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Forum: Physics List
Re: None Physics List for delta electron production (Daniel Cox)
Date: 23 Jun, 2011
From: Joel Long <Joel Long>

On Thu, 23 Jun 2011 17:13:55 GMT, Daniel Cox wrote:
> Hi everyone, I am trying to do a simple simulation that has me confused
> as I'm still very new to geant4.
> What I am attempting to do is fire an ion, in this case Ca48, at a thin
> target, lead, and measure the delta electrons thrown out by this.
> I'm using the physics list from N02, I'm using the whole example
> actually, I've gutted it and surrounded my target with sensitive
> volumes.
> I think it is something to do with either the cuts or something missing
> from the physics list itself but I don't really know how to go about
> finding out what I need to change.
> Thanks in advance for all your help.
> Danny

Hi Danny,

There are a couple possibilities I know of. First, what energy are the Ca48 ions you are firing? If you have not already, try giving them a high energy (1 GeV should do) and perhaps thickening your targets a bit. If you get secondaries when you do this, than the issue is with your production cuts, not with what physics you have included. If you are using the same version of N02 I have, this should be the case.

The production cuts tell the code the bounds on when it should bother producing secondary particles. This is primarily for saving computational power - there are many cases when you do not care about every delta ray produced. There are a couple things you can do to fix this. In the SetCuts() method in the physics list (it is at the bottom of the file in my version) contains the command "SetCutsWithDefault()". Before this, call the command SetDefaultCutValue(G4double newCutValue). The argument is the cut value (in units of distance) you want the constructor to assign particles. Try setting this to a ridiculously low value (eg 10 nm) and see if that solves your problem. You will probably not want to leave the value that low - experiment some to see where you actually want it.

If this method fails, then you can set the energy cutoffs directly using "G4ProductionCutsTable::GetProductionCutsTable()->SetEnergyRange(G4double lowEnergy,G4double highEnergy)". This sets the upper and lower energy bounds for which Geant4 will produce and track secondary particles. Again, you will want to play with the values somewhat to see how low you really want to go. Simply giving it a very low value will have a significant impact on computational time.

Hope this helps! Joel

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