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<font size="-1"><font face="Verdana">Dear Erik and Peter,<br>
<br>
</font></font>Thanks for your answers.<br>
<br>
Le 02/06/2021 à 13:18, Erik B Knudsen a écrit :<br>
<blockquote type="cite"
cite="mid:95563298-5a87-b974-1784-47eaba038e57@fysik.dtu.dk">Dear
Thierry,
<br>
<br>
You could definitely use Single_crystal or, if it is an assembly
of crystals you want, a Union of single crystals for mosaic
crystals. Is there a specific geometry you are targeting?<br>
</blockquote>
<br>
My aim is to optimize the design of a monochromator for an
angle-dispersive reflectometer with a fixed take-off angle, and
whose scattering plane is horizontal. <br>
I would like to estimate the performance of crystals (e.g. Si 111)
which are both mosaic and bent horizontally, along a cylinder. The
bending is expected to result in an additional effective mosaic
contribution, which depends on thickness. This should combine with
intrinsic mosaic and extinction effects.<br>
Ideally I would also like to look at the harmonics contributions.<br>
<br>
As I understood Monochromator_curved cannot do all of these, because
it is infinitely thin, it does not calculate structure factors and
the reflectivity is given empirically rather than being deduced form
the crystal structure.<br>
I started using Monochromator_curved, because I also want the
monochromator to focus vertically. For this I use several crystals,
which are positioned with different angles but not bent in vertical.
This is easily implemented with this component. Maybe the treatment
of the vertical direction could be decoupled from the horizontal, if
things are getting too complicated.<br>
<br>
Concerning Single_crystal, I thought it was not suited, since the
first sentence in the component manual says it "models a thick, flat
single crystal..."<br>
But on the web help
(<a class="moz-txt-link-freetext" href="http://www.mcstas.org/download/components/samples/Single_crystal.html">http://www.mcstas.org/download/components/samples/Single_crystal.html</a>)
it looks quite different:<br>
"The crystal lattice can be bent locally, keeping the external
geometry unchanged.<br>
Curvature is spherical along vertical and horizontal axes."<br>
And I see now that one can enter RX and RY parameters, so I guess it
should work.<br>
<br>
Concerning the other points:<br>
- "4 ways of modelling mosaic, depending on your situation": which
one would you recommend in my case ? I will assume isotropic
mosaicities (except the contribution of bending). Beyond this I did
not try yet to understand the subtleness of the different methods. <br>
- I do not how Union works, and didn't find it in the manual. Is it
something new in McStas 3.0 ? I am learning with 2.6.1 on Windows,
and I am far from being a software expert.<br>
- If Single_crystal does the job, I was wondering why Lucia
Alianelli developped a new component for mosaic crystals. Do you
know if the modelling approach is different, or is it better suited
to particular cases ? As she published some systematic comparisons
with measurements on real crystals, do you know if similar things
were done to validate the Single_Crystal component ? <br>
<br>
Thierry<br>
<br>
<blockquote type="cite"
cite="mid:95563298-5a87-b974-1784-47eaba038e57@fysik.dtu.dk">
<br>
Please note that Single_crystal has effectively 4 ways of
modelling mosaic, depending on your situation.
<br>
<br>
cheers
<br>
Erik
<br>
<br>
On 01/06/2021 19:53, Peter Kjær Willendrup wrote:
<br>
<blockquote type="cite">Dear Thierry,
<br>
<br>
<br>
<blockquote type="cite">On 1 Jun 2021, at 18.57, Thierry Bigault
<<a class="moz-txt-link-abbreviated" href="mailto:bigault@ill.fr">bigault@ill.fr</a> <a class="moz-txt-link-rfc2396E" href="mailto:bigault@ill.fr"><mailto:bigault@ill.fr></a>> wrote:
<br>
<br>
I am trying to make calculations with mosaic crystals. The
following paper states that a new component, called
Monochormator-reflect, was introduced in order to overcome
some limitations of Monochromator_curved:
<br>
<br>
L. Alianelli, N. Wilson, K.H. Andersen, M. Sánchez del Rı́o,
R. Felici, A method for detailed simulations of neutron
diffraction from imperfect crystals, Nucl. Instr. Meth A 529
(2004) 231–233.
<br>
<br>
Does anyone know what this became ? Was it included into
another more sophisticated component that can be used to
simulate monochromators, like Single_crystal ?
<br>
</blockquote>
<br>
I do have a copy of the said component component somewhere, but
could not locate it at first glance. I am also sure both Erik
and Emmanuel has a copy. I am however also sure that it will not
work “out of the box”. :)
<br>
<br>
( The reason that the component never made it into the official
McStas release was in a way simple:
<br>
It relied on an inputfile that was prepared using an IDL
procedure-code, which we thought was a very nasty dependency…)
<br>
<br>
What specific advanced feature(s) are you looking for? We do
have a number of other good alternatives, e.g. Single_crystal or
NCrystal.
<br>
<br>
<br>
Best,
<br>
Peter
<br>
<br>
<br>
Peter Kjær Willendrup
<br>
Forskningsingeniør, Specialkonsulent
<br>
Næstformand for DTU Fysik LSU
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DTU Physics
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Technical University of Denmark
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</blockquote>
<br>
</blockquote>
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