Table of Contents ECSS Model Page
Background Information Geant4 tools
Geant4 Radiation Analysis for Space (GRAS)

Table of contents

  1. Overview of GRAS
  2. GRAS in the SPENVIS environment
  3. Source particles
  4. Source geometry definition
  5. Analysis parameters
    1. Fluence
    2. Non ionising energy loss
    3. Total ionising dose/energy deposition
    4. Dose equivalent analysis
    5. Equivalent dose
  6. GDML definition
  7. Region cuts-in-range
  8. Physics models and production cut-in-range
  9. The normalisation factor
  10. Results
  11. References

Overview of GRAS

GRAS is a Geant4-based tool that provides a general space radiation analysis for 3D geometry models [Santin et al., 2005]. More specifically, GRAS allows the definition of a multi-volume 3D geometry (Mulassis-like geometries can also be defined) and incident particle source. Then, using the Geant4 toolkit it simulates radiation transport through the geometry, treating electromagnetic and nuclear interactions.

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.

GRAS in the SPENVIS environment

The SPENVIS interface to GRAS simplifies the process of defining the run parameters. The user can access a number of input pages (see below) from a table on the main page of the model. On the same table, information about the status and a short summary for each input are also displayed.

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.

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

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: .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.

Source particles

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

For a mission based environment and a GDML execution mode, the recommended 3D angular distribution is a cosine-law.

Source geometry definition

The source can be any of the following types:

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.

Analysis parameters

Five different analysis types are available:

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.

Fluence analysis

The fluence analysis parameters allow the user to control the measurement of particle fluence spectra at the boundaries between the different volumes. The user can select whether the fluence for the source particle, protons, neutrons, electrons, gamma-rays, charged-pions and/or muons (multiple selections are possible) are to be logged and histogrammed. The histogram binning scheme can be defined by the user by providing an energy binning scheme: . The default binning scheme is linear from 0 to 100 MeV comprising 100 bins.

The results are recorded as:

Non ionizing energy loss (NIEL)

The NIEL can be calculated in units of based on the fluence results and NIEL coefficients from ROSE/CERN [Vasilescu and Lindstroem, 2000], JPL/CREME86 (CREME86 JPL Si) [Dale et al., 1993, Holland] or JPL/NRL/NASA 2003 (Silicon, Gallium Arsenide or Indium Phosphide - Proton:[Jun et al., 2003], [Messenger et al., 2003]; Neutron: [ASTM, 2002], [Messenger et al., 2005] and [Griffin]; Electron: [Summers et al., 1993], [Messenger]). For NIEL calculations involving the ROSE/CERN or the JPL/CREME86 the resulting NIEL is only calculated for silicon. Note that the JPL/CREME86 coefficients are only applicable for incident protons [Jun et al., 2003], [Messenger et al, 2003], while the CERN/ROSE data [ROSE NIEL coefficients] can be also used when neutrons, electrons or pions are assumed to be the incident particles. It is the users responsibility to select the appropriate set of coefficients for the material and volume under investigation.

Energy deposition/total ionizing dose (TID)

The total (cumulative) energy deposition can be calculated for each of the selected volumes in units of . The TID analysis also calculates the energy deposited at each event in order to allow the user to get the event pulse height spectrum (PHS).

Dose equivalent

The dose equivalent analysis allows the computation of the total (cumulative) dose equivalent in the selected volumes. The available units are . The dose equivalent calculation takes into account the Relative Biological Effectiveness (RBE) of radiation as a function of particle type and energy using the Quality Factor (QF) [ICRP 60, 1990].

Equivalent dose analysis

The equivalent dose analysis allows the computation of the total (cumulative) equivalent dose in the selected volumes in units of . For the equivalent dose calculation the radiation weighting factor, wR, is used. The user can choose between the values adopted in ICRP 60 [ICRP 60, 1990] or the updated factors given in ICRP 92 [ICRP 92, 2003].

Common analysis module

The common analysis module performs a basic analysis of the events by counting the number of secondary electrons, positrons and gammas generated and the total number of steps performed by all tracks in the event. The output can be used to monitor the Geant4 tracking and the consequence of the secondary particle production cuts in electromagnetic processes.

GDML definition

Users must define their GDML geometry when the GDML execution mode is selected. This can be done by making use of the “GDML definition tool” implemented in SPENVIS.

Region cuts-in-range

Advanced users can define the different cut-in-range to be used by region.

The general principles in Geant4 regarding secondary particle production cuts are the following:

  1. Each process has its intrinsic limit(s) to produce secondary particles.
  2. All particles produced (and accepted) will be tracked up to zero range.
  3. Production cuts are assigned to Regions.
A region is a collection of geometry volumes. There is always a default region covering the whole geometry, for which there is a suggested global cut in range for gamma, electron and positron productions. Volumes that require different cuts from the global ones shall be grouped into regions and each region can be given its own cuts.

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.

Physics models and global cuts-in-range

Space radiation sources range from very low to very high energy and their interactions with the spacecraft sensitive devices and the shielding structures include both electromagnetic and hadronic processes. GRAS includes a very large subset of the physics models available within Geant4, in order to give an almost complete coverage of the main interaction mechanisms for trapped, solar and cosmic radiation in the spacecraft materials.

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 normalisation factor

The normalisation factor for the SPENVIS implementation of GRAS is calculated using the following formula:


where A is the total area of the particle source, theta is the zenith angle and T is the kinetic energy of the incident particles.

The function phi of theta is determined by the angular dependence of the particle source (i.e. isotropic or cosine-law). We assume that



and


for isotropic and cosine-law angular dependence respectively and that


is always true.

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,



i.e. simply subtracting the integral flux at the maximum energy in the simulation from the flux at the minimum energy in the simulation.

Combining all the above we can write



and


for a SPENVIS generated spectrum and a particle source having an isotropic and a cosine-law angular dependence respectively.

Results

GRAS produces the files listed in the table below. An explanation about the format of the files can be brought up by clicking on their description in the table.

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.

Output files generated by GRAS
File name Description
spenvis_gras.g4log Log file
spenvis_gras.g4mac Macro file
spenvis_gras.csv Outputs for the selected analysis type
spenvis_gras_aida.root Output root file for the selected analysis type
spenvis_gras.wrl VRML representation of the geometry
spenvis_gras.eps Cross section view of the geometry
spenvis_gras_aida.ps Output preview of GRAS results (PS)

References

  1. ESA/GRAS website
  2. Geant4 website
  3. Geant4 Physics Reference Manual
  4. ROSE NIEL coefficients
  5. ASTM, Standard Practise for Characterizing Neutron Energy Fluence Spectra in Terms of an Equivalent Monoenergetic Neutron Fluence for Radiation Hardness Testing of Electronics, ASTM International Standard E722-94 (re-approved 2002), American Society for Testing Materials.
  6. Dale et al., Displacement Damage Effects in Mixed Particle Environments for Shielded Spacecraft CCDs, IEEE Trans. Nucl. Sc., Vol 40, No 6, 1628-1637, 1993.
  7. Ferrari, A., ATLAS TDR 1997, and private communication 1997.
  8. Griffin, P. J. et al., SAND92-0094, Sandia Nat. Lab 1993, Private communication 1996.
  9. Holland, A., private communication.
  10. Huhtinen, M., and P. A. Aarnio, NIM A 335, 580, 1993, and private communication.
  11. ICRP 60, 1990 Recommendations of the International Commission of Radiological Protection, Annals of the ICRP, Vol 21, No 1-3, 1991.
  12. ICRP 92, Relative biological effectiveness (RBE), quality factor (Q) and radiation weighting factor (wR), Annals of the ICRP, Vol 33, No 4, 2003.
  13. Jun, I., M. A. Xapsos, S. R. Messenger, E. A. Burke, R. J. Walters, G. P. Summers, and T. Jordan, Proton nonionizing energy loss (NIEL) for device Applications, IEEE Trans. Nucl. Sci., Vol. 50, 1924-1928, 2003.
  14. Konobeyev, A., J. Nucl. Mater., 186, 117, 1992.
  15. Messenger, S. R., NRL, Private communication, c.f. Mott differential scattering.
  16. Messenger, S. R., E. A. Burke, M. A. Xapsos, G. P. Summers, R. J. Walters, I. Jun, and T. M. Jordan, NIEL for heavy ions: An analytical approach, IEEE Trans. Nucl. Sci., Vol. 50, 1919, 2003.
  17. Messenger, S. R., E. A. Burke, J. Lorentzen, R. J. Walters, J. H. Warner, G. P. Summers, S. L. Murray, C. S. Murray, C. J. Crowley, N. A. Elkouh, The correlation of proton and neutron damage in photovoltaics, Proc. 31st IEEE Photovoltaic Specialists Conf., Lake Buena Vista, FL, Jan 3-7, 2005.
  18. Santin, G. et al, GRAS: A general-purpose 3-D modular simulation tool for space environment effects analysis, IEEE Trans. Nucl. Sc., Vol 52, No 6, 2294-2299, 2005.
  19. Summers, G. P., E. A. Burke, P. Shapiro, S. R. Messenger, R. J. Walters, Damage correlations in semiconductors exposed to Gamma, Electron and Proton Radiations, IEEE Trans. Nucl. Sc., Vol. 40, No. 6, 1372, Dec. 1993.
  20. Vasilescu, A. and G. Lindstroem, Notes on the fluence normalisation based on the NIEL scaling hypothesis, ROSE/TN/2000-01, 2000.

Last update: Thu, 16 Jun 2022