In my knowledge, this effect (an edge at about 6 deg 2th) comes from a
scattering of the lower part of the tube housing/shutter window. This
scattered intensity goes straight above the sample, directly into the
detector when no more antiscatter optics follow. Therefore, it can be
observed only without diffracted beam monochromator and without
secondary beam antiscatter slit, typically with such 1D strip detectors.
At our instrument (Empyrean) the effect was independent on the type of
sample, occured even with an empty low-background holder.
The "edge" can be shifted towards lower angles by a "knife edge" scatter
blocker above the sample, but of course this thing reduces the
irradiated area on the sample at higher angles. Another, better
possibility would be an additional antiscatter slit close to the tube
shutter, but unfortunately there is no free position.
Another strange thing with our instrument is a kind of "hump" in the
background at about 15-25°2theta, occurring only when the programmable
divergence slit is used in combination with an 1D strip detector. With a
secondary beam graphite monochromator/propcounter as well as when the
programmable slit was chosen bigger than the primary beam fixed
anti-scatter slit (tungsten rods), we did not observe this effect.
Therefore, my interpretation of this intensity is
fluorescence/scattering from the brass material of the programmable slit
edges. Such instrumental background artifacts are not nice for Rietveld
refinement, as they must be fitted by a modulated background model...
Reinhard
Am 21/11/2013 12:32, schrieb gre...@unisi.it:
with some materials, I observed powder diffraction patterns (Bragg-Brentano,
X'pert) which
show a broad negative peak around 5-6º(2th), instead of the smoothly descending
intensity
coming from the primary beam.
Did some of you observe the same phenomenon, and has this been dealt with
anywhere?
best regards
Miguel
--
Miguel Gregorkiewitz
Dip Scienze della Terra, Università
via Laterina 8, I-53100 Siena, Europe
fon +39'0577'233810 fax 233938
email gre...@unisi.it
--
TU Bergakademie Freiberg
Dr. R. Kleeberg
Mineralogisches Labor
Brennhausgasse 14
D-09596 Freiberg
Tel. ++49 (0) 3731-39-3244
Fax. ++49 (0) 3731-39-3129
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