Dear colleagues!
I have encountered a weird bump in the BKG. Below at the picture you can see that the normal decay of air scattering intensity drops as usual, but then relatively sharply elevates average BKG level. If this would be everywhere this would not be a problem since everything would be on the same level, however such wave makes it very difficult to analyze peaks at lower angles. I tried various ways to organize optics to mitigate this issue and the best I could get is to shift the beginnigh of the bump towards 8 degrees instead of 6 via moving incident slit closer to the sample.
The manufacturer engineer said that this can be eliminated completely if you install parabolic mirror for parallel beam optics. However I personally think that this is BS, and such bump should not be there in the first instance.
Does anyone here have ideas of the origin of such bump and possibly how this could be removed.
The instrument is in reflection geometry, no monochromator, array detector, incident soller slit, knife edge is installed.
Dear Ivan A. Trussov ,
the fact, when shifting the primary slit towards the sample*) and then the background onset shifts a bit, may show that you struggle with Compton scatter arising from parts of the sample support which are left and/or right to the net expected beam footprint at the sample. You should mask (cover) these areas with a bit of lead**) foil (strips). For a first trial, the gap between these shield(s) may be (a bit) smaller than the sample width.
Just have a look what happens to your background...
Your primary beam width may be too wide or the beam center is not at the center of the sample.
Is the position of the primary slit ok? (in length direction of the slit, i.e. the direction normal to the theta-2theta plane)
*) by that shift you decrease the net beam width a bit
**) or other quite high Z material ( Cu, Zn, Mo, W) that has low Compton scatter cross-section...
Good luck and
best regards
G.M.
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