MULASSIS is a Geant4-based M-C simulation based tool for dose and particle fluence analysis associated with the use of radiation shields. Users can define the shielding and detector geometry as planar or spherical layers, with the material in each layer defined by its density and elemental/isotopic composition. Incident particles can be any Geant4 particles, these include protons, neutrons, electrons, gammas, alphas and light ions. There is a wide choice for their initial energy and angular distribution. In addition, radiation spectra produced by SPENVIS can be inputted when the tool is used within this system.

Users can carry out Fluence, Total Ionising / Non-Ionising Energy Loss (NIEL) dose, Pulse Height Spectrum (PHS) and Dose Equivalent analyses for any layer in the geometry. Fluence can be tallied into energy distribution histograms as a function of particle type and particle angular direction. NIEL analysis can be performed for materials for which NIEL coefficients are available (currently Si and GaAs). The histograms are output in Comma Separated Values (CSV) format so they can be easily input into other analysis and plotting tools.

Users who have a local Geant4 installation can compile the MULASSIS code and use the tool interactively on their local system. The user can make full use of the Geant4 visualisation facilities for the shielding geometry and the particle interaction tracks.

MULASSIS has been integrated into the ​ESA SPENVIS system, thus making it one of the tools SPENVIS users can choose for their radiation analysis. The full MULASSIS functionality is available via the SPENVIS user interface. In addition the radiation environment as evaluated by other SPENVIS models can be used as inputs for the MULASSIS simulation, thus making it very easy to obtain the modified radiation spectra behind a specific shield defined by the user.

The main reference paper for MULASSIS is published in ​IEEE Transactions on Nuclear Science Vol 49 No 6 (2002) P2788-2793.