Electromagnetic Physics Electromagnetic Physics http://cern.ch/geant4 The full set of lecture notes of this Geant4 Course is available at http://www.ge.infn.it/geant4/events/nss2003/geant4course.html Geant4 Training 2003
Standard Electromagnetic Physics Standard Electromagnetic Physics Michel Maire LAPP Geant4 Training 2003
Standard electromagnetic physics in Geant4 Standard electromagnetic physics in Geant4 The model assumptions are: The projectile has energy ≥ 1 keV Atomic electrons are quasi-free: their binding energy is neglected (except for the photoelectric effect) The atomic nucleus is free: the recoil momentum is neglected Matter is described as homogeneous, isotropic, amorphous Geant4 Training 2003
Compton scattering Compton scattering Geant4 Training 2003
Standard Compton scattering in Geant4 Standard Compton scattering in Geant4 Geant4 Training 2003
γ conversion conversion γ Geant4 Training 2003
Standard total cross section per atom in Geant4 Standard total cross section per atom in Geant4 Geant4 Training 2003
Ionisation Ionisation Geant4 Training 2003
Mean rate of energy loss Mean rate of energy loss Geant4 Training 2003
Fluctuations in energy loss Fluctuations in energy loss The model in Geant4 The model in Geant4 Geant4 Training 2003
Production of δ δ rays rays Production of 2000 MeV electron, proton and α in Al Geant4 Training 2003
Bremsstrahlung Bremsstrahlung Differential cross section Geant4 Training 2003
Emission of energetic photons and Emission of energetic photons and truncated energy loss rate truncated energy loss rate 1 MeV cut 10 keV cut Geant4 Training 2003
LPM effect LPM effect LPM 10 GeV e- in Pb, γ spectrum Geant4 Training 2003
Multiple Coulomb scattering Multiple Coulomb scattering Geant4 Training 2003
Particle transport in Monte Carlo simulation Particle transport in Monte Carlo simulation Geant4 Training 2003
Multiple scattering in Geant4 Multiple scattering in Geant4 More details in Geant4 Physics Reference Manual Geant4 Training 2003
Cherenkov Cherenkov radiation radiation Cherenkov emission from optical photons in Geant4 Geant4 Training 2003
Optical photons Optical photons Production of optical photons in detectors is mainly due to Cherenkov effect and scintillation Photon entering a light concentrator Processes in Geant4: CTF-Borexino Processes in Geant4: - in-flight absorption - Rayleigh scattering - medium-boundary interactions (reflection, refraction) Geant4 Training 2003
Muons Muons 1 keV up to 1000 PeV scale 1 keV up to 1000 PeV scale simulation of ultra-high energy and cosmic ray physics High energy extensions based on theoretical models 45 GeV muons Geant4 Training 2003
Direct e+e- - pair creation by pair creation by muon muon Direct e+e Geant4 Training 2003
Photo Absorption Ionisation Ionisation (PAI) Model (PAI) Model Photo Absorption Ionisation energy loss produced by charged thin layers of absorbers particles in thin layers 3 GeV/c π in 1.5 cm 5 GeV/c π in 20.5 µ m Si Ar+CH4 Ionisation energy loss distribution produced by pions, PAI model Geant4 Training 2003
Low Energy Electromagnetic Physics Low Energy Electromagnetic Physics Maria Grazia Pia INFN Genova Maria.Grazia.Pia@cern.ch on behalf of the Low Energy Electromagnetic Working Group http://www.ge.infn.it/geant4/lowE/ Geant4 Training 2003
What is What is A package in the Geant4 electromagnetic package A package in the Geant4 electromagnetic package – geant4/source/processes/electromagnetic/lowenergy/ A set of processes extending the coverage of electromagnetic A set of processes extending the coverage of electromagnetic interactions in Geant4 down to “ low” interactions in Geant4 down to “ low” energy energy – 250 eV (in principle even below this limit)/ 100 ev for electrons and photons – down to the approximately the ionisation potential of the interacting material for hadrons and ions A set of processes based on detailed models A set of processes based on detailed models – shell structure of the atom – precise angular distributions Complementary to the “standard” electromagnetic package Complementary to the “standard” electromagnetic package Geant4 Training 2003
Overview of physics Overview of physics In progress Compton scattering – More precise angular distributions Rayleigh scattering (Rayleigh, photoelectric, Photoelectric effect Bremsstrahlung etc.) Pair production – Polarised γ conversion, photoelectric Bremsstrahlung Ionisation in two “flavours” of models: • based on the Livermore Library Livermore Library • à la Penelope Penelope Polarised Compton + atomic relaxation Development plan – fluorescence – Driven by user requirements – Auger effect – Schedule compatible with available resources following processes leaving a vacancy in an atom Geant4 Training 2003
Software Process Software Process A rigorous approach to software engineering in support of a better quality of the software especially relevant in the physics domain of Geant4-LowE EM several mission-critical applications (space, medical…) Spiral approach A life-cycle model that is both iterative and incremental Collaboration-wide Geant4 software process, tailored to the specific projects Public URD Public URD Full traceability through Huge effort invested into SPI current current UR/OOD/implementation/test started from level 1 (CMM) � Testing suite and testing process status status in very early stages: chaotic, � Public documentation of left to heroic improvisation procedures Defect analysis and prevention etc. … Geant4 Training 2003
User requirements User requirements Various methodologies adopted to capture capture URs URs Various methodologies adopted to User Requirements User Requirements Elicitation through interviews and surveys G GE EA AN NT T4 4 L LO OW W E EN NE ER RG GY Y useful to ensure that UR are complete and � EL LE EC CT TR RO OM MA AG GN NE ET TI IC C P PH HY YS SI IC CS S there is wide agreement E Joint workshops with user groups Posted on the WG web site Use cases Analysis of existing Monte Carlo codes User Requirements Document Study of past and current experiments Status: in CVS repository Direct requests from users to WG coordinators Version: 2.4 Project: Geant4-LowE Reference: LowE-URD-V2.4 Created: 22 June 1999 Last modified: 26 March 2001 Prepared by: Petteri Nieminen (ESA) and Maria Grazia Pia (INFN) Geant4 Training 2003
LowE processes based on Livermore Library Geant4 Training 2003
different approach w.r.t. Photons and electrons Photons and electrons Geant4 standard e.m. standard e.m. package Based on evaluated data libraries from LLNL: – EADL (Evaluated Atomic Data Library) – EEDL (Evaluated Electrons Data Library) – EPDL97 (Evaluated Photons Data Library) especially formatted for Geant4 distribution (courtesy of D. Cullen, LLNL) Validity range: 250 eV - 100 GeV – The processes can be used down to 100 eV, with degraded accuracy – In principle the validity range of the data libraries extends down to ~10 eV Elements Z=1 to Z=100 – Atomic relaxation: Z > 5 (transition data available in EADL) Geant4 Training 2003
Calculation of cross sections Calculation of cross sections Interpolation from the data libraries: ( ) ( ) ( ) ( ) σ + σ log log E / E log log E / E ( ( ) ) σ = 1 2 2 1 log E ( ) log E / E 2 1 E 1 and E 2 are the lower and higher energy for which data ( σ 1 and σ 2 ) are available 1 λ = Mean free path for a ( ) ∑ σ ⋅ E n process, at energy E: i i i n i = atomic density of the i th element contributing to the material composition Geant4 Training 2003
Photons Photons Geant4 Training 2003
Compton scattering Compton scattering σ ν ν ν 2 d 1 h h h Klein-Nishina = + − + Θ 2 2 r 0 2 4 cos 0 cross section: Ω ν ν ν 2 d 4 h h h 0 0 Energy distribution of the scattered photon according to the Klein-Nishina formula, multiplied by scattering functions F(q) from EPDL97 data library The effect of scattering function becomes significant at low energies – suppresses forward scattering Angular distribution of the scattered photon and the recoil electron also based on EPDL97 Geant4 Training 2003
Rayleigh scattering scattering Rayleigh Angular distribution: F(E,q)=[1+cos 2 (q)] ⋅ F 2 (q) – where F(q) is the energy-dependent form factor obtained from EPDL97 Improved angular distribution released in 2002, further improvements foreseen Geant4 Training 2003
Photoelectric effect Photoelectric effect Cross section – Integrated cross section (over the shells) from EPDL + interpolation – Shell from which the electron is emitted selected according to the detailed cross sections of the EPDL library Final state generation – Direction of emitted electron = direction of incident photon Deexcitation via the atomic relaxation sub-process – Initial vacancy + following chain of vacancies created Geant4 Training 2003
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