Radioprotection for interplanetary manned missions www.ge.infn.it/geant4/space/remsim Radioprotection for interplanetary manned missions R. Capra1, S. Guatelli1, B. Mascialino1, P. Nieminen2, M. G. Pia1 INFN, Genova, Italy ESA-ESTEC, Noordwijk, The Netherlands Geant4-SPENVIS Workshop 3-7 October 2005 Leuven, Belgium Thanks to ALENIA SPAZIO, C. Lobascio and team

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

Scope of the project Scope Vision The project deals with studies relevant to the AURORA programme Quantitative evaluation of the physical effects of space radiation in interplanetary manned missions Scope Vision A first quantitative analysis of the shielding properties of some innovative conceptual designs of vehicle and surface habitats Comparison among different shielding options

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

adopt a rigorous software process 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 adopt a rigorous software process

Summary of process products See http://www.ge.infn.it/geant4/space/remsim/environment/artifacts.html

Architecture Driven by goals deriving from the Vision Design an agile system capable of providing first indications for the evaluation of vehicle concepts and surface habitat configurations within a short time scale 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

REMSIM Simulation Design

Strategy of the Simulation Study Model the radiation spectrum according to current standards Simplified angular distribution to produce statistically meaningful results Vehicle concepts Surface habitats Astronaut Simplified geometrical configurations retaining the essential characteristics for dosimetry studies 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 Electromagnetic processes + Hadronic processes Evaluate energy deposit/dose in shielding configurations various shielding materials and thicknesses

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 100K primary particles, for each particle type Energy spectrum as in GCR/SPE Scaled according to fluxes for dose calculation GCR: p, α, heavy ions SPE particles: p and α at 1 AU at 1 AU Envelope of CREME96 1977 and CREME86 1975 solar minimum spectra Envelope of CREME96 October 1989 and August 1972 spectra Worst case assumption for a conservative evaluation

Vehicle concepts SIH - Simplified Inflatable Habitat Two (simplified) options of vehicles studied Simplified Rigid Habitat A layer of Al (structure element of the ISS) Simplified Inflatable Habitat 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 Materials and thicknesses by ALENIA SPAZIO The Geant4 geometry model retains the essential characteristics of the vehicle concept relevant for a dosimetry study

Surface Habitats Use of local material Sketch and sizes by ALENIA SPAZIO 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

Astronaut Phantom The Astronaut is approximated as a phantom 30 cm Z 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 30 cm Z 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

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)

Selection of Geant4 Hadronic Physics Models Hadronic Physics for protons and α as incident particles Hadronic inelastic process Binary set Bertini 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 ) ( 2.5 GeV < E < 25. GeV ) High energy range ( 20. GeV < E < 100. GeV ) Quark Gluon String Model + hadronic elastic process

Study of vehicle concepts inflatable habitat 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 Configurations 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

Generating primary particles SIH + 10 cm water First step: Generate GCR particles with the entire spectrum Second step: 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 GCR p with 5 GeV < E < 30 GeV

Electromagnetic and hadronic interactions 100 k events GCR vacuum air phantom multilayer - SIH 10 cm water shielding e.m. physics e.m. + Bertini set e.m. + Binary set GCR p 100 k events e.m. physics e.m. + Binary ion set Adding the hadronic interactions on top of the e.m. interactions increase the energy deposit in the phantom by ~ 25 % GCR α The contribution of the hadronic interactions looks negligible in the calculation of the energy deposit

Simulation results SIH + 10 cm water shielding 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 GCR p Hadronic contribution E.M. contribution

700 MeV/nucl < E < 30GeV/nucl Simulation results SIH + 10 cm water shielding E. M. physics E. M. physics + hadronic physics GCR α 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

e.m. physics + Bertini set GCR vacuum air phantom multilayer - SIH water / poly shielding Shielding materials Comparison between Water Polyethylene Equivalent shielding results Energy deposit given by slices of the GCR p spectrum GCR p 100 k events e.m. physics + Bertini set e.m. physics only 10 cm water 10 cm polyethylene

Shielding thickness 100 k events 10 cm water 5 cm water 10 cm water GCR vacuum air phantom multilayer - SIH 5 / 10 cm water shielding Shielding thickness 100 k events e.m. physics+ Bertini set GCR p 10 cm water 5 cm water GCR α e.m. physics+ hadronic physics 10 cm water 5 cm water Doubling the shielding thickness decreases the energy deposit by ~10% Doubling the shielding thickness decreases the energy deposit ~ 15% 100 k events

Comparison of inflatable and rigid habitat concepts GCR vacuum air phantom Al structure 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 100 k events 2.15 cm Al 10 cm water 5 cm water 4 cm Al GCR p

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 α GCR p

Effects of cosmic ray components GCR vacuum air phantom multilayer - SIH 10 cm water shielding α O-16 C-12 Si-28 Fe-52 e.m. physics processes only Protons Relative contribution to the equivalent dose from some cosmic rays components Particle Equivalent dose (mSv) Protons 1. α 0.86 C-12 0.115 O-16 0.16 Si-28 0.06 Fe-52 0.106 Depth in the phantom (cm) 100 k events The dose contributions from proton and α GCR components result significantly larger than for other ions

SPE shelter model Geant4 model SIH 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 Shelter shielding multilayer phantom Incident radiation vacuum air SPE shelter Geant4 model Approach: Study the e.m. contribution to the energy deposit Add on top the hadronic contribution

SPE: Energy deposit in SIH + 10 cm water configuration phantom SIH + 10 cm water SPE p,α Z 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

Strategy SPE p,α The shelter shields water phantom Strategy SPE p,α SIH + 10 cm water Shelter Z 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) Energy deposit (MeV) with respect to the depth in the phantom (cm) The shelter shields ~ 50% of the energy deposited by GCR p ~ 67 % of the energy deposited by GCR α escaping the SIH shielding E < 400 MeV E > 400 MeV Sum of the two contributions

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

Planetary surface habitats – Moon - SPE SPE p – 0.5 m roof 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 e.m. + hadronic physics (Bertini set) SPE α– 0.5 m roof SPE p – 3.5 m thick roof SPE α – 3.5 m thick roof 100 k events Energy deposit in the phantom given by Solar Particle protons and α particles

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

Future Latest development: the water phantom has been replaced by GCR p, 106 events phantom 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