P. Nieminen

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

Comparison of Geant4 electromagnetic physics models against the NIST reference data

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.

THE Geant4-DNA project

The Geant4-DNA project proposes to develop an open-source simulation software based and fully included in the general-purpose Geant4 Monte-Carlo simulation toolkit. The main objective of this software is to simulate biological damages induced by ionizing radiations at the cellular and sub-cellular scale. This project was originally initiated by the European Space Agency for the prediction of the deleterious effects of radiations that may affect astronauts during future long duration space exploration missions. In this paper, the Geant4-DNA collaboration presents an overview of the whole on-going project, including its most recent developments that are available in the Geant4 toolkit since December 2009 (release 9.3), as well as an illustration example simulating the direct irradiation of a biological chromatin fiber. Expected extensions involving several research domains, such as particle physics, chemistry and cellular and molecular biology, within a fully interdisciplinary activity of the Geant4 collaboration are also discussed.

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

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.

GRAS: a general-purpose 3-D Modular Simulation tool for space environment effects analysis

Geant4 Radiation Analysis for Space (GRAS) is a modular, extendable tool for space environment effects simulation. Analyses include cumulative ionizing and NIEL doses, effects to humans, charging, fluence and transient effects in three-dimensional geometry models.

Geant4 atomic relaxation

The Geant4 simulation toolkit encompasses the low energy electromagnetic package, implementing a precise treatment of electromagnetic interactions of particles with matter down to energies of a few hundred eV. This package includes a component handling the process of atomic relaxation; it models the de-excitation of an atom left in an excited state by the creation of a vacancy originated by a primary, and the emission of X-ray fluorescence and Auger electrons. The design of the package and the physics models implemented are presented.

Low-angle scattering of protons on the XMM-Newton optics and effects on the on-board CCD detectors

Monte Carlo simulations are presented where protons are shown to propagate through X-ray telescope optics by grazing incidence scattering processes. If these protons reach charge coupled device (CCD) detectors in sufficient numbers, they can induce a radiation background, and at certain energies, the nonionising dose can cause degradation of the charge transfer efficiency (CTE). In the course of this work, the telescope optics of the Chandra and XMM-Newton observatories were simulated.

A model for Mars radiation environment characterization

A modeling framework for the prediction of the Martian radiation environment is presented. Features include input solar cycle modulated cosmic ray and solar particle event spectra, based both on CREME-96, the transport of this radiation in the Martian atmosphere and regolith, including creation of secondaries, using the Geant4 Monte Carlo toolkit. Details of the atmosphere are derived from the European Mars Climate Database with a dense topological grid and layering of the atmosphere. Seasonal and diurnal variations are considered. Surface topology is derived from the Mars Orbiter Laser Altimeter (MOLA) and geology is modeled. The outputs are full particle transport histories, maps of radiation fluxes, and doses. The model will be applied to future European Mars missions.

Precision validation of Geant4 electromagnetic physics

The Geant4 toolkit provides an ample set of physics models for electromagnetic interactions. Results from a series of detailed tests with respect to well established reference data sources and experiments are presented, focusing on the precision validation of cross sections and angular distributions of various alternative physics models available in Geant4. Such precision tests are especially relevant for critical applications of simulation models, such as tracking detectors, calorimetry, neutrino and other astroparticle experiments, medical physics.

Geant4 Monte Carlo Simulations of the Belt Proton Radiation Environment On Board the International Space Station/Columbus

A detailed characterization of the trapped-proton-induced radiation environment on board Columbus and the International Space Station (ISS) has been carried out using the Geant4 Monte Carlo particle transport toolkit. Dose and dose equivalent rates, as well as penetrating particle spectra are presented. These results are based on detailed Geant4 geometry models of Columbus and ISS, comprising a total of about 1000 geometry volumes. Simulated trapped-proton dose rates are found to be strongly dependent on ISS altitude. Dose rates for different locations inside the Columbus cabin are presented, as well as for different models of the incident trapped-proton flux. Dose rates resulting from incident anisotropic trapped protons are found to be lower than, or equal to, those of omnidirectional models. The anisotropy induced by the asymmetric shielding distribution of Columbus/ISS is also studied. The simulated trapped-proton dose (equivalent) rates, averaged over different locations inside Columbus, are 120 muGy/d (154 muSv/d) and 79 muGy/d (102 muSv/d) for solar minimum and maximum conditions according to AP8 incident proton spectra and an ISS orbit of 380 km. The solar maximum dose rates are found to be of the same order as measurements in other modules in the present ISS.