S. Guatelli, M.G. Pia – INFN Sezione di Genova Monte Carlo 2005 18-21 April 2005 Radiation...

S. Guatelli, M.G. Pia – INFN Sezione di Genova

Monte Carlo 2005

18-21 April 2005

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

Radiation protection for Radiation protection for interplanetary manned missionsinterplanetary manned missionsS. Guatelli1, B. Mascialino1, P. Nieminen2, M. G. Pia1

1. INFN, Genova, Italy

2. ESA-ESTEC, Noordwijk, The Netherlands


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


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


The REMSIM Simulation Project

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

vehicle vehicle and surface habitatssurface habitats

Comparison among different shielding options

A project in the framework of the AURORA programme of the European Space Agency


Software strategy

Object oriented technology– suitable to long term studies – openness of the software to extensions and evolution– it facilitates the maintainability of the software over a long time scale

Geant4 as Simulation Toolkit– open source, general purpose Monte Carlo code for particle transport

based on OO technology– versatile to describe geometries and materials– rich set of physics models

The data analysis is based on AIDA– abstract interfaces make the software system independent from any

concrete analysis tools– strategy meaningful for a long term project, subject to the future evolution

of software tools


QualityQuality and reliabilityreliability 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

Software process

adopt a rigorous software process

Talk: Experience with software process in physics projects, 18 April, Monte Carlo 2005


Summary of process products

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


Architecture

Driven by goals deriving from the VisionVision

Design an agileagile system– capable of providing first indications for the evaluation of vehicle

concepts and surface habitat configurations within a short time scale

Design an extensibleextensible 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


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 AU at 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 to a dosimetry study

Materials and thicknesses by ALENIA SPAZIO

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 (structure element of the ISS)

Two (simplified) options of vehicles studied


Surface Habitats

Example: surface habitat

Cavity in the moon soil + covering heap

Use of local material

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 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, ICRU Report 49)

“Comparison of Geant4 electromagnetic physics models against the NIST reference data”, submitted to IEEE Trans. Nucl. Sci.

The electromagnetic physics models chosen are accurate

Compatible with NIST data within NIST accuracy (p-value > 0.9)

Talk: Precision Validation of Geant4 electromagnetic physics, 20 April, Monte Carlo 2005


Intrinsic complexity of hadronic physics

Geant4 hadronic physics is still the object of validation studies

The dosimetry studies performed in REMSIM must be considered as a first indicationfirst indication of the hadronic contribution

rather than as a quantitative estimate

Geant4 hadronic physics

Complementary and alternative models

Parameterised, data driven and theory driven models

The most complete hadronic simulation kit available on the marketModels for p and α

Hadronic models for ions in progress


Selection of Geant4 Hadronic Physics Models

Hadronic inelastic process

Binary set Bertini set

Low energy range

(intra-nuclear transport, pre-equilibrium, nuclear deexcitation)

Binary Cascade Bertini Cascade

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


Electromagnetic and hadronic interactions

e.m. physicse.m. + Bertini sete.m. + Binary set

GCR

vacuum air

phantommultilayer - SIH 10 cm water

shieldingGCR p

100 k events

100 k events

GCR α

Adding the hadronic interactions on top of the e.m. interactions increase the energy increase the energy deposit in the phantom by ~ 25 %deposit in the phantom by ~ 25 %

The contribution of the hadronic interactions looks negligible in the calculation of the energy deposit

e.m. physicse.m. + Binary ion set


Shielding materials

Water

Polyethylene

Equivalent shielding results

GCR

vacuum air

phantom

multilayer - SIH water / poly shielding

10 cm water10 cm polyethylene

e.m. physics + Bertini set

e.m. physics only

GCR p

100 k events


Shielding thicknessGCR

vacuum air

phantom

multilayer - SIH 5 / 10 cm watershielding

10 cm water5 cm water

GCR p

100 k eventse.m. physics+ Bertini set

e.m. physics+ hadronic physics

10 cm water5 cm water

GCR α

100 k events

Doubling the shielding thickness decreases the energy deposit by ~10%~10%

Doubling the shielding thickness decreases the energy deposit ~ 15%15%


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

GCR

vacuum air

phantom

Al structure

2.15 cm Al

10 cm water

5 cm water

4 cm Al

100 k events

GCR p


The dose contributions from proton and α GCR components result significantly larger than for other ions

Effects of cosmic ray components ProtonsProtons

αα

O-16O-16

C-12C-12

Si-28Si-28Fe-52Fe-52

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

Relative contribution to the equivalent dose from some cosmic

rays components

e.m. physics processes only

100 k events

GCR

vacuum air

phantommultilayer - SIH 10 cm water

shielding


High energy cosmic ray tail

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

GCR p

E> 30 GeV

8 %

100 k events

e.m. physics + Bertini set

e.m. physics only

GCR

vacuum air

phantom

multilayer - SIH 10 cm water shielding

Energy deposit GCR protons

E > 30 GeV


shielding

multilayer shielding

phantom

Incidentradiation

vacuum airSPE shelter

SPE shelter model

Inflatable habitat

+ additional 10 cm water shielding

+ 70 cm water SPE shelter

Geant4 model

Shelter

SIH


SPE, Inflatable habitat + shielding + shelter

SPE energy deposit (MeV) vs depth (cm)e.m. + hadronic physics

The SPE α contribution is weighted according to the spectrum with respect to protons

SPE p

SPE α SPE E > 300 MeV / nucl

e.m. + hadronic physics – Bertini set

100 K events:100 K events:

4 protons reach the astronaut4 protons reach the astronaut All All αα particles are stopped particles are stopped Study the energy deposit of SPE with E > 300 MeV/nuclStudy the energy deposit of SPE with E > 300 MeV/nucl


Moon surface habitats

Add a log on top with variable height x

x

vacuum moonsoil

GCR SPEbeam

Phantom

x = 0 - 3 m roof thickness

Energy depositin the phantom vs. roof thickness

4 cm Al

4 cm Al

100 k events

GCR pGCR α

e.m. + hadronic physics (Bertini set)

The moon as an intermediate step in the exploration of Mars


Planetary surface habitats – Moon - SPE

Energy deposit resulting from SPE with E > 300 MeV / nucl

The energy deposit of SPE is weighted according to the flux with respect to SPE protons

The roof limits the exposure to SPE particles

SPE p – 0.5 m roof

SPE α– 0.5 m roof

SPE p – 3.5 m thick roof

SPE α – 3.5 m thick roof

e.m. + hadronic physics (Bertini set)

100 k events

Energy deposit in the phantom given by Solar Particle protons and α particles


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


ConclusionsThe REMSIM project represents the first attempt in the European AURORA programme to estimate the radiation protection 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 radiation protection studies

More details in a 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

S. Guatelli, M.G. Pia – INFN Sezione di Genova Monte Carlo 2005 18-21 April 2005 Radiation...

Documents

Transcript of S. Guatelli, M.G. Pia – INFN Sezione di Genova Monte Carlo 2005 18-21 April 2005 Radiation...