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Файл:Моделирование (1 сем, мага) / geant4 / Geant4_3
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Pre-assigned decays
•Geant4 provides decay modes for long-lived particles
User can re-define decay channels if necessary
•Decay modes for heavy flavor particles (b, c, top baryons, tau)
are very complex and they are not provided by Geant4
Use event generators which provide several decay models.
Geant4 can use them by pre-assigned decay channels
only for primaries: the user needs to prepare all necessary information for each
decayed particle in PrimaryGeneratorAction
• Or use an external decayer via the G4VExtDecayer abstract interface
to an external library
can be applied to all particles including secondaries
•See documentation in App. Dev. Guide: Particle Decay Process
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Specialized decay processes
•G4DecayWithSpin
For polarized muons
Produces Michel positron spectrum with first-order
radiative corrections
Initial muon spin is required
Propagates spin in magnetic field (precession) over
remainder of muon lifetime
•G4UnknownDecay
Only for “unknown” particles (Higgs, SUSY, etc.)
Discrete process: only in-flight decays allowed
Pre-assigned decay channels must be supplied by
user or generator
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Optical photons
•Technically, should belong to electromagnetic
category, but
Optical photon wavelength ≫ atomic spacing
Treated as waves: no smooth transition between
optical and gamma particle classes
•Optical photon production processes
G4Cerenkov
G4Scintillation
G4TransitionRadiation
•WARNING: optical photons are generated without
momentum-energy conservation
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Optical photon processes
•Photon can undergo
Rayleigh scattering
Refraction and reflection at medium boundaries
Bulk absorption
Wavelength shifting
•Polarization but not phase (no interference)
•Optical properties can be specified in a
G4MaterialPropertiesTable which is linked to G4Material
reflectivity, transmission efficiency, dielectric
constants, surface properties
•Spectral properties can be also specified in
G4MaterialPropertiesTable
scintillation yield, time structure (fast, slow
components)
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Summary
•Precision of particle stopping and production of
secondaries determined by a global secondary production
threshold in size
•Energy dependence of threshold derived from material
properties
•For complex detectors with multiple types of sensitive
volumes, different thresholds may be defined for regions
within detector
•There is one decay process for all long-lived, unstable
particles
•Optical processes handle reflection, refraction, absorption,
wavelength shifting and scattering of long-wavelength
photons
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Electromagnetic Physics
http://cern.ch/geant4/collaboration/working
_groups/electromagnetic/index.shtml
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Gamma and electron transport
•Photon processes
γ conversion into e+e- pair
Compton scattering
Photoelectric effect
Rayleigh scatteringHEP calorimeter
• Gamma-nuclear interaction in hadronic sub-package CHIPS
•Electron and positron processes
Ionization
Coulomb scattering
Bremsstrahlung
Nuclear interaction in hadronic subpackage CHIPS
Positron annihilation
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Geant4 EM packages
•Standard
gamma, e up to 100 TeV
hadrons up to 100 TeV
ions up to 100 TeV
•Muons
up to 1 PeV
energy loss propagator
•X-rays
X-ray and optical photon
production
processes
•High-energy
processes at high energy
(E>10GeV)
physics for exotic particles
•Polarisation
simulation of polarised beams
•Optical
optical photon interactions
•Low-energy
Livermore library gamma, e- from
250 eV up to 1GeV Livermore
library based polarised processes
PENELOPE gamma, e- , e+ from
250 eV up to 1 GeV hadrons and
ions up to 1 GeV
microdosimetry models for
radiobiology (Geant4-DNA project)
from 4 eV to 10 MeV atomic deexcitation (fluorescence + Auger)
•Adjoint
New sub-library for reverse Monte
Carlo simulation from the detector
of interest back to source of
radiation
•Utils : general EM interfaces
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Software design
•Since the design is uniform for all EM packages
Allowing a coherent approach for high-energy and low-energy applications
A physical interaction or process is described by a process class
Naming scheme : « G4ProcessName »
For example: G4Compton for photon Compton scattering
Assigned to Geant4 particle types
Inherit from G4VEmProcess base class
•A physical process can be simulated according to several models, each model being
described by a model class
Naming scheme : « G4ModelNameProcessNameModel »
For example: G4LivermoreComptonModel
Models can be assigned to certain energy ranges and G4Regions
Inherit from G4VEmModel base class
•Model classes provide the computation of
Cross section and stopping power
Sample selection of atom in compound
Final state (kinematics, production of secondaries…)
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Example : muon energy loss
•Continuous energy loss from processes
Ionisation
Production of e+e Bremsstrahlung
•Ionisation and delta-electron production
G4BetheBlochModel
•Below 200 keV – ICRU’49 parameterization of
dE/dx
G4BraggIonModel
•Radiative corrections to ionization at E > 1 GeV
• G4MuBetheBlochModel
Соседние файлы в папке geant4