INTRODUCTION TO PURGE AND GUDRUN: There are two stages to the correction of GEM data. Firstly the program Purge needs to be run to identify and remove spikes in the data. It produces a number of files including a .grps file which Gudrun uses to correct the data. Once this has been completed, Gudrun is used to normalise and correct the data. The gudrun manual (which can be found in the Installation folder) gives detailed information about how this is done.
Gudrun uses a ‘samplename_dcs.dat’ file to analyse the data. Editing the .dat file by hand is not recommended because it has a very precise format for GudrunGui to read, however detailed annotations of an example file are given here.
THE GUDRUNGUI: The GudrunGUI has 5+ tabs for inputting information. They are INSTRUMENT, BEAM, VANADIUM, SAMPLE BACKGROUND, SAMPLE and then SAMPLE CAN information can also be added is required. Before running Purge and GUDRUN, the information in these tabs should be filled in correctly. At each stage, save the file (samplename_dcs.dat) and check that the information in the tabs has been updated into the notepad document displayed on the right of the window.
Multiple samples can be run add should be added after the sample background with a sample tab, followed by it's container, then the next sample etc. adding new tabs is done through EDIT
What follows is a detailed guide to what information is required by the GUI in each tab.
INSTRUMENT: The instrument tab usually only requires the top four lines to be edited, the rest should be left alone unless you have a specific reason to alter them. The input file directory (1) should link to the folder you are currently using ( i.e. C:\ Gudrun\GudrunGUI_2). (2) should be edited so that is give the directory containing the raw data. (3), (4) and (6) direct the program to the calibration file, the groups file and the neutron scattering (Sears91_gudrun.dat) files respectively, and should not need changing from those in the GEMstartup file if the installation instructions have been followed correctly.
BEAM: The beam tab usually only needs altering if the incident beam size has been altered from 1.5 cm ((1) -0.75 to 0.75) x 4 cm ((2) -2.0 to 2.0). As before, (3) the beam spectrum parameters (spectrum000.dat) should be correctly set up from installation.
NORMALISATION: The normalisation tab requires the run numbers for the vanadium data (1) and the corresponding empty diffractometer data (2) need to be added. The vanadium inner and outer dimensions (3) are set here to be those of the ~8 mm Vrod. If this is not correct, information of the various cans and vanadium rods can be found here. The cross section source (4) should be set to TABLES and no file is required.
SAMPLE BACKGROUND: All that needs entering on this tab is the empty diffractometer run number(s) (1).
SAMPLE: This is the Tab which requires the most alteration.
(1) Firstly the sample run numbers need to be entered.
(2) The elements along with the isotope (0 for natural) and fractional amount are required. If SiO2 was being run there for, the boxes should read
Si 0 0.333
O 0 0.667
Once they have been entered, click onto a new line before saving the file. Then check the details have been updated on the right. If you do not click onto an empty line, the element will not be added to the written file.
(3) The can size needs to be entered. The example file has the can size for an 8.3 mm thin walled can. Information on other can sizes is given here.
(4) The height of the sample in the can is then required, along with the effective density (mass in the can/volume filled)
(5) The sample temperature needs to be changed if a furnace or CCR was used.
(6) Set the cross section to TABLES.
SAMPLE CONTAINER: The sample container, assuming the can in vanadium, only needs to have the can run numbers (1) and the inner and outer dimensions of the can wall (2) added. The various can dimensions can be found here, and the example file uses a ~8.3 mm can. If the can is not vanadium, the composition can be altered in the same way as for the sample.
Once all this information is correct, Gudrun is ready to be run.