Geant4 is a toolkit to create simulations of the passage of particles or radiation through matter. Applications built on Geant4 can simulate any setup or detector and radiation source, and record chosen output of physical quantities due to source particles and secondaries interacting with the material of the setup.

Geant4 provides complete functionality for all areas of the simulation of particle transport. It can be used to

  • create a model of a geometry with shapes and materials,
  • locate points and navigate tracks in that model,
  • apply the effects of physics interactions and generate secondary particles,
  • record selected information either as tallies or create hits (that are used to generate detector response),
  • visualize a setup’s geometry and the particle tracks passing through it, and
  • interact with an application via an extensible terminal or graphical user interface.

It includes a complete set of physics processes for electromagnetic, strong and weak interactions of particles in matter over an energy range that starts from milli-eV (for thermal neutrons), eV (electrons) or typically keV (hadrons), up to hundreds of GeV (or even in part up to 100 TeV). For each type of interaction, a complete set of physics model implementations is provided. Some choices of modeling approaches are available and ready to be used as coherent configurations (named physics lists).

Geant4 source code is available under an open source license, and is written to be readable. The toolkit also includes example applications demonstrating several simpler setups and selected full applications from different domains. For some domains these applications have comprehensive capabilities, whereas others provide a starting point for building your own custom application.

It is also possible to use Geant4 indirectly through a program designed as a customised tool for an application domain, or to create a fully independent stand-alone application for a specific setup or detector.

Any Geant4 application can and must choose whether to preconfigure, select or input beam / source parameters or details of its setup, and whether to record information using standard tallies or create custom ways to collect and output quantities of interest. It will typically select from a set of existing pre-packaged physics configurations (physics lists), developed and typically tested within an application domain, unless its authors undertake the substantially more challenging task of customising or recreating such a configuration from scratch.


Geant4 is used in several areas of science, from high energy, nuclear and accelerator physics, to medical and space science.

What types of Geant4 application exist?

Diverse tools in different application areas are built on top of Geant4, enabling its use without programming. Application areas that are covered range from High Energy and Nuclear Physics (HEP/HENP), medical physics, assessment of material effects in accelerator beamline design, to the evaluation of the effects of space radiation on satellites and planetary bodies.

These applications are tools that provide both a way to create a setup and a mechanism to record those quantities relevant to their area. Many are extendible, so a user can add new capabilities using their structure and Geant4’s capabilities.
Some users and experiments instead choose to create fully custom applications for their setup or experiment, in order to retain full control, to create new capabilities or to interface it into a larger software framework. Such applications have been created by many HEP and nuclear physics experiments.

HEP and nuclear physics experiments have used it to design or optimise future detectors, prepare the software to process their data (before any measurements) and to generate simulated events to be used as part of their analysis of measured data.

Any experiment or user can create a custom application using Geant4 to describe a detector, setup or experiment, and use it to record any arbitrary quantities to compare with experimental data, or to predict its performance.

The list below includes several examples of application of the Geant4 toolkit:


Geant4 source code is available under an open source license.