GUIMesh: A tool to import STEP geometries into Geant4 via GDML

Abstract

Detailed radiation analysis of instruments flown in space is critical to ensure mission safety, often requiring the use of state-of-the-art particle transport simulation tools. Geant4 is one of the most powerful toolkits to simulate the interaction and the passage of particles through matter, but it is not prepared to receive Standard for The Exchange of Product data (STEP) files, the most versatile Computer-Aided Design (CAD) format, as input, requiring previous conversion to other CAD formats. This may lead to loss of detail and under or overestimation of the quantities under study, especially when the instruments have complex shapes, and/or a large number of volumes. Though several solutions have been proposed to import complex geometries from STEP files into Geant4, so far, only commercial options are available. In this paper we present a new tool, GUIMesh, that embeds FreeCAD libraries, an open-source CAD editor, to tessellate volumes, and convert them to Geometry Description Markup Language (GDML), a Geant4 readable format, in a straightforward way. Several degrees of freedom are given to the user regarding mesh precision and choice of material. Different geometries were tested for material definition, geometry and navigation errors, and the method used was successfully validated. Program SummaryProgram Title: GUIMeshProgram Files doi: http://dx.doi.org/10.17632/c3c9xbspzp.1Licensing provisions: GNU General Public License 3 (GPLv3)Programming language: PythonNature of problem: No open-source software allows to import STEP geometries intro Geant4, one of the most powerful toolkits to simulate radiation interaction with matter. Since CAD software is extensively used in the design of particle and radiation detection instruments, it is highly desirable for physicists that STEP geometries can be imported to Geant4 with little effort instead of having to code structures made of a very large number of solid volumes which are difficult to accurately reproduce with Geant4 C++ classes.Solution method: STEP geometries are converted to tessellated volumes (with some margin of error) using FreeCAD libraries. A Python script then writes GDML files based on the results allowing users to import these geometries with Geant4. A graphical user interface provides several options to the user, including material assignment and mesh precision setting for each volume.