Contents
The I15-1 Sample Position
The sample position on I15-1 is defined in the images below. The y stage has a travel range of 500 mm, with ca. 170 mm below the beam position and ca. 330 mm above. The x stage has a travel range of ca. 125 mm. With the sample stage set to x = 0 (furthest back), there is a distance of 420 mm between the sample stage and the beamstop arm. The beamstop arm is located ca. 140 mm below the beam position. The images below depict a standard beamline setup, with a distance of ca. 260 mm between the clean-up and the detector. The beamstop is positioned ca. 100 mm from the detector. These dimensions are liable to change however, as the length of the clean-up, position of the detector and the position of the beamstop can be changed along the z-axis to optimise Qmin for a given experiment where necessary.
Mounting Brackets
This bracket mounts directly onto the Y stage. It is secured by M6 bolts onto the stage and is aligned on two dowel rods for reproducible alignment of the bracket with the stage. There is a slot cut into the surface which acts as a keyed edge for cells to be butted up against, to provide reproducible alignment of the cell with respect to the bracket. The cell should be attached by 3 x M6 bolts spaced 37 mm apart through the rear of the bracket in countersunk holes. The entire mounting bracket can be removed from the stage and reattached reproducibly.
This bracket is mounted onto a Thorlabs breadboard that is attached to the Y stage. Cells should be attached onto this bracket using 4 x M5 bolts. There are 3 keyed edges for the cells to be aligned to, the corners of which have a radius profile, which makes mounting onto this bracket reproducible. This bracket remains attached to the beamline whilst the cell can be removed and reattached to the bracket reproducibly.
Considerations
A good cell for a PDF experiment should have the following characteristics;
- Reproducible mounting of samples - Each sample should be in the same position (especially maintaining a constant sample - detector distance).
- Reproducible and ideally low intensity background - Fused quartz/glass capillaries are ideal for this as the outer diameter and wall thickness is well controlled and consistent between different capillaries, and therefore for different samples. As a result only one background measurement is required which can be subtracted from all other data sets during the data processing stage. The background would ideally be weakly scattering compared to the scattering from the sample.