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www.ge.infn.it/geant4/space/remsim. Radioprotection for interplanetary manned missions. R. Capra 1 , S. Guatelli 1 , B. Mascialino 1 , P. Nieminen 2 , M. G. Pia 1 INFN, Genova, Italy ESA-ESTEC, Noordwijk, The Netherlands. Geant4-SPENVIS Workshop 3-7 October 2005 Leuven, Belgium.

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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
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 of the project

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 firstquantitative analysis of the shielding properties of some innovative conceptual designs of vehicle and surface habitats

Comparison among different shielding options


Software strategy
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


Software process
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
Summary of process products

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


Architecture
Architecture

Driven by goals deriving from the Vision

  • Design an agilesystem

    • 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



Strategy of the simulation study

Vehicle concepts

Surface habitats

Astronaut

Electromagnetic processes

+ Hadronic processes

Strategy of the Simulation Study

  • Model the radiation spectrum according to current standards

    • Simplified angular distribution to produce statistically meaningful results

  • 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

  • Simplified geometrical configurations

  • retaining the essential characteristics for dosimetry studies

  • Evaluate energy deposit/dose in shielding configurations

    • various shielding materials and thicknesses


Space radiation environment
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

Vehicle concepts

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

Sketch and sizes by ALENIA SPAZIO

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


Astronaut phantom

30 cm

Z

Astronaut Phantom

  • The Astronaut is approximated as a phantom

    • a waterbox, 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

  • 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
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
Selection of Geant4 Hadronic Physics Models

Hadronic Physics for protons and α as incident particles

+ hadronic elastic process


Study of vehicle concepts

vacuum

air

GCR particles

shielding

phantom

multilayer - SIH

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

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
Generating primary particles

SIH + 10 cm water

GCR p

  • 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 with

5 GeV < E < 30 GeV


Electromagnetic and hadronic interactions

vacuum

air

e.m. physics

e.m. + Bertini set

e.m. + Binary set

GCR

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

10 cm water

shielding

phantom

multilayer - SIH

Electromagnetic and hadronic interactions

100 k events

GCR p

100 k events

e.m. physics

e.m. + Binary ion set

GCR α

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


Simulation results sih 10 cm water shielding
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


E. M. physics

E. M. physics + hadronic physics

Simulation results SIH + 10 cm water shielding

  • Total energy deposit in the phantomfor 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

GCR α


Shielding materials

vacuum

air

GCR

water / poly

shielding

phantom

multilayer - SIH

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

vacuum

air

GCR

5 / 10 cm water

shielding

phantom

multilayer - SIH

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%

100 k events

Doubling the shielding thickness decreases the energy deposit ~ 15%


Comparison of inflatable and rigid habitat concepts

vacuum

air

GCR

2.15 cm Al

5 cm water

phantom

10 cm water

4 cm Al

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

GCR p


Comparison sih 10 cm water al

SIH + 10 cm water

4 cm Al

Comparison: SIH + 10 cm water / Al

  • Total energy deposit in the phantomfor every slice of the spectrum

  • No difference between SIH + 10 cm water and 4 cm Al

GCR α

GCR p


Effects of cosmic ray components

α

vacuum

air

O-16

C-12

GCR

Fe-52

Si-28

10 cm water

shielding

phantom

multilayer - SIH

Effects of cosmic ray components

Protons

e.m. physics processes only

Relative contribution to the equivalent dose from some cosmic rays components

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

shielding

vacuum

air

Incident

radiation

SPE shelter

phantom

multilayer

shielding

SIH

SPE shelter model

  • 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

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

Z

water

phantom

SPE p,α

SIH

+ 10 cm water

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

water

phantom

Strategy

SPE p,α

SIH

+ 10 cm water

Shelter

Z

The shelter shields

  • ~ 50% of the energy deposited by GCR p

  • ~ 67 % of the energy deposited by GCR α

    escaping the SIH shielding

Observation:

SPE p and α with E > 130 MeV/nucl reach the shelter

SPE p and αwith 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)

E < 400 MeV

E > 400 MeV

Sum of the two contributions


Moon surface habitats

x = 0 - 3 m roof thickness

Add a log on top with variable height x

vacuum

moon

soil

GCR

SPE

beam

x

Phantom

Moon surface habitats

Moon as an intermediate step in the exploration of Mars

Dangerous exposure

to Solar Particle Events

4 cm Al

4 cm Al

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

SPE α– 0.5 m roof

SPE p – 3.5 m thick roof

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

e.m. + hadronic physics (Bertini set)

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
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

phantom

GCR p, 106 events

Future

  • 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


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