The Geant4-DNA project

Contents of this page:

• Purpose
• Publications
• Design of Physics process and model classes
• Available Physics processes and models
• Example Physics list
• Physics builders
• How to access Physics ?
• How to kill particles below a given energy threshold for faster performance ?
• How to decrease the low energy limit of electron processes ?
• How to activate Auger production ?
• Material definition and density change
• How to change geometrical tolerances ?
• Combination with other Physics processes for multi-scale simulations
• Examples ready-to-use

Purpose

Geant4 is being extended with very low energy processes for the modelling of biological damages induced by ionising radiation. Such developments are on-going in the framework of the Geant4-DNA project, initiated by in 2000 P. Nieminen ( European Space Agency/ESTEC) in order to model physics, chemistry and biology processes for the simulation of early biological effects of ionizing radiation.

The first phase of the project was undertaken by INFN Genova in Italy, delivering Work Package reports and a User Requirement Document. The second phase is currently on-going since 2004. It is now coordinated by S. Incerti and it is a full activity of the Low Energy Electromagnetic Physics working group of the Geant4 collaboration.

The rules and regulations of the Geant4-DNA collaboration as well as the list of collaborators are available from this page.

Expected developments include :

• Physics processes in liquid water and other biological materials
• Chemistry and physico-chemistry processes
• Molecular geometries
• Quantification of damages (single-strand, double-strand breaks, ...)

Publications

The Geant4-DNA Physics processes are described in details in the following publications :

• Electron and proton elastic scattering in water vapour, C. Champion, S. Incerti, H. Tran, Z. El Bitar, Nucl. Instrum. and Meth. B (2011) in press (link)
• Combination of electromagnetic Physics processes for microdosimetry in liquid water with the Geant4 Monte Carlo simulation toolkit, V.N. Ivanchenko, S. Incerti, Z. Francis, H.N. Tran, M. Karamitros, M.A. Bernal, C. Champion and P. Guèye, Nucl. Instrum. and Meth. B (2011) in press (link)
• Modeling radiation chemistry in the Geant4 toolkit, M. Karamitros, A. Mantero, S. Incerti et al., in press
• Recent improvements in Geant4 electromagnetic physics models and interfaces, V. Ivantchenko et al., in press
• The invariance of the total direct DNA strand break yield, M. A. Bernal, C. E. de Almeida, C. S. Sampaio, S. Incerti, C. Champion, P. Nieminen, Med. Phys., in press (link)
• Stopping power and ranges of electrons, protons and alpha particles in liquid water using the Geant4-DNA package, Z. Francis, S. Incerti, M. Karamitros, H.N. Tran, C. Villagrasa, Nucl. Instrum. and Meth. B (2011) in press (link)
• Molecular scale track structure simulations in liquid water using the Geant4-DNA Monte Carlo processes, Z. Francis, S. Incerti, R. Capra, B. Mascialino, G. Montarou, V. Stepan, C. Villagrasa, Appl. Radiat. Isot. 69 (2011) 220-226 (link)
• Physical models implemented in the Geant4-DNA extension of the Geant4 toolkit for calculating initial radiation damage at the molecular level, C. Villagrasa, Z. Francis, S. Incerti, Rad. Prot. Dos. 133, 1 (2010) 1-5 (link)
• Comparison of Geant4 very low energy cross section models with experimental data in water, S. Incerti, A. Ivanchenko, M. Karamitros, A. Mantero, P. Moretto, H. N. Tran, B. Mascialino, C. Champion, V. N. Ivanchenko, M. A. Bernal, Z. Francis, C. Villagrasa, G. Baldacchino, P. Guèye, R. Capra, P. Nieminen, C. Zacharatou, Med. Phys. 37 (2010) 4692-4708 (link)
• A free-parameter theoretical model for describing the electron elastic scattering in water in the Geant4 toolkit, C. Champion, S. Incerti, H. Aouchiche, D. Oubaziz, Rad. Phys. Chem. 78 (2009) 745-750 (link)
• The Geant4-DNA project, S. Incerti, G. Baldacchino, M. Bernal, R. Capra, C. Champion, Z. Francis, S. Guatelli, P. Guèye, A. Mantero, B. Mascialino, P. Moretto, P. Nieminen, A. Rosenfeld, C. Villagrasa and C. Zacharatou, Int. J. Model. Simul. Sci. Comput. 1 (2010) 157–178 (link)

this page

Design of Physics process and model classes

The Geant4-DNA design has been adopted by the Standard Electromagnetic Physics working group in 2006. A single physical process can handle several models which are registered to the process.

• All Geant4-DNA process classes derive from the G4VEmProcess abstract base class, which derives from the G4VDiscreteProcess class, since all Geant4-DNA processes are discrete processes. They use the naming format: G4DNAXXX where XXX is the process name (for eg. G4DNAExcitation for excitation). This is the name that will be displayed when using the command /tracking/verbose 1. Several methods are implemented :
  • G4DNAXXX::InitialiseProcess(...) : process initialisation
  • G4DNAXXX::PrintInfo(...) : verbose
  • it is also possible to customize the process name : when a process is added to the process manager in the Physics list (see example below), one can use a user defined name, for eg. "myName" :

          pmanager->AddDiscreteProcess(new G4DNAExcitation("myName"));

• All Geant4-DNA model classes derive from the G4VEmModel abstract base class. They use the naming format: G4DNAYYYModel, where YYY is the model name (for eg. G4DNAEmfietzoglouExcitationModel for excitation). Several methods are implemented :
  • G4DNAYYYModel::Initialise(...) : model initialisation
  • G4DNAYYYModel::CrossSectionPerVolume(...) : computation of model total cross section multiplied by material density (equivalent to inverse mean free path)
  • G4DNAYYYModel::SampleSecondaries(...) : computation of model final state

Available Physics processes and models

We indicate in the table below the Geant4-DNA physics processes, models and particles available in the Geant4 toolkit from June 2009, as well as their energy range of applicability. Each process can handle several alternative or complementary (in energy) models.

Example Physics list

We indicate below a Physics list example for the use of Geant4-DNA physics processes and models only.

...
#include "G4DNAGenericIonsManager.hh"
...
void PhysicsList::ConstructBaryons()
{
...
  // Geant4-DNA particles
  G4GenericIon::GenericIonDefinition();
  G4DNAGenericIonsManager * genericIonsManager;
  genericIonsManager=G4DNAGenericIonsManager::Instance();
  genericIonsManager->GetIon("alpha++");
  genericIonsManager->GetIon("alpha+");
  genericIonsManager->GetIon("helium");
  genericIonsManager->GetIon("hydrogen");
  genericIonsManager->GetIon("carbon");
  genericIonsManager->GetIon("nitrogen");
  genericIonsManager->GetIon("oxygen");
  genericIonsManager->GetIon("iron");

...
}

...
#include "G4DNAElastic.hh"
#include "G4DNAChampionElasticModel.hh"
#include "G4DNAScreenedRutherfordElasticModel.hh"

#include "G4DNAExcitation.hh"
#include "G4DNAMillerGreenExcitationModel.hh"
#include "G4DNABornExcitationModel.hh"

#include "G4DNAIonisation.hh"
#include "G4DNABornIonisationModel.hh"
#include "G4DNARuddIonisationModel.hh"

#include "G4DNAChargeDecrease.hh"
#include "G4DNADingfelderChargeDecreaseModel.hh"

#include "G4DNAChargeIncrease.hh"
#include "G4DNADingfelderChargeIncreaseModel.hh"

#include "G4DNAVibExcitation.hh"
#include "G4DNASancheExcitationModel.hh"

#include "G4DNAAttachment.hh"
#include "G4DNAMeltonAttachmentModel.hh"

...

void PhysicsList::ConstructEM()
{
  theParticleIterator->reset();
  while( (*theParticleIterator)() )
  {
    G4ParticleDefinition* particle = theParticleIterator->value();
    G4ProcessManager* pmanager = particle->GetProcessManager();
    G4String particleName = particle->GetParticleName();

    if (particleName == "e-") {

      G4DNAElastic* theDNAElasticProcess = new G4DNAElastic("e-_G4DNAElastic");
      theDNAElasticProcess->SetModel(new G4DNAChampionElasticModel());
      // or alternative model (faster but much less accurate at low energies)
      // theDNAElasticProcess->SetModel(new G4DNAScreenedRutherfordElasticModel());
      pmanager->AddDiscreteProcess(theDNAElasticProcess);
            
      pmanager->AddDiscreteProcess(new G4DNAExcitation("e-_G4DNAExcitation"));
      pmanager->AddDiscreteProcess(new G4DNAIonisation("e-_G4DNAIonisation"));
      pmanager->AddDiscreteProcess(new G4DNAVibExcitation("e-_G4DNAVibExcitation"));
      pmanager->AddDiscreteProcess(new G4DNAAttachment("e-_G4DNAAttachment"));
            
    } else if ( particleName == "proton" ) {

      pmanager->AddDiscreteProcess(new G4DNAExcitation("proton_G4DNAExcitation"));
      pmanager->AddDiscreteProcess(new G4DNAIonisation("proton_G4DNAIonisation"));
      pmanager->AddDiscreteProcess(new G4DNAChargeDecrease("proton_G4DNAChargeDecrease"));

    } else if ( particleName == "hydrogen" ) {

      pmanager->AddDiscreteProcess(new G4DNAExcitation("hydrogen_G4DNAExcitation"));
      pmanager->AddDiscreteProcess(new G4DNAIonisation("hydrogen_G4DNAIonisation"));
      pmanager->AddDiscreteProcess(new G4DNAChargeIncrease("hydrogen_G4DNAChargeIncrease"));

    } else if ( particleName == "alpha" ) {

      pmanager->AddDiscreteProcess(new G4DNAExcitation("alpha_G4DNAExcitation"));
      pmanager->AddDiscreteProcess(new G4DNAIonisation("alpha_G4DNAIonisation"));
      pmanager->AddDiscreteProcess(new G4DNAChargeDecrease("alpha_G4DNAChargeDecrease"));

    } else if ( particleName == "alpha+" ) {

      pmanager->AddDiscreteProcess(new G4DNAExcitation("alpha+_G4DNAExcitation"));
      pmanager->AddDiscreteProcess(new G4DNAIonisation("alpha+_G4DNAIonisation"));
      pmanager->AddDiscreteProcess(new G4DNAChargeDecrease("alpha+_G4DNAChargeDecrease"));
      pmanager->AddDiscreteProcess(new G4DNAChargeIncrease("alpha+_G4DNAChargeIncrease"));
       
    } else if ( particleName == "helium" ) {

      pmanager->AddDiscreteProcess(new G4DNAExcitation("helium_G4DNAExcitation"));
      pmanager->AddDiscreteProcess(new G4DNAIonisation("helium_G4DNAIonisation"));
      pmanager->AddDiscreteProcess(new G4DNAChargeIncrease("helium_G4DNAChargeIncrease"));

    }

  } // Loop on particles
}

Physics builders

Instead of creating your own Physics list, we recommend the usage of Physics builders. The G4EmDNAPhysics builder is available in $G4INSTALL/source/physics_lists/builders.

This builder contains the same Physics list as above.

For example, the dnaphysics advanced example located in $G4INSTALL/examples/advanced shows how to use the Geant4-DNA Physics builder.

You may also look at the following Physics list that explains how to use a G4EmDNAPhysics object.

How to access Physics ?

It is possible to retrieve Physics quantities using a G4EmCalculator object. For example, in order to retrieve the total cross section of a process with name procName, do as follows :

#include "G4EmCalculator.hh"
...
G4EmCalculator emCalculator;
G4double density = material->GetDensity();
G4double massSigma = emCalculator.ComputeCrossSectionPerVolume(energy,particle,procName,material)/density;                     
G4cout << G4BestUnit(massSigma, "Surface/Mass") << G4endl;

A good example is TestEm14 located in $G4INSTALL/examples/extended/electromagnetic, look in particular at the RunAction.cc class

Note that in order to use the ComputeCrossSectionPerVolume method from the G4EmCalculator class for alpha particles (G4Alpha), it is necessary to add the following condition to G4EmCalculator::UpdateParticle in G4EmCalculator.cc (located in $G4INSTALL/source/processes/electromagnetic/utils/src)

      && currentParticleName != "alpha"

How to kill particles below a given energy threshold for faster performance ?

In case you want to kill particles with energies below an energy threshold value, you may instantiate a G4UserLimits object in your DetectorConstruction class and define the process G4UserSpecialCuts in your PhysicsList class for the affected particles. All details are given in the Geant4 User's Guide For Application Developers.

For example, if you want to kill all electrons below 9 eV, you may use the following lines. All electron tracks below 9 eV will be killed and electrons will deposit locally their total energy :

- in your DetectorConstruction class, if you choose to apply this limit to the World volume :

#include "G4UserLimits.hh"
...
logicWorld->SetUserLimits(new G4UserLimits(DBL_MAX,DBL_MAX,DBL_MAX,9*eV));

- in your PhysicsList class :

#include "G4UserSpecialCuts.hh"
...
if (particleName == "e-") 
{
...
pmanager->AddDiscreteProcess(new G4UserSpecialCuts());
...
}

How to decrease the low energy limit under which electron elastic scattering and vibrational excitation models kill electrons ?

Please do this in your own PhysicsList at your own risk since these models are not experimentally validated at very low energies. You will receive WARNINGS at initialisation.

      // Elastic scattering (can be extended down to 0.025 eV)

      G4DNAElastic* theDNAElasticProcess = new G4DNAElastic("e-_G4DNAElastic");
      theDNAElasticProcess->SetModel(new G4DNAChampionElasticModel());
      
      // or alternative model
      // theDNAElasticProcess->SetModel(new G4DNAScreenedRutherfordElasticModel());

      ((G4DNAChampionElasticModel*)(theDNAElasticProcess->Model()))->SetKillBelowThreshold(0.025*eV);    
      
      // or alternatively
      // ((G4DNAScreenedRutherfordElasticModel*)(theDNAElasticProcess->Model()))->SetKillBelowThreshold(0.025*eV);

      pmanager->AddDiscreteProcess(theDNAElasticProcess);

      // Vibrational excitation (can be extended down to 0.025 eV)
      pmanager->AddDiscreteProcess(new G4DNAVibExcitation("e-_G4DNAVibExcitation"));
      G4DNAVibExcitation* theDNAVibProcess = new G4DNAVibExcitation("e-_G4DNAVib");
      theDNAVibProcess->SetModel(new G4DNASancheExcitationModel()  );
      ((G4DNASancheExcitationModel*)(theDNAVibProcess->Model()))->ExtendLowEnergyLimit(0.025*eV);      
      pmanager->AddDiscreteProcess(theDNAVibProcess);

How to activate Auger production ?

Put the following in your macro file, provided that you use the G4DNAEmPhysics Physics builder.

/run/initialize
/process/em/auger true

Alternatively, consult this link.

Material definition and density change

Geant4-DNA Physics models can only be used in liquid water defined as the NIST material G4_WATER. To do so, you may use the following lines in your detector construction class :

  // Water is defined from NIST material database
  G4NistManager * man = G4NistManager::Instance();
  G4Material * H2O = man->FindOrBuildMaterial("G4_WATER");

  // Default materials in setup.
  waterMaterial = H2O;

In case you need to change the density of water, you may look into the dnaphysics advanced example DetectorConstruction class:

 
  // If one wishes to test other density value for water material, one should use instead:
  G4Material * H2O = man->BuildMaterialWithNewDensity("G4_WATER_MODIFIED","G4_WATER",1000*g/cm/cm/cm);
  
  // Note: any string for "G4_WATER_MODIFIED" parameter is accepted and "G4_WATER" parameter should not be changed

Geometrical tolerances

When using Geant4-DNA processes, the geometrical tolerances of your setup must be adapted to the size of your setup when working with nanometer size dimensions. For this, in your DetectorConstruction class construct() method, you may use for eg. the following lines:

#include "G4GeometryManager.hh"
#include "G4GeometryTolerance.hh"
...

G4double fWorldLength = 100. *nm;
G4GeometryManager::GetInstance()->SetWorldMaximumExtent(fWorldLength);
G4cout << "Surface tolerance = " << G4GeometryTolerance::GetInstance()->GetSurfaceTolerance()/nm
      << " nm - Radial tolerance = "   << G4GeometryTolerance::GetInstance()->GetRadialTolerance()/nm << " nm" <<G4endl;   

Combination with other Physics processes for multi-scale simulations

The new microdosimetry advanced example (link) shows how to use these Geant4-DNA processes in combination with Standard Electromagnetic Physics processes.

Examples ready-to-use

Some examples are already available in Geant4 for you to test Geant4-DNA processes and models.

The corresponding advanced examples are documented here.

If you do not wish to install yourself Geant4, you may freely use our Geant4 Virtual Machine for VmWare and VirtualBox, downloadable from this link.

Main Low Energy WG page