Checking Diffractiometer Alignment
Learning Outcomes: It's important to check your diffractometer performance periodically. The instrument supplier should provide you with a standard sample. Many Bruker instruments come with a NIST 1976 Al2O3 plate and instructions to scan certain peaks and compare their intensity with expected values. On the Durham d9 the protocol was to scan peaks at ~25, ~35, ~89, ~95, ~127 and ~136 degrees for relative times of 5, 3, 40, 40, 40 and 40 s. These are expected to lie within specified tolerances in terms of intensity and angle. The scan provided used 0.3 degree slits.
1. Read the experimental data into Topas using File/Load scan file. You should see the 6 individual peaks which were recorded as different "ranges" in the .raw file. Once you've looked at the data you can clear them from Topas.
2. Open the d9_01918_pkfit.inp input file. You'll see that it contains a macro for fitting each peak and for writing out both intensities and normalised (for time) intensities to a file.
3. Run the input file.
4. Open the file "peaks.res" which contains tabulated values of 2-theta, lor, fwhm, I(obs) and I(obs)/count_time. Paste these columns into the first 5 columns (i.e. boxes a2 to e7) of the excel sheet in the plot_results tab.
5. Inspect the graphs of I(obs) and I(expected) vs
2-theta and see if you are happy with performance - your values should like
within the specified tolerances. Check that the 2-theta error is low and doesn't
vary significantly as a function of 2-theta. Check that the fwhm vs 2-theta
is what you expect for your instrument.
[Modified 06-May-2020 by John S.O. Evans. Pages checked for Google Chrome.]