radioprotection for interplanetary manned missions

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

Geant4-SPENVIS Workshop3-7 October 2005Leuven, Belgium

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

Radioprotection for interplanetary Radioprotection for interplanetary manned missionsmanned missions

R. Capra1, S. Guatelli1, B. Mascialino1, P. Nieminen2, M. G. Pia1

1. INFN, Genova, Italy

2. ESA-ESTEC, Noordwijk, The Netherlands

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

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 deals with studies relevant to the AURORA programme


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


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


Summary of process products

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


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


REMSIM Simulation Design


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


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


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


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


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


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 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


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


Generating primary particles

First step:– Generate GCR particles with the

entire spectrum

Second step:– Generate GCR p and α with defined defined

slices of the spectrum: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


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


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 GeV700 MeV < E < 30 GeV

Simulation results SIH + 10 cm water shielding

GCR p

E.M. contribution

Hadronic contribution


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/nucl700 MeV/nucl < E < 30GeV/nucl

Simulation results SIH + 10 cm water shielding

GCR α

E. M. physicsE. M. physics + hadronic physics


Shielding materialsComparison between

– Water– Polyethylene

Equivalent shielding results

GCR

vacuum air

phantommultilayer - SIH water / poly

shielding

10 cm water10 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


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%


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


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 AlSIH + 10 cm water4 cm Al

GCR pGCR α


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

Depth in the phantom (cm)


shielding

multilayer shielding

phantom

Incidentradiation

vacuum airSPE shelter

SPE shelter modelInflatable 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


SPE: Energy deposit in SIH + 10 cm water configuration

100K SPE p and αE.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

waterphantom

SIH+ 10 cm water

SPE p,α

Z


Strategy

Observation: SPE p and α with E > 130 MeV/nucl reach the shelterSPE p and α with E > 400 MeV/nucl reach the phantom ( < 0.3% of the entire spectrum)

waterphantom

SIH+ 10 cm water

SPE p,α

ZShelter

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 MeVE > 400 MeV

Sum of the two contributionsSum of the two contributions


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


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


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 an anthropomorphicphantom

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, 106 events

phantom

radioprotection for interplanetary manned missions

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