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None Optical photons and Shashlik calorimeter 

Forum: Processes Involving Optical Photons
Date: 09 Nov, 2015
From: Alessandro Berra <Alessandro Berra>

Hi,

I am simulating a shashlik calorimeter readout with WLS fibers, and I need to correctly implement the optical processes to finalize the dimensions of the scintillating and absorbing tiles: I want a detectable signal for MIPs, without detector saturation due to too much optical photons in case of impinging electrons.

The calorimeter is composed of 5 3x3cm2 tiles of scintillator/absorber, with 9 WLS fibers: the baseline is to have 5mm thick scintillator tiles and 15mm thick iron tiles. At the moment I am inserting the tiles in the world volume one by one, with single G4PVPlacement using a for cycle in DetectorConstruction (no replicated volumes).

The WLS fibers logical volumes are embedded (<--> are daughter volumes) directly in each tile, together with the hole used to insert the fiber itself: the fibers have a diameter of 1mm, and the hole is 1.1mm.

I have defined the correct optical properties (refraction indexes, abs. length, time decay constants,ecc...) of the scintillator and the WLS materials: WLS process perfectly works, and the photons are carried by the WLS itself through total internal reflection simply assigning the correct refraction indexes to the core and the claddings. However, I have some problems to understand the different optical interfaces/border surfaces.

At the moment I am in this situation:

1) The scintillator tiles have a polished surface and will be painted with a reflective white paint, thus I think I have to define an array of "polishedfrontpainted" G4LogicalBorder surfaces between the physical volumes of the scintillating and absorbing tiles. Is it correct?

2) The 5mm thickness of each scintillating tile is facing the world volume, thus I need to define another array of "polishedfrontpainted" G4LogicalBorder surface between the scintillating tile and the physical World Volume. Is it correct (again)?

3) All the tiles (iron and scintillating ones) will be mechanically drilled to create the holes to insert the WLS fibers. The holes will be 0.1mm larger than the fiber and no optical grease will be used to fill the holes, thus an air gap will be present. Thus, I think I have to define many G4LogicalBorder surfaces (one for each hole) with "ground" finish between the scintillator tile and the hole physical volumes. Is it correct? If this is the case, the problem is that I don't know a reasonable value of the parameters for this surface: sigma_alpha, specular lobe constant and so on.

Any help would be appreciated. At the following links you can find some sketch of the geometry that can be useful to contextualize the geometry if it is not clear.

https://dl.dropboxusercontent.com/u/19790906/whole_geometry.jpg
https://dl.dropboxusercontent.com/u/19790906/lateral_view_sketch.jpg
https://dl.dropboxusercontent.com/u/19790906/wls_hole_sketch.jpg

Thanks in advance

Alessandro

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1 Feedback: Re: Optical photons and Shashlik calorimeter   (Gumplinger Peter - 09 Nov, 2015)
(_ None: Re: Optical photons and Shashlik calorimeter   (Alessandro Berra - 10 Nov, 2015)
(_ Feedback: Re: Optical photons and Shashlik calorimeter   (Gumplinger Peter - 10 Nov, 2015)
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