Synchrotrone emission profile

marekgocnik

Hello everyone,

First I would like to state that I am competelly new to TOPAS and still learning everything. My research group just recently started with Rietveld analysis of synchrotrone measurements (for us, competelly new area). I am having some trouble setting up the .INP files and are looking for some help.

To my question(s).

1) In the .INP file one has to define the beam parameters (la lo lh) under (lam) in the input file. We have a LaB6 calibrant diff. data and I am wondering, how do I extract these parameters? (lo = wavelength - this one is known)

2) Two additional parameters are troubleling me, goniometry paramters (Rp and Rs). Do you have any suggestions, on how I should choose these parameters?

I am very thankfull for any suggestion and insights you may provide.

Have a nice day,
Marek

johnsoevans

If you're happy to just use an empirical peak shape then you could use an approach like the one at: https://topas.webspace.durham.ac.uk/tutorial_synchy2o3/ which uses data from Andy Fitch's old id31 beamline. Here lh is set to zero which means there's no contribution to the overall broadening from the emission profile. This approach should be fine if you're using the LaB6 as a peak shape standard to define the instrument resolution function.

You would only need to know proper values for Rp and Rs if you're using a fundamental parameters approach. If so, the best person for advice would be the beamline instrument scientist. They'll probably know the best approach for that specific diffractometer.