Simulated Processes

Hadronic Interactions

To simulate the interactions of hadrons with the nuclei of the matter traversed, two alternatives are provided:

1. The generator of the FLUKA [,] hadron shower MonteCarlo and the interface routines to GEANT. See [PHYS520] for more information.
2. The generator of the GHEISHA [] hadron shower MonteCarlo and the interface routines to GEANT. See [PHYS510] for more information.

The code both of the GHEISHA and of the FLUKA generators is contained in the GEANT library. Users should be aware that the routines of these packages do not follow the GEANT naming conventions and therefore they can clash with the names of user procedures.

Electromagnetic Processes

By means of systematic fits to the existing data, the cross-sections of the electromagnetic processes are well reproduced (within a few percent) from 10 keV up to 100 GeV, both for light (low Z) and for heavy materials.

This feature, together with the use of the interface with one of the hadronic shower generators available, makes GEANT useful also for shower simulation in gases.

Muonic interactions

Muonic interactions are simulated up to 10 TeV, making GEANT useful for cosmic rays studies.

Ionisation by charged particles

The following alternatives are provided to simulate this process:

• Sampling from the appropriate distribution around the mean value of the energy loss ( [PHYS332]).
• Explicit generation of $\delta$ -rays (see [PHYS330/331/430]) and restricted fluctuations below the energy threshold for the production of $\delta$ -rays.
• Sampling the contribution of single collisions from statistical distributions. This can be used as an alternative to the first one when simulating energy losses in very thin layers (small value of g $cm-2$ ) (see [PHYS334]).

Multiple Scattering

Two methods are provided:

1. Molière distribution or plural scattering ( [PHYS325], [PHYS328]).
2. Gaussian approximation ( [PHYS320]).

The JMATE data structure

In order to save time during the transport of the particles, relevant energy-dependent quantities are tabulated at the beginning of the run, for all materials, as functions of the kinetic energy of the particle. In particular, the inverse of the total cross-sections of all processes involving photons, electrons and muons and the $dE/dx$ and range tables for electrons, muons and protons are calculated. The actual value of, say, the interaction length for a given process (i.e. the inverse of the macroscopic cross section) is then obtained via a linear interpolation in the tables. The data structure which contains all this information in memory is supported by the link JMATE in the /GCLINK/ common block. See [PHYS100] and [CONS199] for a more information on these tables.

Probability of Interaction

The total cross-section of each process is used at tracking time to evaluate the probability of occurrence of the process. See [PHYS010] for an explanation of the method used.

Note: The section PHYS is closely related to the section CONS. Users wishing to have a complete overview of the physics processes included in GEANT should read both sections.