For collecting small signals in GIXRD, is it better to take repeated scans summing the counts or to just increase the step time to ~20s or more?
Dear Sir,
when recording data (irrespectively of the technique) I would always prefer the repeated scan scenario. Think, e.g., of a sample with aging effects or irradiation damage etc.
In case you increase the step time for each channel, the "left" part of your data
represents the fresh sample while the "right" part represents the aged or damaged sample (or vice versa). The abscissa (angle in your case) is also a time-axis!
In case you work with repeated scans (e.g. 100 scans), the sum of scan #1...scan#10
represents the data for a fresh sample while the sum of scan#90...scan#100 represents
the data for the aged/damaged sample. In any case, the repeated scan scenario
gives acces to an additional parameter, namely time.
Sincerely, FM
what Frank Mueller says is correct. In both cases what you do is to improve counting statistics and the improvement (pointwise) is exactly the same using the two methods. Just remember to consider the overhead (per point) associated with the multiple scans. I mean, the movement of the goniometer can take as much as your scan time and therefore 20 scans @ 1s/point might take twice the time than a single scan @ 20s/point.
So, for an inorganic, well behaving specimen, I would prefer the faster scan @ 20s/point (and be careful in selecting the 2theta step, to avoid wasting time collecting too much redundant information).
Old thread! Let's not forget the errors and aberrations caused by the mechanical system conducting such miniscule changes in angles iteratively. It would, for all the reasons you gentlemen have suggested, be best to acquire the entire 2D XRD signal as well rather than just a "point at a time" with conventional 0D detectors.
Here's an example of 2D XRD signal from a Lysozyme crystal in transmission Laue mode. We did notice a significant transience in the XRD signal for this crystal. Further analyses are underway to examine the potential origin of signal fluctuation. Suggestions would be welcome! The data was collected real time at 10-30fps, 32um spatial resolution, 8-16Bit, SDD 20-25mm, 5kW with a Rigaku rotating anode generator & Ni filter point source. https://www.flickr.com/photos/85210325@N04/15276644041/
https://www.flickr.com/photos/85210325@N04/15093005439/in/photostream/
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