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

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Geant4 developments and applications

We simulated electromagnetic and nuclear processes induced by clinical proton beams in order to select the physics setting for the 8.1 version of the Geant4 toolkit. A modular physics list was constructed allowing for alternative processes and models to be invoked in the simulations. We validated the Monte Carlo by means of measured depth-dose distributions in water for 86 MeV and 209 MeV beams and measured longitudinal charge profiles in a stack of polyethylene absorbers (multilayer Faraday cup) for a 160 MeV beam. Best agreement between simulation and measurement was found for the standard electromagnetic and binary cascade models of Geant4.

Physics Settings for Using the Geant4 Toolkit in Proton Therapy

The Geant4 Simulation Toolkit provides an ample set of physics models describing electromagnetic interactions of particles with matter. This paper presents the results of a series of comparisons for the evaluation of Geant4 electromagnetic processes with respect to United States National Institute of Standards and Technologies (NIST) reference data. A statistical analysis was performed to estimate quantitatively the compatibility of Geant4 electromagnetic models with NIST data; the statistical analysis also highlighted the respective strengths of the different Geant4 models.

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Comparison of Geant4 electromagnetic physics models against the NIST reference data

The Geant4 toolkit provides a wide set of alternative models to describe the electromagnetic interaction of photons with matter. The photon cross-sections that are used by the Geant4 electromagnetic models have been compared to external reference libraries (NIST, EPDL97, SANDIA) for several elements and compounds. The agreement of the Geant4 cross-section with the reference data has been quantified by means of statistical analysis. In particular, the cross-sections of all the Geant4 photon models are in statistical agreement with the NIST database, with the exception of Rayleigh scattering. A critical discussion is presented for those cases where a disagreement is found.

Validation of the Geant4 electromagnetic photon cross-sections for elements and compounds

New physical processes specific for microdosimetry simulation are under development in the Geant4 Low Energy Electromagnetic package. The first set of models implemented for this purpose cover the interactions of electrons, protons and light ions in liquid water; they address a physics domain relevant to the simulation of radiation effects in biological systems, where water represents an important component. The design developed for effectively handling particle interactions down to a low energy scale and the physics models implemented in the first public release of the software are described.

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Geant4 Physics Processes for Microdosimetry Simulation: Design Foundation and Implementation of the First Set of Models

The Geant4 simulation toolkit includes a specialised package, implementing a precise treatment of electromagnetic interactions of particles with matter below 1 keV. The Geant4 low energy electromagnetic package provides a variety of models describing the electromagnetic processes of electrons and positrons, photons, charged hadrons and ions, taking into account detailed features, such as atomic shell effects and charge dependence. Those features are relevant to several experimental domains, such as astrophysics, space science and bio-medical research, and have enabled new simulation studies beyond the conventional applications of Geant4 in high energy physics. The design of the package and the physics models implemented are presented.

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A. Tnndade

Papers

Geant4 low energy electromagnetic physics