Transcript Document

www.ge.infn.it/geant4/space/remsim
Radioprotection for interplanetary
manned missions
R. Capra1, S. Guatelli1, B. Mascialino1, P. Nieminen2,
M. G. Pia1
1. INFN, Genova, Italy
2. ESA-ESTEC, Noordwijk, The Netherlands
Geant4-SPENVIS Workshop
3-7 October 2005
Leuven, Belgium
S. Guatelli, M.G. Pia – INFN Sezione di Genova
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
S. Guatelli, M.G. Pia – INFN Sezione di Genova
Scope of the project
The project deals with studies relevant to the AURORA programme
Scope
Vision
Quantitative evaluation of the physical effects of space
radiation in interplanetary manned missions
A first quantitative analysis of the shielding properties of
some innovative conceptual designs of vehicle and
surface habitats
Comparison among different shielding options
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
Software process
Quality and reliability of the software are essential requirements for a
critical domain like radioprotection in space
adopt a rigorous software process
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
S. Guatelli, M.G. Pia – INFN Sezione di Genova
Summary of process products
S. Guatelli, M.G. Pia – INFN Sezione di Genova
See http://www.ge.infn.it/geant4/space/remsim/environment/artifacts.html
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/SAD_remsim.html
S. Guatelli, M.G. Pia – INFN Sezione di Genova
REMSIM Simulation Design
S. Guatelli, M.G. Pia – INFN Sezione di Genova
Strategy of the Simulation Study
Model the radiation spectrum according to current standards
– Simplified angular distribution to produce statistically meaningful results
Vehicle concepts
Simplified geometrical configurations
retaining the essential characteristics for dosimetry studies
Surface habitats
Astronaut
Physics modeled by Geant4
Electromagnetic processes
– Select appropriate models from the Toolkit
+ Hadronic processes
– 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
S. Guatelli, M.G. Pia – INFN Sezione di Genova
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
GCR: p, α, heavy ions
at 1 AU
Envelope of CREME96 1977 and CREME86
1975 solar minimum spectra
100K primary particles, for each particle type
Energy spectrum as in GCR/SPE
Scaled according to fluxes for dose calculation
SPE particles: p and α
at 1 AU
Envelope of CREME96
October 1989 and August 1972 spectra
Worst case assumption for a conservative evaluation
S. Guatelli, M.G. Pia – INFN Sezione di Genova
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
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


Materials and thicknesses by ALENIA SPAZIO
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
The Geant4 geometry model retains the essential characteristics of the
vehicle concept relevant for a dosimetry study
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 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
30 cm
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
S. Guatelli, M.G. Pia – INFN Sezione di Genova
Z
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)
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 range
Low 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
inflatable habitat
Study of vehicle concepts
Incident spectrum of GCR particles
Energy deposit in phantom due to electromagnetic
interactions
Add the hadronic physics contribution on top
Geant4 model
vacuum
air
GCR particles
phantom
multilayer - SIH
shielding
S. Guatelli, M.G. Pia – INFN Sezione di Genova
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
SIH + 10 cm water
First step:
– Generate GCR particles with the entire
spectrum
GCR p
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
S. Guatelli, M.G. Pia – INFN Sezione di Genova
GCR p with
5 GeV < E < 30 GeV
Electromagnetic and hadronic interactions
100 k events
vacuum
e.m. physics
e.m. + Bertini set
e.m. + Binary set
air
GCR
phantom
multilayer - SIH
GCR p
Adding the hadronic interactions on top of the
e.m. interactions
increase the energy
deposit in the phantom by ~ 25 %
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
S. Guatelli, M.G. Pia – INFN Sezione di Genova
10 cm water
shielding
Simulation results SIH + 10 cm
water shielding
Total energy deposit in
the phantom of each
slice of the energy
spectrum
Hadronic contribution
E.M. contribution
The largest
contribution derives
from the intermediate
energy range:
700 MeV < E < 30 GeV
S. Guatelli, M.G. Pia – INFN Sezione di Genova
GCR p
Simulation results SIH + 10 cm
water shielding
GCR α
E. M. physics
E. M. physics + hadronic physics
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
S. Guatelli, M.G. Pia – INFN Sezione di Genova
Shielding materials
Comparison between
– Water
– Polyethylene
Equivalent shielding results
GCR p
100 k events
e.m. physics + Bertini set
e.m.
physics only
10 cm water
10 cm polyethylene
S. Guatelli, M.G. Pia – INFN Sezione di Genova
vacuum
air
GCR
phantom
multilayer - SIH
water / poly
shielding
Energy deposit given by slices
of the GCR p spectrum
Shielding thickness
vacuum
air
GCR
100 k events
e.m. physics+ Bertini set
GCR p
phantom
10 cm water
5 cm water
5 / 10 cm water
shielding
multilayer - SIH
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%
S. Guatelli, M.G. Pia – INFN Sezione di Genova
100 k events
Comparison of inflatable
and rigid habitat concepts
Aluminum layer replacing the
inflatable habitat
100 k events
– based on similar structures as in
GCR p
the ISS
Two hypotheses of Al thickness
– 4 cm Al
– 2.15 cm Al
vacuum
air
GCR
phantom
Al structure
2.15 cm Al
5 cm water
The shielding performance of the
inflatable habitat is equivalent to
conventional solutions
S. Guatelli, M.G. Pia – INFN Sezione di Genova
10 cm water
4 cm Al
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 p
S. Guatelli, M.G. Pia – INFN Sezione di Genova
GCR α
Effects of cosmic ray components
vacuum
air
GCR
Protons only
e.m. physics processes
phantom
multilayer - SIH
α
10 cm water
shielding
Relative contribution to the
equivalent dose from some cosmic
rays components
O-16
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
C-12
Fe-52
Si-28
100 k events
Depth in the phantom (cm)
The dose contributions from proton and α GCR components result
significantly larger than for other ions
S. Guatelli, M.G. Pia – INFN Sezione di Genova
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
shielding
SPE shelter
air
vacuum
Geant4
model
Approach:
 Study the e.m. contribution
Incident
radiation
to the energy deposit
 Add on top the hadronic
contribution
phantom
multilayer
shielding
S. Guatelli, M.G. Pia – INFN Sezione di Genova
SPE:
Energy deposit in SIH + 10
cm water configuration
SPE p,α
100K SPE p and α
E.m. + hadronic physics (Bertini set)
water
phantom
SIH
+ 10 cm water
Z
• 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
S. Guatelli, M.G. Pia – INFN Sezione di Genova
Strategy
SPE p,α
SIH
+ 10 cm water
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)
water
phantom
Shelter
Z
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
S. Guatelli, M.G. Pia – INFN Sezione di Genova
E < 400 MeV
E > 400 MeV
Sum of the two contributions
Moon surface habitats
Moon as an intermediate step in the
exploration of Mars
4 cm Al
Dangerous exposure
to Solar Particle Events
4 cm Al
Add a log on top with
variable height x
x = 0 - 3 m roof thickness
vacuum
GCR p
GCR α
moon
soil
e.m. + hadronic physics (Bertini set)
GCR
SPE
beam
100 k events
Energy deposit (GeV)
in the phantom vs roof thickness (m)
x
Phantom
S. Guatelli, M.G. Pia – INFN Sezione di Genova
Planetary surface habitats – Moon - SPE
SPE p – 0.5 m roof
E < 300 MeV stopped by the
shielding
e.m. + hadronic physics
(Bertini set)
Energy deposit resulting from
SPE with E > 300 MeV / nucl
SPE α– 0.5 m roof
The energy deposit of SPE α is
weighted according to the flux
with respect to SPE protons
SPE p – 3.5 m thick roof
The roof limits the exposure to
SPE particles
SPE α – 3.5 m thick roof
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
Future
Latest development:
the water phantom has
been replaced by
an anthropomorphic
phantom
phantom
GCR p, 106 events
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
S. Guatelli, M.G. Pia – INFN Sezione di Genova