4th Workshop on Geant4 Bio-medical Developments and Geant4 Physics Validation

1
REMSIM Geant4 Simulation

• S. Guatelli1, B. Mascialino1, P. Nieminen2, M. G.
  Pia1
• INFN Sezione di Genova
• ESA - ESTEC

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

• 4th Workshop on Geant4 Bio-medical Developments
  and Geant4 Physics Validation
• 14th July 2005, Genova, Italy

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 REMSIM Geant4 application
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
Summary of process products
See http//www.ge.infn.it/geant4/space/remsim/envi
ronment/artifacts.html
5
REMSIM Simulation Design
6
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

7
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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Vehicle concepts
SIH - Simplified Inflatable Habitat
Two (simplified) options of vehicles studied
Simplified Rigid Habitat A layer of Al (thickness
suggested by Alenia)

• Modeled as a multilayer structure consisting of
• 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
9
Surface Habitats

• Example surface habitat on the moon
• Cavity in the moon soil covering heap

The Geant4 model retains the essential
characteristics of the surface habitat concept
relevant to a dosimetric study
10
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

11
Selection of Geant4 Physics Models

• E. M. physics
• Geant4 Low Energy Package for p, a, ions and
  their secondaries
• Geant4 Standard Package for positrons
• Hadronic physics
• Elastic scattering
• Inelastic Scattering
• Protons, neutrons, pions two alternative
  approaches (next slide)
• Alpha LEP model ( up to 100 MeV), Binary Ion
  model (80 MeV- 100 GeV/nucl), Tripathi and Shen
  cross sections active
• Neutron fission and capture active

12
Selection of Geant4 Hadronic Physics Models

• Hadronic Physics for protons and a as primary
  particles

Hadronic inelastic process Binary approach Bertini approach
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 lt E lt 25. GeV ) Low Energy Parameterised ( 2.5 GeV lt E lt 25. GeV )
High energy range ( 20. GeV lt E lt 100. GeV ) Quark Gluon String Model Quark Gluon String Model
hadronic elastic process
13
Study of vehicle concepts
SIH

• Incident spectrum of GCR particles
• Energy deposit in phantom due to electromagnetic
  interactions
• Add the hadronic physics contribution to the
  energy deposit 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

The results are obtained with simulations of 100
K events
14
Generating primary particles strategy
SIH 10 cm water

• First step
• Generate GCR particles with the entire input
  energy spectrum
• Second step
• Generate GCR p and a with defined slices of the
  energy spectrum
• 130 MeV/nucl lt E lt 700 MeV/nucl
• 700 MeV/nucl lt E lt 5 GeV/nucl
• 5 GeV/nucl lt E lt 30 GeV/nucl
• E gt 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 lt E lt 30 GeV
15
Analysis of the results

• The Kolmogorov-Smirnov test was used to compare
  the energy deposit in the phantom, in different
  shielding configuration, to point out equivalent
  shielding behaviors
• The test calculates the probability (p-value)
  that two distributions derive from the same
  quantity
• p-value gt 0.05 points out an equivalent
  shielding behavior

16
Simulation results GCR p
Energy deposit with respect to the depth in the
phantom
Z
E.M. physics E.M. hadronic physics binary
set E.M. hadronic physics bertini set

• The Kolmogorov-Smirnov test shows that the effect
  of the Bertini and Binary sets do not differ
  significantly in the calculation of the energy
  deposited (p-value 0.11)
• Adding the hadronic interactions on top of the
  electromagnetic processes increases the energy
  deposited in the phantom of 27.

17
Simulation results GCR a
Energy deposit with respect to the depth in the
phantom
E.M. physics E.M. hadronic physics

• The contribution of the hadronic interactions
  with respect to the electromagnetic one is
  statistically negligible ( Kolmogorov-Smirnov
  test result p-value 0.95)

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Simulation results SIH 10 cm water shielding

• GCR p
• Energy deposit given by both e.m. and hadronic
  interactions in the phantom

130 MeV 700 MeV 700 MeV 5 GeV 5 GeV 30
GeV E gt 30 GeV
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Simulation results SIH 10 cm water shielding

• Total energy deposit in the phantom, given by
  every slice of the GCR p energy spectrum
• The biggest contribution derives from the
  intermediate energy range
• 700 MeV lt E lt 30 GeV

GCR p
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Simulation results SIH 10 cm water shielding
130 MeV/nucl lt E lt 700 MeV/nucl 700 MeV/nucl lt E
lt 5 GeV/nucl 5 GeV/nucl lt E lt 30 GeV/nucl E gt 30
GeV/nucl

• GCR a
• Energy deposit given by both e.m. and hadronic
  interactions in the phantom
• The energy deposit is not weighted with the
  probability of the specific energy spectrum slice

21
Simulation results SIH 10 cm water shielding
The Binary Ion model can be activated also for
energies higher than 10 GeV/nucl but the model is
valid up to 10 GeV/nucl
1 GeV/nucl lt E lt 10 GeV/nucl
E gt 10 GeV/nucl
GCR a
GCR a
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Simulation results SIH 10 cm water shielding
GCR a

• Total energy deposit in the phantom for every
  slice of the spectrum
• Each contribution is weighted for the probability
  of the spectrum slice
• The biggest contribution derives from
• 700 MeV/nucl lt E lt 30GeV/nucl

• The energy deposit of GCR a is not weighted with
  the probability to generate a GCR a with respect
  to GCR p (0.06) at this stage

23
Simulation results SIH 10 cm water shielding

• Contribution of the energy deposit given by the
  GCR ion components 12C, 16O, 28Si, 52Fe

P
Relative contribution to the equivalent dose
Particle Equivalent dose (mSv) p
1. a 0.86 C 0.115
O 0.16 Si 0.06
Fe 0.106
a
C
Fe
O
Si
Only electromagnetic physics active
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Effect of different thicknesses

• Energy deposit in the phantom
• SIH 10 cm water / 5 cm water

Empty triangle - 5 cm water Black circle 10 cm
water
Energy deposit with respect to the depth in the
phantom
GCR p
GCR a
Doubling the shielding thickness corresponds to
decreasing the energy deposited by 11 and 16
approximately for p and a respectively.
25
Effect of different shielding materials

• Comparison between water and polyethylene as
  shielding materials

Energy deposit with respect to the depth in the
phantom
Black 10 cm water polyethylene White 10 cm
water

• The energy deposited in the phantom adopting
  water or polyethylene as shielding is the same
• Kolmogorov-Smirnov test result
• p-value 0.95
• Similar results were obtained comparing the
  shielding properties of the two materials against
  other cosmic ray components

26
GCR p - Comparison water / polyethylene
Energy deposit with respect to the depth in the
phantom
5 GeV lt E lt 30 GeV
130 MeV lt E lt 700 MeV
EM hadronic physics active
27
GCR p - Comparison water / polyethylene
Energy deposit with respect to the depth in the
phantom
E gt 30 GeV
Water and polyethylene have the same shielding
behaviour
EM hadronic physics active
28
Comparison with rigid Al structures

• A simulation was performed to compare the
  shielding properties of an inflatable habitat
  with respect to a conventional rigid structure
• Energy deposit of the GCR components in the
  phantom in the following configurations
• multilayer 10 cm water
• multilayer 5 cm water
• 4 cm Al
• 2.15 cm Al

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Results

• Kolmogorov-Smirnov test demonstrated that the
  shielding performance of the inflatable habitat
  concept is statistically equivalent to
  conventional solutions
• SIH 10 cm water does not differ from a 4 cm Al
  structure (p-value 0.19)
• SIH 5 cm water shielding is not different from
  a 2.15 cm Al (p-value 0.74).

Energy deposit with respect to the depth in the
phantom
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GCR p Comparison 4 cm Al SIH 10 cm water
Energy deposit with respect to the depth in the
phantom
5 GeV lt E lt 30 GeV
130 MeV lt E lt 700 MeV
EM hadronic physics
31
GCR p Comparison 4 cm Al SIH 10 cm water
Energy deposit with respect to the depth in the
phantom
E gt 30 GeV
EM hadronic physics
32
GCR aComparison 4 cm Al SIH 10 cm water
Energy deposit with respect to the depth in the
phantom
700 MeV/nucl lt E lt 5 GeV/nucl
130 MeV/nucl lt E lt 700 MeV/nucl
EM hadronic physics
33
GCR aComparison 4 cm Al SIH 10 cm water
Energy deposit with respect to the depth in the
phantom
5 GeV/nucl lt E lt 30 GeV/nucl
E gt 30 GeV/nucl
EM hadronic physics
34
Comparison SIH 10 cm water / 4 cm Al

• Total energy deposit in the phantom for every
  slice of the spectrum
• No difference between SIH 10 cm water and 4 cm
  Al

GCR a
GCR p

• The energy deposit of GCR a is not weighted with
  the probability to generate a GCR a with respect
  to GCR p (0.06) at this stage

35
SPE shelter model
SIH

• Dosimetric study of SPE p and a
• Comparison of the energy deposit in the cases

Shelter

• SIH 10 cm water
• SIH 10 cm water shelter

Geant4 model
Geant4 model

• Scope evaluation of the dosimetric effect of the
  shelter
• All the results were obtained with simulation of
  100 k events

36
Strategy
Observation SPE p and a with E gt 130 MeV/nucl
arrive to the shelter SPE p and a with E gt 400
MeV/nucl arrive to the phantom

• Energy deposit of SPE in the configuration SIH
  10 cm water
• generating SPE with the entire spectrum
• generating SPE with E lt 400 MeV/ nucl
• generating SPE with E gt 400 MeV/nucl
• Energy deposit of SPE in the configuration SIH
  10 cm water shelter
• generating SPE with E gt 400 MeV/nucl
• Calculate and compare the total energy deposit
  in the two configurations
• SIH 10 cm water shielding
• SIH 10 cm water shielding shelter

37
SPE Energy deposit in SIH 10 cm water
configuration

• E.m. hadronic physics (Bertini set)

Energy deposit with respect to the depth in the
phantom

• 68 SPE p arrive to the phantom
• 14 SPE a arrive to the phantom
• E gt 130 MeV/nucl arrive to the phantom
• E lt 130 MeV/nucl is the 98 of the entire
  spectrum

The energy deposit is not weighted with the
probability to generate a SPE a with respect to
SPE p (0.021)
38
SIH 10 cm water

• 100 K SPE p with E lt 400 MeV
• E.m. hadronic physics Bertini set

Energy deposit with respect to the depth in the
phantom
Energy distribution of primary particles
SPE p
Energy deposit
39
SIH 10 cm water

• SPE p with E gt 400 MeV
• E.m. hadronic physics Bertini set

Energy deposit (MeV) with respect to the depth
in the phantom (cm)
Energy distribution of primary particles
Energy deposit
MeV
100 K SPE p
Depth (cm)
cm
40
SIH 10 cm water SPE p

• Total energy deposit in the phantom

Energy deposit (MeV) with respect to the depth
in the phantom (cm)
E lt 400 MeV E gt 400 MeV Sum of the two
contributions
41
SPE p, Egt 400 MeV
Energy deposit (MeV) with respect to the depth
in the phantom (cm)

• SPE p with E gt 400 MeV
• E.m. hadronic physics Bertini set
• Comparison of the energy deposit
• SIH 10 cm water
• SIH 10 cm water shelter

SIH 10 cm water SIH 10 cm water shelter
100 K events
42
SPE p results

• Energy deposit in the phantom in the
  configuration SIH 10 cm water shielding 42.2
  GeV
• Energy deposit in SIH 10 cm water shelter
  22.47 GeV
• The shelter limits the energy deposit in the
  phantom of about 50

43
SIH 10 cm water SPE alpha

• E gt 130 MeV/nucl traverse SIH 10 cm water
  shielding
• E gt 400 MeV/nucl traverse the shelter and arrive
  to the phantom
• E lt 400 MeV/nucl represents the 99.98 of the
  entire spectrum
• E.m. hadronic physics Bertini set

SIH 10 cm water
44
SPE a - results
Energy deposit (MeV) with respect to the depth
in the phantom (cm)
EM hadronic physics
SIH 10 cm water shelter
SIH 10 cm water
E gt 400 MeV/nucl
E gt 400 MeV/nucl

• Total energy deposit in the phantom with the
  shelter 33 of the tot energy deposit without
  the shelter

45
Planetary surface habitats Moon - GCR
GCR p
GCR a

• x 0 - 3 m roof thickness

46
Planetary surface habitats Moon SPE

• Energy deposited in the phantom from solar event
  protons and a with E gt 300 MeV/nucl
• 105 SPE p and a
• Both electromagnetic and hadronic physics
  (Bertini set) active

Particle Energy deposit (GeV) 0.5 m thick roof Energy deposit (GeV) 3.5 m thick roof
SPE p 5434. 14.9
SPE a 12. 0.37
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Summary of the results

• Simplified Inflatable Habitat shielding
• water / polyethylene are equivalent
• hadronic interactions are significant
• the larger contribution in the energy deposit in
  the phantom derives from intermediate energy
  range of GCR 700 MeV/nucl lt E lt 30 GeV/nucl
• The larger contribution in the energy deposit in
  the phantom derives from GCR p and a
• Aluminum Vehicle
• comparable to SIH
• Moon Habitat
• thick soil roof limits GCR and SPE exposure

48
Comments

• Present situation
• Relative comparison of shielding solutions
• Next future
• Understand the behaviour of the hadronic physics
  models more in depth to explain the results
  obtained
• Generate GCR and SPE from a sphere isotropically
• Calculation of absolute dose in the phantom
• Substitute the phantom (water box) with an
  anthropomorphic phantom

49
Comments

• It is important to model accurately the hadronic
  interactions for radioprotection studies of
  astronauts
• It is important to offer accurate hadronic
  physics models for protons, a, heavier ions (up
  to iron) as incident particles
• Extensive validation of Geant4 hadronic physics
  models is required