I would like to enable PIXE (very time consuming) only for few G4Region of my geometry.
I noticed that in the Geant4 class processes/electromagnetic/utils/src/G4VAtomDeexcitation.cc, the method AlongStepDeexcitation() is called by processes/electromagnetic/utils/src/G4VEnergyLossProcess.cc only if the useDeexcitation parameter is enabled, i.e. only if the PIXE effect is turned on in the PhysicsList with:
G4EmParameters* param = G4EmParameters::Instance();
param->SetPixe(true);
Therefore, it is mandatory to set the PIXE parameter = “true” in order to access the AlongStepDeexcitation() method.
On the other hand, looking at the first lines of AlongStepDeexcitation method:
G4VAtomDeexcitation::AlongStepDeexcitation(std::vector<G4Track*>& tracks,
const G4Step& step,
G4double& eLossMax,
G4int coupleIndex)
{
G4double truelength = step.GetStepLength();
if(!flagPIXE && !activePIXEMedia[coupleIndex]) { return; }
...
}
the method is skipped only when both the parameters flagPIXE and activePIXEMedia[coupleIndex] are false. But flagPIXE=true if “param->SetPixe(true)” is used in the above PhysicsList.
Therefore the activePIXEMedia[coupleIndex], that defines the active G4Region, is ignored in the condition and the AlongStepDeexcitation() is executed even if the region is not active (i.e., if activePIXEMedia[coupleIndex]=false).
In my opinion the correct condition should use “||” instead of “&&”:
if(!flagPIXE || !activePIXEMedia[coupleIndex]) { return; }
or simply
if(!activePIXEMedia[coupleIndex]) { return; }
because AlongStepDeexcitation() is called only when flagPIXE=true
Is it correct?
Geant4 Version: 10.7.3
I am confused about what it is you need to do. Continuing with:
G4EmParameters* param = G4EmParameters::Instance();
param->SetPixe(true);
You can activate PIXE for select regions using
G4Region* pixeLogReg = (G4RegionStore::GetInstance())->GetRegion("pixeLogReg");
param.SetDeexcitationActiveRegion("pixeLogReg");
Where “pixeLogReg” here is a G4Region that contains all the volumes that you want to activate PIXE (here, slide 33). G4regions can include any number of logical volumes including different materials.
Is it correct?
I suspect that it is that way because of the expectation that you would use that method to activate/deactivate PIXE.
Yes, I confirm that I use SetDeexcitationActiveRegion to activate PIXE only in my Target region:
G4EmParameters* param = G4EmParameters::Instance();
param->SetPixe(true);
param.SetDeexcitationActiveRegion("DefaultRegionForTheWorld", true, true, false);
param.SetDeexcitationActiveRegion("Target", true, true, true);
In this case, I would expect PIXE to be active only for the “Target” region, but it seems not to work and PIXE is always executed.
As previously said, I think that the problem is in the G4VAtomDeexcitation::AlongStepDeexcitation(), which is the Geant4 method implementing PIXE.
Indeed, this method is always executed when PIXE is enabled in G4EmParameters by
param->SetPixe(true);
even if the particle is outside of the active G4Region.
It can be deduced from the if statement at the beginning of the AlongStepDeexcitation() method:
if(!flagPIXE && !activePIXEMedia[coupleIndex]) { return; }
where flagPIXE is always true, due to the above statement:
param->SetPixe(true);
You are grabbing the EMoptions instance and then setting its parameters. It will set PIXE in your target region and everywhere else. I think there may be an inadvertent race condition depending on where you are doing this. I have used this before in my physics list file. Try replacing:
G4EmParameters* param = G4EmParameters::Instance();
with
G4EmProcessOptions param;
param.SetPIXE(true);
And then set the region using it. You’ll need to include G4EmProcessOptions.hh
Hi, Justin. If the OP is quoting the in-process check correctly, then I think they’re right:
if(!flagPIXE && !activePIXEMedia[coupleIndex]) { return; }
is equivalent to
if (flagPIXE || activePIXEMedia[coupleIndex]) {
do all the process stuff...
}
which reads, at least to me, like it’ll go through if the global flag is set, even if the per-region flag is false.
Yes, this is the point.
Moreover, it is important to underline that it is mandatory to set the global flag flagPIXE=true to enable PIXE: only in this case the PIXE libraries and code are called.
Therefore, the per-region flag activePIXEMedia[coupleIndex], whatever its value, is completely ignored by Geant.
Just an update.
I changed ‘&&’ to ‘||’ in the if statement and repeated the simulation:
New condition in G4VAtomDeexcitation::AlongStepDeexcitation(),:
if(!flagPIXE || !activePIXEMedia[coupleIndex]) { return; }
The result is consistent with the previous one obtained with ‘&&’ and the simulation was about 100 times faster in my case. Therefore I think that this is a bug that should be corrected in Geant4.
Could you open a bug report?