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Idea Re: Cerenkov photons  

Forum: Processes Involving Optical Photons
Re: Question Cerenkov photons "stuck" in parameterised geometry using v9.6p02 (Sam Blake)
Re: Feedback Re: Cerenkov photons (Gumplinger Peter)
Re: None Re: Cerenkov photons (Sam Blake)
Date: 24 Jul, 2013
From: Gumplinger Peter <Gumplinger Peter>

Hi Sam,

Can you verify that the position:

Position: (-14.5506,0.114811,-0.135845)

is actually on a boundary in your geometry definition.

> 
> EventID = 9     Step # 1        Particle: opticalphoton ParentID: 2
>                 Volume: CoreParam       Copy Number: 0  Process: OpRayleigh     Creator Process:Cerenkov
>                 Position: (-14.5506,0.114811,-0.135845) Energy: 4.3608

This tell us that the process that defined the step is not 'Transportation' but OpRayleigh which would with ~100% probablility produce a step length that doens't exactly end on a volume boundary.

> After turning on the G4OpBoundaryProcess verbose (level 1), I get the
> following output:

> Scattering Photon!
> Old Momentum Direction: (0.813042,0.272653,-0.514416)
> Old Polarization: (-0.376582,-0.427564,-0.821812)
> New Polarization: (0.327999,0.454307,0.828264)
> Polarization Change: (0.327999,0.454307,0.828264)
> New Momentum Direction: (-0.879668,0.466512,0.0924714)
> Momentum Change: (-0.879668,0.466512,0.0924714)

You also turned on verbosity for G4OpRayleigh because the above is written there.

>  Photon at Boundary! 
>  thePrePV:  CoreParam
>  thePostPV: CoreParam
>  *** NotAtBoundary *** 

This is expected. G4OpBoundaryProcess is called at the end of every step of a photon, but it only kicks in if that step is really at a boundary. It tells us it is not: e.g.

(pPostStepPoint->GetStepStatus() != fGeomBoundary)

and so it is not a surprise that both thePrePV and thePostPV are CoreParam.

What is weired is that G4OpRayleigh is being called over and over again (and so it keeps on sampling a scattering angle.

Something else is not right ... maybe unrelated to geometry.

> Currently, I have not defined/associated any optical surfaces

Ok.

I have a suspision ... did you set a finite Rayleigh scattering length for PMMA?

Peter

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1 None: Re: Cerenkov photons   (Sam Blake - 25 Jul, 2013)
(_ Ok: Re: Cerenkov photons   (Sam Blake - 05 Aug, 2013)
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