1. S. Guatelli, M.G. Pia – INFN Sezione di Genova Monte Carlo 2005 18-21 April 2005 www.ge.infn.it/geant4/space/remsim Radiation protection for interplanetary manned missions S. Guatelli 1, B. Mascialino 1, P. Nieminen 2, M. G. Pia 1 1.INFN, Genova, Italy 2.ESA-ESTEC, Noordwijk, The Netherlands

2. S. Guatelli, M.G. Pia – INFN Sezione di Genova Context Planetary exploration has grown into a major player in the vision of space science organizations like ESA and NASA 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 The ESA REMSIM project A project in the European AURORA programme –Protection of the crew from the interplanetary space radiation –Space radiation monitoring –Design of the crew habitats –Trajectories from the Earth to Mars to limit the exposure of astronauts to harmful effects of radiation Transfer vehicles –compare the shielding properties of an inflatable habitat w.r.t. a conventional rigid structure –materials and thicknesses of shielding structures Habitats on a planetary surface –using local resources as building material Radiation environment

4. S. Guatelli, M.G. Pia – INFN Sezione di Genova The REMSIM Simulation Project Vision quantitative analysisshielding properties vehicle surface habitats A first quantitative analysis of the shielding properties of some conceptual designs of vehicle and surface habitats Comparison among different shielding options A project in the framework of the AURORA programme of the European Space Agency

5. S. Guatelli, M.G. Pia – INFN Sezione di Genova Software strategy Object oriented technology –suitable to long term studies –openness of the software to extensions and evolution –it facilitates the maintainability of the software over a long time scale Geant4 as Simulation Toolkit –open source, general purpose Monte Carlo code for particle transport based on OO technology –versatile to describe geometries and materials –rich set of physics models The data analysis is based on AIDA –abstract interfaces make the software system independent from any concrete analysis tools –strategy meaningful for a long term project, subject to the future evolution of software tools

6. 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 Talk: Experience with software process in physics projects, 18 April, Monte Carlo 2005

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

8. 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

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

10. 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

11. 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

12. S. Guatelli, M.G. Pia – INFN Sezione di Genova Vehicle concepts The Geant4 geometry model retains the essential characteristics of the vehicle concept relevant to a dosimetry study Materials and thicknesses by ALENIA SPAZIO A multilayer structure consisting of:  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

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

14. 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

15. 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, ICRU Report 49) “Comparison of Geant4 electromagnetic physics models against the NIST reference data”, submitted to IEEE Trans. Nucl. Sci. The electromagnetic physics models chosen are accurate Compatible with NIST data within NIST accuracy (p-value > 0.9) Talk: Precision Validation of Geant4 electromagnetic physics, 20 April, Monte Carlo 2005

16. S. Guatelli, M.G. Pia – INFN Sezione di Genova Intrinsic complexity of hadronic physics Geant4 hadronic physics is still the object of validation studies first indication The dosimetry studies performed in REMSIM must be considered as a first indication of the hadronic contribution rather than as a quantitative estimate Geant4 hadronic physics Complementary and alternative models Parameterised, data driven and theory driven models The most complete hadronic simulation kit available on the market Models for p and α Hadronic models for ions in progress

17. S. Guatelli, M.G. Pia – INFN Sezione di Genova Selection of Geant4 Hadronic Physics Models Hadronic inelastic process Binary setBertini set Low energy range (intra-nuclear transport, pre-equilibrium, nuclear deexcitation) Binary CascadeBertini Cascade 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

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 Shielding materials 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

20. 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%

21. 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

22. 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

23. S. Guatelli, M.G. Pia – INFN Sezione di Genova High energy cosmic ray tail The relative contribution from hadronic interactions w.r.t. electromagnetic ones increases at higher cosmic ray energies BUT The high energy component represents a small fraction of the cosmic ray spectrum GCR p E> 30 GeV 8 % 100 k events e.m. physics + Bertini set e.m. physics only GCR vacuum air phantom multilayer - SIH 10 cm water shielding Energy deposit GCR protons E > 30 GeV

24. 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 + 70 cm water SPE shelter Geant4 model Shelter SIH

25. S. Guatelli, M.G. Pia – INFN Sezione di Genova SPE, Inflatable habitat + shielding + shelter SPE energy deposit (MeV) vs depth (cm) e.m. + hadronic physics The SPE α contribution is weighted according to the spectrum with respect to protons SPE p SPE α SPE E > 300 MeV / nucl e.m. + hadronic physics – Bertini set 100 K events:  4 protons reach the astronaut  All α particles are stopped Study the energy deposit of SPE with E > 300 MeV/nucl

26. 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 in the phantom vs. roof thickness 4 cm Al 100 k events GCR p GCR α e.m. + hadronic physics (Bertini set) The moon as an intermediate step in the exploration of Mars

27. S. Guatelli, M.G. Pia – INFN Sezione di Genova Planetary surface habitats – Moon - SPE Energy deposit resulting from SPE with E > 300 MeV / nucl The energy deposit of SPE  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

28. 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

29. S. Guatelli, M.G. Pia – INFN Sezione di Genova Conclusions The REMSIM project represents the first attempt in the European AURORA programme to estimate the radiation protection of astronauts quantitatively REMSIM has demonstrated the feasibility of rigorous simulation studies for interplanetary manned missions, based on modern software tools and technologies The advanced software technologies adopted make the REMSIM simulation suitable to future extensions and evolution for more detailed radiation protection studies More details in a paper on Geant4 REMSIM Simulation in preparation Thanks to all REMSIM team members for their collaboration –in particular to V. Guarnieri, C. Lobascio, P. Parodi and R. Rampini