Geant4 Hadronic Physics - IIgeant4.slac.stanford.edu/MSFC2012/G4_hadronic-II_tutorial_dbrandt.pdf · Daniel Brandt, 18 April 2012 •At thermal energies, neutron scattering needs

Geant4 Hadronic Physics – II Tutorial

Daniel Brandt, 18 April 2012

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

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)

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...)

5

Verification of HP processes



0.001

0.01

0.1

1

10

Ela

stic

Cap

ture

Inela

stic

Inela

stic

Inela

stic

Inela

stic

Inela

stic

Inela

stic

(n,nγ) (n,2n) (n,nα) (n,np) (n,p) (n,α)

Cro

ssSection [

barn

]

G4

ENDF

20 MeV Neutrons on 157 Gd

6

Verification of HP processes - II



Verification of High Precision Neutron models

Energy Spectrum of Secondary Particles

Gd154 (n,2n) channel

0.0E+005.0E-081.0E-07

1.5E-072.0E-072.5E-073.0E-07

3.5E-074.0E-074.5E-07

0 2E+06 4E+06 6E+06 8E+06 1E+07 1E+07

secondary neutron energy [eV]

ENDF

G4 result

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 );

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 .

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)


theNeutronElasticProcess->AddDataSet( theNeutronElasticModel-

>GiveHPXSectionDataSet() );

•Notice that rather than acquiring data from a library, the data

set is provided by the HPorLE model

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:

; ,2

,

SE

E

kTEE b

•Based on momentum transfer α, energy transfer β:

kT

EE

AkT

EEEE

,

2

11

Thermal Scattering Physics List




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);

•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

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


•Geant4 also provides a process for EM dissociation

13

Ion Physics – Inelastic collisions





•Interactions between nuclei can be modelled by physics based

cascade models or by less computationally intensive


•Geant4 also provides a process for EM dissociation

14

Ion Physics – cross sections



•Geant4 provides many different cross-section formulae from


•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

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, EFermi] and taken into account for collision

probability and final state caluclation

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

17

Validating Binary Cascade Model - II



Si 453 MeV/n on Al

1

10

100

1000

Al Mg Na Ne F O N C

Particle Species

Cro

ss S

ection [

mb]

DATA

G4

Si 490 MeV/n on Cu

1

10

100

1000

Al Mg Na Ne F O N C

Particle SpeciesC

ross

Section [

mb]

DATA

G4

Fragment Production

According to F. Flesch et al., J, RM, 34 237 2001

18

Binary Cascade Physics List





//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 );

19

Abrasion/Ablation Model



•Basic idea: Use geometric arguments to simulate nuclear-

nuclear interactions without running full cascade model

Ablation

process

Abrasion

process

target

nucleus

projectile •Ablation simulates

de-excitation of

nuclear pre-

fragments –

increases accuracy

of geometric models

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

21

Validating Abrasion/Ablation



12C-C 1050 MeV/nuc

0.1

1.0

10.0

100.0

C11 C10 B11 B10 Be10 Be9 Be7 Li8 Li7 Li6 He6

Fragment

cro

ss-s

ecti

on

[m

b]

Abrasion + ablation

Experiment

NUCFRG2

22

Abrasion Physics List






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);




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

24

EM Dissocation Physics List






G4EMDissociationCrossSection* EMDCrossSec = new G4EMDissociationCrossSection();

theIPGenericIon->AddDataSet( EMDCrossSect );

// Model

G4EMDissociation* theEMDModel = new G4EMDissociation;

theIPGenericIon->RegisterMe(theEMDModel);




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

26

Appendix A – Cross section references



Tripathi Formula NASA Technical Paper TP-3621 (1997)

Tripathi Light System NASA Technical Paper TP-209726 (1999)

Kox Formula Phys. Rev. C 35 1678 (1987)

Shen Formula Nuclear Physics. A 49 1130 (1989)

Sihver Formula Phys. Rev. C 47 1225 (1993)

27

Appendix B – Cascade Validation



•400 MeV neutrons incident on

Carbon

28

Appendix B – Cascade Validation II



Copper Thick Target Lead Thick Target

29

Appendix C – EM Dissociation Validation



Projectile Energy

[GeV/nuc]

Product from ED G4EM

Dissociation

[mbarn]

Experiment

[mbarn]

Mg-24 3.7 Na-23 + p 124 2 154 31

Si-28 3.7 Al-27 + p 107 1 186 56

14.5 Al-27 + p 216 2 165 24†

128 33‡

O-16 200 N-15 + p 331 2 293 39†

342 22*

M A Jilany, Nucl Phys, A705, 477-493, 2002.

Target Emulsion nuclei: Ag 61.7%, Br 34.2%, CNO 4.0% and H 0.1%Target Emulsion nuclei: Ag 61.7%, Br 34.2%, CNO 4.0% and H 0.1%

Documents

Geant4 Hadronic Physics - IIgeant4.slac.stanford.edu/MSFC2012/G4_hadronic-II_tutorial_dbrandt.pdf · Daniel Brandt, 18 April 2012 •At thermal energies, neutron scattering needs