A GUI for Setting and Running Radiation Simulations for Complex CAD Geometries
RSim enables users to set up a simulation for modeling radiation effects via a user-friendly interface. Users can create a geometry from geometry primitives (spheres, cones, boxes, etc.) and boolean operations (intersections, unions) on primitives, or import a CAD file. After creating or importing a geometry, users can assign materials to the geometry, specify common radiation sources, and formulate tallies (dose, fluence, etc.). RSim translates the simulation setup into Geant4 input then runs the simulation.
RSim runs on Linux, macOS, and Windows.
Included examples help users quickly learn RSim so they can create their own new simulations.
RSim is an application providing a GUI for setting up and running radiation simulations. The current release RSim 1.0 is implemented for using GRAS  as its simulation engine. GRAS (Geant4 Radiation Analysis for Space) was developed by ESA as a wrapper for Geant4  and offers a generic application, allowing users to specify the geometry, radiation environment and analysis purely by the extended input language of Geant4 (.mac file). In particular, one imports geometry using GDML (Geometry Definition Markup Language ) files, defines sets up the analysis using GRAS UI commands and use GPS  (General Particle Source) for defining radiation environment.
GRAS should be downloaded independently from RSim at https://essr.esa.int/register. A path to GRAS executable is communicated to RSim via the preferences of the application.
Users of RSim can import complex CAD geometries, define radiation sources and tallies for radiation analysis and run simulations (see Fig. 1) without a need to write C++ code or manually editing input files. In the next release of RSim, we will add support for PHITS.
Defining Radiation Sources in RSim
Setting up a source begins with type selection (see Fig 5). If a surface or volume source is chosen, the user next attaches a geometry primitive (created prior to selecting the source type), which serves as the origin of tracks.
Next users can set up a type of spectrum (see Fig. 6) and edit its parameters as shown on Fig. 7. A particularly useful type of spectrum is 2 Column File because the radiation environment is often specified in tabular data format expressed as differential fluences vs. energy.
On the backend, RSim translates radiation source data into GPS format for Geant4/GRAS. Sources can be visualized in RSim (see Fig. 8), which makes debugging of setups much easier.
In the current release of RSim0.1 Tech-X implemented and tested volume and mesh tallies for energy deposition, and fluence/fluxes (see Fig. 9). Through the RSim GUI, users can choose a part of CAD geometry to which to apply the tally.
Users can choose materials from the RSim database, which contains more than 700 common materials,as well as create custom materials such as isotopes, molecules, and mixtures. Annotation of solids with material information can be applied interactively (manually) or automatically by using a file to associate CAD parts with common material names.
In the next release we will address (1) support for PHITS simulations and (2) visualization of Geant4 and PHITS simulation results for easy comparison and cross-validations of these radiation transport models.
 Santin, Giovanni, Vladimir Ivanchenko, Hugh Evans, Petteri Nieminen, and Eamonn Daly. "GRAS: A general-purpose 3-D modular simulation tool for space environment effects analysis." IEEE Transactions on Nuclear Science 52, no. 6 (2005): 2294-2299. DOI: 10.1109/TNS.2005.860749
 STEP format: https://en.wikipedia.org/wiki/CAD_data_exchange