The version that has been integrated into SPENVIS allows the user to execute GRAS remotely without the need to install Geant4 and the GRAS code on his/her local computer. However, users preferring a local version of this tool can download the source code from the ESA/GRAS website.
Users can go to any particular input page and enter their settings. Note that some input is obligatory. After they have provided their data on a particular input page, they can press the button and return to the main model page. Once they are satisfied with all their input, they can press on the button to generate the macro file. Pressing the button will start the calculation and bring up the results page.
Since the model uses a Monte-Carlo simulation-based code, execution time can be very long. In order to guarantee consistency between the different models available in the SPENVIS system, the user project is 'blocked' while running the GRAS simulation. Nevertheless, navigation remains possible. The excution is limited to ten minutes of CPU-time on the simulation server. If the GRAS run exceeds this limit, the simulation will be terminated and intermediate results returned to the user.
There are two execution modes available for the SPENVIS GRAS implementation: GDMLMulassis.For the Mulassis execution mode the user is referred to the Mulassis help page since the input pages are the same. However, note that some of the input for the two models might differ (e.g. different analysis types available for Mulassis and GRAS).
The following sections describe the user input for the GDML execution mode.
For a mission based environment and a GDML execution mode, the recommended 3D angular distribution is a cosine-law.
The user can locate the source anywhere inside the GDML geometry by selecting a particular GDML volume (see later) and providing the Cartesian coordinates with respect to the centre of that volume. For a point or a disk source, the user can also specify where the source is pointing to by selecting another volume and providing again the Cartesian coordinates with respect to the centre of that volume. Note that the two reference volumes can coincide. When the source is assumed to be a disk or a sphere, an additional input for the source radius is required. The Cartesian coordinates and the source radius can be defined in terms of [mm], [cm] or [m].
The default geometry source is a point source located inside the volume “world” at x=0, y=0 and z=100 [mm] pointing at the centre of “world”. For a mission based environment and a GDML execution mode, a spherical source is recommended. However, it is the responsibility of the user to position correctly the source with respect to the GDML geometry.
Finally, it is possible to produce a graphical representation of the chosen geometry. This can be generated in two formats, i.e. PostScript or VRML, with or without the visualisation of the 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 user can select only one analysis type at a time.
In addition, a common analysis module is automatically inserted by GRAS (no user action is required) and its results are output at the end of the simulation.
For fluence and NIEL, users can select a number of volume interfaces for the analysis. Then, a count is registered only when the particle crosses the selected boundary in the direction specified by the user (i.e. the order of the volume names). For TID, dose equivalent and equivalent dose the user can specify the number and the name of the volumes where the particular analysis will be performed.
The results are recorded as:
The general principles in Geant4 regarding secondary particle production cuts are the following:
In GRAS, the user has the option to change the global production cuts (see later). Region cuts-in-range can be defined as a single cut for gamma, electron and positron productions, or different cuts for each type of the three particles. In addition the user can group the GDML geometry volumes into different regions and apply different cuts to each region.
Note that the default is no region cuts-in-range.
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.
The function phi of theta is determined by the angular dependence of the particle source (i.e. isotropic or cosine-law). We assume that
Finally, the factor for the flux in the energy range of the simulation depends on the source energy spectrum selected by the user and is calculated by integrating the differential particle spectrum over the energy limits of the simulation. For the SPENVIS generated spectra, the integral spectrum is provided. Thus,
Combining all the above we can write
The log file spenvis_gras.g4log records the output from GRAS to stdout and stderr. The output file spenvis_gras.csv containing tabulated results (fluence, NIEL, TID, dose equivalent or equivalent dose) for the selected analysis. The graphics files spenvis_gras.wrl and spenvis_gras.eps show the 3D geometry or the shield cross section.
spenvis_gras.g4log
spenvis_gras.csv
spenvis_gras.wrl
spenvis_gras.eps
spenvis_gras.g4mac
spenvis_gras_aida.root
spenvis_gras_aida.ps