Geant4 Hadronic Physics

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Geant4 Hadronic Physics

• http//cern.ch/geant4

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Acnowledgements

• These slides are based on Dennis Wright, Aatos
  Helkkinen IEEE 2003 and IEEE 2004 Geant4 lecture
  notes and Tatsumi Koi from SLAC 2006 Course

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Outline

• Processes and hadronic physics
• Hadronic cross sections
• Parametrised models
• Theoretical models
• Model framework
• Physics lists
• Code examples
• Physics validation against experimental data
• Radioactive Decay Module and Ion Physics

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Hadronic physics challenge

• Even though there is an underlying theory (QCD),
  applying it is much more difficult than applying
  QED for simulating electromagnetic interactions
• We must deal with at least three energy régimes
• Chiral perturbation theory (lt 100 MeV)
• Resonance and cascade region (100 MeV 20 GeV)
• QCD strings (gt 20 GeV)
• Within each regime there are several
  (sub)-models
• Many of these are phenomenological

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The Geant4 philosophy of hadronics (1/2)

• Provide a general model framework that allows
  implementation of processes and models at many
  levels
• Separate models and processes in framework
• Hadronic models and cross sections implement
  processes
• Provide processes containing
• Many possible models and cross sections
• Default cross sections for each model

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The Geant4 philosophy of hadronics (2/2)

• Provide several optional models and cross section
  sets in each region
• Let the user decide which physics is best
• Complex task is handled with physics lists
• Educated guess physics lists are provided by
  use-case
• Validate new models against latest data
• Extensive and systematic validation program
• Understand the trade-off between performance,
  physics and general applicability vs. energy
  there is only one nature

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Geant4 process

• A process uses cross sections to decide when and
  where an interaction will occur
• GetPhysicalInteractionLength()
• A process uses an interaction model to generate
  the final state
• DoIt()
• Three types of process
• AtRest
• AlongStep
• PostStep
• Each particle has its own process manager
• Each process has a set of models coordinated with
  energy range manager

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Hadronic process

• At rest
• Stopped muon, pion, kaon, anti-proton
• Radioactive decay
• Elastic
• Same process for all long-lived hadrons
• Inelastic
• Different process for each hadron
• Photo-nuclear
• Electro-nuclear
• Capture
• Pion- and kaon- in flight
• Fission

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Cross sections

• Default cross section sets are provided for each
  type of hadronic process
• Fission, capture, elastic, inelastic
• Can be overridden or completely replaced
• Different types of cross section sets
• Some contain only a few numbers to parameterize
  cross section
• Some represent large databases (data driven
  models)
• Cross Section Management
• GetCrossSection() sees last set loaded for energy
  range

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Alternative cross sections

• Low energy neutrons
• G4NDL available as Geant4 distribution data files
• Available with or without thermal cross sections
• Neutron and proton reaction cross sections
• 20 MeV lt E lt 20 GeV
• Ion-nucleus reaction cross sections
• Good for E/A lt 1 GeV
• Isotope production data
• E lt 100 MeV

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Different types of hadronic shower models

• Data driven models
• Parametrisation driven models
• Theory driven models

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Models in hadronic framework
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Data driven models (1/2)

• Characterized by lots of data
• Cross section
• Angular distribution
• Multiplicity
• To get interaction length and final state, models
  simply interpolate data
• Usually linear interpolation of cross section,
  and Legendre polynomials
• Examples
• Coherent elastic scattering (pp, np, nn)
• Radioactive decay
• Neutrons (E lt 20 MeV)

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Data driven models (2/2)

• Transport of low energy neutrons in matter
• The energy coverage of these models is from
  thermal energies to 20 MeV
• The modeling is based on the data formats of
  ENDF/B-VI, and all distributions of this standard
  data format are implemented
• The data sets used are selected from data
  libraries that conform to these standard formats
• The file system is used in order to allow
  granular access to, and flexibility in, the use
  of the cross-sections for different isotopes, and
  channels
• Code in sub-directory /source/processes/hadronic/
  models/neutron_hp

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Parametrisation driven models (1/2)

• Depends on both data and theory
• Enough data to parameterize cross sections,
  multiplicities, angular distributions
• Final states determined by theory, sampling
• Use conservation laws to get charge, energy, etc.
  
• Examples
• Fission
• Capture
• LEP, GEISHA based HEP models

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Parametrisation driven models (2/2)

• Based on GHEISHA package of Geant3.21, two sets
  of models exist for inelastic scattering of
  particles in flight
• Low energy models
• E lt 20 GeV
• /hadronic/models/low_energy
• High energy models
• 20 GeV lt E lt O(TeV)
• /hadronic/models/high_energy
• Original approach to primary interaction, nuclear
  excitation, intra-nuclear cascade and evaporation
  is kept
• Fission, capture and coherent elastic scattering
  are also modeled through parametrised models

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Theory driven models (1/2)

• Dominated by theory (QCD, strings, chiral
  perturbation theory)
• Data used mainly for normalization and validation
  
• Final states determined by sampling theoretical
  distributions
• Philosophy implies the usage physics lists,
  providing wanted collection of models, such as
• Parton string models at high energies, of
  intra-nuclear transport models at intermediate
  energies, and of statistical break-up models for
  de-excitation

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Theory driven models (2/2)

• Parton string
• Projectiles with E gt 5 GeV
• /hadronic/models/parton_string
• Chiral invariant phase space, CHIPS
• All energies
• Quark-level event generator for the fragmentation
  of hadronic systems into hadrons
• Interactions between hadrons are treated as
  purely kinematic effects of quark exchange
• Decay of excited hadronic systems is treated as
  the fusion of two quark-partons within the system
• Includes nonrelativistic phase space of nucleons
  to explain evaporation
• /hadronic/models/chiral_inv_phase_space
• Nuclear de-excitation and breakup

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Bertini intra-nuclear cascade (1/2)

• Collection of theory driven models with
  parametrisation features
• /hadronic/models/cascade
• Intermediate energies 100 keV 10MeV
• Models included
• Bertini INC model with exitons
• Pre-equilibrium model
• Nucleus explosion model
• Fission model
• Evaporation model

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Bertini intra-nuclear cascade (2/2)

• For Agt4 a nuclei model is composed of three
  concentric spheres
• Impulse distribution in each region follows Fermi
  distribution with zero temperature
• Particle treated p,n, pions, photon evaporation
  and nuclear isotope remnats
• Latest addition include incident kaons up to an
  energy of 15 GeV
• Final states, will be included for K, K-, K0,
  K0bar, lambda, sigma, sigma0, sigma-, xi0 and xi-

Schematic presentation of the intra-nuclear
cascade. A hadron with 400 MeV energy is forming
an INC history. Crosses present the Pauli
exclusion principle in action.
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Hadronic model inventory
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Physics Lists putting physics into your
simulation

• User must implement a physics list
• Derive a class from G4VUserPhysicsList
• Define the particles required
• Register models and cross sections with processes
  
• Register processes with particles
• Set secondary production cuts
• In main(), register your physics list with the
  Run Manager
• Care is required
• Multiple models, cross sections allowed per
  process
• No single model covers all energies, or all
  particles
• Choice of model is heavily dependent on physics
  studied

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Physics lists by use case

• Geant4 recommendation
• Use example physics lists
• Go to Geant4 home page gt Site Index gt physics
  lists
• Many hadronic physics lists available including
• Low and high energy nucleon penetration shielding
  
• Low energy dosimetric applications
• Medical neutron applications
• Low background experiments (underground)

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Code Example (1/2)

• void MyPhysicsListConstructProton()
• G4ParticleDefinition proton
  G4ProtonProtonDefinition()
• G4ProcessManager protonProcessManager
• 
  proton-gtGetProcessManager()
• // Elastic scattering
• G4HadronElasticProcess protonElasticProcess
  
• 
  new G4HadronElasticProcess()
• G4LElastic protonElasticModel new
  G4LElastic()
• protonElasticProcess-gtRegisterMe(protonElastic
  Model)
• protonProcessManager-gtAddDiscreteProcess(proto
  nElasticProcess)
• ...

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Code example (2/2)

• ...
• // Inelastic scattering
• G4ProtonInelasticProcess protonInelasticProcess
  
  new G4ProtonInelasticProcess()
• G4LEProtonInelastic protonLowEnergyInelasticModel
  
• 
  new G4LEProtonInelastic()
• protonLowEnergyInelasticModel-gtSetMaxEnergy(20.0G
  eV)
• protonInelasticProcess-gtRegisterMe(protonLowEnergy
  InelasticModel)
• G4HEProtonInelasticprotonHighEnergyInelasticModel
  
• 
  new G4HEProtonInelastic()
• protonHighEnergyInelasticModel-gtSetMinEnergy(20.0
  GeV)
• protonInelasticProcess-gtRegisterMe(protonHighEnerg
  yInelasticModel)

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Gean3.21 based Geant4 LEP model pion production
from 730 MeV proton on Carbon
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Bertini cascade model pion production from 730
MeV proton on Carbon
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Bertini cascade model nuclei fragmet production
from 170 MeV proton on Uranium
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Double differential cross-section for neutrons
produced by 256 MeV protons.
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Comparison of differential pion yields for
positive and negative pions in pion Magnesium
reactions at 320 GeV lab momentum. The dots are
data and the open circles are Monte Carlo
predictions by G4QGSModel.
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Geant4 simulation of gammas from 14 MeV neutron
capture on uranium.
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Summary (1)

• Geant4 hadronic physics allows user to choose how
  a physics process should be implemented
• cross sections
• models
• Many processes, models and cross sections to
  choose from
• hadronic framework makes it easier for users to
  add more

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Summary (2)

• Parameterized models (LEP, HEP) handle the most
  particle types over the largest energy range
• based on fits to data and some theory
• not very detailed
• fast
  
• Cascade models (Bertini, Binary) are valid for
  fewer particles over a smaller energy range
• more theory-based
• more detailed
• slower

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Low energy (lt 20MeV) neutrons physics

• High Precision Neutron Models (and Cross Section
  Data Sets)
• G4NDL
• ENDF
• Elastic
• Inelastic
• Capture
• Fission
• NeutronHPorLEModel(s)

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G4NDL(Geant4 Neutron Data Library)

• The neutron data files for High Precision Neutron
  models
• The data are including both cross sections and
  final states.
• The data are derived evaluations based on the
  following evaluated data libraries (in alphabetic
  order)
• Brond-2.1
• CENDL2.2
• EFF-3
• ENDF/B-VI.0, 1, 4
• FENDL/E2.0
• JEF2.2
• JENDL-FF
• JENDL-3.1,2
• MENDL-2
• The data format is similar ENDF, however it is
  not equal to.

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Evaluated Nuclear Data File-6

• ENDF is used in two meanings
• One is Data Formats and Procedures
• How to write Nuclear Data files
• How to use the Nuclear Data files
• The other is Name of recommended libraries of USA
  nuclear data projects.
• ENDF/B-VI.8 (latest)
• 313 isotopes including 5 isomers
• 15 elements
• After G4NDL3.8 we concentrated translation from
  ENDF library.
• No more evaluation by ourselves.

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Ion PhysicsInelastic Reactions

• Cross Sections
• Model
• G4BinaryLightIon
• G4WilsonAbrasion

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Cross Sections

• Many cross section formulae for NN collisions are
  included in Geant4
• Tripathi, Shen, Kox and Sihver
• These are empirical and parameterized formulae
  with theoretical insights.
• G4GeneralSpaceNNCrossSection was prepared to
  assist users in selecting the appropriate cross
  section formula.

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References to NN Cross Section Formulae
implemented in Geant4

• Tripathi Formula
• NASA Technical Paper TP-3621 (1997)
• Tripathi Light System
• NASA Technical Paper TP-209726 (1999)
• Kox Formula
• Phys. Rev. C 35 1678 (1987)
• Shen Formula
• Nuclear Physics. A 49 1130 (1989)
• Sihver Formula
• Phys. Rev. C 47 1225 (1993)

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Ion PhysicsRadio Active Decay

• To simulate the decay of radioactive nuclei
• Empirical and data-driven model
• a, ß, ß- decay electron capture (EC) are
  implemented
• Data (RadioactiveDecay) derived from Evaluated
  Nuclear Structure Data File (ENSDF) 
• nuclear half-lives
• nuclear level structure for the parent or
  daughter nuclide
• decay branching ratios
• the energy of the decay process.
• If the daughter of a nuclear decay is an excited
  isomer, its prompt nuclear de-excitation is
  treated using the G4PhotonEvapolation
• Internal conversion is also implemented

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Radio Active Decay

• Analog sampling is default
• Biasing sampling also implemented
• The decays occur more frequently at certain times
  
• For a given decay mode the branching ratios can
  be sampled with equal probability
• split parent nuclide into a user-defined number
  of nuclides

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Radio Active DecayImportant notice for v8.0 users

• Problem report 843
• Previously, G4GenericIon was derived from G4VIon,
  which overloaded GetAtomicMass() to return the
  baryon number. G4GenericIon now inherits from
  G4ParticleDefinition, whose GetAtomicMass()
  returns a (default) atomic mass number of 0. This
  makes G4RadioactiveDecayIsApplicable(G4GenericIo
  n) fail (atomic mass is out-of-range), and hence
  renders G4RadioactiveDecay essentially unusable
  any physics lists attempting to add
  G4RadioactiveDecay to ions will exit with an
  error. A fix users can apply until this bug is
  fixed is to get the G4GenericIon and call
  SetAtomicMass(1) before adding G4RadioactiveDecay.
  
• ------- Additional Comments From
  kurasige_at_phys.sci.kobe-u.ac.jp 02/24/06 2205
  ------- Fixed tag of particles-V08-00-01 will be
  included next release.
• Before the next release, users need to call
  SetAtomicMass(1) for GenericIon before adding
  G4RadioactiveDecay.

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Summary

• High Precision Neutron models are data driven
  models and its used evaluated data libraries.
• However the library is not complete because there
  are no data for several key elements.
• Geant4 has abundant processes for Ion
  interactions with matter and also without matter.
• Without any extra modules, users may simulate ion
  transportation in the complex and realistic
  geometries of Geant4.
• Validation has begun and the first results show
  reasonable agreement with data. This work
  continues.

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Conclusion

• Geant4 provides a large number of hadronic
  physics models for use in simulation
• Cross sections, either calculated or from
  databases, are available to be assigned to
  processes
• Interactions are implemented by models which are
  then assigned to processes.
• For hadrons there are many models to choose from,
  so physics lists are provided by use-case