Physics & Biasing

Physics & Biasing#

Physics macro commands#

Macro commands related to Electromagnetic and Hadronic physics of the simulation.

See brief descriptions of the different available physics modules and models in the Physics List section.

Macro command

Type

M?

Description

Example value

Default value

/SEE/physics/addPhysics

string

n

Adding a G4 Physics module

G4IonPhysics

See Physics List

/SEE/physics/removeProcess

string, string

n

Remove a process of a particle type

e-, eIoni

-

Caution

Define physics with caution, since missing (not added or removed) physics models/processes can lead to wrong conclusions!

Cut macro commands#

Production range cuts#

Macro commands related to secondary particle production range cuts.

Macro command

Type

M?

Description

Example value

Default value

/cuts/setLowEdge

double u

n

Lower limit of production threshold when range cut is converted to energy

100 eV

990 eV

/SEE/cuts/gammaCutWorld

double u

n

Production range cut for \(\gamma\) in World region

2.5 mm

1 m

/SEE/cuts/electronCutWorld

double u

n

Production range cut for \(e^-\) in World region

100 um

1 m

/SEE/cuts/positronCutWorld

double u

n

Production range cut for \(e^+\) in World region

10 um

1 m

/SEE/cuts/hadronsCutWorld

double u

n

Production range cut for \(p\) and other hadrons in World region

200 nm

1 mm

/SEE/cuts/allCutsWorld

double u

n

Production range cut for all particles in World region

1 um

-

/SEE/cuts/gamma

string, double u

n

Production range cut for \(\gamma\) in the selected region

SV 2.5 mm

1 mm for Bulk, SV & BEOL

/SEE/cuts/electron

string, double u

n

Production range cut for \(e^-\) in the selected region

Bulk 100 um

1 \(\mu\)m for Bulk, SV & BEOL

/SEE/cuts/positron

string, double u

n

Production range cut for \(e^+\) in the selected region

BEOL 10 um

1 \(\mu\)m for Bulk, SV & BEOL

/SEE/cuts/hadrons

string, double u

n

Production range cut for \(p\) and other hadrons in the selected region

SV 200 nm

1 nm for Bulk, SV & BEOL

Production range cuts are converted to kinetic energy threshold internally by Geant4.

Default production cuts (both in range and energy values) used for Bulk, SV and BEOL regions (in this case in Silicon material):

Index : 1     used in the geometry : Yes
 Material : G4_Si
 Range cuts        :  gamma  1 mm           e-  1 um        e+  1 um      proton 1 nm 
 Energy thresholds :  gamma  6.93672 keV    e-  990 eV      e+  990 eV    proton 100 meV
 Region(s) which use this couple : 
    BEOL
    Bulk
    Sensitive

Attention

Set suitable production range cuts for your regions! Lower production range cuts can result in more accurate simulation, but significantly increase running time.

Tracking cuts#

Macro commands related to particle tracking cuts.

Macro command

Type

M?

Description

Example value

Default value

/process/em/lowestElectronEnergy

double u

n

Tracking cut for \(e^-\) and \(e^+\)

50 eV

100 eV or 1 keV *

/process/em/lowestMuHadEnergy

double u

n

Tracking cut for \(\mu\) and hadrons

10 eV

1 keV

In all ionization processes which simulate energy loss along step, tracking cuts are the lowest energy limit which forces full energy deposition of electrons and positrons (or muons and hadrons) at a step independently on material.

* Default value is 100 eV for G4EmStandardPhysics_option4 (default EM physics), G4EmStandardPhysics_option3, G4EmPenelopePhysics and G4EmLivermorePhysics, otherwise default value is 1 keV.

Attention

Set suitable tracking cuts! Lower tracking cuts can result in more accurate simulation, but significantly increase running time.

See also

Geant4 Low Energy Electromagnetic Physics

Biasing macro commands#

Macro commands related to microscopic cross-section (XS) biasing of particle interactions.

Caution

When biasing is used, the simulation becomes a non-analog Monte Carlo simulation! Use with caution, since over- and under-biasing can distort simulation results and therefore lead to wrong conclusions!

Macro command

Type

M?

Description

Example values

Default value

/SEE/biasing/biasParticle

string

n

Particle name to apply XS biasing for

proton, neutron, alpha, gamma, etc.

-

/SEE/biasing/biasProcess

string

n

Particle process name to be biased, can be used multiple times after biasParticle command

protonInelastic, hadElastic, etc.

-

/SEE/biasing/biasFactor

double

n

XS bias weight factor per particle (>0.)

1000

-

/SEE/biasing/biasNonPrimariesToo

bool

n

Apply XS bias for non-primary particles as well, by default only primary processes are biased

true

false

  • Multiple processes of particle species can be biased by using /SEE/biasing/biasProcess multiple times after the /SEE/biasing/biasParticle

  • By default, only primary particles are biased

  • For biasing particles that are non-primary particles, enable this by the /SEE/biasing/biasNonPrimariesToo command

  • Multiple particle species can be also biased by using a biasParticle command per each particle, and then the related biasProcess to define at least one process, plus the biasNonPrimariesToo is needed too

The Standard Scoring output histograms always contain the bias weight corrected data, so there is nothing to do with these histograms from a biasing point of view. The Detailed Scoring Hits output data is not corrected, however contains the inverse biasing weight of each particle and event in separate column (weight), which is equals to 1, when XS biasing is not used. For more, see Output Files.

Particles#

By default, all the particles available in Geant4 are defined in G4SEE (including short-lived, exotic particles and antiparticles).

Geant4 naming convention is applicable everywhere, where particles could be defined or referenced.

Ions/nuclei heavier than alpha are GenericIon particles (defined by \(Z\) atomic and \(A\) nucleon numbers, and optionally \(Q\) ionic charge).

Physics List#

G4SEE Physics list is a Modular Physics list, which can be build up from different (e.g. EM, elastic hadronic, inelastic hadronic, etc.) physics modules.

Physics modules are sets of physics models implemented for different particle processes (interactions).

One can add these physics modules listed below via the /SEE/physics/addPhysics macro command.

Note

Running time (or CPU time) of G4 strongly depends on the physics modules used. One can sacrifice some accuracy and precision in order to improve the performance and run the simulation faster.

Electromagnetic physics#

One of the EM modules (listed below) is mandatory and only one can be used for a run.

  • G4EmStandardPhysics_option4 - DEFAULT, RECOMMENDED (added and used by default, no need to add)

  • G4EmStandardPhysics_option3

    • (was) used for medical and space applications, accurate, but not as accurate as EM Opt4

    • G4 doc / EM Opt3

  • G4EmStandardPhysics_option2 - Do not use!

    • for HEP (calorimeters), fast but not precise, nor accurate, used by LHCb

  • G4EmStandardPhysics_option1 - Do not use!

    • for HEP (calorimeters), fast but not precise, nor accurate, used by CMS

  • G4EmStandardPhysics_option - Do not use!

    • used by ATLAS

  • G4EmPenelopePhysics

    • Specific low-energy Penelope models are used for \(\gamma\), \(e^{\pm}\) between 250 eV and 1 GeV energy

    • Above 1 GeV and for all other charged particle, it is the same as the EM Opt4

  • G4EmLivermorePhysics

  • G4MicroElecPhysics - EXPERIMENTAL (not recommended yet)

    • Low-energy microdosimetry for Silicon only, >16.7 eV energy

    • This module is limited to the Sensitive volume only

    • Extremely CPU time-consuming

Hadron & Ion Elastic physics#

XS = Cross-Section; FS = Final State

Elastic physics modules for hadrons or heavy ions. Only one can be chosen from the elastic modules denoted by (*).

  • G4HadronElasticPhysics (*)

    • Hadron nuclear elastic process for all hadrons (except GenericIon)

    • proton: Barashenkov-Glauber-Gribov XS; Chips FS

    • neutron: G4NeutronElasticXS; Chips FS

  • G4HadronElasticPhysicsHP (*) - recommended for neutrons

    • Same as G4HadronElasticPhysics, but for neutron < 20 MeV: NeutronHP XS & FS

  • G4HadronDElasticPhysics (*)

    • Hadron nuclear elastic process for all hadrons (except GenericIon)

    • proton: Barashenkov-Glauber-Gribov XS; Diffuse model FS where applicable, else Gheisha

    • neutron: G4NeutronElasticXS; Diffuse model FS where applicable, else Gheisha

  • G4HadronHElasticPhysics (*)

    • Hadron nuclear elastic process for all hadrons (except GenericIon)

    • proton: Barashenkov-Glauber-Gribov XS; Diffuse model FS (except for Hydrogen where Chips is used)

    • neutron: G4NeutronElasticXS; Diffuse model FS (except for Hydrogen where Chips is used)

  • G4IonElasticPhysics - recommended for heavy ions

    • Elastic process only for GenericIon: Glauber-Gribov XS and Diffuse model FS

  • G4ThermalNeutrons - recommended for thermal neutrons

    • High Precision thermal scattering model, only for neutron < 4 eV

    • Based on thermal scattering data of evaluated nuclear data libraries (ENDF/B-VI, Release 2)

    • Materials (elements): TS_Aluminium_Metal (Al), TS_Beryllium_Metal (Be), TS_Iron_Metal (Fe), G4_BERYLLIUM_OXIDE (Be, O), G4_GRAPHITE (C), G4_POLYETHYLENE (H), G4_URANIUM_OXIDE (U, O), G4_WATER (H) (only the relevant ones are listed here)

    • Should be added as the last (elastic, inelastic) hadronic physics module, since it overwrites any previously added neutron model between 0-4 eV

Hadron Inelastic physics#

Inelastic physics modules are combinations of several models applicable on different energy ranges. The major models are:

  • QGS: Quark-Gluon string models (>15 GeV)

  • FTF: Fritiof Parton model (>5 GeV)

  • BIC: Binary Cascade model (<10 GeV)

  • BERT: Bertini Intranuclear Cascade model (<10 GeV)

  • INCLXX: Liège Intranuclear Cascade model (<10 GeV)

  • P: Precompound/de-excitation model

  • HP: High Precision neutron model (<20 MeV)

Inelastic physics modules have a specific naming convention, indicating the consisting sub-modules: <String(s)>_<PreComp>_<Cascade>_<Neutron>. The same naming convention is also used by the Reference (pre-packaged) Physics lists (not applicable to G4SEE).

It is not trivial which one to use and there is no best option to choose in general. It is heavily depends on the actual simulation case or study. It is strongly recommended to run the simulation several times adding different inelastic modules for comparison. In most cases, they result the same or very similar distribution, but there could be a discrepancy in the higher energy range of the \(E_{dep}\) distribution (hadronic tail).

Modules containing HP neutron model (their names ending with HP) are recommended for neutrons.

Only one can be chosen from the inelastic modules listed below. All of them are optional.

  • G4HadronInelasticQBBC

    • Recommended for accurate simulation of low-energy transport of protons and neutrons. Best agreement below 1 GeV for thin target experiments, It is also recommended for medical and space applications

    • For higher energies it is the same as the FTFP_BERT

    • G4 doc / QBBC (inelastic part only)

  • G4HadronPhysicsFTFP_BERT

    • Recommended for cosmic rays where good treatment of very high energy particles is required, but only below 10 TeV

    • Recommended for collider physics applications, best agreement with test beam calorimeter data, including shower shape, energy response and resolution

    • G4 doc / FTFP_BERT (inelastic part only)

  • G4HadronPhysicsFTFP_BERT_HP

  • G4HadronPhysicsFTFP_BERT_ATL

  • G4HadronPhysicsFTFQGSP_BERT

  • G4HadronPhysicsFTF_BIC

  • G4HadronPhysicsINCLXX

  • G4HadronPhysicsQGSP_BERT

  • G4HadronPhysicsQGSP_BERT_HP

  • G4HadronPhysicsQGS_BIC

  • G4HadronPhysicsQGSP_BIC

  • G4HadronPhysicsQGSP_BIC_HP

  • G4HadronPhysicsQGSP_FTFP_BERT

High Precision model settings#

For inelastic neutron-carbon interactions, the following commands should be used (see examples/diamond_detector.mac). This enables the NRESP71 model for neutron-carbon interactions, which is not enabled (false) by default.

/process/had/particle_hp/do_not_adjust_final_state    true
/process/had/particle_hp/use_NRESP71_model            true

All HP model related commands with their default values:

# Force the use of the Photon Evaporation model, instead of the neutron capture final state data.
/process/had/particle_hp/use_photo_evaporation        false
# Use only exact isotope data files, instead of allowing nearby isotope files to be used. 
# In this case if the exact file is not available, the cross section will be set to zero. 
/process/had/particle_hp/skip_missing_isotopes        false
# Switch off the Doppler broadening due to the thermal motion of the target nucleus. 
# This option provides a significant CPU performance advantage. 
/process/had/particle_hp/neglect_Doppler_broadening   false
# Disable to adjust final state for getting better conservation.
/process/had/particle_hp/do_not_adjust_final_state    false
# Enable to generate fission fragments.
/process/had/particle_hp/produce_fission_fragment     false
# Enable use of Wendt fission model. 
/process/had/particle_hp/use_Wendt_fission_model      false
# Enable to use NRESP71 model for n on C reaction.      
/process/had/particle_hp/use_NRESP71_model            false
# Set Verbose level of ParticleHP package.
/process/had/particle_hp/verbose                      1

Ion Inelastic physics#

Inelastic ion-ion processes for deuteron, triton, He3, alpha and GenericIon projectiles. Only one can be chosen from the ion inelastic modules listed below. All of them are optional.

  • G4IonPhysics

    • With Glauber-Gribov XS and Binary Light Ion (BIC, with Precompound/de-excitation) and FTFP (Fritiof string model with Precompound/de-excitation) for the final state. BIC is used for projectiles of kinetic energies below 6 GeV/nucleon, and FTF above 3 GeV/nucleon.

  • G4IonQMDPhysics

    • With Glauber-Gribov XS and BIC, QMD and FTFP for the final state. These three final-state models are used in the following intervals of projectile kinetic energy: BIC below 110 MeV/nucleon, QMD between 100 and 10 000 MeV/nucleon, and FTF above 9990 MeV/nucleon.

  • G4IonINCLXXPhysics

    • With Glauber-Gribov XS and INCLXX and FTFP for the final state. INCLXX is used below 3 GeV/nucleon, and FTF above 2.9 GeV/nucleon.

Decay physics#

Decay processes of unstable particles

  • G4DecayPhysics - DEFAULT, MANDATORY (used by default and can not be removed)

  • G4RadioactiveDecayPhysics (optional)

Transportation#

  • Transportation - DEFAULT, MANDATORY (used by default and can not be removed)