[Gate-users] materials in GATE

[John Apostolakis]

A small amplification/simplification on Niklas' correct explanation:

- Production thresholds are necessary in a simulation to ensure that  
simulation time is not spent on a large number of very small energy  
tracks which deposit all their energy right next to where they are  
created.  (Large number due to the infra-red divergence of  delta  
electrons created by ionisation.)

- A simple geometry can have only one set of production thresholds  
( value for gammas, value for electrons ).

- In a complex geometry or one with regions with different importance  
or characteristics, tuning the the production thresholds allows Geant4  
to spend more time tracking particles important to the result.

- In order to save memory, Geant4 create only those combinations  
(couples) of materials and cuts which are required by the definition  
of the Regions in the setup, their corresponding cuts chosen by the  
users, and the materials in the volumes of those regions.

- The report of the cuts-couples created can be turned off by a user  
command (which I don't have in front of me, but could ask someone to  
dig up.)

Regards,
John Apostolakis

On Jul 9, 2009, at 9:49 AM, Niklas Rehfeld wrote:

> Dear Ali Asghar,
>
> On Wed, 08 Jul 2009 17:11:45 +0200, AliAsghar Parach <aaparach at gmail.com 
> >
> wrote:
>
>> Dear gate users,
>> I have 2 questions about material properties in GATE:
>> 1- what means registered couples in GATE running page? and what is  
>> the
>> difference between registered couples and  Nb of materials that are
>> differentially pointed out in GATE running page at each run?
>
> - A G4Material defines the physical properties of a piece of the  
> simulated
> world (density, elements etc)
>
> - A G4MaterialCutsCouple includes the G4Material _and_ production  
> cuts.
> These cut values are not physically motivated but need to be set for
> computational reasons
> (for example specifying energy intervals for which cross sections for
> particles should be computed). For each G4Region (a set of
> G4LogicalVolumes) a different G4MaterialCutsCouples can be assigned.
>
>
>> 2- in voxelised phantom when i define only one material (eg:Water)  
>> in my
>> voxel phantom in range.dat file, GATE shows Water,Air,Vacuum in  
>> it's running
>> page (in registered couples and  Nb of materials). what is it's  
>> reason?
>
> There are other volumes in your simulation that are made of Air or  
> Vacuum
> (for example the world volume).
>
> Niklas
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