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Keywords: negative step length
Forum: Event and Track Management
Date: 06 Jul, 2004
From: Ma yunzhi <Ma yunzhi>

dear all ,

I was simulating 30 keV electrons in water, but I was confused by the negative steplength shown as below.

I am using geant4.5.2.p02. range cut and production cut(energy) was set as below.

Note that the problem was irrelevent to the G4Electron physics model, i.e., either G4LowEnergy series ,G4Penelope series or G4Standard series face the problem.

does this indicate my code faults somewhere ? hope for any helpful discuss.

CUTS:

========= Table of registered couples ==============================

Index : 0     used in the geometry : Yes     recalculation needed : No 
 Material : Water
 Range cuts        :  gamma 1 mum    e- 1 mum    e+ 1 mum
 Energy thresholds :  gamma 250 eV     e- 250 eV     e+ 250 eV 
 Region(s) which use this couple : 
    DefaultRegionForTheWorld

====================================================================

OUTPUT:

### Run 0 start.

--------- Ranecu engine status ---------
 Initial seed (index) = 0
 Current couple of seeds = 9876, 54321
----------------------------------------

---> Begin of Event: 0

---> Begin of Event: 100

---> Begin of Event: 200

.....omited

---> Begin of Event: 3300

---> Begin of Event: 3400
  G4VParticleChange::CheckIt    : the true step length is negative  !!
  Difference:  9.84225e-09[MeV] 
 G4VParticleChange::CheckIt 
      -----------------------------------------------
        G4ParticleChange Information  
      -----------------------------------------------
        # of 2ndaries       :                    0
      -----------------------------------------------
        Energy Deposit (MeV):                    0
        Track Status        :                Alive
        True Path Length (mm) :            -9.84e-09
        Stepping Control     :                    0

        Mass (GeV)   :                    0
        Charge (eplus)   :                    0
        Position - x (mm)   :            -2.92e-08
        Position - y (mm)   :             -1.8e-08
        Position - z (mm)   :               0.0045
        Time (ns)           :             4.57e-05
        Proper Time (ns)    :             1.93e-09
        Momentum Direct - x :               -0.838
        Momentum Direct - y :               -0.471
        Momentum Direct - z :               -0.274
        Kinetic Energy (MeV):             0.000872
        Polarization - x    :                    0
        Polarization - y    :                    0
        Polarization - z    :                    0
        Track Weight      :                    0
        Touchable (pointer) :            0x85adc68
  G4VParticleChange::CheckIt    : the energy deposit  is negative  !!
  Difference:  1.18e-07[MeV] 
  G4VParticleChange::CheckIt    : the true step length is negative  !!
  Difference:  9.84e-09[MeV] 
 G4VParticleChange::CheckIt 
      -----------------------------------------------
        G4ParticleChange Information  
      -----------------------------------------------
        # of 2ndaries       :                    0
      -----------------------------------------------
        Energy Deposit (MeV):            -1.18e-07
        Track Status        :                Alive
        True Path Length (mm) :            -9.84e-09
        Stepping Control     :                    0

        Mass (GeV)   :             0.000511
        Charge (eplus)   :                   -1
        Position - x (mm)   :            -3.74e-08
        Position - y (mm)   :            -2.26e-08
        Position - z (mm)   :               0.0045
        Time (ns)           :             4.57e-05
        Proper Time (ns)    :              2.5e-09
        Momentum Direct - x :               -0.838
        Momentum Direct - y :               -0.471
        Momentum Direct - z :               -0.274
        Kinetic Energy (MeV):             0.000872
        Polarization - x    :                    0
        Polarization - y    :                    0
        Polarization - z    :                    0
        Track Weight      :                    1

---> Begin of Event: 3500

---> Begin of Event: 3600

---> Begin of Event: 3700

---> Begin of Event: 3800

---> Begin of Event: 3900

---> Begin of Event: 4000

---> Begin of Event: 4100

---> Begin of Event: 4200

---> Begin of Event: 4300

---> Begin of Event: 4400

---> Begin of Event: 4500

---> Begin of Event: 4600

---> Begin of Event: 4700

---> Begin of Event: 4800

---> Begin of Event: 4900

---> Begin of Event: 5000
  G4ParticleChange::CheckIt    : the global time goes back  !!
  Difference:  3.06e-06[ns] 
  G4ParticleChange::CheckIt    : the proper time goes back  !!
  Difference:  3.06e-06[ns] 
 G4ParticleChange::CheckIt 
      -----------------------------------------------
        G4ParticleChange Information  
      -----------------------------------------------
        # of 2ndaries       :                    0
      -----------------------------------------------
        Energy Deposit (MeV):                    0
        Track Status        :                Alive
        True Path Length (mm) :            -3.17e-05
        Stepping Control     :                    0

        Mass (GeV)   :                    0
        Charge (eplus)   :                    0
        Position - x (mm)   :            -1.61e-05
        Position - y (mm)   :            -2.62e-05
        Position - z (mm)   :              0.00451
        Time (ns)           :             4.27e-05
        Proper Time (ns)    :            -3.06e-06
        Momentum Direct - x :                0.541
        Momentum Direct - y :                0.824
        Momentum Direct - z :               -0.169
        Kinetic Energy (MeV):             0.000304
        Polarization - x    :                    0
        Polarization - y    :                    0
        Polarization - z    :                    0
        Track Weight      :                    0
        Touchable (pointer) :            0x85ae980
  G4VParticleChange::CheckIt    : the energy deposit  is negative  !!
  Difference:  0.000728[MeV] 
  G4VParticleChange::CheckIt    : the true step length is negative  !!
  Difference:  3.17e-05[MeV] 
 G4VParticleChange::CheckIt 
      -----------------------------------------------
        G4ParticleChange Information  
      -----------------------------------------------
        # of 2ndaries       :                    0
      -----------------------------------------------
        Energy Deposit (MeV):            -0.000728
        Track Status        :                Alive
        True Path Length (mm) :            -3.17e-05
        Stepping Control     :                    0

        Mass (GeV)   :             0.000511
        Charge (eplus)   :                   -1
        Position - x (mm)   :             1.04e-06
        Position - y (mm)   :            -6.48e-08
        Position - z (mm)   :               0.0045
        Time (ns)           :             4.57e-05
        Proper Time (ns)    :                    0
        Momentum Direct - x :                0.541
        Momentum Direct - y :                0.824
        Momentum Direct - z :               -0.169
        Kinetic Energy (MeV):              0.00103
        Polarization - x    :                    0
        Polarization - y    :                    0
        Polarization - z    :                    0
        Track Weight      :                    1

---> Begin of Event: 5100

---> Begin of Event: 5200

---> Begin of Event: 5300

...omited

--------- Ranecu engine status ---------
 Initial seed (index) = 0
 Current couple of seeds = 621004454, 661497005
----------------------------------------
Graphics systems deleted.
Visualization Manager deleting...

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