REMSIM Geant4 Simulation

S. Guatelli – INFN Sezione di Genova

4th Workshop on Geant4 Bio-medical Developments and Geant4 Physics Validation14th July 2005, Genova, Italy

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

REMSIM Geant4 SimulationREMSIM Geant4 SimulationS. Guatelli1, B. Mascialino1, P. Nieminen2, M. G. Pia1

1. INFN Sezione di Genova

2. ESA - ESTEC


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


Scope of the REMSIM Geant4 application

ScopeScope

VisionVision A first quantitative analysisquantitative analysis of the shielding properties shielding properties of some innovative conceptual designs of vehicle vehicle and

surface habitatssurface habitats

Comparison among different shielding options

Quantitative evaluation of the physical effects of space radiation in interplanetary manned missions

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


Summary of process products

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


REMSIM Simulation Design


Physics 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

Strategy of the Simulation Study

Simplified geometrical geometrical configurationsconfigurations retaining the essential characteristicsessential characteristics for dosimetry studies

Electromagnetic processes

+ Hadronic processes

Model the radiation spectrum according to current standards– simplified angular distribution to produce statistically meaningful results

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

Vehicle concepts

Surface habitats

Astronaut


Space radiation environmentGalactic Cosmic Rays

– Protons, α particles and heavy ions (C -12, O -16, Si - 28, Fe - 52)Solar Particle Events

– Protons and α particles

Envelope of CREME96 1977 and CREME86 1975 solar minimum spectra

SPE particles: p and αGCR: p, α, heavy ions

Envelope of CREME96 October 1989 and August 1972 spectra

at 1 AUat 1 AU

Worst case assumption for a conservative evaluationWorst case assumption for a conservative evaluation

100K primary particles, for each particle typeEnergy spectrum as in GCR/SPE

Scaled according to fluxes for dose calculation


Vehicle concepts

The Geant4 geometry model retains the essential characteristics of the vehicle concept relevant for a dosimetry study

Materials and thicknesses by ALENIA SPAZIO

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

SIH - Simplified Inflatable Habitat

Simplified Rigid Habitat

A layer of Al (thickness suggested by Alenia)

Two (simplified) options of vehicles studied


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

Sketch and sizes by ALENIA SPAZIO


Astronaut Phantom

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

30 cm Z

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


Selection of Geant4 Physics ModelsE. M. physics:

– Geant4 Low Energy Package for p, α, 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


Selection of Geant4 Hadronic Physics Models

Hadronic Physics for protons and α 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 rangeLow 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


Study of vehicle concepts

Incident spectrum of GCR particlesEnergy deposit in phantom due to electromagnetic interactionsAdd the hadronic physics contribution to the energy deposit on top

GCR particles

vacuum air

phantom

multilayer - SIH shielding

Geant4 model

• 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

ConfigurationsConfigurations

SIH

The results are obtained with simulations of 100 K events


Generating primary particles: strategy

First step:– Generate GCR particles with the

entire input energy spectrum

Second step:– Generate GCR p and α with defined defined

slices of the energy spectrum:slices of the energy 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

SIH + 10 cm water

GCR p with 5 GeV < E < 30 GeV


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 > 0.05 points out an equivalent shielding behavior


The Kolmogorov-Smirnov test shows that the effect of the Bertini and Binary sets the Bertini and Binary sets do not differ significantlydo 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%.~27%.

Simulation results – GCR p

E.M. physicsE.M. + hadronic physics – binary setE.M. + hadronic physics – bertini set

waterphantom

SIH+ 10 cm water

GCR p

Z

Energy deposit with respect to the depth in the phantom


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

Simulation results – GCR α

E.M. physicsE.M. + hadronic physics


waterphantom

SIH+ 10 cm water

GCR α

Z


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 MeV700 MeV – 5 GeV5 GeV – 30 GeVE > 30 GeV

waterphantom

SIH+ 10 cm water

GCR α

Z


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 < E < 30 GeV700 MeV < E < 30 GeV


GCR p



GCR α

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

130 MeV/nucl < E < 700 MeV/nucl130 MeV/nucl < E < 700 MeV/nucl700 MeV/nucl < E < 5 GeV/nucl700 MeV/nucl < E < 5 GeV/nucl

5 GeV/nucl < E < 30 GeV/nucl5 GeV/nucl < E < 30 GeV/nuclE > 30 GeV/nuclE > 30 GeV/nucl

waterphantom

SIH+ 10 cm water

GCR α

Z



waterphantom

SIH+ 10 cm water

GCR α

Z

EM physicsEM + hadronic physics

1 GeV/nucl < E < 10 GeV/nucl E > 10 GeV/nucl

GCR α GCR α

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


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 < E < 30GeV/nucl700 MeV/nucl < E < 30GeV/nucl


GCR α

E. M. physicsE. M. physics + hadronic physics

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


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


Relative contribution to the equivalent dose

Particle Equivalent dose (mSv)

p 1. α 0.86 C 0.115 O 0.16 Si 0.06 Fe 0.106

Only electromagnetic physics active

P

α

C

O

Si

Fe

waterphantom

SIH+ 10 cm water

GCR α

Z


Effect of different thicknesses

Energy deposit in the phantom:– SIH + 10 cm water / 5 cm water

GCR p GCR α

Empty triangle - 5 cm waterBlack circle – 10 cm water

waterphantom

SIH+ water

GCR p,α

Z


Doubling the shielding thickness corresponds to decreasing the energy deposited by 11% and 16% approximately for p and α respectively.


Effect of different shielding materials

Comparison between water and polyethylene as shielding materials

waterphantom

SIH+ water / poly

GCR p,α

Z

GCR p

E.M. physics

E.M. + hadronic physics


• 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

Black – 10 cm water polyethyleneWhite – 10 cm water


5 GeV < E < 30 GeV

GCR p - Comparison water / polyethylene

waterphantom

SIH+ water / poly

GCR p,α

Z

SIH + 10 cm waterSIH + 10 cm poly

130 MeV < E < 700 MeV


EM + hadronic physics active


GCR p - Comparison water / polyethylene

waterphantom

SIH+ water / poly

GCR p,α

Z

SIH + 10 cm waterSIH + 10 cm poly


EM + hadronic physics active

E > 30 GeV

Water and polyethylene have the same shielding behaviour


Comparison with rigid Al structuresA 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

waterphantom

SIH+ water

GCR p,α, ions

Z

waterphantom

Aluminum

GCR p,α, ions

Z


ResultsKolmogorov-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).

GCR p

SIH + 10 cm water

4 cm Al

SIH + 5 cm water

2.15 cm Al



GCR p Comparison 4 cm Al – SIH + 10 cm water

SIH + 10 cm water4 cm Al

130 MeV < E < 700 MeV 5 GeV < E < 30 GeV


EM + hadronic physics




E > 30 GeV


GCR p Comparison 4 cm Al – SIH + 10 cm water



130 MeV/nucl < E < 700 MeV/nucl 700 MeV/nucl < E < 5 GeV/nucl



GCR αComparison 4 cm Al – SIH + 10 cm water



5 GeV/nucl < E < 30 GeV/nucl E > 30 GeV/nucl



GCR αComparison 4 cm Al – SIH + 10 cm water


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 pGCR α

The energy deposit of GCR α is not weighted with the probability to generate a GCR α with respect to GCR p

(0.06) at this stage


SPE shelter modelDosimetric study of SPE p and α

Comparison of the energy deposit in the cases:

Geant4 model

vacuum

air

Multilayer (28 layers) Phantom

Shelter

vacuum

SIH + 10 cm water

GCR and SPEparticles

Shelter

SIH

Geant4 model

• SIH + 10 cm water• SIH + 10 cm water + shelter

Scope: evaluation of the dosimetric effect of the shelter

All the results were obtained with simulation of 100 k events


Strategy

Energy deposit of SPE in the configuration SIH + 10 cm water– generating SPE with the entire spectrum– generating SPE with E < 400 MeV/ nucl– generating SPE with E > 400 MeV/nucl

Energy deposit of SPE in the configuration: SIH + 10 cm water + shelter – generating SPE with E > 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

Observation: SPE p and α with E > 130 MeV/nucl arrive to the shelterSPE p and α with E > 400 MeV/nucl arrive to the phantom

vacuum

air

Multilayer (28 layers) Phantom

Shelter

vacuum

SIH + 10 cm water

SPEparticles


SPE: Energy deposit in SIH + 10 cm water configuration

E.m. + hadronic physics (Bertini set)

• 68 SPE p arrive to the phantom

• 14 SPE α arrive to the phantom

• E > 130 MeV/nucl arrive to the phantom

• E < 130 MeV/nucl is the ~98% of the entire spectrum

waterphantom

SIH+ 10 cm water

SPE p

Z

The energy deposit is not weighted with the probability to generate a SPE α with

respect to SPE p (0.021)



SIH + 10 cm water 100 K SPE p with E < 400 MeV

E.m. + hadronic physics – Bertini set

SPE energy spectrum with E> 400 MeV

Energy deposit

SPE p


Energy distribution of primary particles

waterphantom

SIH+ 10 cm water

SPE p

Z


SIH + 10 cm water

Depth (cm)

SPE p with E > 400 MeV


MeV

Energy deposit

100 K SPE p

Energy deposit (MeV) with respect to the depth in the phantom (cm)

Energy distribution of primary particles

waterphantom

SIH+ 10 cm water

SPE p

Z

cm


SIH + 10 cm water – SPE p

Total energy deposit in the phantom


E < 400 MeVE > 400 MeVSum of the two contributions


SPE p, E> 400 MeV

SPE p with E > 400 MeV


Comparison of the energy deposit

– SIH + 10 cm water – SIH + 10 cm water +

shelter

SIH + 10 cm waterSIH + 10 cm water + shelter

100 K events


waterphantom

SIH+ 10 cm water

SPE p

Z


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%


SIH + 10 cm water SPE alpha

E > 130 MeV/nucl traverse SIH + 10 cm water shielding

E > 400 MeV/nucl traverse the shelter and arrive to the phantom

E < 400 MeV/nucl represents the 99.98 % of the entire spectrum


waterphantom

SIH+ 10 cm water

SPE α

Z

SPE alpha E < 400 MeV

E < 400 MeV/nucl

100 k events


SIH + 10 cm water


SPE α - results

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

SIH + 10 cm water + shelter

E > 400 MeV/nucl


SIH + 10 cm water


E > 400 MeV/nucl


Planetary surface habitats – Moon - GCRAdd a log on top with variable

height x

x

vacuum Moonsoil

GCR SPEbeam

Phantom

x = 0 - 3 m roof thickness Energy deposit of GCR p in 4 cm Al configurationEnergy deposit of GCR α in 4 cm Al configuration

GCR p

GCR α


Energy deposited in the phantom from solar event protons and α with E > 300 MeV/nucl

105 SPE p and α

Both electromagnetic and hadronic physics (Bertini set) active

Planetary surface habitats – Moon SPE

Add a log on top with variable height x

x

vacuum Moonsoil

GCR SPEbeam

Phantom

Particle Energy deposit (GeV)

0.5 m thick roof

Energy deposit (GeV)

3.5 m thick roof

SPE p 5434. 14.9

SPE α 12. 0.37


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 < E < 30 GeV/nucl

– The larger contribution in the energy deposit in the phantom derives from GCR p and α

Aluminum Vehicle– comparable to SIH

Moon Habitat– thick soil roof limits GCR and SPE exposure


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


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, α, heavier ions (up to iron) as incident particles

Extensive validation of Geant4 hadronic physics models is required

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REMSIM Geant4 Simulation

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