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Forum: Geometry
Re: Question Is there a particular way to define crystalline structures in GEANT4? (Aqsa)
Date: Feb 01, 15:28
From: Michael H. Kelsey <Michael H. Kelsey>

On Wed, 12 Dec 2018 05:15:44 GMT, Aqsa wrote:
> I am currently developing a program where I need to define a geometry
> with YAG (yttrium aluminum garnet; Y3Al5O12) material. It is a
> crystalline structure. I was wondering can I simply define it by giving
> its fractional parts like:
> 
>     G4Material* H2O = new G4Material(name="Water",density,ncomponents=2);
>     H2O->AddElement(elH, natoms=2);
>     H2O->AddElement(elO, natoms=1);
> 
> Or is there a particular way to define crystal?
> 
> If there is pre-defined YAG material in GEANT4 database, please let me
> know. My work will become easier.

Geant4 treats all materials (solid, liquid, or gas) as a simple, isotropic and homogenous, continuum. For example, the interaction length of a particle is computed as a float, and at the end of that trajectory there will be an interaction with an atom. No account is taken of lattice spacing, orientation, or other crystal features. If your simulation involves just the bulk properties of YAG (density, index of refraction, and so on), then you create it just as above, with the stoichiometry of the elements.

If you are expecting to do a simulation which depends on the crystal lattice (things like defect behaviour), you may need to investigate other simulation software available in the solid state community.

A very recent addition to Geant4 is some support for crystals for purpose of doing charged particle "channeling" (where a bent lattice can guide GeV electrons around a curve). This is specific to that case, and not general support for crystals.

There is also an external package, G4CMP, which provides simplified physics for the production and propagation of acoustic phonons and charge carriers (drifting electrons and holes) in lattices. The package currently only includes silicon and germanium with predefined parameter sets, and the physics is limited to essentially millikelvin applications.

  -- Michael Kelsey

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