|Message: Re: 1-2 MeV protons are NOT scattered, 3 and more MeV are scattered||Not Logged In (login)|
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On Tue, 24 Oct 2006, Gorelick Sergey wrote: > *** Discussion title: Hadronic Processes > Email replies to PublicHyperNews@slac.stanford.edu must include: > In-Reply-To: <"/hadronprocess/588/1/1"@geant4-hn.slac.stanford.edu> > Subject: ...change this to be about your reply. > > Hello Vladimir, > > thank you for your reply. I was experimenting with the Cut Values, and > it does seem to improve the behavior of the protons in foils. However, I > am afraid I don't exactly understand the concept of the "cut values" or > the philosophy behind them. The official CERN's G4 manual states that > > "To avoid infrared divergence, some electromagnetic processes require a > threshold below which no secondary will be generated. Because of this > requirement, gammas, electrons and positrons require production > thresholds which the user should define. This threshold should be > defined as a distance, or range cut-off, which is internally converted > to an energy for individual materials." and "Each particle has a > suggested cut in range (which is converted to energy for all materials)" > > The explanations are somewhat unclear. I cannot figure out how (and why) > reducing the Cut Values can "improve" the simulation, or make the motion > of the particles in the media more real. I did not notice big difference > in time needed to calculate the whole simulations even when I used 10 nm > cut value. > > Thank you. > Hello, When we use cuts we never "improve" situation but only allow ourself to run Monte Carlo in reasonable time. It is always simplification and in your case one should worry about possible biase of the results. The value of the defined cut is printed out in the default output. In the both standard and low-energy G4 hadron ionization processes there is an internal limit equal to mean ionistion potential of the absober, below which cut cannot be set. If you really want to simulate protons without any cut you ned to use PAI model, which is not our default. How to use it, please, consult $G4INSTALL/exemples/extended/electromagnetic/TestEm8 VI
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