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Forum: Processes Involving Optical Photons
Re: Question Adapting geometry to work w/ optical photon (Nicolas Maurissen)
Date: 06 Nov, 2013
From: Gumplinger Peter <Gumplinger Peter>

Dear Nicolas,

> but when the photon is not
> absorbed, I have line on my terminal telling me
> $ Photon at Boundary!
> $ thePrePV : Styrene // (name changed for ease)
> $ thePostPV : Aluminum front plate // (name changed for ease)
> $ Old Momentum Direction : (values)
> $ Old Polarization : (values)
> $ ***NoRINDEX***
> I guess that mean that I didn&#65533;t correctly add the &#65533;optical properties&#65533;
> to the correct volumes in my geometry.

You have an interface (surface) between styrene and aluminum. The aluminum is the reflector - and a metal - you must define the surface as 'dielectric_metal' and give the aluminum a reflectivity (there is an example code in the App. Dev. Guide). Since you didn't define the surface (I presume), the program assumes the default which is dielectric_dielectric and thus complains because the aluminum has no index of refraction.

> Concerning my current geometry, as you can see on the attached file, the
> styrene scintillator is made of one box, covered with aluminum plates
> (one per face, those being the detector reflectors), themselves covered
> with a polyethylene layer.

For the simulation of optical photons the polyethylene layer is not needed since no optical photon can penetrate through the aluminum. Thus you don't need to give the polyethylene optical properties.

> I used multiple volumes for the two coatings
> to be able to make the hole for the PMT. The quartz (glass) part of the
> PMT is in direct contact with the styrene scintillator.

You'll need to give the quartz an index of refraction. If you are content with a perfectly smooth surface between the quarz and the scintillator you don't need to define a G4OpSurface; see above my comment as to what is the default.

> To which material do I need to add &#65533;optical properties&#65533; ?

styrene and quarz need, at a minimum, index of refraction. The Al/styrene surface must be defined and defined as dielectric_metal and the Al given, at a minimum, a reflectivity.

> Do I have to define surfaces (or skin ?) between volumes ?

Only between styrene and Al (see above) and between the glass and Al.

> Is this the way to make my aluminum plates act as reflectors ?

Yes, your geometry looks ok - except I would construct it differently by putting the styrene inside - as a daughter - of a solid Al box. Thus, you don't need six Al slabs! You can also put a glass disk at the PMT entrance window location as a daughter of the Al box - with an extra cylinder behind to complement the full entrance window cylinder length (again as a Russian doll of quarz inside a solid Al cylinder) with the back face (disk) a separate daughter volume to identify your sensitive PMT photo cathode.

One surface in touch with the glass (I presume the back - behind the glass) - must be specified as your 'photon detector' (PMT - not Al) and defined also as dielectric_metal.

> If I need to define surfaces for my reflectors, is it ok to have two
> kind of surfaces sharing a same volume (aluminum / scintillator and
> quartz / scintillator on top of my detector) ? If not, how may I correct
> it ?

As you know, the boundaries are defined according to volumes' names - not what they are made of. So, yes, you can have a surface between the scintillator and the quartz window (volume) and between the scintillator and its Al housing.


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1 Ok: Re: Adapting geometry to work w/ optical photon   (Nicolas Maurissen - 08 Nov, 2013)
(_ Feedback: Re: Adapting geometry to work w/ optical photon   (Gumplinger Peter - 08 Nov, 2013)
(_ Ok: Re: Adapting geometry to work w/ optical photon   (Nicolas Maurissen - 14 Nov, 2013)
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