[mcstas-users] texture simulaion

[Peter Kjær Willendrup]

Hello again Dariusz,



Since my last email I have checked around a little - and there are multiple developments in the pipe:

* The Union component suite from Mads Bertelsen (UCPH - soon ESS) will receive an update before next McStas release. This should include an set of new developments from Victor Laliena (Zaragoza) including a texture / multi-granular crystal mode

* The authors of the NCrystal library have further let me know that this library could in principle support this by means of a “user-specified” orientation distribution. Currently there are two modes available, a single crystal model (Gaussian distribution) and layered crystal model (gaussian along one axis and uniform for the other two axes) - for modelling Pyrolytic Graphite.

* And then there is the model from Erik Knudsen (DTU) mentioned earlier, used for the PhD work of Alberto Cereser. This uses a “volume map” of orientations and our usual single crystal.



Let’s hope something reasonable can be there in the short to medium term.

Best and have a nice weekend,


Peter


Peter Kjær Willendrup
Forskningsingeniør, Specialkonsulent
Næstformand for DTU Fysik LSU

DTU Physics


[cid:b6339554-7f28-441d-9f31-5944f811397c at win.dtu.dk]


Technical University of Denmark


[cid:e108e480-fcab-46e2-9531-b38165079572 at win.dtu.dk]



Department of Physics
Fysikvej
Building 307
DK-2800 Kongens Lyngby
Direct +45 2125 4612
Mobil +45 2125 4612
Fax +45 4593 2399
pkwi at fysik.dtu.dk<mailto:pkwi at fysik.dtu.dk>

On 13 Dec 2018, at 12.43, Peter Kjær Willendrup <pkwi at fysik.dtu.dk<mailto:pkwi at fysik.dtu.dk>> wrote:

Dear Dariusz,


On 13 Dec 2018, at 12.14, Dariusz Wardecki - UKRI STFC <dariusz.wardecki at stfc.ac.uk<mailto:dariusz.wardecki at stfc.ac.uk>> wrote:

I am trying to simulate texture in a powder sample using McStas-2.4.1. For this purpose I wanted to use the Single_crystal component with the "powder" parameter. I started with an ideal powder using powder=1 and two monitors PSD_4pi and TOF at 90 deg to test the results. It turns out that when I compare this result with the one from the PowderN component I get completely different distribution of neutrons on the sphere as well as the wrong intensities from TOF.  It does not look like an ideal powder at all.


Does anybody have an idea what I  am doing wrong?


I use the following option:

SPLIT 200 COMPONENT sample = Single_crystal(radius=0.002, yheight=0.01,
         reflections="Al.lau", powder=1, order=1, mosaic=5)

As I remember, the only ever “agreement” that was established between the output of PowderN and Single_crystal was that the scattering pattern looked “about the same” and with the same order of magnitude.

To achieve that, I also remember adjusting mosaicity and delta_d_d to quite excessive values.

I will put on my list for the next release that this is documented by means of an instrument file! As I remember Erik Knudsen also has a solution in the pipe which is more along the lines of actual texture “maps”/distributions, it may be that we can also include that in the next release.

(Whether this will be 2.5.1 or 2.6 or… is currently not completely clear as 2.5 was released yesterday. :-) )


Best and hope this makes things a little clearer,

Peter Willendrup


Peter Kjær Willendrup
Forskningsingeniør, Specialkonsulent
Næstformand for DTU Fysik LSU

DTU Physics


<image001.gif>


Technical University of Denmark


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Department of Physics
Fysikvej
Building 307
DK-2800 Kongens Lyngby
Direct +45 2125 4612
Mobil +45 2125 4612
Fax +45 4593 2399
pkwi at fysik.dtu.dk<mailto:pkwi at fysik.dtu.dk>

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