[Gate-users] Brothers volumes at the same position what's occuring

Thu Feb 27 17:17:03 CET 2014

Hi,

David is right, there should not be overlapping volumes, but still I think
we can predict what happens ;-)

The first rule is that the particle will be in the first volume it crosses.
If it continues its way in this volume while passing through an overlapping
volume, it will ignore the overlapping volume until it exits the first
volume (because G4 uses DistanceToIn and DistanceToOut strategies to
compute the way in/out through the different volumes).

The second rule is (I don't know it but I deduce it from your experiment),
if it crosses 2 (or more) volumes at a same place while being in another
volume, it will enter the last declared volume, because volumes in G4 are
organised as a tree, and I can imagine that when scanning the tree, the
program always does it in the same way (so here probably by starting with
the last volume).

Still, be careful with overlapping volumes !

Cheers,
Simon

On Thu, Feb 27, 2014 at 5:06 PM, David Sarrut <
David.Sarrut at creatis.insa-lyon.fr> wrote:

> Hello,
>
> In G4 (thus in gate), you could *not* have overlapping volumes. If some
> volumes overlap, the result is undefined. To my knowledge, you don't have
> the choice, you need to change your geometry.
>
> There is a feature in G4 to deal with overlapping volumes (called parallel
> world), but it is not available through gate.
>
> Sincerely,
> David
>
> Le jeudi 27 février 2014, MELISSAS Maximilien (SAFRAN) <
> maximilien.melissas-alten at safran.fr> a écrit :
>
>   Dear Gaters,
>>
>> A question related to my question from yesterday,
>> When 2 brothers volume are crossing, what's happening at the crossingpoint.
>> Here is a quick example of what I mean, with a mother box having2 daughtersvolume Castor and Pollux
>>  /gate/motherbox/daughters/name Castor
>> /gate/motherbox/daughters/insert cylinder
>> /gate/Castor/geometry/setHeight 20. mm
>> /gate/Castor/geometry/setRmin 0. mm
>> /gate/Castor/geometry/setRmax 5. mm
>> /gate/Castor/placement/setTranslation +2. -0. 0.  mm
>>
>>  /gate/motherbox/daughters/name Pollux
>> /gate/motherbox/daughters/insert cylinder
>> /gate/Pollux/geometry/setHeight 20. mm
>> /gate/Pollux/geometry/setRmin 0. mm
>> /gate/Pollux/geometry/setRmax 5. mm
>> /gate/Pollux/placement/setTranslation -2. -0. 0.  mm
>>
>> these  volumes should have a big overlap at the center of motherbox.
>>
>> Now what's occuring when a particle pass through the middle of motherbox?
>> Is the particle inside of Pollux ?
>> Is the particle inside of Pollux and Castor, and can interact with both
>> Does the particle belong to the first volume it crossed ?
>>
>>
>> If the last the volume always on-top ?  If yes, this answers myquestion fromyesterday,
>>
>> the later-declared volume being on-top photons spend more time inside
>>  this one and thus scatter more from the last one.
>>
>> Cheers,
>> Maximilien
>>
>>  ------------------------------
>> *De :* gate-users-bounces at lists.opengatecollaboration.org [
>> gate-users-bounces at lists.opengatecollaboration.org] de la part de
>> MELISSAS Maximilien (SAFRAN) [maximilien.melissas-alten at safran.fr]
>> *Date d'envoi :* mercredi 26 février 2014 15:12
>> *À :* gate-users at lists.opengatecollaboration.org
>> *Objet :* [SUSPECTED SPOOFING] [Gate-users] (no subject)
>>
>>    Dear Gaters,
>>
>> I am facing an issue I don't understand, with my current description
>> of my setup, it seems that the X rays scattering depends on the orderin which volumes
>> have been declared
>>
>>
>>
>> To mimic the CT scan of a composite material (I am using Gateto understanda CT-Scan setup usedfor Aeronauticalpart testing),
>> I am introducing a periodic network of carbon fiber along each direction
>> in my test phantom (Let's call these direction 1, 2, 3)
>>
>>
>>
>> If I check the branches ComptVolName and RayleighVolName in the Hit Tree
>> , there is always one direction producing more scattering. However
>> , whatever the rotation of the phantom, the later-declared direction is
>>  always the one producing the most scattered hits.
>>
>> Here is a pseudo phantom.mac
>>
>> /gate/world/daughters/name epoxyBox
>>
>> #Define an epoxy box,
>>
>> /gate/epoxyBox/daughters/name CCylinder1
>>
>> #Define and rotate an array of carbon Cylinder using Repeater
>>
>> /gate/epoxyBox/daughters/name CCylinder2
>>
>> #Define and rotate an array of carbon Cylinder using Repeater
>>
>> /gate/epoxyBox/daughters/name CCylinder3
>>
>> #Define and rotate an array of carbon Cylinder using Repeater
>>
>>
>>
>> All the Carbon cylinders are copy-pasted and I change only the
>> rotation along X/Y/Z . After running the simulation, if I check whichvolumes producesthe most
>>  scattered hits (from Hits/CompVolName and Hits/RayleighVolName) the
>> volume producing the most scattered hits is CCylinder3 whatever the
>> rotation of the epoxyBox
>>
>> If now I declare the CCylinder in a different order i.e
>>
>> /gate/epoxyBox/daughters/name CCylinder3
>>
>> #Define and rotate an array of carbon Cylinder using Repeater
>>
>> /gate/epoxyBox/daughters/name CCylinder1
>>
>> #Define and rotate an array of carbon Cylinder using Repeater
>>
>> /gate/epoxyBox/daughters/name CCylinder2
>>
>> #Define and rotate an array of carbon Cylinder using Repeater
>>
>> Now the CCylinder producing the most scattered hits is CCylinder 2
>> (whatever the rotation of the epoxy box)
>>
>> I made all the rotation testing with few photons (around 100 000) to save
>>  Computing time, and I ran another orientation with 10 000 000 photons
>> to be sure I am not seeing statistical fluctuations
>>
>>
>>
>> Am I misunderstanding the meaning of the Rayleigh/ComptVolName (actually,
>> how is this leaf filled when a photon has been scattered several times)?
>>  Is it another feature that I don't understand or am I facing a bug?
>>
>>
>>
>> Cheers,
>>
>> Maximilien
>>
>>
>>
>> --
>>
>> Maximilien MELISSAS
>>
>> Consultant, Alten technology
>>
>> Image processing for CT NDT @ Safran composite
>>
>> http://www.alten.com
>>
>>
>>
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>
>
> --
> David Sarrut, Phd
> Directeur de recherche CNRS
> CREATIS, UMR CNRS 5220, Inserm U 1044
> Centre de lutte contre le cancer Léon Bérard
> 28 rue Laënnec, 69373 Lyon cedex 08
> Tel : 04 78 78 51 51 / 06 74 72 05 42
> http://www.creatis.insa-lyon.fr/~dsarrut
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