Shay,
I have to disagree with much of the previous discussion. Yes, there are
aberrations in two-theta with sample displacement in a pseudo-parallel beam
instrument and they are different for displacement along the beam direction and
for displacement perpendicular to the beam (but in the detection plane).
Typically you can only see the first correction when data are collected over a
very wide angular range (>150 degrees) so this is almost never noticed with
x-rays. The functional form for the corrections is coded into GSAS-II, so if
you want read through the source code you can see what they are or you can do
some simulations to see the effect. The functional form for these corrections
are completely different from those for Bragg-Brentato geometry, which is
extremely sensitive to the sample height and in some cases sample transparency.
The Debye-Sherrer geometry corrections are typically very minor. When only
the second term is needed, the correction can be replaced with small shifts in
the two-theta zero correction and lattice constants. This is why in practice
with synchrotrons and CW neutrons one does not see the problems with sample
placement that leads to large peak shifts in a Bragg-Brentano geometry, making
it much easier to index patterns from synchrotron data, but it is not true that
there are no corrections.
Brian
On Feb 2, 2017, at 9:14 AM, Shay Tirosh
<[email protected]<mailto:[email protected]>> wrote:
Dear Rietvelders
Does the 2-teta shift due to sample displacement in parallel beam is similar to
Bragg Brentano mode?
If not then what is the mathematical expression in parallel beam?
Thanks
Shay
--
_________________________________________________
Dr. Shay Tirosh
Institute for Nanotechnology & Advanced Materials
Bar Ilan University
Ramat Gan, 52900
Israel
Phone: +972-(0)30-531-7320
Mobile: +972-(0)54-8834533
Email: [email protected]<mailto:[email protected]>
_________________________________________________
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
Please do NOT attach files to the whole list
<[email protected]<mailto:[email protected]>>
Send commands to <[email protected]<mailto:[email protected]>> eg: HELP as the
subject with no body text
The Rietveld_L list archive is on http://www.mail-archive.com/[email protected]/
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
Please do NOT attach files to the whole list <[email protected]>
Send commands to <[email protected]> eg: HELP as the subject with no body text
The Rietveld_L list archive is on http://www.mail-archive.com/[email protected]/
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
