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

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:

• TID, DD, fluence, energy-deposition spectra

• 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

• PHS: SEU rates calculated based on experimental ion data
• Path-length: used with environment h-ion LET data
• Analysis of coincidence events

• 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

• Wide choice of binning scheme, inc. arbitrary
• Output in CSV format

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

Summary

• 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