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Forum: Event and Track Management
Re: Question Energy loss by alpha particle in dense material (Noor)
Date: 24 Jul, 2017
From: michel maire <michel maire>

On Fri, 21 Jul 2017 14:14:52 GMT, Noor wrote:
> Dear All, I am trying to simulate a range of alpha particle in a dense
> material and 0.01mm layer. Layer compose of H and C with density 1.5
> g/cc,
> 
> I am shooting 1 MeV Alpha beam directly to the layer,
> 
> as a result I found
> 
>  G4Track Information:   Particle = alpha,   Track ID = 1,   Parent ID = 0
> *********************************************************************************
> 
> Step#   X(mm)  Y(mm)   Z(mm) KinE(MeV)  dE(MeV) StepLeng  NextVolume ProcName
>   0      0       0       0         1       0      0           Scin InitStep
>   1   0.00358    0       0         0    0.977  0.00358        Scin ionIoni
> 
> if we checked the table we find that alpha lose its energy in the firs
> step and lose around 97% of its energy, which is not accurate
> physically. GEANT4 manual says that the energy loss tables are saved,
> and the step will be adjusted until the total energy loss per step is
> maximum 20% of its energy. this means this output must also be wrong.
> 
> please any suggestion about this issue.
> 

  More direct answer:  Physics Reference Manual, chapter 7.1.3

  StepFunction has two parameters. The limitation to 20% (dRoverRange) is applied until the remaining range becomes too small (finalRange). Then this constraint is abandoned.
 Default finalRange is 1 mm (or 100 um), well above the total range of 1 MeV alpha in plastic (~ 5 um).
 Therefore alpha travels always in one step only. For more accurate tracking, you must set finalRange to ~ 0.1 um 

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