Geant4 Microdosimetry for Aerospace Radiation Effects Pete Truscott, Fan Lei, Clive Dyer

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Geant4 Microdosimetry for Aerospace Radiation Effects

  • Pete Truscott, Fan Lei, Clive Dyer

  • QinetiQ Ltd, Farnborough

  • Bart Quaghebeur Ramon Nartallo

  • BIRA, Brussels Rhea Systems SA, Belgium

  • Geant4 Space Users Workshop, Pasadena, CA 6th-11th November 2006

  • QinetiQ developments and research funded by ESA under contract 19103/05/NL/JD, and by the UK MOD under contract C/MAT/N03517 and C/MAT/N02503E

Geant4 Radiation Transport Toolkit The Virtues

  • Comprehensive Monte Carlo simulation of all particles in 3D geometries

  • Variety of physics models covering electromagnetic, hadronic (nuclear), decay processes with treatment over 1PeV to ~100eV (and to thermal energies for neutrons)

  • Developed initially for the HEP community (LHC at CERN, BarBar at SLAC and KEK) with contributions from 100 scientists from 40 institutes World-wide

  • This toolkit continues to be supported through HEP, medical physics, space, etc communities as applications and requirements grow - new physics, new tools, new validations

  • Implementation in C++ - aids enhancement of code through class inheritance

Geant4 Radiation Transport Toolkit - The Vices

  • It is a toolkit

    • Geant4 philosophy considers it the responsibility of the user to write the application and the develop post-processing tools
    • Need for applications like MULASSIS, SSAT, GRAS
  • Although there is extensive documentation, it’s a long and steep learning-curve

Multi-Layered Shielding Simulation Software (MULASSIS)

  • Geant4 application to allow radiation analysis for 1D geometries (slab & sphere)

  • Provide Shieldose-type information with the physics of G4

  • SPENVIS or standalone versions

  • Simple specification of geometry (comprising any materials), source particle, physics, and analysis:

  • Graded shielding analysis for electron/ sources to shielding properties of concrete and boronated polythenes to neutrons <20MeV

GEant4 Microdosimetry Analysis Tool - GEMAT

  • A Geant4-based application for microdosimetry analysis of microelectronics

  • Easy to use geometry builder

    • Handles volumes more complex than regular parallelepipeds
  • GRAS-based physics list

    • Making use of the full G4 physics capability
  • Built-in analysis modes

  • SPENVIS-based to allow wider usage without having to download Geant4

Material Definition Commands

Geometry Construction Commands

  • A layered geometry structure

    • Arbitrary number of layers of different materials
  • One layer is designated as the Contact Layer

    • Contact Volumes (CVs) can be added
  • One layer is designated as the Depleted Layer

    • Sensitive Volumes (SVs) can be added

CV/DV Shapes

  • Basic shapes

    • Cylinder: 2 parameters
    • Box: 2 parameters
    • L-shape: 4 parameters
    • U-shape: 4 parameters
  • All can be tapered at top/bottom

  • Position (x,y) in the layer

  • Material & Visualisation Attrib.

Physics List

  • G4LowEnergyEM

  • G4HPNeutron

  • G4Binary/G4Bertini

  • G4BinaryLightIon

  • G4Abrasion/G4Ablation

  • G4RadioactiveDecay

Analysis Manager

  • Quantities tallied:

    • Fluence
    • Pulse height spectrum (PHS)
    • Path-length
  • Applied to selected sensitive volumes (SVs)

  • Coincidence analysis:

    • Between up to 3 DVs
    • Each volume can have its own threshold
  • Built-in histogram capability

GEMAT Implementation in SPENVIS

  • Implementation into SPENVIS is currently being completed at BIRA

  • Use other parts of SPENVIS to generate incident particle spectra

  • Like MULASSIS, web-page access to control generation of Geant4 macro file:

    • Can be executed at SPENVIS server - no need to download Geant4 to your local computer
    • “Lazy-Boy” approach: download macro and execute with local copy of G4+GEMAT application

An application Example: 4 Mbit SRAMs

  • A large quantity of beam test data available, from heavy Ion to thermal neutrons

  • Good knowledge of the device geometry

  • Two types of simulations using

    • Detailed geometry at cell level
    • An array of simple cells

Hitachi HM628512 ALP-7 Data compared with simulation

Hitachi HM628512 ALP-7 Data compared with simulation

In-Beam Neutron Scattering

  • In several cases QDOS was located relatively far downstream of the neutron source

  • Whilst beam divergence from the Li-foil (3m upstream of the monitor) had been accounted for, loss of neutrons through scattering within the experiments hadn’t

  • Adapted the MULASSIS code for long-thin geometries instead of short-fat geometries to simulate neutron interactions in PCBs, ICs, Cd foil, Al enclosures

Ion-Electromagnetic Physics

  • Stopping power models

    • G4 Std EM
    • G4 Low-E models (Ziegler 1985 & ICRU-49)
    • Work of Sigmund et al, including ICRU-73 (2006)
    • Ziegler 2003


  • Geant4 is playing an important role in QinetiQ’s work on understanding radiation effects on semiconductor devices and detectors

  • ESA-sponsored work has led to development of an easier-to-use engineering tool GEMAT, currently being implemented at SPENVIS

  • It is vitally important that we pay attention to the detailed physical models (kinematics of highly-ionising secondaries):

    • ion-EM physics
    • energetic proton/neutron-nuclear interactions and nuclear-nuclear
    • low-energy neutrons - down to thermal energies for B-neutron interactions
  • Hopeful of new 4½-year contract with MOD - will support micro-/nanodosimetry and device physics simulation efforts

Backup Slides

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