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Re: Question optical photons in plastic scintillator (Balint Radics)
Date: 08 Nov, 2013
From: Gumplinger Peter <Gumplinger Peter>

Hello Balint,

> I am using geant4-09-05-patch-02. I have a plastic scintillator
> implementation which has scintillation yield 8400/MeV. I get sometimes
> several tens of thousands of optical photons in an event in my
> scintillator and in such a case subsequently the Geant4 runs are
> extremely slow...(~several seconds per event, while previously I had
> around 100 times faster event rate).

Sorry, but what do you mean with 'previously'; do you mean without tracking optical photons or in an earlier version of G4?

Clearly, tracking thousands of tracks is going to slow your simulation right down. What you can do, should you know the photo efficiency of your photon detector, is apply it in StackingAction and don't bother tracking those that don't survive.

You can also reduce the scintillation yield by 1/F, knowing that your simulation is biased now and that counting rate results need to be multiplied by F. Often it is not necessary to simulate the full photon statistics to get an idea of ones investigation within your allowed errors.

> Is there any other parameter that might speed up the code? Perhaps some
> additional/coarser step limits can be configured for these guys?

These guys (optical photons) bounce from geometry boundary to geometry boundary until they are absorbed somewhere. Steplimiter don't apply to them.

> Or other suggestions how to speed up the optical photon processsing in
> Geant?

The G4 navigator is perhaps not the fastest stepper out there and the logic in G4OpBoundaryProcess is lengthy (there are dedicated optical simulators available that are reportedly faster) but the great advantage of G4 is that you can do this type of simulation in complicated geometries.


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1 Agree: Re: optical photons in plastic scintillator   (Balint Radics - 08 Nov, 2013)
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