Geant4 User's Guide for Application Developers - Geant4 - CERN

Tracking and Physicsspecifies only the abstract interface between physics processes and their data sets, and leaves the user free toimplement whatever sort of underlying structure is appropriate.The current implementation of the data set G4HadronCrossSections reuses the total cross-sections for inelastic andelastic scattering, radiative capture and fission as used with GHEISHA to provide cross-sections for calculationof the respective mean free paths of a given particle in a given material.Cross-sections for low energy neutron transportThe cross section data for low energy neutron transport are organized in a set of files that are read in bythe corresponding data set classes at time zero. Hereby the file system is used, in order to allow highly granularaccess to the data. The ``root'' directory of the cross-section directory structure is accessed through anenvironment variable, NeutronHPCrossSections, which is to be set by the user. The classes accessingthe total cross-sections of the individual processes, i.e., the cross-section data set classes for low energyneutron transport, are G4NeutronHPElasticData, G4NeutronHPCaptureData, G4NeutronHPFissionData, andG4NeutronHPInelasticData.For detailed descriptions of the low energy neutron total cross-sections, they may be registered by the user asdescribed above with the data stores of the corresponding processes for neutron interactions.It should be noted that using these total cross section classes does not require that the neutron_hp models also beused. It is up to the user to decide whethee this is desirable or not for his particular problem.A prototype of the compact version of neutron cross sections derived from HP database are provided with newclasses G4NeutronHPElasticData, G4NeutronCaptureXS, G4NeutronElasticXS, and G4NeutronInelasticXS.5.2.2.2. Hadrons at RestList of implemented "Hadron at Rest" processesThe following process classes have been implemented:• pi- absorption (class name G4PionMinusAbsorptionAtRest or G4PiMinusAbsorptionAtRest)• kaon- absorption (class name G4KaonMinusAbsorptionAtRest or G4KaonMinusAbsorption)• neutron capture (class name G4NeutronCaptureAtRest)• anti-proton annihilation (class name G4AntiProtonAnnihilationAtRest)• anti-neutron annihilation (class name G4AntiNeutronAnnihilationAtRest)• mu- capture (class name G4MuonMinusCaptureAtRest)• alternative CHIPS model for any negativly charged particle (class name G4QCaptureAtRest)Obviously the last process does not, strictly speaking, deal with a ``hadron at rest''. It does, nonetheless, sharecommon features with the others in the above list because of the implementation model chosen. The differencesbetween the alternative implementation for kaon and pion absorption concern the fast part of the emitted particlespectrum. G4PiMinusAbsorptionAtRest, and G4KaonMinusAbsorptionAtRest focus especially on a good descriptionof this part of the spectrum.Implementation Interface to Geant4All of these classes are derived from the abstract class G4VRestProcess. In addition to the constructor and destructormethods, the following public methods of the abstract class have been implemented for each of the abovesix processes:• AtRestGetPhysicalInteractionLength( const G4Track&, G4ForceCondition* )This method returns the time taken before the interaction actually occurs. In all processes listed above, except formuon capture, a value of zero is returned. For the muon capture process the muon capture lifetime is returned.• AtRestDoIt( const G4Track&, const G4Step&)This method generates the secondary particles produced by the process.• IsApplicable( const G4ParticleDefinition& )160