11 Detector Simulation
499
GEANT4 Bertini-type cascade [71]. A correction factor is used for the depletion of
nuclear shells by earlier interactions in both FLUKA and GEANT4 Bertini.
It uses ‘free-space’ cross-sections derived from hadron–proton measurements,
or, in some cases cross-sections modified for the presence of the nuclear medium
[72]. FLUKA accounts for nuclear medium effect on the resonance properties in
the treatment of pion interactions [20].
Hadrons may move in curved trajectories according to a chosen nuclear potential,
as in GEANT4 Binary and FLUKA, or in straight lines (GEANT4 Bertini). In
both cases, the potential is used to update the momentum of all hadrons before
interactions. Interaction products can use models or be sampled from data, must
observe the Pauli exclusion principle, and are subject to a hard-core nucleon
repulsion. Particles arriving at the nuclear boundary with enough energy are ejected,
while others are reflected and continue to interact. The difference of the total energy
of the remaining nucleons and the ground state energy that corresponds to them is
the excitation energy.
After either a fixed time or once the excitation energy has dipped below a
threshold, the remaining nucleons are handed to a pre-equilibrium or de-excitation
module. A pre-equilibrium model, such as the Precompound model, can eject higher
energy nucleons and is used with the GEANT4 Binary cascade. A similar model is
used in FLUKA. The subsequent de-excitation module combines evaporation, Fermibreakup for light nuclei, fission for heavy nuclei and other competitive channels.
A common de-excitation module is shared by all models in FLUKA. A custom
simpler de-excitation module is used in GEANT4 Bertini; recent extensions enabled
it to use the default “Preco” Pre Compound and de-excitation module, used after
Binary cascade and the higher energy string models (QGS and FTF). In MCNPX,
MARS and MCNP a common module is used with different parameters by the CEM
cascade and the higher energy LAQGSM [67] model.
Most cascade models are expected to work up to 1.5–3 GeV, yet they can
provide good results from 30 MeV up to 3–5 GeV. At higher energies their
assumptions break down, because quark degrees of freedom become important.
Including additional reactions with larger multiplicities of products, and effects such
as formation time (a simplified treatment of quantum-mechanical effects as a time
interval before secondary hadrons can interact) allows a cascade model to have a
higher energy limit. This is the case for the GINC/PEANUT cascade in FLUKA and
the GEANT4 Bertini cascade.
Early versions of GEANT4 until 9.6 also included the CHIPS model [73]
applicable for intermediate energies. It described a nucleus in terms of nucleon
clusters, and interactions as exchanges of quarks and was part of physics lists used
in LHC Run 1.
The GEANT4 Bertini cascade underwent a substantial rewrite and upgrade [74].
As a result, all long-lived hadrons can be projectiles (adding K, , , and ). It
also implements gamma- and lepto-nuclear reactions. Its energy range was extended
up to 15–20 GeV, with the addition of final states with higher multiplicities, up to
nine for proton–proton. Total and partial cross sections and final states were obtained
from the CERN-HERA data compilations, and completed using symmetries and
499
GEANT4 Bertini-type cascade [71]. A correction factor is used for the depletion of
nuclear shells by earlier interactions in both FLUKA and GEANT4 Bertini.
It uses ‘free-space’ cross-sections derived from hadron–proton measurements,
or, in some cases cross-sections modified for the presence of the nuclear medium
[72]. FLUKA accounts for nuclear medium effect on the resonance properties in
the treatment of pion interactions [20].
Hadrons may move in curved trajectories according to a chosen nuclear potential,
as in GEANT4 Binary and FLUKA, or in straight lines (GEANT4 Bertini). In
both cases, the potential is used to update the momentum of all hadrons before
interactions. Interaction products can use models or be sampled from data, must
observe the Pauli exclusion principle, and are subject to a hard-core nucleon
repulsion. Particles arriving at the nuclear boundary with enough energy are ejected,
while others are reflected and continue to interact. The difference of the total energy
of the remaining nucleons and the ground state energy that corresponds to them is
the excitation energy.
After either a fixed time or once the excitation energy has dipped below a
threshold, the remaining nucleons are handed to a pre-equilibrium or de-excitation
module. A pre-equilibrium model, such as the Precompound model, can eject higher
energy nucleons and is used with the GEANT4 Binary cascade. A similar model is
used in FLUKA. The subsequent de-excitation module combines evaporation, Fermibreakup for light nuclei, fission for heavy nuclei and other competitive channels.
A common de-excitation module is shared by all models in FLUKA. A custom
simpler de-excitation module is used in GEANT4 Bertini; recent extensions enabled
it to use the default “Preco” Pre Compound and de-excitation module, used after
Binary cascade and the higher energy string models (QGS and FTF). In MCNPX,
MARS and MCNP a common module is used with different parameters by the CEM
cascade and the higher energy LAQGSM [67] model.
Most cascade models are expected to work up to 1.5–3 GeV, yet they can
provide good results from 30 MeV up to 3–5 GeV. At higher energies their
assumptions break down, because quark degrees of freedom become important.
Including additional reactions with larger multiplicities of products, and effects such
as formation time (a simplified treatment of quantum-mechanical effects as a time
interval before secondary hadrons can interact) allows a cascade model to have a
higher energy limit. This is the case for the GINC/PEANUT cascade in FLUKA and
the GEANT4 Bertini cascade.
Early versions of GEANT4 until 9.6 also included the CHIPS model [73]
applicable for intermediate energies. It described a nucleus in terms of nucleon
clusters, and interactions as exchanges of quarks and was part of physics lists used
in LHC Run 1.
The GEANT4 Bertini cascade underwent a substantial rewrite and upgrade [74].
As a result, all long-lived hadrons can be projectiles (adding K, , , and ). It
also implements gamma- and lepto-nuclear reactions. Its energy range was extended
up to 15–20 GeV, with the addition of final states with higher multiplicities, up to
nine for proton–proton. Total and partial cross sections and final states were obtained
from the CERN-HERA data compilations, and completed using symmetries and