[mcstas-users] Guide_gravity Problem

[Kim Lefmann]

Hi Shen,

It is also my understanding that the k value is the momentum transfer.

Sorry, I do not have the time to look into you problem now.

best, Kim


On 2/7/19 4:53 PM, ls8vm at virginia.edu wrote:
>
> Hi all,
>
>             I checked the supermirror_m3.rfl file and it ranges from 0 
> to 0.09 [Angs-1] so I’m really confused with the k value in the first 
> column of reflectivity file. I thought it represent the total momentum 
> transferred. Can you explain more on “better the k values in the 
> reflectivity file to be around e.g. 1.0 Angs-1.” Does the 
> guide_gravity component have a different definition on reflectivity 
> file? My actual source wavelength ranges from 0 to 10 [Angs].
>
> And also for Peter, my actual problem is to optimize a polarizer which 
> is built by stack of supermirror. I’m trying to find a way to get the 
> most transmission through that setup. So I want to calculate the ratio 
> neutron_out/neutron_in. Now it seems that I should just divide the 
> intensity instead of event numbers?
>
> Happy Lunar New Year,
>
> Lingnan Shen
>
> *From: *Peter Kjær Willendrup <mailto:pkwi at fysik.dtu.dk>
> *Sent: *Tuesday, February 5, 2019 4:20 AM
> *To: *Lingnan Shen <mailto:ls8vm at virginia.edu>
> *Cc: *Emmanuel Farhi <mailto:farhi at ill.fr>
> *Subject: *Re: [mcstas-users] Guide_gravity Problem
>
> Hello again,
>
> A better starting point for understanding Guide_gravity and 
> reflectivity files may be the instrument file Test_Guides which is 
> included with your McStas installation, in combination with one of the 
> example reflectivity files from the data folder - e.g. supermirror_m3.rdl.
>
> Also, for a pencil beam with controllable divergence, an option is to 
> use Source_div.
>
> Hope this helps - otherwise you are welcome to write again, preferably 
> with a good description of what exact problem you are trying to solve. :-)
>
> Best,
>
> Peter
>
>
>
>     On 5 Feb 2019, at 10.12, Peter Kjær Willendrup <pkwi at fysik.dtu.dk
>     <mailto:pkwi at fysik.dtu.dk>> wrote:
>
>     Hello Lingnan,
>
>     Agree with Emmanuel.
>
>     Further, the combination of a pencil-beam, i.e. almost
>     non-divergent source and using 500 channels in a rotated
>     Guide_gravity means that transport through the guide becomes close
>     to impossible.
>
>     With regard to your second question you should always consider the
>     transported intensity I. The event count is simply a measure of
>     statistics (of "neutron rays", not “neutrons”).
>
>     Best,
>
>     Peter Willendrup
>
>         On 5 Feb 2019, at 10.01, Emmanuel FARHI <farhi at ill.fr
>         <mailto:farhi at ill.fr>> wrote:
>
>         Hello Lingnan,
>
>         Your reflectivity file is given for k=0 to 0.14 Angs-1. This
>         is very small and covers neutrons around lambda=60 Angs, which
>         are not even created by your source. Change either the lambda
>         setting at the source, or better the k values in the
>         reflectivity file to be around e.g. 1.0 Angs-1.
>
>         Cheers, Emmanuel.
>
>         On 2/5/19 7:17 AM, Lingnan Shen wrote:
>
>             Hi all,
>
>                     I was trying to learn how to use the guide_gravity
>             component. I tried to define the reflectivity curve but I
>             get zero neutrons at the wavelength monitor in the end of
>             guide. I have attached my .instr and .rfl file. I also
>             found that even if the neutron beam just go through the
>             guide. The detector at the end still see nothing.
>
>                     Also another question about transmission of
>             certain setup. To calculate the ratio of neutron_in /
>             neutron_out. I want to know how much neutron remained
>             after passing through that setup. Should I use the flux or
>             the events count?
>
>             Sincerely,
>
>             Lingnan Shen
>
>
>
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>         -- 
>
>         Emmanuel FARHI,                                           \|/ ____ \|/
>
>         Spectroscopy Group Institut Laue-Langevin (ILL) Grenoble  ~@-/ oO \-@~
>
>         71 av des Martyrs,CS 20156,38042 Grenoble Cedex 9,France  /_( \__/ )_\
>
>         Work :Tel (33/0) 4 76 20 71 35. Fax (33/0) 4 76 48 39 06     \__U_/
>
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>
>     Peter Kjær Willendrup
>     Forskningsingeniør, Specialkonsulent
>     Næstformand for DTU Fysik LSU
>
>     DTU Physics
>
>
>     <image001.gif>
>
>
>     Technical University of Denmark
>
>
>     <image002.gif>
>
>
>
>     Department of Physics
>     Fysikvej
>     Building 307
>     DK-2800 Kongens Lyngby
>     Direct +45 2125 4612
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>
>
> 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>
>
>
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