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Forum: Physics List
Re: None Reference physics lists + StepLimiter (Kyrre Ness Sjøbæk)
Re: Note Re: Reference physics lists + StepLimiter (Kyrre Ness Sjøbæk)
Re: Idea Re: Reference physics lists + StepLimiter (Vladimir Ivanchenko)
Re: Ok Re: Reference physics lists + StepLimiter (Kyrre Ness Sjøbæk)
Date: 28 Jan, 2010
From: John Allison <John Allison>

Please keep the discussion on-line. It is very relevant for me.

I think Vladimir is referring to

  std::vector<G4ThreeVector>*
  G4ElectronIonPair::SampleIonsAlongStep
  (const G4ThreeVector& prePos,
   const G4ThreeVector& postPos,
   G4double meanion)

in processes/electromagnetic/utils. It returns the coordinates of ion pairs along a step. However, if I read the code correctly, it assumes that the ion pairs are produced independently, one ion pair for each meanion of deposited ionising energy. (I think meanion is about 3.66 eV per ion pair in silicon.)

In fact, I believe, the ion pairs are produced in "clumps", where, for a minimum ionsing particle in silicon, the mean clump energy is 60-80 keV, with large fluctuations, with many pairs per clump. See H. Bichsel, Straggling in thin silicon detectors, Rev. Mod. Phys., Vol. 60, no. 3, July 1988. Bichsel distributes data and algorithms. I implemented something in C outside Geant4 but it would be nice to have it in Geant4.

The fact that energy is deposited in clumps makes the fluctuations in energy and position greater than simple Poisson. In Geant4, some energy fluctuation (Landau) has already been generated, so we have to be careful not to repeat this in the position distribution algorithm.

As I said, it would be nice to have this in Geant4. If there is a need from users, maybe we can do it. Is this possible, Vladimir?

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1 More: Re: Reference physics lists + StepLimiter   (Vladimir Ivanchenko - 28 Jan, 2010)
(_ Ok: Re: Reference physics lists + StepLimiter   (Kyrre Ness Sjøbæk - 29 Jan, 2010)
(_ None: Re: Reference physics lists + StepLimiter   (Colin Paul Gloster - 29 Jan, 2010)
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