Dear Gaia
Indeed, the collimator is not positioned where Flair shows it.
In the geometry transformations, the translation is always applied
before any rotation. The reason is that translation can be applied
immediately while reading the geometry, rotation instead has to be
applied runtime because it can modify the body "type".
( from the manual, section 8.2.5.4 "$Start_expansion takes precedence
over $Start_translat, which in turn
takes precedence over $Start_transform.")
Thus, independently of the order of $start_translat and $start_transform
in the input, fluka will always perform the translation first, which is
not what you wanted here.
Flair instead only issue a warning, you can see it tin the flair output
window, when the input ordering is not correct, but it proceeds to plot
the geometry following the input ordering, that in your case is not the
fluka ordering. This is a regrettable behavior that we'll modify as soon
as possible.
To solve your problem, you can add the translation as last step of the
definition of your roto-translation matrices, with the ROT-DEFI card,
and avoid the translat directive in the geometry.
Regards
Paola
On 11/3/23 17:19, Gaia Franciosini wrote:
> Dear FLUKA Experts,
> I am writing to you for an issue I've encountered while running a
> FLUKA simulation.
> I have created an input file for a simulation involving a rectangular
> electron beam (8x8 cm) that is directed towards a water box. Before
> interacting with the water box, the beam is expected to pass through a
> collimator. This collimator has been defined as an RPP with numerous
> small rectangular holes, and it is was at first positioned at the
> origin (0,0,0).
> To orient the collimator perpendicular to the beam, I have applied two
> rotations and a translation.
> Upon inspecting the geometry of the simulation, the input file appears
> to be correctly defined, with the collimator positioned approximately
> 40 cm (arbitrary) from the point where the pencil beam is aimed, which
> is [-1.876, -0.766, -3.3].
>
> However, when I run the simulation and visually inspect the particle
> tracks, it seems that the beam is not interacting with the collimator….
>
>
> *
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> Scrivi il codice fiscale dell'Università *80209930587
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>
>
>
>
>
> Could you please review the input file and my geometry definitions to
> help me identify any potential issues?
>
> Thank you for your time.
>
> Sincerely,
>
> Gaia Franciosini
>
>
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Received on Tue Nov 07 2023 - 12:09:06 CET