Physics Reference Manual

Scope of this Manual

The Physics Reference Manual provides detailed explanations of the physics implemented in the Geant4 toolkit.

The manual’s purpose is threefold:

• to present the theoretical formulation, model, or parameterization of the physics interactions included in Geant4,

• to describe the probability of the occurrence of an interaction and the sampling mechanisms required to simulate it, and

• to serve as a reference for toolkit users and developers who wish to consult the underlying physics of an interaction.

This manual does not discuss code implementation or how to use the implemented physics interactions in a simulation. These topics are discussed in the User’s Guide for Application Developers. Details of the object-oriented design and functionality of the Geant4 toolkit are given in the User’s Guide for Toolkit Developers. The Installation Guide for Setting up |Geant4| in Your Computing Environment describes how to get the Geant4 code, install it, and run it.

Contents

• General Information
  • Definition of Terms Used in this Guide
  • Monte Carlo Methods
    • Bibliography
  • Particle Transport
    • Particle transport
    • True Step Length
    • Transportation
• Decay
  • Particle Decay
    • Mean Free Path for Decay in Flight
    • Branching Ratios and Decay Channels
  • Decays of orthopositronium at rest to 3 photons
    • Random polarization
    • Polarized model
• Electromagnetic Interactions
  • Electromagnetic Physics in Geant4
    • Introduction
    • EM physics sub-packages
    • Low Energy Livermore Model
    • Penelope Models
    • Generic Calculation of Total Cross Sections
  • Gamma incident
    • Introduction to Gamma Processes
    • Elastic Scattering
    • PhotoElectric Effect
    • Compton scattering
    • Gamma Conversion into e⁺e^- Pair
    • Livermore Triple Gamma Conversion
    • Gamma Conversion into Lepton Pair
    • X-ray reflection
  • Energy Loss of Charged Particles
    • Discrete Processes for Charged Particles
    • Mean Energy Loss
    • Energy Loss Fluctuations
    • Correcting the Cross Section for Energy Variation
    • Conversion from Cut in Range to Energy Threshold
    • Photoabsorption Ionisation Model
    • ATIMA energy-loss model
  • Elastic scattering
    • Multiple Scattering
    • Single Scattering
    • Ion Scattering
    • Single Scattering, Screened Coulomb Potential and NIEL
    • Electron Screened Single Scattering and NIEL
    • G4eSingleScatteringModel
  • Atomic Relaxation
    • Atomic relaxation
    • Alternative models for impact ionisation by hadrons and PIXE
  • Electron and Positron Incident
    • Ionisation
    • Bremsstrahlung
    • Positron - Electron Annihilation
    • Positron Annihilation into \(\mu ^+\mu ^-\) Pair in Media
    • Positron Annihilation into Hadrons in Media
  • Muon incident
    • Muon Ionisation
    • Bremsstrahlung
    • Positron - Electron Pair Production by Muons
    • Muon Photonuclear Interaction
  • Charged Hadron Incident
    • Hadron and Ion Ionisation
    • Low energy extensions
  • Polarized Electron/Positron/Gamma Incident
    • Introduction
    • Ionisation
    • Positron - Electron Annihilation
    • Polarized Compton scattering
    • Polarized Bremsstrahlung for electron and positron
    • Polarized Gamma conversion into an electron–positron pair
    • Polarized Photoelectric Effect
    • Compton Scattering by Linearly Polarized Gamma Rays - Livermore Model
    • Pair production by Linearly Polarized Gamma Rays - Livermore Model
    • Pair production by Linearly Polarized Gamma Rays - Five-dimensional (5D) Bethe-Heitler Model
  • X-Ray production
    • Transition radiation
    • Scintillation
    • Čerenkov Effect
    • Synchrotron Radiation
  • Optical Photons
    • Interactions of optical photons
  • Geant4-DNA
    • Geant4-DNA physics processes and models
  • Microelectronics
    • The MicroElec extension for microelectronics applications
  • Shower Parameterizations
    • Gflash Shower Parameterizations
• Hadronic Physics in Geant4
  • Hadronic Cross Sections in Geant4
    • Hadron-nucleus Cross Sections
    • Total Reaction Cross Section in Nucleus-nucleus Reactions
  • Coherent elastic scattering
    • Nucleon-Nucleon elastic Scattering
  • Hadron-nucleus Elastic Scattering at Medium and High Energy
    • Method of Calculation
  • Parton string model
    • Reaction initial state simulation.
    • Sample of collision participants in nuclear collisions.
    • Longitudinal string excitation
    • Longitudinal string decay.
    • Bibliography
  • Fritiof (FTF) Model
    • Introduction
  • The Geant4 Bertini Intranuclear Cascade Model
    • Introduction
    • The Geant4 Cascade Model
    • Interfacing Bertini implementation
  • The Geant4 Binary Cascade Model
    • Modeling overview
    • Comparison with experiments
    • Neutrons Comparison with Experimental Data
    • Bibliography
  • INCL++: the Liège Intranuclear Cascade Model
    • Introduction
    • Generalities of the INCL++ cascade
    • Physics ingredients
    • Physics performance
  • Precompound model
    • Reaction initial state.
    • Simulation of pre-compound reaction
    • Bibliography
  • Evaporation Model
    • Introduction
    • Evaporation model
    • GEM model
    • Nuclear fission
    • Photon evaporation
    • Sampling procedure
    • Bibliography
  • Fission model
    • Reaction initial state.
    • Fission process simulation.
    • Bibliography
  • Fermi Break-up Model
    • Fermi break-up simulation for light nuclei
    • Bibliography
  • Multifragmentation Model
    • Multifragmentation process simulation
    • Bibliography
  • ABLA++ evaporation/fission model
    • Introduction
    • Evaporation
    • Level densities
    • Fission
    • Multifragmentation
    • External data file required
    • How to use ABLA++
  • Quantum Molecular Dynamics for Heavy Ions
    • Equations of Motion
    • Ion-ion Implementation
    • Cross Sections
  • Abrasion-ablation Model
    • Introduction
    • Initial nuclear dynamics and impact parameter
    • Abrasion process
    • Abraded nucleon spectrum
    • De-excitation of the projectile and target nuclear pre-fragments by standard Geant4 de-excitation physics
    • De-excitation of the projectile and target nuclear pre-fragments by nuclear ablation
    • Definition of the functions P and F used in the abrasion model
  • Electromagnetic Dissociation Model
    • The Model
  • Interactions of Stopping Particles
    • Complementary parameterised and theoretical treatment
    • Pion absorption at rest
  • Low Energy Neutron Interactions
    • Introduction
    • Physics and Verification
    • Elastic Scattering
    • Radiative Capture
    • Fission
    • Inelastic Scattering
    • Unresolved Resonance Region (URR) description with Probability Tables (PT)
    • Neutron Data Library (G4NDL) Format
    • High Precision Models and Low Energy Parameterized Models
    • NuDEX
    • Summary and Important Remark
    • Bibliography
  • LowEnergyChargedParticles
    • Low Energy Charged Particle Interactions
  • Geant4 Low Energy Nuclear Data (LEND) Package
    • Low Energy Nuclear Data
  • Radioactive Decay
    • The Radioactive Decay Module
    • Alpha Decay
    • Beta Decay
    • Electron Capture
    • Recoil Nucleus Correction
    • Biasing Methods
• Gamma- and Lepto-Nuclear Interactions
  • Introduction
  • Cross-sections in Photonuclear and Electronuclear Reactions
    • Approximation of Photonuclear Cross Sections
    • Electronuclear Cross Sections and Reactions
    • Common Notation for Different Approaches to Electronuclear Reactions
  • Gamma-nuclear Interactions
    • Process and Cross Section
    • Final State Generation
    • Low Energy Nuclear Data Model
  • Electro-nuclear Interactions
    • Process and Cross Section
    • Final State Generation
  • Muon-nuclear Interactions
    • Process and Cross Section
    • Final State Generation
• Neutrino Interactions
  • Geant4 neutrino interaction processes
    • Neutrino oscillation process
    • Neutrino-electron process
    • Neutrino-nucleus process
    • Example
• Solid State Physics
  • Phonon-Lattice interactions
    • Introduction
    • Phonon Propagation
    • Lattice Parameters
    • Scattering and Mode Mixing
    • Anharmonic Downconversion
  • Crystal Channeling Physics
    • Channeling of relativistic particles
    • Channeling Fast Simulation Model

Status of this Document

A description of the available physics models and processes within the Geant4 toolkit.

• Rev 1.0: First sphinx version implemented for Geant4 Release 10.4, 8th Dec 2017

• Rev 2.0: Updates and fixes in documentation for Geant4 Release 10.4, 15th May 2018

• Rev 3.0: Geant4 Release 10.5, 11th December 2018

• Rev 3.1: Geant4 Updates and fixes - especially to search functionality, 5th March 2019

• Rev 4.0: Geant4 Release 10.6, 6th December 2019

• Rev 5.0: Geant4 Release 10.7, 4th December 2020

• Rev 6.0: Geant4 Release 11.0, 10th December 2021

• Rev 7.0: Geant4 Release 11.1, 9th December 2022

• Rev 7.1: Geant4 Fixes to http links, 15th July 2023

• Rev 8.0: Geant4 Release 11.2, 8th December 2023

• Rev 9.0: Geant4 Release 11.3, 6th December 2024