Dear Alexandra,
The 1/4 divergence and 1/2 anti-scatter slits are narrow enough to give a
reasonably low background after 5 degrees 2Theta. First I would check that the
background is not related to the sample itself. It may be done by measuring an
empty sample holder.
The background may also be due to scattering from sample holder edges if the
holder diameter is small and the primary beam mask is wide or/and the Soller
slit divergence is big.
The automated sample changer can not produce background, but I am not sure if
the beam knife can be installed together with the changer. The beam knife cuts
the air scattering which is essential in the low-angle region. The standard
beam knife supplied by PANal is rather thick and if it is installed too close
to the sample surface it may attenuate intensity at high angles. With fixed 1/4
divergence slit the knife should be put about 3-4 mm under the sample surface
which must be safe for measurements up to 100 degrees 2Theta. To check if the
knife attenuates high angle reflections it is necessary to measure the same
sample with and without knife and then compare the intensities.
On my X’Pert I simply replaced the standard knife by a thin (ca. 1 mm)
stainless steel screen, and installed it 3 mm above the sample surface which
allows preserving intensity up to 150 degrees 2Theta even with the 1/2
divergence primary slit and have a reasonable low-angle background. Of course,
the knife should also be properly centered on the diffractometer axis and
aligned vertically.
Best regards,
Leonid
*******************************************************
Leonid A. Solovyov
Institute of Chemistry and Chemical Technology
660049, K. Marx 42, Krasnoyarsk, Russia
www.icct.ru/eng/content/persons/Sol_LA
sites.google.com/site/solovyovleonid
*******************************************************
--- On Mon, 11/30/09, Alexandra Seclaman <seclaman_alexan...@yahoo.com> wrote:
> From: Alexandra Seclaman <seclaman_alexan...@yahoo.com>
> Subject: RE: Configuration of PANalytical X'pert Pro
> To: rietveld_l@ill.fr
> Date: Monday, November 30, 2009, 2:05 PM
> Thank
> you for all of your answers, it was more than I hoped for.
>
> I did a Rietveld refinement on stibnite (Sb2S3). And I
> mesured it from 5 2theta to 90. But from 5 to 20 2Θ i
> had a serious background noise and general trend similar to
> that of glass. This trend and the background noise are there
> no matter what I measure.
> I can't get to the lab until Wednesday, but from what I
> recall, from the X ray source to the X'celerator
> detector: there are 1/4 +1/2 fixed divergence,the widthest
> mask and the slit (i'm not shure if that is the proper
> name) in front of the X'celerator is also the widthest.
>
> The automated system of "handling" the sample is
> installed, should i changed it?
> And I forgot to mention, the system is MPD.
>
> I can give you more details on Wednesday.
>
> I'm sorry for my not technical terms, but is very hard
> for me
> to speak about diffraction in English.
>
>
> Alexandra Seclaman
>
> seclaman_alexan...@yahoo.com
>
> a.c.secla...@gmail.com
>
> --- On Sun, 11/29/09, Tony Raftery
> <a.raft...@qut.edu.au> wrote:
>
> From: Tony Raftery <a.raft...@qut.edu.au>
> Subject: RE: Configuration of PANalytical X'pert Pro
> To: "Alexandra Seclaman"
> <seclaman_alexan...@yahoo.com>
> Date: Sunday, November 29, 2009, 11:57 PM
>
> Alexandra,
>
> while there is no such thing as a standard configuration,
> choices can be made to help in the modelling. Another
> corresponant (to the Rietveld list) made some
> suggestions that I only partly agree with. A lot depends on
> you goals ans available instrumentation - for instance if
> you have an X'cellerator detector and a monochromator.
> If you are interested in the low angle region (as I think
> you are) or not. If you were looking at some phases or
> phases where the peaks began after
> 25 deg 2theta, you could afford to go to larger divergence
> than if the peaks started at 5 deg 2theta.
>
> I see little use for beam knifes except over restricted low
> angle ranges (they always interfere at high angle, where
> they interfere depends on how they are set). It see little
> use for varable divergence slits for all sorts of reasons
> (firstly as there is no rock solid conversion from automatic
> to fixed intensities, secondly the resolution changes with
> angle with variable slits that can't be modelled -
> unless a more sofisticated model than that of Highcore Plus
> is used).
>
> What I agree with is that you need to use and properly
> adjust the anti-scatter slits.
>
> Fro memory (I am away from the lab for a few weeks) my
> conditions are for scans 3.5 deg to 140 deg 2theata - a
> general scan, well crystalled phases
> fixed divergence 0.5 deg, a-scatter (incident) 1 deg,
> sollers (incident) 0.04 rad
> 3.4mm (diffracted) a-scatter, mono fot
> X'cellerator, X'cellerator set full )about 2 deg)
> step 0.02 deg (or what X'cellerator allows, in my case
> 0.0167 deg), step-time to give about 10,000 counts full
> scale
> ________________________________________
> From: Alexandra Seclaman [seclaman_alexan...@yahoo.com]
> Sent: Saturday, 28 November 2009 3:09 AM
> To: rietveld_l@ill.fr
> Subject: Configuration of PANalytical X'pert Pro
>
> Hello,
>
> I have done a Rietveld refinement using a PANalytical
> X'pert Pro but the standard configuration is giving me a
> lot of troubles. This configuration is somewhat
> "blind" to the small 2 theta angles and it
> introduces (because of the poorly focused X ray beam) a
> heavy background. I've manage to remove that background
> by refinement but I'm sure that the quality of the
> acquisition can be improved.
> I am no engineer, so the inner workings of that machine are
> somewhat a mystery to me. I am asking if someone else has
> used a PANalytical for Rietveld and if you can give me a
> better configuration of slots, masks etc. I have tried
> different configurations with no success.
>
> Please take into consideration, while writing your reply,
> that I'm still a student and I have yet a lot to learn.
>
> Thank you!
>
> Alexandra Seclaman
> seclaman_alexan...@yahoo.com
> a.c.secla...@gmail.com
>
>
>
>
>
>
>
