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The space electronics physics list contains the best-guess selection of electromagnetic and hadronic physics processes required to run simulations of micro-electronics applications in a space environment. The processes and models are organized using a modular physics list SEPhysicsList.hh , SEPhysicsList.cc , and a set of physics constructors which allow related physics processes, models and particles to be grouped together. The physics constructors handle:
The boson physics constructor SEBosonPhysics.hh , SEBosonPhysics.cc , defines the gamma and two fictitious particles, the Geantino and the ChargedGeantino.
Three processes are assigned to the gamma:
The Geantino is a chargeless, massless, completely non-interacting particle which can be used for geometry and tracking diagnostics. The ChargedGeantino is also massless and non-interacting, but has a charge so that it can be tracked properly in a magnetic field. Aside from the transportation process, neither of these particles can be assigned an interaction process.
Two hadronic models are required to describe photon interactions with nuclei and nucleons. Hadronic models are discussed further in Hadron Physics.
The lepton physics constructor SELeptonPhysics.hh , SELeptonPhysics.cc , defines electrons, muons and taus along with their corresponding neutrinos. The following processes are assigned to each particle:
Note that the ionization and bremsstrahlung processes for e+/e- are different from those for mu+/mu-. They are specially tuned for the mass difference and other effects. The hadron ionization process is used for the tau because of its large mass.
One hadronic model is required to describe electron- and positron-induced nuclear reactions. The electro-nuclear reaction model relies on the method of equivalent photons to calculate a virtual photon spectrum, which in turn is interacted with the nucleus and nucleons using a photo-nuclear model similar to that in Boson Physics.
The ordering in the above list reflects the process ordering integers used in the phyiscs list (see code). This ordering is important due to the coupling between multiple scattering and energy loss processes.
No processes, except transportation, currently exist for the neutrinos.
Caution: Multiple scattering, ionization and bremsstrahlung processes should always be used together, and in the proper order. Removing one or more of them from their assigned particles will cause a crash or at least unpredictable behavior.
The hadron physics constructor SEHadronPhysics.hh , SEHadronPhysics.cc , defines all stable and long-lived baryons, except for the neutron, and all long-lived mesons. These are the particles that Geant4 can track and therefore require processes to be assigned. Short-lived particles are not tracked, but they appear in some hadronic models, so a large list of resonances, quarks and diquarks is also defined.
In this physics constructor electromagnetic and hadronic processes are assigned to the long-lived hadrons. For the hadronic processes an extra level of detail must be addressed. Cross sections and physics models must be assigned to the various processes before the processes are assigned to the particles. Default cross sections are provided by Geant4 and will be used unless otherwise indicated.
For hadron elastic scattering, the same process, G4HadronElasticProcess, is assigned to all the long-lived hadrons. The hadronic model which implements this process is G4LElastic, which has its origins in the GHEISHA model of Geant3. It is used for all incident particle energies. For hadron inelastic scattering, each long-lived hadron has its own process. Each of these processes is typically implemented by the combination of two or more models.
The following processes are assigned to each particle:
The backbone of this, and most, hadronic physics lists consists of the high energy (HEP) and low energy parameterized (LEP) models. They cover all the long-lived particles at all incident energies. These models are fast but usually not very detailed. Better models exist, but they do not apply to all particles at all energies. Where they apply, the better models are used. For instance, the Bertini cascade model is clearly better in the energy range 0 - 10 GeV but is only valid for protons, neutrons and pions. For energies above 15 GeV, the Quark-Gluon String model is best model, but it is only valid for pions, kaons, protons and neutrons.
For convenience, neutron physics is treated in its own constructor, SENeutronPhysics.hh , SENeutronPhysics.cc , and not as part of the hadron physics constructor. The neutron constructor defines the neutron and its associated models, procesess and cross sections. An option for the inclusion of high-precision neutron models is automatically invoked when the environment variable NeutronHPCrossSections is set. This variable must be set to a directory which contains the G4NDL3.7 neutron data library:
setenv NeutronHPCrossSections somedir/G4NDL3.7If this variable is not set, the LEP and Bertini cascade models will be invoked instead. The models used in this physics list are listed here:
The same medium- and high-energy hadronic inelastic processes and models are used for the neutron as for the proton in the hadron module above, that is the Low Energy Parameterized, Bertini Cascade and Quark-gluon String with Precompound models.
The ion physics constructor SEIonPhysics.hh , SEIonPhysics.cc , defines deuterons, tritons, 3He and alphas, as well as a generic ion. The processes and models assigned to the d, t, and alpha are essentially identical. Also, all three particles are covered by the same set of inelastic cross sections.
3He and generic ions are treated differently. There are currently no elastic hadronic processes or models for these particles. However, the inelastic reaction can be handled by the G4HadronInelasticProcess and G4BinaryLightIonReaction. The cross section data sets are the same as those for d, t and alpha, with the exception that the Tripathi light ion cross section must not be used for ions heavier than alphas.
The Binary Light Ion Reaction model has been applied to light and generic ions. However it is not recommended for use with incident ions having masses greater than 12C.
The decay physics constructor SEDecayPhysics.hh , SEDecayPhysics.cc , handles the decay channels for all unstable particles defined in the physics list. The same process is assigned to all unstable particles.