts that are longer than 70 mm will not fit on the instrument!
Angle adjustments (manual):
The sample has two manual rotation axes to adjust the omega angle.
The coarse-adjust stage allows the sample to be quickly and accurately rotated by increments of 90°. It has a black locking pin. Lift the pin to rotate the sample stage, and the pin will drop at the required 90° interval.
The fine-adjust stage allows the sample to be rotated to position a desired axis or crystal face with respect to the incident beam. This stage has a locking nut - ensure that it is loosened before trying to adjust the rotation.
Motorised axes:
OrientExpress has three motorised axes that are controlled from NOMAD:
Omega rotates the sample about the vertical axis.
Tilt1 and Tilt2 rotate the sample about orthogonal horizontal axes.
