REMSIM Geant4 simulation ESA/ESTEC 3-4 May 2004

1. REMSIM Geant4 simulationESA/ESTEC3-4 May 2004 S. Guatelli, M.G. Pia INFN Genova, Italy

2. Vision • Geant4 REMSIM simulation performs a quantitative evaluation of the physical effects of space radiation • Its main objectives are : • a critical analysis of Geant4 tools necessary for this kind of study • first dosimetric evaluation of proposed shielding options in vehicle and surface habitat concepts

3. Vehicle concepts Moon surface habitats Electromagnetic physics + hadronic physics Strategy The process consisted of a series of iterations • Each iteration adds: • a refinement in the experimental model • the usage of further Geant4 functionality • Simplified geometrical configurations Essentialcharacteristics for dosimetric studies kept • Physics processes

4. Outline • Model of the radiation environment • Model of vehicle concepts • Simulation with electromagnetic processes • Evaluation of GCR and SPE shielding options • Same simulation with hadronic physics on top • Model of moon surface habitat concepts • Simulation with electromagnetic processes • Evaluation of GCR and SPE shielding options • Same simulation with hadronic physics on top • Parallelisation of the REMSIM Geant4 application • Conclusion

5. Implementation • Elements of the REMSIM application • Primary Particle • Geometry • Astronaut • Physics • Messengers • Visualisation • Analysis

6. Primary Particles • Definition of primary particle type, primary vertex and momentum • Primary particles can be originated in different conditions • The user can choose the type of particle • The user can originate beams with defined energy, initial position and initial direction • The user can choose to originate particles with a defined energy spectrum • The user can originate particles from a hemisphere

7. Geometry • Each geometrical component is defined by means of • Shape • Material • Position in the experimental set-up • Sensitivity • The user can choose different set-ups • Vehicle concepts • Moon habitat concepts • The implementation of each geometrical component has been tested with DAVID to verify geometry consistency

8. Materials • A material can be defined as • Element (Z, A, density) • Mixture of elements (density and fraction in mass of the elements) • A heterogeneous materials (mixture of materials) • Material with Z, A, pressure, temperature and density

9. 30 cm Z Astronaut • The Astronaut is the volume where the energy deposit is collected • The energy deposit is given by the primary particles and all the secondaries originated • The Astronaut is a water box • The Astronaut is sliced in voxels

10. Particles Component concerning the instantiation of particles • Some particles are pre-defined in the Geant4 simulation toolkit (for example protons, alpha, e+, e-, photons, etc.) • Ions have been defined through the information of Z, A and mass • C-12, O-16, Si-28, Fe-52 • Use of G4VIonInterface

11. Physics • Selection of processes is a mandatory task of the user • Processes are activated for each particle involved • Electromagnetic and hadronic processes are activated • The user can choose the processes and the physics models interactively • The threshold of production of secondaries must be fixed

12. Messengers • Messengers allow to change simulation parameters interactively • Geant4 REMSIM application has messengers to control • Visualisation • Primary particles in terms of initial energy, position and direction • Geometry set-up

13. Visualisation • The Geant4 REMSIM application is interfaced with visualisation external tools • The user can visualise the experimental set-up with different visualisation packages • OpenGL • DAWN • vrml

14. Analysis • The Geant4 REMSIM application is interfaced to external analysis tools • AIDA 3.0 and Anaphe 5.0.5 • It is possible to store the results of the simulation in histograms, ntuples, data vectors • Output: xml or hbook files

15. Data Analysis AIDA Histograms Ntuples Functions Data vectors Fit Plotting Abstract Interfaces for Data Analysis Lizard AIDA allows to use different concrete analysis tools • Interactive analysis • OO Technology • Based on Python • AIDA compliant • OO technology • Developed in LHC domain

16. Space radiation environment Selected space radiation components: • Galactic Cosmic rays • Protons, alpha particles and heavy ions • Solar Particle Events • Protons and alpha particles Heavy ions considered: C-12, O-16, Si-28, Fe-52 The ions are completely stripped

17. GCR spectra • GCR and SPE spectra provided by ALENIA-SPAZIO • The energy spectra are predicted for 1 AU • The spectra correspond to the solar minimum activity Envelope of CREME96 1977 and CRÈME 86 1975 solar minimum spectra

18. SPE particle events • SPE protons and alpha particles are modeled • ALENIA-SPAZIO provided the energy spectra of SPE particles at 1 AU. Envelope of CREME96 October 1989 and August 1972 spectra

19. Strategy • GCR energy spectra are formatted in ASCII files to be loaded • The flux is used as probability to generate a particle with a given energy • Every energy spectrum is normalised (the sum of the probabilities must be one) • The relative probability of generating protons, alpha particles and ions is calculated • For 100 GCR protons • Alpha ~4 • C12 ~0.127 • O16 ~0.127 • Si28~ 0.026 • Fe52 ~0.0186

20. Selection of physics processes • Electromagnetic physics • Hadronic physics

21. EM Physics in Geant4 • Geant4 offers alternative electromagnetic physics models • Standard • LowEnergy • Physics models validated in comparison to available experimental data and reference protocol data • REMSIM activity profits of the extensive investment of time and manpower in Geant4 physics development and validation • 10 INFN physicists involved • Many Geant4 collaborators involved in physics development and validation from many years

22. Alternative models for the same physics process High energy models fundamental for LHC experiments, cosmic ray experiments etc. Low energy models fundamental for space and medical applications, neutrino experiments, antimatter spectroscopy etc. multiple scattering Bremsstrahlung ionisation annihilation photoelectric effect Compton scattering Rayleigh effect gamma conversion e+e- pair production synchrotron radiation transition radiation Cherenkov refraction reflection absorption scintillation fluorescence Auger Standard Package LowEnergy Package Geant4 e.m. package Muon Package Optical photon Package • It handles • electrons and positrons • gamma, X-ray and optical photons • muons • charged hadrons • ions Geant4 Electromagnetic Physics

23. shell effects Bragg peak protons antiprotons e, down to 250 eV ions Based on EPDL97, EEDL and EADL evaluated data libraries Photon attenuation Hadron and ionmodels based on Ziegler and ICRU data and parameterisations Low energy e.m. extensions Fundamental for neutrino/dark matter experiments, space and medical applications, antimatter spectroscopy etc.

24. Selection of electromagnetic processes • Low Energy Package • e-, photon, p, alpha particles, ions • Standard Package • e+ • muons

25. Verification of REMSIM Physics List • Proton and alpha Stopping Power and CSDA Range are calculated for materials of interest • Proton energy range of test: from 1 MeV to 10 GeV • Alpha energy range of test: from 1MeV to 1GeV • Comparison of the test results to ICRU Report 49

26. Summary of tests • Protons are generated in the center of a box, the box is filled with a given material • Experimental set-up: • EM Physics is activated • Ionisation • No multiple scattering • No fluctuations in energy loss • The threshold of production of secondaries is fixed to 100 Km • The maximum step allowed in the box is fixed • Materials under study: water, hydrogen, graphite, nitrogen, oxygen, aluminum, silicon, iron. Same as NIST

27. Results water

28. Results hydrogen

29. Results graphite

30. Results oxygen

31. Results aluminum

32. Results silicon

33. Results nitrogen

34. Results iron

35. Analysis of tests • Uncertainties for Stopping Power given by ICRU Report 49: • Elements • E<1 MeV : ~5% • E>1 MeV : ~2% • Compounds : • E< 1MeV : ~5% • E>1 MeV : 4% • The electromagnetic physics models chosen are accurate: the differences between test results and ICRU Report 49 are compatible with ICRU errors bars • In graphite for E =2 MeV, the difference between Geant4 test and ICRU Report 49 is about ~4%

36. Alpha EM Physics verification Same experimental set-up conditions as proton electromagnetic physics verification

37. Results water

38. Results hydrogen

39. Results graphite

40. Results oxygen

41. Results nitrogen

42. Results aluminum

43. Results silicon

44. Results iron

45. Analysis of tests • Uncertainties of Stopping Power given by ICRU Report 49: • Elements • E<2 MeV : ~5% • E>2 MeV : ~2% • Compounds : • E< 2MeV : ~5% • E>2 MeV : 4% • The electromagnetic physics models chosen are accurate: the differences between test results and ICRU Report 49 errors are compatible • In graphite for 6MeV<E<10MeV, the difference between Geant4 test and ICRU Report 49 is about ~5%,6%

46. SP and CSDA Range for proton1MeV – 100 GeV in water

47. SP and CSDA Range for alpha1 MeV – 100 GeV in water

48. SP and CSDA Range for ions1 MeV – 100 GeV in water

49. Dosimetric studies in vehicle concepts • Optimisation of the simulation • Dose calculation accuracy versus performance • Preliminary study with monochromatic beams of protons, alpha, ions impinging on vehicle concepts • GCR particles interacting with vehicle concepts • Study of various shielding options

50. incident radiation Z 30 cm Optimisation of the performance Scope: optimise the performance of the simulation without affecting the accuracy of the dose calculation • Optimisation of the max step allowed in the geometry • Optimisation of the threshold of production of secondaries • Prerequisite: considerations on the Astronaut (sensitive detector where the energy deposit is collected) • Voxel = 1 cm thick slice along the z Axis • 30 voxels