S. Guatelli, M.G. Pia – INFN Sezione di Genova Monte Carlo April 2005 Chattanooga, TN, USA Radioprotection 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

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

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 takes place in the framework of the AURORA programme of the European Space Agency

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

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 Software process adopt a rigorous software process Talk: Experience with software process in physics projects, 18 th April, Monte Carlo 2005

S. Guatelli, M.G. Pia – INFN Sezione di Genova Summary of process products See

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

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

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

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 CREME and CREME 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

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

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

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

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

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, submitted to IEEE Transactions on Nuclear Science 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, 20th April, Monte Carlo 2005

S. Guatelli, M.G. Pia – INFN Sezione di Genova Intrinsic complexity of hadronic physics Geant4 hadronic physics is still 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 quantitative estimates 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

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

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

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

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

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%

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

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 O Si Fe 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

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

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 Geant4 model Shelter SIH Approach: Study the e.m. contribution to the energy deposit Add on top the hadronic contribution

S. Guatelli, M.G. Pia – INFN Sezione di Genova Results – SPE, SIH + 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 GCR protons SPE p SPE α SPE E > 300 MeV / nucl e.m. + hadronic physics – Bertini set 100 K events: 4 protons reach the astronaut 4 protons reach the astronaut All α particles are stopped All α particles are stopped Study the energy deposit of SPE with E > 300 MeV/nucl

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 = 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

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 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

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

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 radioprotection 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 radioprotection studies 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