1. Radioprotection for interplanetary manned missions
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

2. 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

3. 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

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. 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

6. Summary of process products
See

7. 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

8. REMSIM Simulation Design

9. 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

10. 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 CREME and CREME solar minimum spectra
Envelope of CREME96
October 1989 and August 1972 spectra
Worst case assumption for a conservative evaluation

11. 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

12. 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

13. 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

14. 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 , 2005
The electromagnetic physics models chosen are accurate
Compatible with NIST data within NIST accuracy (p-value > 0.9)

15. 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

16. 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

17. 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

18. 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

19. 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

20. 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

21. 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

22. 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

23. 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

24. 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

25. 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

26. 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

27. 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

28. 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

29. 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 = 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)

30. 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

31. 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

32. 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