Table of Contents ECSS Model Page
Background Information Geant4 tools
Geant4-based Microdosimetry Analysis Tool (GEMAT)

Table of contents

  1. Overview of GEMAT
  2. GEMAT in the SPENVIS environment
  3. Geometry definition
  4. Material definition
  5. Source particles
  6. Physics models and production cuts-in-range
  7. Analysis parameters
    1. Fluence analysis
    2. Energy deposition pulse-height spectrum
    3. Path length distribution
    4. Coincidence event rates
  8. Results
  9. References

Overview of GEMAT

The Geant4-based Microdosimetry Analysis Tool (GEMAT) is a computer code to study microdosimetry effects of space radiation on micro-electronics and micro-sensors. Please consult the GEMAT website for a full description of GEMAT and downloads of binaries and source code.

GEMAT in the SPENVIS environment

The SPENVIS interface to GEMAT simplifies the process of defining run parameters via a number of input pages (see below) that a user can access from a table on the main page of the model. In addition, some information on the status and a short summary of the user input is also displayed.

Users can go to any particular input page and enter their settings. After they are done, they can hit the button and return to the main model page. Once they are satisfied with all their input they can use the button to generate the macro file. Pressing the button will start the calculation and bring up the results page.

Advanced users have the option to input a number of fine-tuning parameters.

As the model uses a Monte-Carlo simulation-based code, execution times can be very long. In order to guarantee the consistency between the different models available in the SPENVIS system (e.g. particle spectrum vs. total ionising dose), the user project is 'blocked' while running the multi-layered shielding simulation, but navigation remains possible. The excution is limited to ten minutes of CPU-time on the simulation machine. If the GEMAT run exceeds this limit, the simulation will be terminated and intermediate results returned to the user.

Geometry definition

In GEMAT the simulation geometry is constructed in terms of layers, contact volumes (CV) and depletion volumes (DV). The default geometry set-up in GEMAT, which consists of 6 layers, 2 CVs and 4 DVs, is shown below.

All layers have the same surface dimensions. By default, the dimension of the layers is 10 times the total thickness of the layers, but this can be overridden. For each layer, the user can define the layer material, the thickness and the colour to use in the graphical representation. For the material selection, four default materials are available: vacuum, air, aluminium and silicon. In addition, pressing the button in the header of the table opens the material definition page where other materials can be selected or defined.

The next option is to get a VRML graphical representation of the chosen geometry (with or without particle tracks). Note that no particle tracks would be represented in the graphics file if more than hundred primary particles are requested for the simulation.

The following shapes are available for the contact and depletion volumes: cylinder, box, L shape and U shape. Each volume is defined in terms of a volume material, the layer in which it is positioned, a colour for the graphical representation, two position coordinates, a number of dimensions (dependent on the shape of the volume), and the units for the position and size parameters. Contact volumes are defined as follows:

Depletion volumes are defined in the same way, with one additional parameter: the increase Delta in the dimensions at the bottom surface of the depletion layer, which allows the volume to have a trapezoidal shape.

Material definition

Users can employ the material definition tool to either specify their own material or make use of the predefined lists.

Source particles

Users can specify the incident particle, its energy spectrum and angular distribution using the source particles template that is common for the Geant4 tools in SPENVIS.

Physics models and production cuts-in-range

Physics processes

Advanced users can specify the physics scenario and the global cut-in-range using the physics models template that is common for the Geant4 tools in SPENVIS.

Production cuts-in-range by region

A region is a collection of geometry volumes. Volumes that require different cuts-in-range from the global ones can be grouped into regions and each region can be given its own cuts.

In GEMAT, the depletion volumes have been grouped into one single region, and different cuts can be applied to this region. Advanced users can specify a single cut for gamma, electron and positron productions, or different cuts for each type of the three particles.

Analysis parameters

Currently, four types of analysis are performed by GEMAT: The path length distribution is performed when the incident particles are geantino's. For all other particle types, the other three types of analysis are performed. All analysis results are normalized to per incident particle.

Fluence analysis

The fluence analysis allows the user to measure the number of particles entering each depletion volume and to record their energy spectrum. Please note that in this analysis the weight of each recorded particle has not been modified by 1/cosθ, where θ is the entering angle of the particle with respect to the surface normal of the depletion volume.

The user can specify the particle type to be included in the fluence analysis: protons, neutrons, electrons, gamma rays and charged pions. An option is available to select the incident particle type. Multiple selections are allowed. At least one particle type has to be selected.

The spectrum binning scheme can be defined by the user:

Energy deposition pulse height spectrum

The pulse height spectrum of energy deposition in each depletion volume is obtained at the end of the execution. The user can control the energy binning scheme in the same way as for the fluence analysis.

Path length distribution

If geantino's were selected as the incident particle type, the pulse height spectrum obtained for each depletion volume is in fact the path length distribution in units of events/bin per incident particle. The path length is calculated in μm regardless of the energy units defined in the binning scheme.

Coincidence event rates

The following event rates are produced at the end of a run: The trigger energy threshold of each depletion volume can be set by the user. This type of analysis is only performed when more than one depletion volume were defined.

Results

GEMAT 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_ger.txt contains details of the inputs and outputs. The log file spenvis_gep.txt records the output from GEMAT to stdout and stderr. The output file spenvis_geo.txt contains tabulated results (fluences, pulse height spectra, path length distributions, coincidence rates) for the various analysis types. The graphics file spenvis_gem.wrl shows the 3D geometry.

Output files generated by GEMAT
File name Description
spenvis_ger.txt Report file
spenvis_gep.txt Log file
spenvis_geo.txt Outputs for the various analysis type
spenvis_gem.wrl VRML representation of the geometry

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. REAT website
  2. Geant4 website
  3. Geant4 Physics Reference Manual


Last update: Mon, 12 Mar 2018