6.2 GEM Linear Sample Changer

The GEM linear sample changer is designed to automatically position up to 10 samples in the beam.

The samples are mounted one above another in a vertical line. Special sample cans must be used with the linear sample changer. These cans are made of 25 micron vanadium foil to minimise the background and the corrections for can absorption and scattering. At present, the only cans available are of diameter 5mm, but other sizes are planned for the future. Currently the sample space in the cans is 4.56 cm long, leading to a sample volume of 0.895 cm³ for the 5mm diameter cans.

The sample changer may be sent to position 5 (for example) by typing the camac command cset lsc 0.05 on the VMS computer.

At present, if the beam size is set to be 40mm high then the beam will clip the stainless steel can end-pieces and small stainless steel Bragg peaks are observed in the diffraction data. Hence it is necessary to work with a beam which is 35mm high.

The GEM linear sample changer is controlled by means of the LabView PC in the GEM cabin. It is essential that you click on the initialise button on the LabView PC before commencing the experiment. If you do not do this then it is likely that the samples will not be correctly positioned in the beam.

The linear sample changer was designed by Paul Busby at Salford University.

Here are some relevant pictures...

Photo of the linear sample changer
Close-up of the sample cans
Drawing of linear sample changer
Drawing of sample can for linear sample changer

Last updated on 16 Feb 2001 by Alex Hannon (a.c.hannon@rl.ac.uk)