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Question Porous medium 

Forum: Geometry
Date: 10 Sep, 2009
From: Guillaume Guérin <Guillaume Guérin>

I am working on dosimetry questions in sedimentary media. For this purpose, I first worked on homogeneous media: I defined a sediment cube (a:1m, composition: siliceous sediment) and I homogeneously and isotropically emitted photons inside of it. The detector is made of a homogeneous cube (same composition) placed at the centre of this world volume.
Then, in order to see the effects of moisture content in sediments I defined a porous detector: I use the cubic centered structure, so finally I define (with the G4VPVParameterisation tool) a number of quartz balls inside the detecting cell which is - between the balls - filled with air (dry case).
The packing is compact, and the density of the balls is set so that the porous cube density is the same as the siliceous sediment's one, so for a fixed number of primary photons I expect to record the same energy in the detecting cube in both cases (homogeneous and porous).
When the radius of the quartz balls is of 500µm, it indeed is the case. The problem is that I would like to simulate smaller balls, and when I set the radius at 400µm the deposited energy is not the same (5% lower). However since the compacity is fixed, the same volume is filled with quartz, density doesn't change, so physics say that the deposited energy should be the same.
I thus tried to play with the cut-offs, productionCuts, maxStepSize, but I could never find the right result.

Would you have any idea where the problem might be ? I guess geant4 must be suited to simulate matter in such details, isn't it ?

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