1.2 A Dummy's Guide to Doing a Run on GEM
A checklist is given here of absolutely everything you must do to record a dataset on GEM for a sample under ambient conditions. If sample environment equipment is being used then most of the same steps (plus some extra steps) will be required.
Fill a vanadium can with a sample. If you want to correct the data for a correlation function type analysis then you need to weigh the sample and measure its height in the can. A good balance is available in a chemistry lab on the north side of the ISIS hall.
Screw the sample can onto the candle-stick. This is best done with the candle-stick clamped to the alignment jig. Then adjust the height of the candle-stick so that the sample will be in the beam but the can lid will not be in the beam.
If necessary, adjust the apertures and the beam-scraper so that the beam dimensions are suitable for your sample.
Put the candle-stick into the hole in the Tomkinson flange and do up the clamps.
Close the door to the sample position and slide the floor shielding in place. Remove the interlock keys from the door and floor and insert these two keys into the blue box.
Remove the master key from the blue box and insert it in the green box. Now open the shutter.
Start the vacuum pumps.
Type in a new title on the instrument control PC. Either type change title=”My sample" in an OpenGenie window, or use the SECI system as follows; click on DAE in the SECI tree, click on Change, type in your new title, click on OK.
Start data acquisition: Either type begin in an OpenGenie window on the instrument control PC (or type upd if you want to do repeated runs), or use the SECI system as follows; click on DAE in the SECI tree, click on Begin Run. Usually (if the pcheck command has been used) it is not necessary to wait for the vacuum to be established – the computer will wait for this automatically.
Use the GEMSQRAW software or the ariel software to inspect the data.
When you have accumulated sufficient data, stop data acquisition and save the data: Either type end in an OpenGenie window on the instrument control PC, or use the SECI system as follows; click on DAE in the SECI tree, click on End Run.
When data acquisition has ceased, the proton current indicated on the dashboard will drop to zero. Also the monitor counts on the dashboard will stop incrementing every 5 seconds. Then close the shutter and stop the vacuum (only use the emergency vent if the polycold is off).
Remove the master key from the green box and insert it in the blue box. Then remove two auxiliary keys and use them to release the door and floor at the sample position. Open the door and slide back the floor shielding.
Do not attempt to remove the candle-stick from the sample position until the sample tank is at atmospheric pressure. This will be indicated by the yellow vacuum light going off and a cessation of the hissing due to dry air entering the sample tank.
Undo the clamps on the candle-stick and then raise it carefully so that the sample is not knocked as you remove it from the sample tank. Then clamp the candle-stick to the alignment jig.
GO BACK TO THE START AND REPEAT AS NECESSARY
Last updated on 27 Oct 2005 by Alex Hannon (a.c.hannon@rl.ac.uk)