Geant4 scintillation

Physics Processes, Models and Cross Sections
1

Dear expert,

I am suffering from “Scintillation” in process name.

I am using Geant4.10.5p1 and constructed pure-water cherenkov detector, so I don’t expect that any scintillation process occurs.
When I checked the process name for pi^- by

thePostPoint = theStep->GetPostStepPoint();
theProcess = thePostPoint->GetProcessDefinedStep();
process_name = theProcess->GetProcessName();

in SteppingAction, I saw the stopping process of pi^- is “Scintillation”.
But I don’t expected it, and it should be pi^- capture or other process.
Do you know why the stopping process become scintillation??

1 Like
2

Hi,

Can you check what the energy loss in the step is (“dEStep” in /tracking/verbose 1). The last step occurs with the particle already stopped, so it’s really the previous step that stopped the particle. In the development version of Geant4, the process that limits the last step is given as NoProcess (see output below). In previous versions (I don’t know when it changed) the process listed was arbitrary.

Also try
/process/optical/processActivation Scintillation false
and you should see the exact same results, but with Scintillation replaced by a different process for that last step.

G4WT0 > Step#      X         Y         Z        KineE     Velocity   dEStep  StepLeng  TrakLeng       Volume     Process
G4WT0 >     0  -1.57 m     -16 cm  -14.6 cm   1.21 keV  2.06 cm/ns     0 eV      0 fm      0 fm        World    initStep
G4WT0 >     1  -1.57 m     -16 cm  -14.6 cm   1.05 keV  2.06 cm/ns   159 eV   5.67 um   5.67 um        World         msc
G4WT0 >     2  -1.57 m     -16 cm  -14.6 cm    806 eV   1.92 cm/ns   242 eV   26.1 um   31.7 um        World       eIoni
G4WT0 >     3  -1.57 m     -16 cm  -14.6 cm    491 eV   1.68 cm/ns   314 eV   21.8 um   53.5 um        World       eIoni
G4WT0 >     4  -1.57 m     -16 cm  -14.6 cm      0 eV   1.31 cm/ns   491 eV   16.2 um   69.7 um        World       eIoni
G4WT0 >     5  -1.57 m     -16 cm  -14.6 cm      0 eV      0 mm/s      0 eV      0 fm   69.7 um        World   NoProcess
3

I checked the dEStep. As you said, the last capture process was occured after KinE=0.
I saw that the process name of last step is Scintillation.
But the process looks pion minas capture, by looking at secondary particles in last steps


*********************************************************************************************************
* G4Track Information:   Particle = pi-,   Track ID = 1,   Parent ID = 0
*********************************************************************************************************
Step#    X(mm)    Y(mm)    Z(mm) KinE(MeV)  dE(MeV) StepLeng TrackLeng  NextVolume ProcName
・
・
・
296    -22.1     39.9     -734      1.08    0.536    0.113       737      InvoPV hIoni
297    -22.1     39.8     -735     0.457    0.625   0.0817       737      InvoPV hIoni
298    -22.1     39.8     -735    0.0206    0.437   0.0241       737      InvoPV hIoni
299    -22.1     39.8     -735   0.00164    0.019  0.00068       737      InvoPV hIoni
300    -22.1     39.8     -735         0  0.00164  0.00034       737      InvoPV hIoni
301    -22.1     39.8     -735         0        0        0       737      InvoPV Scintillation

Also try
/process/optical/processActivation Scintillation false
and you should see the exact same results, but with Scintillation replaced by a different process for that last step.
Yes, I tried to turn off the scintillation for pion, the pion minas process is recovered. But I don’t know the artificial treatment is okay or not…