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

Monte Carlo 200518-21 April 2005

Chattanooga, TN, USA

www.ge.infn.it/geant4/space/remsim

Radioprotection for interplanetary Radioprotection for interplanetary manned missionsmanned missions

S. Guatelli1, B. Mascialino1, P. Nieminen2, M. G. Pia1

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

ScopeScope

VisionVision A first quantitative analysisquantitative analysis of the shielding properties shielding properties of some innovative conceptual designs of vehicle vehicle and

surface habitatssurface 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

QualityQuality and reliabilityreliability 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, 18th April, Monte Carlo 2005

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

Summary of process products

See http://www.ge.infn.it/geant4/space/remsim/environment/artifacts.html

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

Architecture

Driven by goals deriving from the VisionVision

Design an agileagile system– capable of providing first indications for the evaluation of vehicle

concepts and surface habitat configurations within a short time scale

Design an extensibleextensible 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

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

Simplified geometrical geometrical configurationsconfigurations retaining the essential characteristicsessential characteristics for dosimetry studies

Electromagnetic processes

+ Hadronic processes

Model the radiation spectrum according to current standards– Simplified angular distribution to produce statistically meaningful results

Evaluate energy deposit/doseenergy 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 environmentGalactic 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 αGCR: p, α, heavy ions

Envelope of CREME96 October 1989 and August 1972 spectra

at 1 AU at 1 AU

Worst case assumption for a conservative evaluationWorst case assumption for a conservative evaluation

100K primary particles, for each particle typeEnergy 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

The dosimetry studies performed in REMSIM must be considered as a first indicationfirst 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 marketModels 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 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 rangeLow 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 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

ConfigurationsConfigurations

inflatable habitat

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

Electromagnetic and hadronic interactions

e.m. physicse.m. + Bertini sete.m. + Binary set

GCR

vacuum air

phantommultilayer - SIH 10 cm water

shieldingGCR p

100 k events

100 k events

GCR α

Adding the hadronic interactions on top of the e.m. interactions increase the energy increase the energy deposit in the phantom by ~ 25 %deposit in the phantom by ~ 25 %

The contribution of the hadronic interactions looks negligible in the calculation of the energy deposit

e.m. physicse.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 water10 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 thicknessGCR

vacuum air

phantom

multilayer - SIH 5 / 10 cm watershielding

10 cm water5 cm water

GCR p

100 k eventse.m. physics+ Bertini set

e.m. physics+ hadronic physics

10 cm water5 cm water

GCR α

100 k events

Doubling the shielding thickness decreases the energy deposit by ~10%~10%

Doubling the shielding thickness decreases the energy deposit ~ 15%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 ProtonsProtons

αα

O-16O-16

C-12C-12

Si-28Si-28Fe-52Fe-52

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

Relative contribution to the equivalent dose from some cosmic

rays components

e.m. physics processes only

100 k events

GCR

vacuum air

phantommultilayer - 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

Incidentradiation

vacuum airSPE shelter

SPE shelter modelInflatable 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:100 K events:

4 protons reach the astronaut4 protons reach the astronaut All All αα particles are stopped particles are stopped Study the energy deposit of SPE with E > 300 MeV/nuclStudy 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 moonsoil

GCR SPEbeam

Phantom

x = 0 - 3 m roof thickness

Energy deposit (GeV)in the phantom vs roof thickness (m)

4 cm Al

4 cm Al

100 k events

GCR pGCR 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

ConclusionsThe 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