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None What is the "wrapping" in the dielectric_dielectric backpaint? 

Forum: Processes Involving Optical Photons
Date: 29 Aug, 2013
From: Guillaume <Guillaume>

I have a LYSO scintillator volume with index of refraction (n) of 1.82 surrounded by air (n=1). At the interface, I have inserted a Tyvek surface with n=1.

The Tyvek is type dielectric_dielectric, model unified, finish groundbackpainted, with a sigmaalpha of 1.3 degrees.

I have read as much information on this forum as well as other locations, including this flowchart: http://hypernews.slac.stanford.edu/HyperNews/geant4/get/AUX/2012/05/23/23.20-70533-ces_in_geant4_revised.png

I have trouble understanding what "wrapping" means in the groundbackpainted description. My understanding is that the Tyvek surface is a kind of wrapping around my LYSO crystal. The flowchart seems to imply that this surface that I view as a kind of wrapping itself has its own wrapping. As if the surface in question comes standard with a second wrapping surface because of its groundbackpainted finish. Furthermore, the description refers to a crystal-air gap interface. I don't understand what that means. My understanding was that the layers through which light would go through in my setup is:

LYSO -> Tyvek -> Air

Is the groundbackpainted finish somehow inserting an additional layer called a "crystal-air gap interface" for the light to interact with?

The slide on page 7 of this document:

http://hypernews.slac.stanford.edu/HyperNews/geant4/get/AUX/2011/12/05/03.01-31709-optical_surface.pdf

is not helping me, since all I see for the groundbackpainted model is a thicker green interface area than the non-backpainted models, rather than what I would have expected from the groundbackpainted description of the flowchart: some sort of additional wrapping layer.

I am obviously very confused at the way geant is modelling this. If someone could reply with an enumerated list of every layer that a photon originating in the LYSO crystal goes through, given my setup, I would appreciated it.

Some additional info about the tyvek surface:

Specular Lobe 1.00 Specular Spike 0.00 Backscatter 0 Index of Refraction 1.00 Reflectivity 0.98 Efficiency 0.00

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1 Feedback: Re: What is the   (Gumplinger Peter - 29 Aug, 2013)
(_ None: Re: What is the   (Guillaume - 30 Aug, 2013)
(_ Feedback: Re: What is the   (Gumplinger Peter - 30 Aug, 2013)
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