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Forum: Geometry
Re: Question Track stuck with LUT surface model (Felix Liang)
Date: 02 Jul, 2014
From: Gumplinger Peter <Gumplinger Peter>

Dear Felix Liang,

The better forum for your post would have been 'Optical Physics' - hence this delayed reply.

> I use
> "groundteflonair" from the Look-Up-Table to specify the surface treatment
> because the scintillator surfaces are rough and wrapped with Teflon tape.

OK

> (1) Do I need to create a MaterialPropertiesTable to include RINDEX,
>     EFFICIENCY, and REFLECTIVITY when I use the LUT method?

You also need to provide the REFLECTIVITY if it is anything less than perfect (1. is default)! I am sorry, the documentation is not very clear on this. The code should read as your code below, plus:

  G4MaterialPropertiesTable* SMPT = new G4MaterialPropertiesTable();

  SMPT -> AddProperty("REFLECTIVITY",pp,reflectivity,NUM);

  opCrystalSurface->SetMaterialPropertiesTable(MPT);

(while you don't have to specify RINDEX and EFFICIENCY)

> (2) When I ran the code, the warning message "Track stuck or not moving"
>     kept scrolling on the computer screen. I calculated the location of the
>     points where they are stuck. They were all on the cylindrical surface.
>     The scintillator was constructed with
> 
>     G4Tubs* tubsCrystal =
>       new G4Tubs("tubsCrystal", 0, fCrystal_x/2.,
>                  fCrystal_z/2.,0.*deg,360.*deg);
>     scint_logV =
>       new G4LogicalVolume(tubsCrystal,NaI,"ScintLogV",0,0,0);
> 
>     Did I miss something for using the LUT method?

No, except if you wanted less than perfect LUT reflection. I have no explanation for why you get the warning message.

>     However, when I switched to use the UNIFIED model for the surface
>     properties, the warning message "Track stuck or not moving" disappeared
>     completely. I did not change anything else in the scintillator
>     construction when I switched from the LUT to the UNIFIED model.
> 
>     Here are the codes for using the LUT model and the UNIFIED model.
> 
>    ---------- LUT ----------
> 
>   G4OpticalSurface* opCrystalSurface = new G4OpticalSurface("CrystalSurface");
>   opCrystalSurface->SetType(dielectric_LUT);
>   opCrystalSurface->SetFinish(groundteflonair);
>   opCrystalSurface->SetModel(LUT);
>   G4LogicalBorderSurface* bSurface =
>     new G4LogicalBorderSurface("CrystalSurface",scint_physV,
>                              lightBox_physV,opCrystalSurface);
> 
>   ---------- UNIFIED ----------
>   G4OpticalSurface* opCrystalSurface = new G4OpticalSurface("CrystalSurface");
>   G4LogicalBorderSurface* bSurface =
>     new G4LogicalBorderSurface("CrystalSurface",scint_physV,
>                              lightBox_physV,opCrystalSurface);
> 
>   G4double sigma_alpha = 12.00*degree;
>   opCrystalSurface -> SetType(dielectric_dielectric);
>   opCrystalSurface -> SetModel(unified);
>   opCrystalSurface -> SetFinish(groundbackpainted);
>   opCrystalSurface -> SetSigmaAlpha(sigma_alpha);
> 
>   const G4int NUM = 2;
>   G4double pp[NUM] = {2.038*eV, 4.144*eV};
>   G4double specularlobe[NUM] = {1.0, 1.0};
>   G4double rindex[NUM] = {1.0, 1.0};
>   G4double reflectivity[NUM] = {0.99, 0.99};
>   G4double efficiency[NUM] = {0.0, 0.0};
> 
>   G4MaterialPropertiesTable* SMPT = new G4MaterialPropertiesTable();
>   SMPT -> AddProperty("RINDEX",pp,rindex,NUM);
>   SMPT -> AddProperty("SPECULARLOBECONSTANT",pp,specularlobe,NUM);
>   SMPT -> AddProperty("REFLECTIVITY",pp,reflectivity,NUM);
>   SMPT -> AddProperty("EFFICIENCY",pp,efficiency,NUM);
>   opCrystalSurface -> SetMaterialPropertiesTable(SMPT);
> 
>   ----------
> 
> Your help is very much appreciated.

If your code is not very involved (e.g. linking to external libraries) you can send a tar file to me and I'll look into this.

Peter

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