J. Apostolakis

Geant4 developments and applications

Geant4 is a software toolkit for the simulation of the passage of particles through matter. It is used by a large number of experiments and projects in a variety of application domains, including high energy physics, astrophysics and space science, medical physics and radiation protection. Its functionality and modeling capabilities continue to be extended, while its performance is enhanced. An overview of recent developments in diverse areas of the toolkit is presented. These include performance optimization for complex setups; improvements for the propagation in fields; new options for event biasing; and additions and improvements in geometry, physics processes and interactive capabilities

An implementation of ionisation energy loss in very thin absorbers for the GEANT4 simulation package

Abstract We discuss an implementation of Photo Absorption Ionisation model describing ionisation energy loss produced by a relativistic charged particle in very thin absorbers. The implementation allows us to calculate ionisation energy losses in any material consisting of elements with atomic numbers in the range 1–100. Comparisons of simulation with the experimental data from gaseous and solid state detectors are presented.

Validation and verification of Geant4 standard electromagnetic physics

The software tools developed for the validation and verification of the standard electromagnetic physics package of Geant4 are described. The validation is being performed versus experimental data and in regression to a previous version of Geant4. Examples of validation results are presented.

The performance of the Geant4 standard EM package for LHC and other applications

Current status of the Standard electro-magnetic (EM) package of the Geant4 toolkit is described. We report on the stability of results with respect to variation of production threshold and Physics List. This illustrates the trade between CPU time and precision of simulation predictions. New comparisons of the Geant4 simulation with the experimental data are shown. The CPU benchmark results are discussed.

Progress in hadronic physics modelling in Geant4

Geant4 offers a set of models to simulate hadronic showers in calorimeters. Recent improvements to several models relevant to the modelling of hadronic showers are discussed. These include improved cross sections, a revision of the FTF model, the addition of quasi-elastic scattering to the QGS model, and enhancements in the nuclear precompound and de-excitation models. The validation of physics models against thin target experiments has been extended especially in the energy region 10 GeV and below. Examples of new validation results are shown.

GEANT4 Physics Lists for HEP

In GEANT4, a Physics List is a consistent set of physics models that is able to cover all combinations of incident particle type, energy, and target material. Various Physics Lists are possible and useful, according to the specific application domains (e.g. high-energy physics, shielding, space-application, medical physics, etc.), and the best compromise between accuracy and CPU time that the user can accept. Users are allowed to write their own preferred Physics List, but several pre-defined ones are available in GEANT4 for convenience, and indeed they are used by the large majority of users. We present here the Physics Lists that are of interest for high-energy physics applications.

Parameterization models for X-ray transition radiation in the GEANT4 package

We discuss an implementation of parameterization models provided by the GEANT4 package for the description of the X-ray transition radiation (XTR) produced by a relativistic charged particle in a multi layered medium. The implementation allows us to calculate the number of XTR photons, their energy and angular spectra in a number of XTR radiators of practical interest. Comparison of simulation with experimental data from gaseous detectors is presented.

Geant4 electromagnetic physics for high statistic simulation of LHC experiments

An overview of the current status of electromagnetic physics (EM) of the Geant4 toolkit is presented. Recent improvements are focused on the performance of large scale production for LHC and on the precision of simulation results over a wide energy range. Significant efforts have been made to improve the accuracy without compromising of CPU speed for EM particle transport. New biasing options have been introduced, which are applicable to any EM process. These include algorithms to enhance and suppress processes, force interactions or splitting of secondary particles. It is shown that the performance of the EM sub-package is improved. We will report extensions of the testing suite allowing high statistics validation of EM physics. It includes validation of multiple scattering, bremsstrahlung and other models. Cross checks between standard and low-energy EM models have been performed using evaluated data libraries and reference benchmark results.

A technique for optimised navigation in regular geometries

The simulation of a DICOM file describing the geometry of a patient through a 3-dimensional grid of several million voxels represents a big challenge in terms of time and memory consumption. We have developed a fast technique to navigate in these regular voxelised geometries in the GEANT4 framework. It takes advantage of the regular structure of the geometry to optimise the location of voxels at tracking time. An option to skip on the fly the voxel boundaries when two contiguous voxels share the same material reduces the number of steps and therefore the simulation time. When the number of materials in the phantom is of the order a few dozens, enough to reach the required precision in medical physics applications, this technique is several times faster than the optimised navigation algorithms implemented in GEANT4, while keeping optimal memory and initialisation time.

Parallel geometries in Geant4: Foundation and recent enhancements

The Geant4 software toolkit simulates the passage of particles through matter. It is utilized in high energy and nuclear physics experiments, in medical physics and space applications.