Table of Contents ECSS Model Page
Background Information Radiation sources and effects
Shielded flux (MFLUX)

Table of contents

  1. Overview of MFLUX
  2. MULASSIS look-up tables
  3. Source definition
  4. Shielding definition
  5. Results
  6. References

Overview of MFLUX

MFLUX allows the user to define the incident particle source (Trapped particles or Solar energetic proton), the total thickness of the spacecraft shielding (in units of [g cm-2]) and the Tantalum to Aluminium mass ratio for this particular shielding (i.e. ratio of Tantalum to Aluminium thicknesses in units of [g cm-2]). Then, it utilises the MULASSIS look-up tables included in SPENVIS in order to calculate the proton, electron and neutron fluence/flux behind the shielding.

The approximations used for calculating the particle fluence/flux behind the shielding seems to work rather good for protons and neutrons. On the other hand, it is less successful when electrons are considered. This has been somehow expected because of the more complex interactions of the electrons with the shielding. Therefore, the electron results should be used with caution.

MULASSIS look-up tables

MFLUX makes use of two separate look-up tables corresponding to incident protons and electrons respectively (almost mono-energetic spectra around the energy values displayed on Table 1). The look-up table data include:

Table 1 Different values for incident particle energy, total shielding and Ta to Al mass ratio.
Proton energy
[MeV]		 Electron energy
[MeV]		 Total shielding
[g cm-2]		 Ta to Al mass ratio
[%]
10.0 0.1 0.1 0
30.0 1.0 0.5 5
50.0 3.0 1.0 15
80.0 10.0 2.0 35
100.0 30.0 3.0  
300.0 100.0 5.0  
500.0 300.0    
800.0      
1000.0      

For the generation of the look-up tables multiple runs of MULASSIS were required, using different values for the incident particle energy, E0, the total thicknesses of the shield and the Tantalum to Aluminium mass ratio (see Table 1). Hence, some simplifying assumptions have been made:

  1. Geometry: Planar slab with three layers (Al shielding, Ta shielding and Si target). Shielding could vary while target was assumed to be a thin detector of 0.023 [g cm-2] (100 [m]);
  2. Source: Incident particles are almost mono-energetic (constant energy spectrum over a very small energy range) protons or electrons, following an omni-directional angular distribution;
  3. Analysis: Fluence/flux behing the shielding.
Figure 1. Basic geometry configuration assumed for the generation of the
MULASSIS look-up tables.

Also, for the physics scenario standard electromagnetic (EM) processes and hadronic nuclear interactions were considered. Finally, for better Monte Carlo (Geant4 ) simulation results the number of events was assumes to be equal to 107.

Source definition

The source selection depends on which SPENVIS radiation model (i.e. Trapped radiation or the Long-term solar particle fluences models) has run before and users can select one or more incident particle spectra.

Shield definition

This model assumes a maximum of two layers for the spacecraft shielding (see Figure 1). Users can define the total thickness of the spacecraft shielding in units of [g cm-2] by selecting one of the following values: . Also, the following options are available for defining the Tantalum to Aluminium mass ratio for the shielding: [%].

The thicknesses of the two layers are calculated automatically and displayed in units of [mm].

Results

MFLUX produces the files listed in the table below. A description of the format of the files can be brought up by clicking on their description in the table.

The report file spenvis_mfr.txt contains details of the inputs and outputs. The output file spenvis_mfo.txt containing tabulated flux results The output file spenvis_mfm.txt containing binned MULASSIS-like fluence results. For generating the MFLUX output forty six energy bins have been defined, covering an energy spectrum from 0.04 to 1000 [MeV].

Output files generated by MFLUX
File name Description
spenvis_mfr.html Report file
spenvis_mfo.txt Flux outputs
spenvis_mfl.txt Fluence binned outputs

To generate plots, select the plot type(s), options and graphics format, and click the button. The current page will be updated with the newly generated plot files.

References

  1. ESA European Space Software Repository
  2. Geant4 website
  3. Geant4 Physics Reference Manual
  4. Lei, F. et al., MULASSIS: A Geant4 Based Multi-Layered Shielding Simulation Tool, IEEE Trans. Nucl. Sci. 49, 2788, 2002

Last update: Thu, 16 Jun 2022