Hi All,
A most interesting discussion. However, I think that the comments on tube tails
have got away from the original question. I interpret the comment “…. some
shoulders in the left part of the peaks ..” and the appearance of the supplied
plot to be due to the effect of absorption of the Bremsstrahlung from the X-ray
tube by the beta filter. This can be difficult to model using conventional
background functions but TOPAS Version 5 incorporates an appropriate correction
for this using the error function.
Cheers
o----------------------------oo0oo----------------------------o
Ian Madsen
Team Leader - Diffraction Science
CSIRO Process Science and Engineering
Box 312, Clayton South 3169
Victoria, AUSTRALIA
Phone +61 3 9545 8785 direct
+61 3 9545 8500 switch
+61 (0) 417 554 935 mobile
FAX +61 3 9562 8919
Email [email protected]
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From: [email protected] [mailto:[email protected]] On Behalf Of
Reinhard Kleeberg
Sent: Tuesday, 17 September 2013 3:53 PM
To: Alan Coelho
Cc: 'Matt Beekman'; [email protected]
Subject: Re: Instrumental resolution function
Tubetails are simply the result of emission of the target radiation from
outside the wanted line focus, some mm around. Depending on tube quality, age
and operating power, one can have varying shapes when projected on the 2theta
scale. Examples:
http://www.bgmn.de/tubetails.html
As you can see, the shape are not hats as assumed in Topas but may have
discrete maxima at both sides, may by assymetric.
Especially for sharp peaks, the correction strongly improves the result of
profile fitting:
Bergmann, J., Kleeberg, R., Haase, A., Breidenstein, B. (2000) Advanced
fundamental parameter model for improved profile analysis. Mat. Sci. Forum
Vols. 347-349(2) 303-308.
In general, the tubetails more strongly influence the peak shape for
instruments with smaller goniometer radius and when the equatorial divergence
slit is placed closer to the sample.
In general. Alan's statement that the width/shape of the tubetails is 2Th
independent is correct, as it is simply a projection on the measuring circle.
But, as a part of the tubetails diffracted intensity is generated outside the
projection of the wanted focus via the divergence slit on the sample, tubetails
may be cut by a limited size of the sample. Such cutting of the tubetails
effect may happen at low angles for fixed slit systems and at higher angles
when using automatic slit systems. In consequence, the intensity and shape of
the tails effect can become dependent on 2Theta, in a complicated way.
In BGMN/GEOMET we try to convolute an experimentally measured focus profile
into the geometrical contribution of the MonteCarlo simulation. As this
procedure is done at discrete angular steps and the resulting geometrical
profiles are interpolated later, we hope to have introduced correctly such
secondary effects.
Reinhard
Am 17/09/2013 03:53, schrieb Alan Coelho:
Matt
I am not sure I understand how you would account for the additional
wavelengths in the beam.
Tube tails is spectrally independent and its aberration shape is 2Th
independent. Its realized in TOPAS by a convolution called stacked_hats
which, as its name suggests, convolutes a series of stacked impulse
functions. An intense narrow hat represents the beam and wider hats the
penetration of the electrons in the tube.
Cheers
Alan
-----Original Message-----
From: Matt Beekman [mailto:[email protected]]
Sent: Tuesday, 17 September 2013 2:08 AM
To: Peter Y. Zavalij; Alan Coelho;
[email protected]<mailto:[email protected]>;
[email protected]<mailto:[email protected]>
Subject: RE: Instrumental resolution function
Alan, Peter,
Would you mind briefly elaborating on the procedure used to "fit tube
tails?" I personally have only used GSAS for Rietveld refinement, and other
than adding another phase(s) with slightly different lattice parameter(s) I
am not sure I understand how you would account for the additional
wavelengths in the beam.
Many thanks in advance!
Matt
--
Matt Beekman, Ph.D.
Assistant Professor of Physics
Department of Natural Sciences
Oregon Institute of Technology
3201 Campus Drive
Klamath Falls, OR 97601
Tel: 541-885-1940
Fax: 541-885-1849
Email: [email protected]<mailto:[email protected]>
Web:
http://www.oit.edu/faculty-staff/home-pages/natural-science/matt-beekman
-----Original Message-----
From: [email protected]<mailto:[email protected]>
[mailto:[email protected]] On Behalf
Of Peter Y. Zavalij
Sent: Monday, September 16, 2013 6:11 AM
To: Alan Coelho; [email protected]<mailto:[email protected]>;
[email protected]<mailto:[email protected]>
Subject: RE: Instrumental resolution function
I do exactly the same - fit tube tails using LaB6 standard and use the
parameters (usually w/o fitting) in all other refinements. Although tube
tails fitting helps a lot it's not perfect.
Peter Zavalij
-----Original Message-----
From: Alan Coelho [mailto:[email protected]]
Sent: Sunday, September 15, 2013 10:05 PM
To: Peter Y. Zavalij;
[email protected]<mailto:[email protected]>;
[email protected]<mailto:[email protected]>
Subject: RE: Instrumental resolution function
Hi Peter, Mario
I happen to have a Ni filter, Cu, LaB6 pattern that has a very similar look
to the one sent by Mario. Probably best to look at the 21.35 degrees 2Th
peak. The Ni filter cut-off occurs at 20.6 degrees 2Th, the satellite group
is hard to see due to the low angle and hence compression of the emission
profile. What made sense in the pattern was to fit Tube tails. Across the
whole patter the Rwp was reduced by 2.1% where Tube tails was considered and
the fit at the shoulders was good.
Cheers
Alan
-----Original Message-----
From: [email protected]<mailto:[email protected]>
[mailto:[email protected]] On Behalf
Of Peter Y. Zavalij
Sent: Monday, 16 September 2013 10:55 AM
To: [email protected]<mailto:[email protected]>;
[email protected]<mailto:[email protected]>
Subject: RE: Instrumental resolution function
Hi Mario,
The shoulder you observe is what's left from "white" after it is cut off by
beta-filer. You could check the absorption edge of Ni and it is right at the
shoulder you observe.
Peter
__________________________________
Peter Zavalij
X-ray Crystallographic Center
University of Maryland
College Park, MD 20742
Phone/Fax: (301)405-1861
http:/www.chem.umd.edu/crystallography<http://www.chem.umd.edu/crystallography>
-----Original Message-----
From: [email protected]<mailto:[email protected]>
[mailto:[email protected]] On Behalf
Of [email protected]<mailto:[email protected]>
Sent: Sunday, September 15, 2013 6:08 PM
To: [email protected]<mailto:[email protected]>
Subject: Instrumental resolution function
Dear All,
I am calculating the corresponding instrumental resolution function of our
Bruker diffractometer which is operating in Bragg-Brentano geometry with Cu
radiation, using a nickel filter and LynxEye detector.
The calculation is carried out by the Rietveld analysis of the LaB6 (660b)
NIST-standard. We observed the Kbeta peaks, but also some shoulders in the
left part of the peaks. We have some ideas about this but taking into
account that I'm not an actual expert, your comments will be very important
to me.
In the attached file, I send an image to make a better illustration of my
doubts.
Thanks in advance for your help.
Best Regards,
Mario A. Macías
Universidad Industrial de Santander
Bucaramanga-Colombia.
--
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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