Monte Carlo 2005

1
Radioprotection for interplanetary manned missions

• S. Guatelli1, B. Mascialino1, P. Nieminen2, M. G.
  Pia1
• INFN, Genova, Italy
• ESA-ESTEC, Noordwijk, The Netherlands

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

• Monte Carlo 2005
• 18-21 April 2005
• Chattanooga, TN, USA

2
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

3
Scope of the project
The project takes place in the framework of the
AURORA programme of the European Space Agency
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
4
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

5
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
Talk Experience with software process in physics
projects, 18th April, Monte Carlo 2005
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Summary of process products
See http//www.ge.infn.it/geant4/space/remsim/envi
ronment/artifacts.html
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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/S
  AD_remsim.html

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REMSIM Simulation Design
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Strategy of the Simulation Study

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

• 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

• Evaluate energy deposit/dose in shielding
  configurations
• various shielding materials and thicknesses

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Space radiation environment

• Galactic Cosmic Rays
• Protons, a particles and heavy ions (C -12, O
  -16, Si - 28, Fe - 52)
• Solar Particle Events
• Protons and a particles

100K primary particles, for each particle
type Energy spectrum as in GCR/SPE Scaled
according to fluxes for dose calculation
GCR p, a, heavy ions
SPE particles p and a
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
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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

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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
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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
14
Astronaut Phantom

• 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

• 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

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Selection of Geant4 EM Physics Models

• Geant4 Low Energy Package for p, a, 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 gt 0.9)
Talk Precision Validation of Geant4
electromagnetic physics, 20th April, Monte Carlo
2005
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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 a Hadronic models for ions in
progress
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 indication of the hadronic
contribution rather than as quantitative estimates
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Selection of Geant4 Hadronic Physics Models

• Hadronic Physics for protons and a as incident
  particles

hadronic elastic process
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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

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Electromagnetic and hadronic interactions
100 k events
GCR p
100 k events
e.m. physics e.m. Binary ion set

GCR a
The contribution of the hadronic interactions
looks negligible in the calculation of the energy
deposit
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Shielding materials

• Water
• Polyethylene
• Equivalent shielding results

100 k events
GCR p
e.m. physics Bertini set
e.m. physics only
10 cm water 10 cm polyethylene
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Shielding thickness
100 k events
e.m. physics Bertini set
GCR p
10 cm water 5 cm water
GCR a
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
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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
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Effects of cosmic ray components
Protons
e.m. physics processes only
Relative contribution to the equivalent dose from
some cosmic rays components
100 k events
The dose contributions from proton and a GCR
components result significantly larger than for
other ions
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High energy cosmic ray tail
100 k events
e.m. physics Bertini set e.m. physics only

• 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

Energy deposit GCR protons E gt 30 GeV
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SPE shelter model
SIH

• Inflatable habitat additional 10. cm water
  shielding SPE shelter

Shelter

• Approach
• Study the e.m. contribution to the energy
  deposit
• Add on top the hadronic contribution

Geant4 model
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Results SPE, SIH shielding shelter
SPE energy deposit (MeV) vs depth (cm) e.m.
hadronic physics The SPE a contribution is
weighted according to the spectrum with respect
to GCR protons

• 100 K events
• 4 protons reach the astronaut
• All a particles are stopped

Study the energy deposit of SPE with E gt 300
MeV/nucl
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Moon surface habitats
4 cm Al
Moon as an intermediate step in the exploration
of Mars Dangerous exposure to Solar Particle
Events
4 cm Al

• x 0 - 3 m roof thickness

GCR p GCR a
e.m. hadronic physics (Bertini set)
100 k events
Energy deposit (GeV) in the phantom vs roof
thickness (m)
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Planetary surface habitats Moon - SPE

• Energy deposit resulting from SPE with E gt 300
  MeV / nucl
• The energy deposit of SPE a 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 a 3.5 m thick roof
100 k events
Energy deposit in the phantom given by Solar
Particle protons and a particles
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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

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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