How to construct a gaussian geometry?

[yozhao]

Dear experts,

Does anyone know how to construct a gaussian-like shaped detector geometry?

The length or thickness of the detector and the radius of the detector follow a gaussian function:

L = Gaus (R, mean = 0, sigma)

as shown in the figure:

Thanks very much in advance!

Best,
Yongke

[loydms]

You can probably approximate a gaussian using a connical geometery

https://geant4-userdoc.web.cern.ch/UsersGuides/ForApplicationDeveloper/html/Detector/Geometry/geomSolids.html

Otherwise, you can convert a CAD model into a tessellated surface and import into a G4TessellatedSolid

[atolosad]

Hi,

An alternative to CAD or Tessellated solid is the Polycon, ie

    auto R0 = 1*cm;
    auto zmax = 1*cm;
    auto sigma=0.1*cm;
    std::vector<G4double> zPlane = {0.05*zmax, 0.1*zmax, 0.2*zmax, 0.5*zmax, 0.9*zmax};
    auto numZPlanes = zPlane.size();
    std::vector<G4double> rInner( numZPlanes, 0.0 );
    // function that calculates the outer radius as gausian. 
    // Takes by reference R0 and sigma
    auto fgaus = [&](double x){return sigma*std::sqrt(-2*std::log(x/R0)); };
    std::vector<G4double> rOuter = { fgaus(zPlane[0]), fgaus(zPlane[1]), fgaus(zPlane[2]), fgaus(zPlane[3]), fgaus(zPlane[4]) };
    
    G4Polycone*         targetSolid   = new G4Polycone("solid-Target",    // name
                  					0.0,  		  // G4double  phiStart,
                  					2*pi, 		  // G4double  phiTotal,
                  					numZPlanes,	  // G4int     numZPlanes,
                  					zPlane.data(),	  // const G4double  zPlane[],
                 					rInner.data(),	  // const G4double  rInner[],
                  					rOuter.data()	  // const G4double  rOuter[])
							);

Which results in:

I hope it works

Best,
Alvaro

[yozhao]

Dear Alvaro,

That sounds quite a good idea. Thanks very much!

Best,
Yongke

[yozhao]

Dear loydms,

Thanks very much for your advice!

Best,
Yongke