I've had lots of helpful tips from some people. I've tried changing my
0.04� Soller slits for 0.02� and this seems to reduce the asymmetry quite a
lot. Unfortunately, this also increase measurement time, since it reduces
intensity. The influence of the background at low angles is almost
negligable, since with the secondary curved Cu monochromator, the background
is practically eliminated completely (if there is no amorphous substance in
the sample).
I was wondering if anybody has any experience in the influence of the
divergence slit size with automatic divergence slits. As I reported
earlier, I didn't detect any change (except for the expected reduced
intensity) when I changed the irradiated length from 15mm to 5mm. With
tripled measurement times, the two resulting spectra can be superposed quite
perfectly, with only slight differences in the background.
A second question is entirely different in origin. Has anybody got any
experience with the program Endeavour ? It is a refinement program based on
a combined optimization of the difference between the calculated and
measured diffraction pattern and of the potential energy of the system
("Pareto-optimization"). It's based on the Diamond-program from Crystal
Impact. I was quite impressed by the possibilities, but I haven't used it
for cases other than the examples that are included. For those interested :
http://www.crystalimpact.com/endeavour/start.htm.
Thanks,
Sven Van den Berghe
> -----Original Message-----
> From: Van den Berghe Sven [mailto:[EMAIL PROTECTED]]
> Sent: Friday 1 September 2000 11:48
> To: '[EMAIL PROTECTED]'
> Subject: Asymmetry at low angles
>
>
> Hello everybody,
>
> I think my question is rather basic, so I apologize for my
> ignorance. I'm
> relatively new to the field of diffraction and Rietveld
> analysis, so I'm
> trying to learn as quickly as possible.
>
> In my latest analyses, I've found that at low angles, my
> peaks are rather
> asymmetric, with a tail towards the low angle side. Since
> Rietveld programs
> fit the entire spectrum, this asymmetry is often a cause of reduced
> reliability of my refinements. I was wondering what causes
> this asymmetry.
> I'm using a Philips X'Pert Pro goniometer with programmable
> divergence and
> anti-scatter slits. I set these at a constant irradiated
> surface of 15mm,
> but reducing this to 5 mm does not change the asymmetry. The
> receiving slit
> is set at 0.05mm to reduce peak width.
>
> Anybody ?
>
> Sven Van den Berghe
>
> ****************************************************************
> Sven Van den Berghe
> Assistant Scientific Researcher
> Reactor Materials Research Department (RMO)
> Laboratory for High and Medium Activity (LHMA)
> Boeretang 200
> B-2400 Mol
> Belgium
> Tel. : +32 14 33 30 64
> Fax : +32 14 32 12 16
> E-mail : [EMAIL PROTECTED] <mailto:[EMAIL PROTECTED]>
> ****************************************************************
>
