Precision Validation of Geant4 Electromagnetic Physics

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Precision Validation of Geant4 Electromagnetic
Physics
Geant4 DNA Project Meeting 26 July 2004, CERN
Michela Piergentili INFN Genova, Italy
S. Guatelli (INFN Genova), V. Ivanchenko
(Budker), M. Maire (LAPP), A. Mantero (INFN
Genova), B. Mascialino (INFN Genova), P. Nieminen
(ESA), L. Pandola (INFN LNGS), S. Parlati (INFN
LNGS), A. Pfeiffer (CERN), M.G. Pia (INFN
Genova), M. Piergentili (INFN Genova), L. Urban
(Budapest)
http//www.ge.infn.it/geant4/analysis/test
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Geant4 Electromagnetic Physics

• It handles
• electrons and positrons
• gamma, X-ray and optical photons
• muons
• charged hadrons
• ions

• multiple scattering
• Bremsstrahlung
• ionisation
• annihilation
• photoelectric effect
• Compton scattering
• Rayleigh effect
• gamma conversion
• ee- pair production
• synchrotron radiation
• transition radiation
• Cherenkov
• refraction
• reflection
• absorption
• scintillation
• fluorescence
• Auger

• Alternative models for the same physics process
• High energy models
• fundamental for LHC experiments, cosmic ray
  experiments etc.
• Low energy models
• fundamental for space and medical applications,
  neutrino experiments, antimatter spectroscopy etc.

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Standard electromagnetic processes
1 keV up to 100 TeV

• Photons
• Compton scattering
• - g conversion
• photoelectric effect
• Electrons and positrons
• Bremsstrahlung
• Ionisation
• - d ray production
• positron annihilation
• synchrotron radiation
• Charged hadrons
• Variety of models for ionisation and energy loss

Shower shapes
Courtesy of D. Wright (Babar)
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Geant4 Low Energy Package

• Geant4 Low Energy Package is fundamental for
• Biomedical applications
• Space Science
• Neutrino and dark matter experiments
• Geant4 Low Energy Package describes the
  interactions of photons, electrons, positrons,
  hadrons and ions with matter down to low
  energies.
• Extensions of the physics models
• down to 250 eV / 100 eV for electrons and photons
• down to lt 1 keV for protons, antiprotons, ions
• Two models available
• based on evaluated data libraries
• based on Penelope analytical models

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Low energy e.m. extensions
Fundamental for neutrino/dark matter experiments,
space and medical applications, antimatter
spectroscopy etc.
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Processes à la Penelope

• The whole physics content of the Penelope Monte
  Carlo code has been re-engineered into Geant4
  (except for multiple scattering)
• for photons, electrons, positrons
• Physics models by F. Salvat (University of
  Barcelona, Spain),
• J.M. Fernandez-Varea (University of
  Barcelona, Spain), E. Acosta
• (University of Cordoba, Argentina), J.
  Sempau (University of Catalonia, Spain)
• Power of the OO technology
• extending the software system
• is easy
• all processes obey to the same
• abstract interfaces
• using new implementations in
• application code is simple

x-ray attenuation coeff in Al
Attenuation coeff. (cm2/g)
NIST data Penelope
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E.M. Physics Validation

• Validation is fundamental in Geant4
• Validations at different levels
• Comparisons to experimental measurements and
  recognised standard references

• Unit, integration, system testing
• Microscopic physics validation
• Macroscopic validation experimental use cases

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Microscopic validation

• Validation of Geant4 electromagnetic physics
  models
• Attenuation coefficients, CSDA ranges, Stopping
  Power, distributions of physics quantities
• Quantitative comparisons to experimental data and
  recognised standard references

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Photon mass attenuation coefficient
x-ray attenuation coeff in U
NIST data Penelope
c219.3 n22 p0.63
Absorber Materials Be, Al, Si, Ge, Fe, Cs, Au,
Pb, U
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Electron stopping power and CSDA range
G4 Standard G4 LowE-EPDL NIST
Absorber Materials Be, Al, Si, Ge, Fe, Cs, Au,
Pb, U
G4 Standard G4 LowE-EPDL NIST
CSDA range particle range without energy loss
fluctuations and multiple scattering
Experimental set-up
centre
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Transmission tests
Experimental set-up
e- beam
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Backscattering coefficient E100keV
Backscattered e-
Experimental set-up
Incident e- beam
Angle of incidence (with respect to the normal to
the sample surface) 0
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The problem of validation finding reliable data
Note Geant4 validation is not always
easy experimental data often exhibit large
differences!
Backscattering low energies - Au
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Conclusions

• Geant4 electromagnetic package encompasses an
  ample set of physics models, specialised for
  particle type, energy range and detector
  applications
• Exploitation of OO technology and sound
  architectural design make it possible to extend
  the Geant4 physics capabilities
• LowE / Livermore extensions
• LowE / Penelope
• LowE/ hadrons and ions
• Geant4 e.m. physics is subject to a rigorous
  testing and validation process
• Geant4 e.m. physics validation is in progress
  with Geant4 6.2
• IEEE TNS paper to be submitted in October

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Geant4 Physics Book

• A project has been launched for a Geant4 Physics
  Book
• To have a solid and comprehensive reference on
  Geant4 physics
• Wide effort involving Geant4 Collaboration
• Main focus of the project is Geant4 physics
  models validation