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Idea Re: Air Gap 

Forum: Processes Involving Optical Photons
Re: Question Air Gap (Eric)
Date: 03 Oct, 2011
From: Benton Pahlka <Benton Pahlka>

Hi Eric,

I don't have a solution, but you could try the following:

1. Use a G4ThreeVector to output the final location of your photons (w & wo gap). Or use an event viewer. 2. Try a smaller gap. In the limiting case, you should regain all your photons. Having said that, you should expect some total internal reflection where your PMT used to be if your scintillator refractive index is reasonable (i.e. larger than air) which will keep these photons from being collected. 3. Try placing a logical volume of air (or some other material?) in between to see the effect.

 Questions:  Do you have a refractive index for your PMT?  Are you including the PMT glass in your model?  If not, put some glass in your 0.5 mm gap and see what happens.  


On Mon, 03 Oct 2011 17:50:55 GMT, Eric wrote:

> Hi All-
> I am trying to add a small air gap into a simulation, in between a
> scintillator and a PMT. We estimate it to be about .5 mm. I tried just
> creating a separation of .5 mm between the PMT and scintillator (the
> environment is all air), but this cut my signal way down. It seems there
> should be a way with surfaces to do this, but my experience with optical
> surfaces in Geant is that they are designed to simulate reflective
> wrappings and wouldn't be real useful in this case.
> Any suggestions?
> Thanks.
> -Eric

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