Yes it is mainly down to the Soller slits, there was a very large thread on
soller slits somewhere in the Rietveld archives about this discussion. I think
the down side of changing the soller slits is a move away from the
optimum FWHM
that can be obtained?
Quoting Leonid Solovyov <[EMAIL PROTECTED]>:
Xpert Pros are fantastic machines. Collections times are
significantly
reduced
with their new semi-conductor PSDs. The only snag with the machines
is=20
that the
asymmetry at low angle is very stark - so much so that in effect you=20
are having
to model a multiple diffractometer situation.......
In fact, the problem of asymmetry is related to the Soller slit choice
(and to the diffractometer radius), but not to the detector. By default
PANal supplies their machines with Soller slits of 0.04 rad divergence
that give highly asymmetric peaks, but one may choose Sollers of 0.02
or 0.01 rad to reduce the asymmetry. Additionally, the secondary
monochromator for X=92Celerator or PIXcel detectors makes the peaks even
more symmetric as it suppresses the axial divergence.
Leonid Solovyov
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William Bisson
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