Geant4 Hadronic Physics - II

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1 Geant4 Hadronic Physics - II Geant4 Tutorial, Marshall Space Flight Center April 2012 Daniel Brandt (based on slides by T. Koi) based on Geant4 v9.5-p01

2 Overview Low energy neutron physics High-precision (HP) models Low-energy (LE) models Thermal scattering & chemical bonds Ion physics Cascade models Abrasion/Ablation models EM Dissociation 2

3 Low Energy Neutron Physics Low energy: <20 MeV High precision (HP) models are built by extrapolating data sets Datasets G4 Neutron Data Library (G4NDL) based on file format similar to Evaluated Nuclear data Library (ENDL) 3

4 HP processes available Elastic scattering - G4NeutronHPElastic Differential cross sections tabulated in cos θ, E Inelastic scattering - G4NeutronHPInelastic Supporting a large number of final states and secondary distribution models (isotropic emission, discrete two-body kinematics...) Capture - G4NeutronHPCapture Final capture state described by photon multiplicity or production cross-section given by data libraries Fission - G4NeutronHPFission Currently, only Uranium data available. Different neutron energy distribution functions are provided (tabulated, Maxwellian, evaporation spectrum...) 4

5 Elastic Capture Inelastic Inelastic Inelastic Inelastic Inelastic Inelastic CrossSection [barn] Verification of HP processes MeV Neutrons on 157 Gd G4 ENDF (n,nγ) (n,2n) (n,nα) (n,np) (n,p) (n,α) 5

6 Verification of HP processes - II Verification of High Precision Neutron models Energy Spectrum of Secondary Particles Gd154 (n,2n) channel 4.5E E E E E E E E E E E+06 4E+06 6E+06 8E+06 1E+07 1E+07 secondary neutron energy [ev] ENDF G4 result 6

7 Physics List for NeutronHP Create HP process and register data & model //For example elastic scattering below 20 MeV G4HadronElasticProcess* theneutronelasticprocess = new G4HadronElasticProcess(); // Cross Section Data set G4NeutronHPElasticData* thehpelasticdata = new G4NeutronHPElasticData(); theneutronelasticprocess->adddataset( thehpelasticdata ); // Model G4NeutronHPElastic* theneutronelasticmodel = new G4NeutronHPElastic(); theneutronelasticprocess->registerme(theneutronelasticmodel) Register the process with G4ProcessManager G4ProcessManager* pmanager = G4Neutron::Neutron()-> GetProcessManager(); pmanager->adddiscreteprocess( theneutronelasticprocess ); 7

8 Low Energy models In some cases, data for HP models may not be available When no HP model is available, the G4NeutronHPorLE models can be used G4NeutronHPorLE models provide low energy parametrization models/cross sections to replace the data-driven HP models. Elastic, inelastic, fission and capture models are available as G4NeutronHPorLE. 8

9 Physics List for NeutronHPorLE Create HPorLE process and register data & model //For example Elastic scattering below 20 MeV G4HadronElasticProcess* theneutronelasticprocess = new G4HadronElasticProcess(); // Model G4NeutronHPorLElasticModel* theneutronelasticmodel = new G4NeutronHPorLElasticModel(); theneutronelasticprocess->registerme(theneutronelasticmodel) // Cross Section Data set theneutronelasticprocess->adddataset( theneutronelasticmodel- >GiveHPXSectionDataSet() ); Notice that rather than acquiring data from a library, the data set is provided by the HPorLE model 9

10 Thermal Neutron Scattering At thermal energies, neutron scattering needs to take into account properties of chemically bound atoms: Translational motion, vibration and rotation of chemically bound atoms influences cross-sections and scattering energies Scattering cross section: E b E 2kT E Based on momentum transfer α, energy transfer β: E, S, ; E E 2 AkT E E, E E kt 10

11 Thermal Scattering Physics List Thermal scattering is created like any other neutron process Since it is only valid for thermal energies (~a few ev), usually combined with HP model so that scattering still works at higher E // Cross Section Data set theneutronelasticprocess->adddataset(new G4NeutronHPElasticData() ); theneutronelasticprocess->adddataset(new G4NeutronHPThermalScatteringData() ); // Neutron HP Elasctic scattering > 4eV G4NeutronHPElastic* theneutronelasticmodel = new G4NeutronHPElastic(); theneutronelasticmodel->setminenergy ( 4.0*eV ); // Neutron thermal Elasctic scattering < 4eV G4NeutronHPThermalScattering* thethermalmodel = new G4NeutronHPThermalScattering(); thethermalmodel->setmaxenergy ( 4.0*eV ); //register thermal and HP models theneutronelasticprocess->registerme(theneutronelasticmodel); theneutronelasticprocess->registerme(thethermalmodel); 11

12 Ion Physics Inelastic collisions Geant4 provides cross sections for N-N interactions from empirical, parametrized models Interactions between nuclei can be modelled by physics based cascade models or by less computationally intensive Abrasion/Ablation models Geant4 also provides a process for EM dissociation 12

13 Ion Physics Inelastic collisions Geant4 provides cross sections for N-N interactions from empirical, parametrized models Interactions between nuclei can be modelled by physics based cascade models or by less computationally intensive Abrasion/Ablation models Geant4 also provides a process for EM dissociation 13

14 Ion Physics cross sections Geant4 provides many different cross-section formulae from empirical, parametrized models The G4GeneralSpaceNNCrossSection class was created to help in selection of the model References for the different models used are provided in the appendix to this presentation 14

15 Binary Cascade Model 3-D model of nucleus constructed from A, Z A<16: Use harmonic oscillator shell model A>16: Use Woods Saxon model Each nucleon is treated as Gaussian wave packet, total nucleus wave function is product of all of these For every interacting nucleon, its momentum is sampled from the range [0, E Fermi ] and taken into account for collision probability and final state caluclation 15

16 Validating Binary Cascade Model 400 MeV neutrons incident on Carbon For low scattering angles, very good agreement between models and data Additional validation graphs in Appendix B of this presentation 16

17 Cross Section [mb] Cross Section [mb] Validating Binary Cascade Model - II Fragment Production Si 453 MeV/n on Al Si 490 MeV/n on Cu DATA G4 DATA G Al Mg Na Ne F O N C Particle Species 1 Al Mg Na Ne F O N C Particle Species According to F. Flesch et al., J, RM,

18 Binary Cascade Physics List Geant4 provides cross sections for N-N interactions from empirical, parametrized models //create process G4HadronInelasticProcess* theipgenericion = new G4HadronInelasticProcess("IonInelastic", G4GenericIon::GenericIon() ); // Cross Section Data Set G4TripathiCrossSection * TripathiCrossSection= new G4TripathiCrossSection; G4IonsShenCrossSection * ashen = new G4IonsShenCrossSection; theipgenericion->adddataset(ashen); theipgenericion->adddataset(tripathicrosssection); // Model G4BinaryLightIonReaction * thegenionbc= new G4BinaryLightIonReaction(); theipgenericion->registerme(thegenionbc); //Apply Processes to Process Manager of Neutron G4ProcessManager* pmanager = G4GenericIon:: GenericIon()-> GetProcessManager(); pmanager->adddiscreteprocess( theipgenericion ); 18

19 Abrasion/Ablation Model Basic idea: Use geometric arguments to simulate nuclearnuclear interactions without running full cascade model Ablation simulates de-excitation of nuclear prefragments increases accuracy of geometric models Ablation process Abrasion process projectile target nucleus 19

20 Abrasion/Ablation Model - II Abrasion/Ablation models are much less computationally expensive than full cascade models Provides reduced accuracy Ablation/Abrasion processes are provided by G4WilsonAbrasionModel and G4WilsonAblationModel Ablation is simulated using Geant4 nuclear excitation models 20

21 cross-section [mb] Validating Abrasion/Ablation 12 C-C 1050 MeV/nuc Abrasion + ablation Experiment NUCFRG C11 C10 B11 B10 Be10 Be9 Be7 Li8 Li7 Li6 He6 Fragment 21

22 Abrasion Physics List G4HadronInelasticProcess* theipgenericion = new G4HadronInelasticProcess("IonInelastic", G4GenericIon::GenericIon() ); // Cross Section Data Set G4IonsShenCrossSection * ashen = new G4IonsShenCrossSection; theipgenericion->adddataset(ashen); // Low-E model G4BinaryLightIonReaction * thegenionbc= new G4BinaryLightIonReaction; thegenionbc->setminenergy(0*mev); thegenionbc->setmaxenergy(0.07*gev); // High-E model using abrasion for faster simulation theipgenericion->registerme(thegenionbc); G4WilsonAbrasionModel* thegenionabrasion = new G4WilsonAbrasionModel(); theipgenericion->registerme(thegenionabrasion); //Apply Processes to Process Manager of Neutron G4ProcessManager* pmanager = G4GenericIon:: GenericIon()-> GetProcessManager(); pmanager->adddiscreteprocess( theipgenericion ); 22

23 EM Dissocation In the EM Dissociation process a relativistic nucleus causes a target nucleus to fragment by exhange of a virtual photon Especially important for nuclei with large proton numbers Geant4 EM dissociation is based on NUCFRG2 (NASA TP 3533), validation table provided in Appendix C 23

24 EM Dissocation Physics List G4HadronInelasticProcess* theipgenericion = new G4HadronInelasticProcess("IonInelastic", G4GenericIon::GenericIon() ); // Cross Section Data Set G4EMDissociationCrossSection* EMDCrossSec = new G4EMDissociationCrossSection(); theipgenericion->adddataset( EMDCrossSect ); // Model G4EMDissociation* theemdmodel = new G4EMDissociation; theipgenericion->registerme(theemdmodel); //Apply Processes to Process Manager of Neutron G4ProcessManager* pmanager = G4GenericIon:: GenericIon()-> GetProcessManager(); pmanager->adddiscreteprocess( theipgenericion ); 24

25 Summary Geant4 provides high-precision (HP) data-drivven neutron elastic, inelastic, fission and capture processes Parametrized models are provided where no HP data is available Thermal neutron scattering takes into account chemical properties Geant4 provides sophisticated models for N-N interaction of varying computational complexity There is a wealth of validation information for all hadronic processes, indicating good agreement between experiment and simualtion 25

26 Appendix A Cross section references Tripathi Formula NASA Technical Paper TP-3621 (1997) Tripathi Light System NASA Technical Paper TP (1999) Kox Formula Phys. Rev. C (1987) Shen Formula Nuclear Physics. A (1989) Sihver Formula Phys. Rev. C (1993) 26

27 Appendix B Cascade Validation 400 MeV neutrons incident on Carbon 27

28 Appendix B Cascade Validation II Copper Thick Target Lead Thick Target 28

29 Appendix C EM Dissociation Validation Target Emulsion nuclei: Ag 61.7%, Br 34.2%, CNO 4.0% and H 0.1% Projectile Energy [GeV/nuc] Product from ED G4EM Dissociation [mbarn] Experiment [mbarn] Mg Na-23 + p Si Al-27 + p Al-27 + p O N-15 + p * M A Jilany, Nucl Phys, A705, ,