Tony,
These days many if not most powder instruments (~100% of those at
synchrotron and neutron sources) do some sort of data processing to take raw
measurements and convert them to diffractograms that are used in Rietveld. The
key for how to know if this is done properly is to ask if any experimental
measurement ends up in being used in more than one bin in the final
diffractogram. If this rule is broken, such as the mode in FIT2D that smooths
patterns by pixel-splitting) then one introduces correlation between points in
the pattern and the statistically expected R becomes overestimated (and reduced
chi-squared values can drop below 1). That could be handled in theory (using a
weight matrix in construction of the Hessian), but no Rietveld code does.
Brian
On Sep 25, 2019, at 10:40 PM, iangie <ian...@126.com<mailto:ian...@126.com>>
wrote:
Dear Rietvelder,
I hope you are doing well.
It is generally acknolwdged that Rietveld refinement should be performed on raw
data, without any data processing.
One of our diffractometer/PSD scans data at its minimal step size (users can
see that the step size during scan is much smaller than what was set), and upon
finishing, the measurement software re-bin the counts to the step size what
users set (so the data also looks smoother, after re-bin).
My I ask is this re-bined data from the measurement software considered as "raw
data" or "treated data"? And can we apply Rietveld refinement on this data?
Any comments are welcome. :)
--
Dr. Xiaodong (Tony) Wang
Research Infrastructure Specialist (XRD)
Central Analytical Research Facility (CARF) | Institute for Future
Environments
Queensland University of Technology
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