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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)
Re: Idea Re: Cerenkov photons (Gumplinger Peter)
Date: 25 Jul, 2013
From: Sam Blake <Sam Blake>

Hi Peter,

> Can you verify that the position:
> Position: (-14.5506,0.114811,-0.135845)
> is actually on a boundary in your geometry definition.

I checked using the visualization and that position is actually not on a boundary - the geometry as I currently have it only uses a single fiber (the parameterised volume enables the use of an array of fibers, and this same error was occurring when I used multiple fibers, but for simplicity I am currently just using a single fiber). The dimensions of the fiber are currently x = -15 to 0 mm, and y&z = -5 to+5 mm - so this particular photon is within the fiber when it gets stuck.

> 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.

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

I actually have not specified a scattering length for the PMMA, however a finite Rayleigh scattering length has been specified for the logicCore's material (called 'PhosphorMaterial').

Thanks once again for following up on this.


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