Definition of Terms Used in this Guide

Several terms used throughout the Physics Reference Manual have specific meaning within Geant4, but are not well-defined in general usage. The definitions of these terms are given here.

• process - a C++ class which describes how and when a specific kind of physical interaction takes place along a particle track. A given particle type typically has several processes assigned to it. Occasionally “process” refers to the interaction which the process class describes.

• model - a C++ class whose methods implement the details of an interaction, such as its kinematics. One or more models may be assigned to each process. In sections discussing the theory of an interaction, “model” may refer to the formulae or parameterization on which the model class is based.

• Geant3 - a previous physics simulation tool written in Fortran, and the direct predecessor of Geant4. Although some references are still made to Geant3, no knowledge of it is required to understand this manual.

• Verification - in terms of physics modelling we define verification of testing a model at the thin target level to determine if it performs as expected normally in terms of double differential cross-sections. This is as much a computational unit test as a theoretical investigation.

• Validation - a comparison between a physics model and real experimental data. This may be at the microscopic (thin target) level whereby the experiment have provided derived cross sections from their data, or at a larger macroscopic (thick target) level whereby experimental data are directly compared with experiment.