Introduction to the Geant4-based analysis tools MULASSIS and GEMAT

The Geant4-based Microdosimetry Analysis Tool (GEMAT) and Multi-Layered Shielding Simulation Software (MULASSIS) are application programs for the study of SEP radiation effects based on the Geant4 radiation transport simulation toolkit. GEMAT studies microdosimetry effects of space radiation on microelectronics/micro-sensors and MULASSIS uses one-dimensional multi-layered planar or spherical shield geometries to assess radiation shielding performance, particularly for the evaluation of secondary radiation. The types of analysis provided in GEMAT and MULASSIS are summarised in the table below.

Fluence of particle entering each SV and record their energy spectrum Fluence spectra at the boundaries between the different layers
Pulse-height spectrum of energy deposition in each SV Non-ionizing energy loss (NIEL) analysis at the boundaries of layers
Path length distribution in units of events .bin-1 per incident particle Energy deposition/Total ionizing dose in any layer
Coincidence rates between the SVs Pulse-height spectrum (PHS) of energy deposition at any layer

Geant4 is a Monte Carlo radiation transport toolkit used to simulate the complex electromagnetic and nuclear interactions of high-energy particles in virtually any material. As part of the Monte Carlo simulation, all secondary particles are tracked to the range cut-off limits defined for the geometry. However, note that MULASSIS functions in a very different approach when simulating SEP protons and heavier ions:

Irrespective of whether a simulation is performed in MC or non-MC mode, MULASSIS geometries comprise one or more layers, the composition and thickness of which is defined by the user. There is a wide list of predefined materials.


In SEPEM both tools can be applied by users with no programming experience and very little knowledge of Geant4 itself. SEPEM users only have to define the data table, the particle species, the device geometry and the device material(s). Appopriate physics lists are selected by the SEPEM software from the table below, depending on the type of simulation.

List of Geant4 physics scenarios applicable for solar protons:
scenarios 1-8 are treated by MULASSIS and scenario 4 and 8 are treated by GEMAT.


[1] Geant4:
[2] GEMAT: URD and SSD

The Space Environment and Effects Section at ESA/ESTEC is maintaining a repository of Geant4-related codes developed by ESA-funded projects.

Last modified: 24 October 2017