[mcstas-users] Radial collimator at primary side

Peter Link Peter.Link at frm2.tum.de
Tue Aug 17 08:56:07 CEST 2021

Hi Erik,

as far as I can see the problem is that in McStas Components the 
particle is always transported to the "entrance". Here if you have a 
look into the code of the component you realize that it uses the inner 
radius as entrance. If you turn it by 180 degrees in the instr. file 
this makes the code propagating the neutron directly to the exit. In 
short this component doesn't allow for inverted use.

Best regards


Am 17.08.2021 um 08:36 schrieb Walz, Erik:
> Dear All,
> We currently are trying to use a radial collimator in front of the 
> sample (primary side) to achieve a defined gauge volume width at the 
> sample position. Thus, the collimator is rotated and the neutrons 
> enter from the opposite side than usual. Unfortunately, results make 
> no sense at all. If we turn the collimator the other way around as a 
> test, we see a reasonable image on the detector, so the component 
> itself seems to be logically defined.
> The file is attached below. We would be very grateful about tips or 
> suggestions to solve the issue for using a radial collimator at the 
> primary side.
> Best regards,
> Erik Walz
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Dr. Peter Link
Leiter Neutronenoptik
Technische Universität München
Heinz Maier-Leibnitz Zentrum (MLZ)
Lichtenbergstr. 1
85747 Garching
Tel.: +49 (0)89 289 14622
Fax: +49 (0) 89 289 11694

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