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The GEANT SimulationPackage and its use inCompton Telescope Design
The GEANT SimulationPackage and its use inCompton Telescope Design
R. Marc KippenSpace and Remote Sensing Sciences GroupLos Alamos National Laboratory
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Astronomy with Radioactivities IV May 26–30, 2003 – 2 –R. Marc Kippen
The Role of Simulation in DesignThe Role of Simulation in Design
+ =
: Realistic componentperformance
6 Expensive and timeconsuming
6 Inflexibleconfiguration
6 Unrealisticenvironment
: Inexpensive andcomparatively rapid
: Flexibleconfiguration
: Flexible environment6 Must model the
componentperformance
MEGA Prototype
Prototypes, Balloons, etc.
MEGA Prototype Simulation Model
Simulations, Models, etc.
MEGA Flight Concept
Scientific Mission
n Successful flightexperiment, where:® Realistic estimates
of performancehelp “sell” themission
® Instrument designis optimized forscientific missionand environment
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Astronomy with Radioactivities IV May 26–30, 2003 – 3 –R. Marc Kippen
Simulating Compton TelescopesSimulating Compton Telescopes
n Analytical modeling ofCompton imager physicalresponse is impractical due tocomplexities of geometry,scattering, and secondaryproduction
n The most viable approach isMonte Carlo radiation transportsimulation — probabilistictracking individual “testparticles”
n Other simulations important toinstrument design: mechanical,thermal, electronics, etc.
PhotonsElectrons
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Astronomy with Radioactivities IV May 26–30, 2003 – 4 –R. Marc Kippen
Instrument Simulation FrameworkInstrument Simulation Framework
ScienceGoal
Inputs
BackgroundInputs
OrbitalEnvironment
Model
PhysicalSimulation
Engine
InstrumentMass Model
SpacecraftMass Model
Test Dataand/orModels
InstrumentalEffects Engine
Data Processingand Analysis
Mechanical Model(s)
Physics Data/Models
SciencePerformanceEvaluation
AuxiliaryData/Models
Iterate at All Levels
Credible Simulation Requires Credible Inputs at All Levels
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Astronomy with Radioactivities IV May 26–30, 2003 – 5 –R. Marc Kippen
n Requirements for ComptonTelescope simulations:
® Detailed electromagnetic physicsfor direct telescope response(~1 keV – 100 MeV)
® Competent hadronic cascadephysics for simulation of promptcosmic-ray–induced background
® Isotope excitation and radioactivedecay for simulations of delayedactivation-induced background
® Convenient and flexible handlingof complex geometry andmaterials for rapid design studies
® Modern, modular architecturethat allows customization
Monte Carlo Radiation Transport PackagesMonte Carlo Radiation Transport Packages
n The particle and nuclearphysics communities havedeveloped several “general-purpose” Monte Carlo transportpackages, including:
® EGS® FLUKA® HETC/MORSE/MICAP® CALOR® MCNP/MCNPX® GEANT/GEANT4
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Astronomy with Radioactivities IV May 26–30, 2003 – 6 –R. Marc Kippen
Capabilities of GEANT4Capabilities of GEANT4
n GEANT := GEometry And Tracking
n Complex 3D geometry, materials,MC transport, and visualization inone package
n Developed & maintained by CERN+ large collaboration
n Modern, object-oriented (C++)“toolkit” architecture
n Comprehensive (nearly) suite of EMand hadronic physics
n Straightforward installation and useon many platforms® Wintel, Sun, HP, Linux, Darwin
n ESA Space Specific Modules
n General Source Particle Module® Tookit for input spatial/spectral sampling
n Radioactive Decay Module® Provides the capability to model
activation-induced background inorbit
® Uses detailed Evaluated NuclearStructure Data Files
n Low-energy EM physics® Uses detailed cross sections from LLNL
Evaluated Photon/Electron/Atomic DataLibraries
® Applicable above ~250 eV® Ties X-ray and Gamma-ray applications
´ Important omission: electronbinding effects in Compton
geant4.web.cern.chgeant4.web.cern.ch www.space.qinetiq.comwww.space.qinetiq.com
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Astronomy with Radioactivities IV May 26–30, 2003 – 7 –R. Marc Kippen
Effects of Atomic Electron BindingEffects of Atomic Electron Binding
n Suppresses forward scattering,particularly at low energies
n Suppresses total scatteringprobability at low energies
0.4
0.3
0.2
0.1
0.0
sto
t (cm
–1)
10 100 1000 10000
Photon Energy (keV)
Atomic Silicon
Free e- Atomic e-
0.08
0.06
0.04
0.02
0.00
ds/d
W (b
arn
· sr–1
)
1801501209060300
Photon Scatter Angle (deg)
Atomic Silicon
100 keV
Free e- Atomic e-
n GEANT4 Low-energy Compton process includes these effects
†
d2sdWdk
Ê
Ë Á
ˆ
¯ ˜
i
=ro
2
4k f kko
2
Ê
Ë Á
ˆ
¯ ˜
k f
ko+
kok f
- sin2 jÊ
Ë Á Á
ˆ
¯ ˜ ˜
dpz
dkJi pz( )
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Astronomy with Radioactivities IV May 26–30, 2003 – 8 –R. Marc Kippen
Doppler Broadening Physics & EffectsDoppler Broadening Physics & Effects
1.0
0.8
0.6
0.4
0.2
0.0
Norm
alize
d Av
erag
e J(
Q)
-30 -20 -10 0 10 20 30Bound Momentum Q (keV/c)
Compton ProfilesJ(Q)
CZTHWHM = 4.5 keV/c
SiliconHWHM = 2.1 keV/c
k = ko -kokEo
1 - cosj( ) - pz ko - k
For bound atomic electron:
kfree = ko -kok
moc2 1 - cosj( )
For free electron: pz = 0 ; Eo = moc2
†
fi Dk = k - kfree; Dj = j -j free
Doppler broadening error:
jko
k
Eo, pz
E, p
Biggs,Mendelsohn,& Mann (1975)
14
12
10
8
6
4
2
0
Scat
ter A
ngle
Erro
r (de
g)
1801501209060300Scatter Angle (deg)
CZT Silicon
100 keV
1 MeV
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Astronomy with Radioactivities IV May 26–30, 2003 – 9 –R. Marc Kippen
GLECS & G4LECSGLECS & G4LECS
n GLECS = GEANT Low-Energy Compton Scattering® Thanks to Doug Swartz (USRA, Huntsville) for early help
n Incorporates Doppler broadening into GEANT & GEANT4
n Algorithm based closely on EGS Implementation® Namito, Ban, & Hirayama, NIM A349, 489 (1994)® Relativistic impulse approximation (ignore atomic electron interactions)® Uses EPDL for total cross sections® Uses EPDL differential cross sections (scattering form factors)® Uses shellwise Compton profiles (Biggs, Mendlesohn, & Mann 1975) to
sample Doppler broadened scattered photon energies® Also fixes Rayleigh (coherent) scattering physics with EPDL data® Computing performance within 5% of G4LowEnergy classes
n Soon to come: combined polarization and Doppler broadening
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Astronomy with Radioactivities IV May 26–30, 2003 – 10 –R. Marc Kippen
Verification of G4LECSVerification of G4LECS
n G4LECS compared to synchrotron beam experiment® Namito, Ban, Hirayama, et al. (1994, 1995)
Experiment(Polarized Beam)
Simulation(Unpolarized Beam)
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Astronomy with Radioactivities IV May 26–30, 2003 – 11 –R. Marc Kippen
Test ResultsTest Results
10-6
10-5
10-4
10-3
10-2
Coun
ts (p
eak
norm
alize
d)
403836343230
Scattered Energy Deposition [keV]
Data (Namito et al.) G4LECS Simulation G4LowEnergy Simulation
v4.4.1
Carbon 40 keV
10-6
10-5
10-4
10-3
10-2
Coun
ts (p
eak
norm
alize
d)
403836343230
Scattered Energy Deposition [keV]
Data (Namito et al.) G4LECS Simulation G4LowEnergy Simulation
v4.4.1
Copper 40 keV
10-6
10-5
10-4
10-3
10-2
Coun
ts (p
eak
norm
alize
d)
403836343230
Scattered Energy Deposition [keV]
Data (Namito et al.) G4LECS Simulation G4LowEnergy Simulation
v4.4.1
Lead 40 keV
n Good agreement in Compton andRayleigh peaks (and Ge-K escape)
n Some differences in multi-Compton continuum probably dueto approximated geometry
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Astronomy with Radioactivities IV May 26–30, 2003 – 12 –R. Marc Kippen
Application to Compton Telescope DesignApplication to Compton Telescope Design
Doppler Limit Angular ResolutionZoglauer & Kanbach, Proc. SPIE 4851, 1302 (2003)
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Astronomy with Radioactivities IV May 26–30, 2003 – 13 –R. Marc Kippen
Telescope Design Study ExampleTelescope Design Study Example
Si + CZTmulti-scatterDesign
14121086420An
gula
r Res
. (FW
HM, d
eg)
10 100 1000 10000Energy (keV)
100¥100 cm2
NoDoppler
10-3
10-2
10-1
100 E
2 • Se
nsitiv
ity (k
eV ·
cm-2 s
-1)
10 100 1000 10000Energy (keV)
1 Msec
BATSECOMPTEL
New Design
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Astronomy with Radioactivities IV May 26–30, 2003 – 14 –R. Marc Kippen
http://nis-www.lanl.gov/~mkippen/actsim/
http://nis-www.lanl.gov/~mkippen/actsim/