Geant4 is a toolkit for simulating the passage of particles through matter. It is the reference simulation engine for the LHC experiments at CERN and other high energy physics labs worldwide.

Geant4 covers all relevant physics processes, electromagnetic, hadronic, decay, optical, for long and short lived particles, for energy range spanning from tens of eV to TeV scale. The transport of low energy neutrons down to thermal energies can also be handled. The software can also simulate remnants of hadronic interactions, including atomic de-excitation and provides extension to low energies down to the DNA scale for biological modelling.

The software is based on a sound object-oriented design which favours a variety of application development by the community, like for example the propagation of acoustic phonons in cryogenic crystals, the Geant4 Application for Tomographic Emission (GATE), the beam line simulation (G4BEAMLINE) and others.


Geant4 is written in C++ and runs on Linux, Mac OS, Windows and different types of UNIX flavours, 32 or 64 bits, and on modern parallel architectures. 
User support is provided through the Geant4 website where documentation is available as well. 

Reference Publications

  • S. Agostinelli et al., “Geant4 - a simulation toolkit”, Nuclear Instruments and Methods in Physics Research A 506 (2003) 250-303 

  • J. Allison et al., “Geant4 developments and applications”, IEEE Transactions on Nuclear Science 53 No. 1 (2006) 270-278 

Advantages & Applications


  • High-Energy Physics experiments and detector design
  • Radiation shielding
  • Calorimetry
  • Cosmic rays
  • Neutrino physics
  • Dosimetry
  • Radiotherapy
  • Biological damage studies
  • Assessment of radiation damage to the electronics of satellites
  • Study of the radiation environment of planets.


  • State-of-the-art physics models, regularly checked and validated against experimental data, combinable to achieve the highest simulation quality.
  • Support for complex 3D geometries such as the detectors of the LHC experiments and models in motion of the human body.
  • Geometry modeller able to efficiently track particles within complex geometries ranging from the molecular scale to the size of a planet.
  • Full description of materials making up specific setups in terms of their elements and isotopes.
  • Biasing techniques to reduce computational time for intensive applications including ‘reverse Monte Carlo’ techniques for concentrating the radiation effects on very small targets and a framework for combining detailed and fast/parameterised simulation.
  • Easily extendible and adaptable to external software frameworks.
  • Powerful user interface and visualisation engine. 

Geant4 is available under an open source licence based on the EU Datagrid Licence. The copyright of the Geant4 software is vested in the members of the Geant4 Collaboration. 
For commercial consultancy and other enquiries please contact CERN KT.
Geant4 is available under an open source licence (Geant4 Software License)