> Xpert Pros are fantastic machines. Collections times are
significantly
> reduced
> with their new semi-conductor PSDs. The only snag with the machines
is
> that the
> asymmetry at low angle is very stark - so much so that in effect you
> 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 XCelerator or PIXcel detectors makes the peaks even
more symmetric as it suppresses the axial divergence.
Leonid Solovyov
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