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.
| GEMAT | MULASSIS |
| 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:
- For protons, MULASSIS operates in normal Monte Carlo (MC) simulation
mode, tracking particle histories and all secondaries produced by
interaction.
- For α particles and heavier ions, MULASSIS uses a non-MC
simulation (so-called "IRONSSIS" mode) to use Geant4's ion
range-versus-energy and stopping-power-versus-energy tables to derive
the same quantities as the traditional MULASSIS MC calculation, but
using the continuous slowing-down approximation (CSDA) straight ahead
approach. This greatly speeds up the calculation whilst retaining good
accuracy of the results for residual ion fluxes after shielding, and
ionising and non-ionising dose estimates. This provides significant
advantages if response functions need to be generated for a wide range
of ions (potentially from Z=2 to 92) at 11 energy channels. However, the
disadvantage is there is no treatment of secondary particles,
particularly neutrons from energetic ion-nuclear interactions.
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.
MULASSIS and GEMAT in SEPEM
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.
|
References
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
