Presented by M G Pia (CERN, INFN)

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• Presented by M G Pia (CERN, INFN)
• Authors
• P Truscott F Lei
• (Defence Evaluation Research Agency, UK)
• C Ferguson R Gurriaran (University of
  Southampton, UK)
• P Nieminen E Daly
• (ESA /ESTEC)
• J Apostolakis, S Giani, M G Pia (CERN,
  Switzerland)
• L Urban (KFKI Hungary)
• M Maire (LAPP, France)

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Principal Sources of Radiation in theNear-Earth
Environment
Extra-Solar System ?-rays, X-rays
Galactic Cosmic Rays (protons heavier
nuclei) 1MeV/nuc - 100s GeV/nuc
Solar Protons Heavier Ions (up to 100
MeV/nuc) X-rays, ?-rays
Trapped Particles protons (1 MeV - 100s
MeV) electrons (1 keV - several MeV)
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• The Environment
• Spacecraft are required to operate in a severe,
  energetic radiation environment comprising
  cosmic-ray protons and heavier nuclei, trapped
  protons and electrons that form the Van Allen
  radiation belts, and solar particles emitted
  during flare events and coronal mass ejections.
  The interactions of these particles in spacecraft
  materials not only attenuates the radiation, but
  may also give rise to secondary particles (e.g.
  protons, neutrons, bremsstrahlung) that may have
  higher fluxes and/or greater effects than the
  primaries.
• The Effects
• The radiation environment can give rise to a
  range of deleterious effects in spacecraft
  microelectronics, solar arrays, sensors and
  specialised (mission-specific) instruments such
  as ?-ray detectors
• Total ionising dose
• Atomic displacement (bulk) damage
• Single event effects (SEE), in which ionisation
  by single particles can temporarily upset or
  destroy integrated circuits
• Induced radioactivity and enhanced background
  rates in sensors

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• Applications for Radiation Transport Models
• Spacecraft instrument design/operation for
  mitigation of effects Radiation transport
  models may be used to predict the effects of the
  environment on the systems making up the
  spacecraft platform and payload, and to allow
  designers to develop and optimise hardening
  strategies. The planning of spacecraft
  operations must take into consideration
  variations in the environment during the mission
  (such as solar particle events) and radiation
  transport models help quantify the threat to
  instruments and the effectiveness of possible
  operational measures.
• Trouble-shooting Such tools are also valuable
  for trouble-shooting in-flight anomalies
  experienced in spacecraft that have already been
  launched, and for assessing possible mitigation
  strategies.
• Optimise detector/sensor designs Simulation of
  radiation transport is necessary for optimising
  the design of radiation detectors, such as those
  used for ?-ray or X-ray missions.
• Data interpretation The interpretation of data
  from such instruments may also be critically
  dependent upon model results, e.g. predictions of
  induced X-ray yields from asteroids/moons are
  required to derive composition from detected
  X-ray fluxes.

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Spacecraft Missions and Radiation Effects
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• Geant4 Overview and Features (see CHEP 2000 Paper
  140)
• The result of a world-wide collaboration of 100
  scientists and computer engineers from 40
  institutes
• Latest release is Geant4.1.0 issued 8th Dec 99
• Monte Carlo simulation for nuclei, hadrons,
  leptons and bosons in 3D
• Object Oriented design (implemented in C)
• Geant4 Adaptive GUI available
• Excellent facilities for visualisation (essential
  for geometry debugging)
• Comprehensive range of physical processes already
  implemented as well as planned
• Fast simulation mode - response of a volume may
  be parameterised based on empirical or simulation
  data
• Facilities for event biasing
• Geometry can be constructed from solid simple
  volumes or breps
• Defined by user-written C
• STEP interpreter for geometry input from CAD
  tools

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Applications of Geant4 Physical Processes
Hadron-nucleon or hadron-nuclear
Parameterised
Parton-string (gt5GeV)
Cosmic ray nuclei and secondaries
Kinetic (10MeV - 10GeV)
Trapped protons and secondaries
QMD models
Pre-compound (2-100 MeV)
Secondary neutrons, including atmospheric/planetar
y albedo neutrons
Low-energy neutron (thermal - 20 MeV)
Induced radioactive background calculations
Isotope production
Nuclearde-excitation
Evaporation (Agt16)
Treatment for seondaries from cosmic ray nuclei
and trapped protons, esp. important in
calculation of single event effects
(microdosimetry)
Fermi break-up (A?16)
Fission (A?65)
Multi-fragmentation
Photo-evaporation (ENSDF)
Induced and natural radioactive backgrounds
Radioactive decay (ENSDF)
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Applications of Geant4 Physical Processes
Electromagnetic
Ionisation
Important for treatment of SEE (microdosimetry
from nuclear recoil and evaporation prods)
Multiple scattering
?-ray production
Trapped electron effects
Bremsstrahlung
annihilation
Photo-electric effect
Compton scattering
Rayleigh scattering
Pair-production
Atomic relaxation
Induced and natural radioactive backgrounds
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Space Specific GEANT4 Modules

• Clearly Geant4 offers a very comprehensive
  environment to specify a geometry, perform
  particle tracking, and model a wide range of
  physical interaction processes. Furthermore the
  object-oriented design allows relatively
  straightforward extension of the toolkit through
  class inheritance.
• The particular requirements of spacecraft
  radiation effects studies have led the European
  Space Agency to sponsor the development of a
  number of space-specific components. These are
  now discussed.

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• MGA for Geant4 STEP Interface
• The CAD STEP (Standard for Exchange of Product
  Data - ISO 10303) interface provides an efficient
  method of defining spacecraft system geometries
  for Geant4, especially since the use of CAD tools
  is widespread in the aerospace industry. In
  addition, a number of commercial CAD tools
  already have STEP interfaces.
• However, the protocol (AP203) of STEP does not
  allow the association of materials information
  with each volume. The Materials and Geometry
  Association (MGA) tool is a Java-based utility to
  attribute material information and visualisation
  properties with volumes in a STEP file. This can
  be achieved manually by the user through the
  Graphical User Interface, or automatically if the
  CAD engineer uses pre-defind meta-data
  information in the PRODUCT records for each
  volume in the STEP file. The user can draw upon
  a database of standard spacecraft materials, or
  create her own materials by defining elemental
  and nuclide composition. Once this association
  is complete, both the STEP and MGA files are read
  by Geant4 to obtain a complete description of the
  geometry.

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Evaluation of CAD Tools

• CAD Product Suitability for G4 based
• ProEngineer (Parametric) yes
• Euclid (Matra Datavision) yes (with translator)
• Catia (IBM Dassault) yes
• MicroStation (Bentley) translator released ?
• AutoCAD (AutoDesk) yes (R14.01 )
• I-deas (SDRC) yes

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MGA Data Entry Windows
Volume, material and Vis attribute association
Materials specification window
Creation of internal databases (materials and
colours)
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• Low-Energy Electromagnetic Interactions
• Previously, the minimum energies for accurate
  ?-ray and electron transport in Geant3 and in EGS
  and ITS was 10 keV and 1 keV respectively. A key
  requirement identified by ESA for a general space
  radiation tool was that it treat X-ray
  fluorescence from the surfaces of asteroids and
  moons. This necessitates cut-offs of 250 eV. To
  achieve this, new processes (for low-energy
  Compton, Rayleigh, photo-electric effect,
  Bremsstrahlung, ionisation and fluorescence) have
  been introduced which utilise data
  parameterisations to evaluated data from Lawrence
  Livermore National Laboratory (EPDL97, EEDL and
  EADL).
• It is planned to also extend the low-energy EM
  physics for positrons to below 1 keV, as well as
  treat Auger electron production.
• The physics for ionisation caused by low-energy
  hadrons, ions has been extended using
  parameterisations to particle range and stopping
  power data from Ziegler and ICRU, permitting
  accurate tracking down to 1 keV. Accurate
  treatment of these physical processes is
  essential for simulating single event effects in
  microelectronics as a result of proton- or
  neutron-nuclear interactions. A similar extension
  is in progress for antiprotons.

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Low-Energy Electromagnetic Interactions
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• Radioactive Decay Module
• Long-term (gt1?s) radioactive decay induced by
  spallation interactions can represent an
  important contributor to background levels in
  spaceborne ?-ray and X-ray instruments, as the
  ionisation events that result often occur outside
  the time-scales of any veto pulse. The
  Radioactive Decay Module (RDM) treats the nuclear
  de-excitation following prompt photo-evaporation
  by simulating the production of ?, ?-, ?, ? and
  anti-?, as well as the de-excitation ?-rays. The
  model can follow all the descendants of the decay
  chain, applying, if required, variance reduction
  schemes to bias the decays to occur at
  user-specified times of observation. The
  branching ratio and decay scheme data are based
  on the Evaluated Nuclear Structure Data File
  (ENSDF), and the existing Geant4
  photo-evaporation model is used to treat prompt
  nuclear de-excitation following decay to an
  excited level in the daughter nucleus. (Atomic
  de-excitation following nuclear decay is treated
  by the Geant4 EM physics processes.)
• The RDM has applications in the study of induced
  radioactive background in space-borne detectors
  and the determination of solar system body
  composition from radioactive ?- ray emission.

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• Sector Shielding Analysis Tool
• It is often possible to obtain a first-order
  estimate of the radiation dose received within a
  spacecraft as a function of location using shield
  distribution data for that location in
  conjunction with dose-versus-depth information.
  The Sector Shielding Analysis Tool can provide
  shield distribution data using particle tracking
  facilities in Geant4. The so-called geantino
  particle is used to determine the path-lengths
  between material boundaries for rays emanating
  from a user-defined point. The

user is able to define the limits of the solid
angle analysed (the direction window) based on an
arbitrary co-ordinate system, and then sub-divide
divisions in this solid angle. Geantino rays can
be sampled randomly within each sub-division so
that the shielding can be assessed as a function
of ? and ?. Analysis output can be provided as a
function of material in units of g/cm2, cm or
radiation lengths, or for overall thickness
irrespective of material type.
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• General Source Particle Module
• The space radiation environment is often quite
  complex in energy and angular distribution, and
  requires sophisticated sampling algorithms. The
  General Source Particle Module (GSPM) allows the
  user to define his source particle distribution
  (without the need for coding) in terms of the
  following
• Spectrum linear, exponential, power-law,
  black-body, or piece-wise linear (or logarithmic)
  fit to data
• Angular unidirectional, isotropic, cosine-law,
  or arbitrary (user-defined)
• Spatial sampling from simple 2D or 3D surfaces,
  such as discs, spheres, boxes, cylinders
• The GSPM also provides the option of biasing the
  sampling distribution. This is advantageous, for
  example, for sampling the area of a spacecraft
  where greater sensitivity to radiation effects is
  expected (e.g. where radiation detectors are
  located) or increasing the number of high-energy
  particles simulated, since these may produce
  greater numbers of secondaries.

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Summary

• Geant4 is a new-generation toolkit for Monte
  Carlo particle simulation
• Unlike other codes Geant4 has been developed to
  provide comprehensive particle simulation in a
  single tool, but due to its OO design, it permits
  easy extension of physics modelled . if required
• The Geant4 Toolkit has wide applications
  including not only HEP, but also space and
  medicine
• Geant4 fulfils the functions required for space
  radiation effects studies and will be the basis
  of ESAs next generation of spacecraft radiation
  shielding tools

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Visit Our Web Sites

• ESA/DERA/UoS Spacecraft Radiation Shielding and
  Effects
• http//www.estec.esa.nl/wmwww/WMA/research/Shieldi
  ng_tools.html http//www.space.dera.gov.uk/space_e
  nv/geant_mn.html
• Geant4 collaboration at CERN
• http//wwwinfo.cern.ch/asd/geant4/geant4.html