1. S. Guatelli, M.G. Pia – INFN Sezione di Genova Geant4-SPENVIS Workshop 3-7 October 2005 Leuven, Belgium www.ge.infn.it/geant4/space/remsim Radioprotection for interplanetary manned missions R. Capra 1, S. Guatelli 1, B. Mascialino 1, P. Nieminen 2, M. G. Pia 1 1.INFN, Genova, Italy 2.ESA-ESTEC, Noordwijk, The Netherlands Thanks to ALENIA SPAZIO, C. Lobascio and team

2. S. Guatelli, M.G. Pia – INFN Sezione di Genova Context The study of the effects of space radiation on astronauts is an important concern of missions for the human exploration of the solar system The radiation hazard can be limited –selecting traveling periods and trajectories –providing adequate shielding in the transport vehicles and surface habitats

3. S. Guatelli, M.G. Pia – INFN Sezione di Genova Scope of the project Scope Vision quantitative analysisshielding properties vehicle surface habitats A first quantitative analysis of the shielding properties of some innovative conceptual designs of vehicle and surface habitats Comparison among different shielding options Quantitative evaluation of the physical effects of space radiation in interplanetary manned missions The project deals with studies relevant to the AURORA programme

4. S. Guatelli, M.G. Pia – INFN Sezione di Genova Software strategy The object oriented technology has been adopted –Suitable to long term application studies –Openness of the software to extensions and evolution –It facilitates the maintainability of the software over a long time scale Geant4 has been adopted as Simulation Toolkit because it is –Open source, general purpose Monte Carlo code for particle transport based on OO technology –Versatile to describe geometries and materials –It offers a rich set of physics models The data analysis is based on AIDA –Abstract interfaces make the software system independent from any concrete analysis tools –This strategy is meaningful for a long term project, subject to the future evolution of software tools

5. S. Guatelli, M.G. Pia – INFN Sezione di Genova Qualityreliability Quality and reliability of the software are essential requirements for a critical domain like radioprotection in space Iterative and incremental process model –Develop, extend and refine the software in a series of steps –Get a product with a concrete value and produce results at each step –Assess quality at each step Rational Unified Process (RUP) adopted as process framework –Mapped onto ISO 15504 Software process adopt a rigorous software process

6. S. Guatelli, M.G. Pia – INFN Sezione di Genova Summary of process products See http://www.ge.infn.it/geant4/space/remsim/environment/artifacts.htmlhttp://www.ge.infn.it/geant4/space/remsim/environment/artifacts.html

7. S. Guatelli, M.G. Pia – INFN Sezione di Genova Architecture Vision Driven by goals deriving from the Vision agile Design an agile system –capable of providing first indications for the evaluation of vehicle concepts and surface habitat configurations within a short time scale extensible Design an extensible system –capable of evolution for further more refined studies, without requiring changes to the kernel architecture Documented in the Software Architecture Document http://www.ge.infn.it/geant4/space/remsim/design/SAD_remsim.html

8. S. Guatelli, M.G. Pia – INFN Sezione di Genova REMSIM Simulation Design

9. S. Guatelli, M.G. Pia – INFN Sezione di Genova Physics Physics modeled by Geant4 –Select appropriate models from the Toolkit –Verify the accuracy of the physics models –Distinguish e.m. and hadronic contributions to the dose Strategy of the Simulation Study geometrical configurations Simplified geometrical configurations essential characteristics retaining the essential characteristics for dosimetry studies Electromagnetic processes + Hadronic processes Model the radiation spectrum according to current standards –Simplified angular distribution to produce statistically meaningful results energy deposit/dose Evaluate energy deposit/dose in shielding configurations –various shielding materials and thicknesses Vehicle concepts Surface habitats Astronaut

10. S. Guatelli, M.G. Pia – INFN Sezione di Genova Space radiation environment Galactic Cosmic Rays –Protons, α particles and heavy ions (C -12, O -16, Si - 28, Fe - 52) Solar Particle Events –Protons and α particles Envelope of CREME96 1977 and CREME86 1975 solar minimum spectra SPE particles: p and α GCR: p, α, heavy ions Envelope of CREME96 October 1989 and August 1972 spectra at 1 AU Worst case assumption for a conservative evaluation 100K primary particles, for each particle type Energy spectrum as in GCR/SPE Scaled according to fluxes for dose calculation

11. S. Guatelli, M.G. Pia – INFN Sezione di Genova Vehicle concepts The Geant4 geometry model retains the essential characteristics of the vehicle concept relevant for a dosimetry study Materials and thicknesses by ALENIA SPAZIO Modeled as a multilayer structure  MLI: external thermal protection blanket - Betacloth and Mylar  Meteoroid and debris protection - Nextel (bullet proof material) and open cell foam  Structural layer - Kevlar  Rebundant bladder - Polyethylene, polyacrylate, EVOH, kevlar, nomex SIH - Simplified Inflatable Habitat Simplified Rigid Habitat A layer of Al (structure element of the ISS) Two (simplified) options of vehicles studied Simplified Inflatable Habitat

12. S. Guatelli, M.G. Pia – INFN Sezione di Genova Surface Habitats Use of local material Cavity in the moon soil + covering heap The Geant4 model retains the essential characteristics of the surface habitat concept relevant to a dosimetric study Sketch and sizes by ALENIA SPAZIO

13. S. Guatelli, M.G. Pia – INFN Sezione di Genova Astronaut Phantom The phantom is the volume where the energy deposit is collected –The energy deposit is given by the primary particles and all the secondaries created 30 cm Z The Astronaut is approximated as a phantom –a water box, sliced into voxels along the axis perpendicular to the incident particles –the transversal size of the phantom is optimized to contain the shower generated by the interacting particles –the longitudinal size of the phantom is a “realistic” human body thickness

14. S. Guatelli, M.G. Pia – INFN Sezione di Genova Selection of Geant4 EM Physics Models Geant4 Low Energy Package for p, α, ions and their secondaries Geant4 Standard Package for positrons Verification of the Geant4 e.m. physics processes with respect to protocol data (NIST reference data) “Comparison of Geant4 electromagnetic physics models against the NIST reference data”, IEEE Transactions on Nuclear Science, vol. 52 (4), pp. 910-918, 2005 The electromagnetic physics models chosen are accurate Compatible with NIST data within NIST accuracy (p-value > 0.9)

15. S. Guatelli, M.G. Pia – INFN Sezione di Genova Selection of Geant4 Hadronic Physics Models Hadronic Physics for protons and α as incident particles Hadronic inelastic process Binary setBertini set Low energy range (cascade + precompound + nuclear deexcitation) Binary Cascade ( up to 10. GeV ) Bertini Cascade ( up to 3.2 GeV ) Intermediate energy range Low Energy Parameterised ( 8. GeV < E < 25. GeV ) Low Energy Parameterised ( 2.5 GeV < E < 25. GeV ) High energy range ( 20. GeV < E < 100. GeV ) Quark Gluon String Model + hadronic elastic process

16. S. Guatelli, M.G. Pia – INFN Sezione di Genova Study of vehicle concepts Incident spectrum of GCR particles Energy deposit in phantom due to electromagnetic interactions Add the hadronic physics contribution on top GCR particles vacuum air phantom multilayer - SIH shielding Geant4 model SIH only, no shielding SIH + 10 cm water / polyethylene shielding SIH + 5 cm water / polyethylene shielding 2.15 cm aluminum structure 4 cm aluminum structure Configurations inflatable habitat

17. S. Guatelli, M.G. Pia – INFN Sezione di Genova Generating primary particles First step: –Generate GCR particles with the entire spectrum Second step: defined slices of the spectrum: –Generate GCR p and α with defined slices of the spectrum: 130 MeV/ nucl < E < 700 MeV / nucl 700 MeV/ nucl < E < 5 GeV / nucl 5 GeV / nucl < E < 30 GeV / nucl E > 30 GeV / nucl –Study the energy deposit in the phantom with respect to the slice of the energy spectrum of the primaries GCR p SIH + 10 cm water GCR p with 5 GeV < E < 30 GeV

18. S. Guatelli, M.G. Pia – INFN Sezione di Genova Electromagnetic and hadronic interactions e.m. physics e.m. + Bertini set e.m. + Binary set GCR vacuum air phantom multilayer - SIH 10 cm water shielding GCR p 100 k events GCR α increase the energy deposit in the phantom by ~ 25 % Adding the hadronic interactions on top of the e.m. interactions increase the energy deposit in the phantom by ~ 25 % The contribution of the hadronic interactions looks negligible in the calculation of the energy deposit e.m. physics e.m. + Binary ion set

19. S. Guatelli, M.G. Pia – INFN Sezione di Genova Total energy deposit in the phantom of each slice of the energy spectrum The largest contribution derives from the intermediate energy range: 700 MeV < E < 30 GeV Simulation results SIH + 10 cm water shielding GCR p E.M. contribution Hadronic contribution

20. S. Guatelli, M.G. Pia – INFN Sezione di Genova Total energy deposit in the phantom for every slice of the spectrum Each contribution is weighted for the probability of the spectrum slice The largest contribution derives from: 700 MeV/nucl < E < 30GeV/nucl Simulation results SIH + 10 cm water shielding GCR α E. M. physics E. M. physics + hadronic physics

21. S. Guatelli, M.G. Pia – INFN Sezione di Genova Shielding materials Comparison between –Water –Polyethylene Equivalent shielding results GCR vacuum air phantom multilayer - SIH water / poly shielding 10 cm water 10 cm polyethylene e.m. physics + Bertini set e.m. physics only GCR p 100 k events Energy deposit given by slices of the GCR p spectrum

22. S. Guatelli, M.G. Pia – INFN Sezione di Genova Shielding thickness GCR vacuum air phantom multilayer - SIH 5 / 10 cm water shielding 10 cm water 5 cm water GCR p 100 k events e.m. physics+ Bertini set e.m. physics+ hadronic physics 10 cm water 5 cm water GCR α 100 k events ~10% Doubling the shielding thickness decreases the energy deposit by ~10% 15% Doubling the shielding thickness decreases the energy deposit ~ 15%

23. S. Guatelli, M.G. Pia – INFN Sezione di Genova Comparison of inflatable and rigid habitat concepts Aluminum layer replacing the inflatable habitat –based on similar structures as in the ISS Two hypotheses of Al thickness –4 cm Al –2.15 cm Al The shielding performance of the inflatable habitat is equivalent to conventional solutions GCR vacuum air phantom Al structure 2.15 cm Al 10 cm water 5 cm water 4 cm Al 100 k events GCR p

24. S. Guatelli, M.G. Pia – INFN Sezione di Genova Comparison: SIH + 10 cm water / Al Total energy deposit in the phantom for every slice of the spectrum No difference between SIH + 10 cm water and 4 cm Al SIH + 10 cm water 4 cm Al GCR p GCR α

25. S. Guatelli, M.G. Pia – INFN Sezione di Genova The dose contributions from proton and α GCR components result significantly larger than for other ions Effects of cosmic ray components Protons α O-16 C-12 Si-28 Fe-52 ParticleEquivalent dose (mSv) Protons1. α0.86 C-120.115 O-160.16 Si-280.06 Fe-520.106 Relative contribution to the equivalent dose from some cosmic rays components e.m. physics processes only 100 k events GCR vacuum air phantom multilayer - SIH 10 cm water shielding Depth in the phantom (cm)

26. S. Guatelli, M.G. Pia – INFN Sezione di Genova shielding multilayer shielding phantom Incident radiation vacuumair SPE shelter SPE shelter model Inflatable habitat + additional 10. cm water shielding + SPE shelter Comparison of the energy deposit in the cases: –SIH + 10 cm water shielding –SIH + 10 cm water shielding + SPE shelter Geant4 model Shelter SIH Approach:  Study the e.m. contribution to the energy deposit  Add on top the hadronic contribution

27. S. Guatelli, M.G. Pia – INFN Sezione di Genova SPE: Energy deposit in SIH + 10 cm water configuration 100K SPE p and α E.m. + hadronic physics (Bertini set) 68 SPE protons reach the phantom 14 SPE alpha reach the phantom E > 130 MeV/nucl reach the astronaut (~2.8% of the entire spectrum) The contribute of alpha is not weighted water phantom SIH + 10 cm water SPE p,α Z

28. S. Guatelli, M.G. Pia – INFN Sezione di Genova Strategy Observation: SPE p and α with E > 130 MeV/nucl reach the shelter SPE p and α with E > 400 MeV/nucl reach the phantom ( < 0.3% of the entire spectrum) water phantom SIH + 10 cm water SPE p,α Z Shelter The shelter shields ~ 50% of the energy deposited by GCR p ~ 67 % of the energy deposited by GCR α escaping the SIH shielding Energy deposit (MeV) with respect to the depth in the phantom (cm) E < 400 MeV E > 400 MeV Sum of the two contributions

29. S. Guatelli, M.G. Pia – INFN Sezione di Genova Moon surface habitats Add a log on top with variable height x x vacuum moon soil GCR SPE beam Phantom x = 0 - 3 m roof thickness Energy deposit (GeV) in the phantom vs roof thickness (m) 4 cm Al 100 k events GCR p GCR α e.m. + hadronic physics (Bertini set) Moon as an intermediate step in the exploration of Mars Dangerous exposure to Solar Particle Events

30. S. Guatelli, M.G. Pia – INFN Sezione di Genova Planetary surface habitats – Moon - SPE E < 300 MeV stopped by the shielding Energy deposit resulting from SPE with E > 300 MeV / nucl The energy deposit of SPE α is weighted according to the flux with respect to SPE protons The roof limits the exposure to SPE particles SPE p – 0.5 m roof SPE α– 0.5 m roof SPE p – 3.5 m thick roof SPE α – 3.5 m thick roof e.m. + hadronic physics (Bertini set) 100 k events Energy deposit in the phantom given by Solar Particle protons and α particles

31. S. Guatelli, M.G. Pia – INFN Sezione di Genova Comments on the results Simplified Inflatable Habitat + shielding –water / polyethylene are equivalent as shielding material –optimisation of shielding thickness is needed –hadronic interactions are significant –an additional shielding layer, enclosing a special shelter zone, is effective against SPE The shielding properties of an inflatable habitat are comparable to the ones of a conventional aluminum structure Moon Habitat –thick soil roof limits GCR and SPE exposure –its shielding capabilities against GCR are better than conventional Al structures similar to ISS

32. S. Guatelli, M.G. Pia – INFN Sezione di Genova Future Latest development: the water phantom has been replaced by an anthropomorphic phantom Next steps: –3D model of the experimental set-up –Isotropic generation of GCR and SPE –Calculation of the energy deposit and of the dose in the organs of the anthropomorphic phantom GCR p, 10 6 events phantom