XFIT Startup Defaults for Inserting Peak

• In the Options box, if you press the Ins/Del Peaks you bring up the Peak Edit Options box.
• The startup default for inserting peaks in XFIT is Fundamental Parameters. These work by using the machine geometry and experimental conditions to best fit the peaks.
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• For standard (geometry independent) peak fitting, it is best to use the Psuedo-Voight (PV) for symmetrical peaks, and Split Pearson VII for asymmetrical peaks. Fitting a Split Pearson to symmetrical peaks gives the system an unnecessary degree of freedom that could cause problems.
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  Setting for Inserting Pseudo Voight peaks
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  Setting for Inserting Split Pearson VII peaks

Exercise Showing Effect of Inappropriately using Fundamental Parameters Peaks

• Run XFIT, (maximise the screen if you wish) and do File, Load Data and open the y2o3.dat data set. You can maximize the data to fit the entire XFIT screen. It should look something like the following. (if you can see the active mouse output on the bottom right of the XFIT screen - maximise your XFIT window)
  
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• Zoom into the area around 68 and 80 degrees. This is done using the left mouse button to define the lower angle and the right mouse button to define the upper angle.
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• To tell XFIT that you are using Copper X-ray data from a lab source, use the Options box to go into the File Details, and click on the Assign LAMs to Files
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• Then tell click below the Assign LAM Files to the right of the y2o3.dat file so that you bring up the Assign option in the Options area.
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• Then click on the Assign option in the Options area to bring up the browse box, and go to the c:\koalarie directory and assign/load the Cuka_5.lam. This describes the emmission spectrum for the tube (actually 5 characteristic lines - you can do the traditional approximation of Alpha1 and Alpha2 by loading the Cuka_2.lam file)
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• Go to the Options Box, click on Ins/Del peaks to bring up the Peak Edit Options box. Use the starting default FP (Fundamental Parameters fitting). Then with use the mouse and left button to select ONLY the alpha-1 components of the peak. If you incorrectly add a peak, go the left of the peak and click the right mouse button to delete it.
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• From the top menu bar, select Fit, Fit Marqardt.
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• This brings up Fit Details box. You have the option to step through the fitting cycles one at a time. You can stop on the next cycle - and keep all the information refined up to that point.
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• Click on the Start to start the peak refinement. This can go rather quickly and when the refinement converges, you will get a Refinement converged prompt. However, you will notice that the fit is rather hopeless - due to the belief that a PV or PVII is being used.
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