[mcstas-users] Guide_gravity Problem

Sat Feb 9 22:56:36 CET 2019

Hi all,

        I now have my reflectivity file working and I'm trying to
understand how many reflections happened in the guide. I followed the
example in the component manual in the end of section 9.8.7. It didn't
work. I attached the .instr and .rfl file to this email.
        Thanks for all the great help.

Sincerely,
Lingnan Shen

On Sat, Feb 9, 2019 at 2:42 AM Kim Lefmann <lefmann at nbi.ku.dk> wrote:

> 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 <pkwi at fysik.dtu.dk>
> *Sent: *Tuesday, February 5, 2019 4:20 AM
> *To: *Lingnan Shen <ls8vm at virginia.edu>
> *Cc: *Emmanuel Farhi <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> 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> 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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>
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>
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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
> Mobil +45 2125 4612
> Fax +45 4593 2399
> pkwi at fysik.dtu.dk
>
>
>
>
>
>
> Peter Kjær Willendrup
> Forskningsingeniør, Specialkonsulent
> Næstformand for DTU Fysik LSU
>
> DTU Physics
>
>
> [image: cid:b6339554-7f28-441d-9f31-5944f811397c at win.dtu.dk]
>
>
> Technical University of Denmark
>
>
> [image: 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
>
>
>
>
>
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