Cannot set particle production cuts for ComptonScattering process

Physics Processes, Models and Cross Sections
1

Hi all:

I have some problem when setting production cuts.
I want to set generation cut to disable the generation of electron with energy less than 0.25 MeV (which correspongs to the Cherenkov generation threshold in water). So I use following physics list, which mainly copy from FTFP_BERT.

#include "PhysicsList.hh"

#include "G4DecayPhysics.hh"

#include "G4EmStandardPhysics.hh"

#include "G4EmStandardPhysics_option2.hh"

#include "G4RadioactiveDecayPhysics.hh"

#include "G4OpticalPhysics.hh"

#include "G4EmExtraPhysics.hh"

#include "G4HadronElasticPhysics.hh"

#include "G4HadronPhysicsFTFP_BERT.hh"

#include "G4StoppingPhysics.hh"

#include "G4NeutronTrackingCut.hh"

#include "G4IonPhysics.hh"

#include "G4NeutronTrackingCut.hh"

#include "G4UnitsTable.hh"

#include "G4SystemOfUnits.hh"

PhysicsList::PhysicsList()

    : G4VModularPhysicsList()

{

  SetVerboseLevel(1);

  // Default physics

  RegisterPhysics(new G4DecayPhysics());

  // EM physics

  RegisterPhysics(new G4EmStandardPhysics_option2);

  // Synchroton Radiation & GN Physics

  RegisterPhysics(new G4EmExtraPhysics());

  // Hadron Elastic scattering

  RegisterPhysics(new G4HadronElasticPhysics());

  // Hadron Physics

  RegisterPhysics(new G4HadronPhysicsFTFP_BERT());

  // Stopping Physics

  RegisterPhysics(new G4StoppingPhysics());

  // Ion Physics

  RegisterPhysics(new G4IonPhysics());

  // Neutron tracking cut

  RegisterPhysics(new G4NeutronTrackingCut());

  // Radioactive decay

  RegisterPhysics(new G4RadioactiveDecayPhysics());

  // optical physics

  G4OpticalPhysics *opticalPhysics = new G4OpticalPhysics();

  opticalPhysics->SetMaxNumPhotonsPerStep(400);

  opticalPhysics->SetTrackSecondariesFirst(kCerenkov, true);

  // RegisterPhysics(opticalPhysics);

  DumpCutValuesTable();

}

//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......

PhysicsList::~PhysicsList()

{

}

//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......

void PhysicsList::SetCuts()

{
  // fixe lower limit for cut

  G4double lowlimit = 0.25 * keV;

  G4ProductionCutsTable::GetProductionCutsTable()->SetEnergyRange(lowlimit, 100. * TeV);

  // call base class method to set cuts which default value can be

  // modified via /run/setCut/* commands

  G4VUserPhysicsList::SetCuts();

  DumpCutValuesTable();

}

And I am using following macro to set the production cut

# run initialization
/run/initialize

# set verbose
/control/verbose  2
/run/verbose      2
/event/verbose    2
/tracking/verbose 2
/analysis/verbose 2

# set hist
/analysis/h1/set      0 100 0 1000 keV
/analysis/h1/setXaxis 0 "Energy [keV]"
/analysis/h1/setYaxis 0 "Number of electrons"
/analysis/h1/set      1 35 1.5 5 eV
/analysis/h1/setXaxis 1 "Energy [eV]"
/analysis/h1/setYaxis 1 "Number of photons"
/analysis/h1/set      2 100 0 100 m
/analysis/h1/setXaxis 2 "Propagation Length [m]"
/analysis/h1/setYaxis 2 "Number of photons"

# set cut in run
/run/setCut 0.1 cm
/run/setCutForAGivenParticle gamma 50 cm

# set particle gun
/gun/particle  pi+
/gun/energy    1 GeV
/run/beamOn    1

In my simulation result, I find the ionization process no longer produce low energy electrons. However, the Compron scattering of gamma still produce low energy electrons.

*********************************************************************************************************
* G4Track Information:   Particle = gamma,   Track ID = 401,   Parent ID = 356
*********************************************************************************************************

Step#    X(mm)    Y(mm)    Z(mm) KinE(MeV)  dE(MeV) StepLeng TrackLeng  NextVolume ProcName
    0 3.19e+03 -2.74e+03 1.74e+03      3.89        0        0         0    World_PV initStep
    1 3.25e+03 -2.79e+03 1.61e+03     0.536        0      152       152    World_PV compt
    :----- List of 2ndaries - #SpawnInStep=  1(Rest= 0,Along= 0,Post= 1), #SpawnTotal=  1 ---------------
    :  3.25e+03 -2.79e+03  1.61e+03      3.35                 e-
    :----------------------------------------------------------------- EndOf2ndaries Info ---------------
    2 3.29e+03 -2.68e+03 1.57e+03     0.213        0      124       276    World_PV compt
    :----- List of 2ndaries - #SpawnInStep=  1(Rest= 0,Along= 0,Post= 1), #SpawnTotal=  2 ---------------
    :  3.29e+03 -2.68e+03  1.57e+03     0.323                 e-
    :----------------------------------------------------------------- EndOf2ndaries Info ---------------
    3 3.28e+03 -2.68e+03  1.6e+03     0.202        0     33.8       310    World_PV compt
    :----- List of 2ndaries - #SpawnInStep=  1(Rest= 0,Along= 0,Post= 1), #SpawnTotal=  3 ---------------
    :  3.28e+03 -2.68e+03   1.6e+03    0.0112                 e-
    :----------------------------------------------------------------- EndOf2ndaries Info ---------------
    4 3.29e+03 -2.68e+03 1.62e+03     0.137        0     26.4       337    World_PV compt
    :----- List of 2ndaries - #SpawnInStep=  1(Rest= 0,Along= 0,Post= 1), #SpawnTotal=  4 ---------------
    :  3.29e+03 -2.68e+03  1.62e+03    0.0641                 e-
    :----------------------------------------------------------------- EndOf2ndaries Info ---------------
    5 3.29e+03 -2.69e+03 1.62e+03     0.119        0     13.9       350    World_PV compt
    :----- List of 2ndaries - #SpawnInStep=  1(Rest= 0,Along= 0,Post= 1), #SpawnTotal=  5 ---------------
    :  3.29e+03 -2.69e+03  1.62e+03    0.0183                 e-
    :----------------------------------------------------------------- EndOf2ndaries Info ---------------
    6 3.26e+03 -2.74e+03 1.61e+03     0.102        0     65.7       416    World_PV compt
    :----- List of 2ndaries - #SpawnInStep=  1(Rest= 0,Along= 0,Post= 1), #SpawnTotal=  6 ---------------
    :  3.26e+03 -2.74e+03  1.61e+03    0.0173                 e-
    :----------------------------------------------------------------- EndOf2ndaries Info ---------------
    7 3.25e+03 -2.74e+03 1.57e+03    0.0852        0     44.5       461    World_PV compt
    :----- List of 2ndaries - #SpawnInStep=  1(Rest= 0,Along= 0,Post= 1), #SpawnTotal=  7 ---------------
    :  3.25e+03 -2.74e+03  1.57e+03    0.0166                 e-
    :----------------------------------------------------------------- EndOf2ndaries Info ---------------
    8 3.21e+03 -2.81e+03 1.58e+03         0 2.83e-05       76       537    World_PV phot
    :----- List of 2ndaries - #SpawnInStep=  2(Rest= 0,Along= 0,Post= 2), #SpawnTotal=  9 ---------------
    :  3.21e+03 -2.81e+03  1.58e+03    0.0847                 e-
    :  3.21e+03 -2.81e+03  1.58e+03  0.000509                 e-
    :----------------------------------------------------------------- EndOf2ndaries Info ---------------

How should I disable this process?

Thanks
Fan

2

I fixed this problem by replacing G4EmStandardPhysics_option2 by G4EmStandardPhysics_option1. Now the generation cut can successfully apply to Compton Scattering process.

I compared the source code in G4EmStandardPhysics_option2.cc and G4G4EmStandardPhysics_option1.cc. And I found that G4EmParameters in option2 set ApplyCut to false.

// code section from G4EmStandardPhysics_option2.cc
// begine at line 122

G4EmStandardPhysics_option2::G4EmStandardPhysics_option2(G4int ver, 
							 const G4String&)
  : G4VPhysicsConstructor("G4EmStandard_opt2"), verbose(ver)
{
  G4EmParameters* param = G4EmParameters::Instance();
  param->SetDefaults();
  param->SetVerbose(verbose);
  param->SetApplyCuts(false);
  param->SetMscRangeFactor(0.2);
  param->SetLateralDisplacement(false);
  param->SetMscStepLimitType(fMinimal);
  SetPhysicsType(bElectromagnetic);
}

So, I change my physicsList to the following codes:

  // EM physics
  RegisterPhysics(new G4EmStandardPhysics_option2);
  G4EmParameters* param = G4EmParameters::Instance();
  param->SetApplyCuts(true);

Now the option2 works well.

Dose any one know why in option2, the ApplyCut is set to false? I think it is odd because it restrict user’s operation.
And why Compton Scatering is different from ionization?

Thanks,
Fan

3

Hello,

This EM Physics List configuration “option2” was chosen to be the same as is used by LHCb experiment at CERN. Your recent modification is correct.

VI