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<font size="-1"><font face="Verdana">Dear McStas,<br>
<br>
Here is my problem: <br>
I would like to simulate the exit of a cold neutron guide with a
source. The aim is to concentrate on the instrument optics,
without having to calculate all the guide from the reactor.<br>
A simplified and quite general description of a guide exit is a
beam with a fixed "m-value" divergence: for a given wavelength,
the width of the angular divergence (either box-type, Gaussian
or whatever) is essentially proportional to the m-value of the
guide coating and to the wavelength.<br>
If the guide has different supermirror coatings on horizontal
and on vertical faces, this leads to different angular widths.<br>
I assume the beam characteristics does not depend on the
position at the guide exit in this approach.<br>
My question is : what is the simplest way to simulate such a
secondary (or virtual) source in McStas ? I only found
components where the angular width is geometrically fixed (in
degrees), therefore wavelength-independent.<br>
Ideally I would also like to include a non-flat wavelength
intensity distribution, but this can probably be done by adding
a Filter_gen after the source.<br>
I am thinking of making several calculations at different
wavelengths, but if anyone knows a all-in-one solution I am
interested.<br>
<br>
Thierry<br>
<br>
<br>
<br>
<br>
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<div style="margin-top: 2px; color: # 1A2A69; font-size:
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BIGAULT</div>
<div style="color: #1A2A69; font-size: 11px; line-height:
14px;">Research Engineer </div>
<div style="color: #1A2A69; font-size: 11px; line-height:
14px;">Multlayer Neutron Optics </div>
<div style="color: #1A2A69; font-size: 11px; line-height:
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