Geant4 入射粒子设置

在 PrimaryGeneratorAction 中设置 G4ParticleGun.

注意：关于粒子种类的定义，有两个位置可以定义，第一是在 PrimaryGeneratorAction 类的构造函数中定义，第二是在 GeneratePrimaries() 函数中定义。

在 PrimaryGeneratorAction 类的构造函数中定义，粒子种类可以在 .mac 文件中修改，举例代码取自 example B2：

1 B2PrimaryGeneratorAction::B2PrimaryGeneratorAction()2 : G4VUserPrimaryGeneratorAction()3 {4 G4int nofParticles = 1;5 fParticleGun = newG4ParticleGun(nofParticles);6

7 //default particle kinematic

8

9 G4ParticleDefinition*particleDefinition10 = G4ParticleTable::GetParticleTable()->FindParticle("proton");11

12 fParticleGun->SetParticleDefinition(particleDefinition);13 fParticleGun->SetParticleMomentumDirection(G4ThreeVector(0.,0.,1.));14 fParticleGun->SetParticleEnergy(3.0*GeV);15 }

在 GeneratePrimaries() 函数中定义，粒子种类可以在 .mac 文件中修改，举例代码取自 example B5：

1 #include "B5PrimaryGeneratorAction.hh"

2

3 #include "G4Event.hh"

4 #include "G4ParticleGun.hh"

5 #include "G4ParticleTable.hh"

6 #include "G4ParticleDefinition.hh"

7 #include "G4GenericMessenger.hh"

8 #include "G4SystemOfUnits.hh"

9 #include "Randomize.hh"

10

11 //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......

12

13 B5PrimaryGeneratorAction::B5PrimaryGeneratorAction()14 : G4VUserPrimaryGeneratorAction(),15 fParticleGun(nullptr), fMessenger(nullptr),16 fPositron(nullptr), fMuon(nullptr), fPion(nullptr),17 fKaon(nullptr), fProton(nullptr),18 fMomentum(1000.*MeV),19 fSigmaMomentum(50.*MeV),20 fSigmaAngle(2.*deg),21 fRandomizePrimary(true)22 {23 G4int nofParticles = 1;24 fParticleGun = newG4ParticleGun(nofParticles);25

26 auto particleTable =G4ParticleTable::GetParticleTable();27 fPositron = particleTable->FindParticle("e+");28 fMuon = particleTable->FindParticle("mu+");29 fPion = particleTable->FindParticle("pi+");30 fKaon = particleTable->FindParticle("kaon+");31 fProton = particleTable->FindParticle("proton");32

33 //default particle kinematics

34 fParticleGun->SetParticlePosition(G4ThreeVector(0.,0.,-8.*m));35 fParticleGun->SetParticleDefinition(fPositron);36

37 //define commands for this class

38 DefineCommands();39 }40

41 //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......

42

43 B5PrimaryGeneratorAction::~B5PrimaryGeneratorAction()44 {45 deletefParticleGun;46 deletefMessenger;47 }48

49 //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......

50

51 void B5PrimaryGeneratorAction::GeneratePrimaries(G4Event* event)52 {53 G4ParticleDefinition*particle;54 if(fRandomizePrimary) {55 G4int i = (int)(5.*G4UniformRand());56 switch(i) {57 case 0:58 particle =fPositron;59 break;60 case 1:61 particle =fMuon;62 break;63 case 2:64 particle =fPion;65 break;66 case 3:67 particle =fKaon;68 break;69 default:70 particle =fProton;71 break;72 }73 fParticleGun->SetParticleDefinition(particle);74 }75 else{76 particle = fParticleGun->GetParticleDefinition();77 }78

79 auto pp = fMomentum + (G4UniformRand()-0.5)*fSigmaMomentum;80 auto mass = particle->GetPDGMass();81 auto ekin = std::sqrt(pp*pp+mass*mass)-mass;82 fParticleGun->SetParticleEnergy(ekin);83

84 auto angle = (G4UniformRand()-0.5)*fSigmaAngle;85 fParticleGun->SetParticleMomentumDirection(86 G4ThreeVector(std::sin(angle),0.,std::cos(angle)));87

88 fParticleGun->GeneratePrimaryVertex(event);89 }90

91 //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......

92

93 voidB5PrimaryGeneratorAction::DefineCommands()94 {95 //Define /B5/generator command directory using generic messenger class

96 fMessenger97 = new G4GenericMessenger(this,98 "/B5/generator/",99 "Primary generator control");100

101 //momentum command

102 auto&momentumCmd103 = fMessenger->DeclarePropertyWithUnit("momentum", "GeV", fMomentum,104 "Mean momentum of primaries.");105 momentumCmd.SetParameterName("p", true);106 momentumCmd.SetRange("p>=0.");107 momentumCmd.SetDefaultValue("1.");108 //ok109 //momentumCmd.SetParameterName("p", true);110 //momentumCmd.SetRange("p>=0.");111

112 //sigmaMomentum command

113 auto&sigmaMomentumCmd114 = fMessenger->DeclarePropertyWithUnit("sigmaMomentum",115 "MeV", fSigmaMomentum, "Sigma momentum of primaries.");116 sigmaMomentumCmd.SetParameterName("sp", true);117 sigmaMomentumCmd.SetRange("sp>=0.");118 sigmaMomentumCmd.SetDefaultValue("50.");119

120 //sigmaAngle command

121 auto&sigmaAngleCmd122 = fMessenger->DeclarePropertyWithUnit("sigmaAngle", "deg", fSigmaAngle,123 "Sigma angle divergence of primaries.");124 sigmaAngleCmd.SetParameterName("t", true);125 sigmaAngleCmd.SetRange("t>=0.");126 sigmaAngleCmd.SetDefaultValue("2.");127

128 //randomizePrimary command

129 auto&randomCmd130 = fMessenger->DeclareProperty("randomizePrimary", fRandomizePrimary);131 G4String guidance132 = "Boolean flag for randomizing primary particle types.\n";133 guidance134 += "In case this flag is false, you can select the primary particle\n";135 guidance += "with /gun/particle command.";136 randomCmd.SetGuidance(guidance);137 randomCmd.SetParameterName("flg", true);138 randomCmd.SetDefaultValue("true");139 }140

141 //..oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......

第 54 - 72 行，粒子源随机出射一种粒子。

DefineCommands() 函数中定义了 macro 文件中使用的一些命令，有待研究。

可以使用 G4GeneralParticleSource 替代 G4ParticleGun

“For many applications G4ParticleGun is a suitable particle generator. However if you want to generate primary particles in more sophisticated manner, you can utilize G4GeneralParticleSource, the GEANT4 General Particle Source module (GPS), discussed in the next section ( General Particle Source).” Geant4 手册原话。

代码举例，取自 HPGe_60Co

PrimaryGeneratorAction.hh 文件

1 #ifndef PrimaryGeneratorAction_h2 #define PrimaryGeneratorAction_h 1

3

4 #include "G4VUserPrimaryGeneratorAction.hh"

5 #include "globals.hh"

6

7 classG4GeneralParticleSource;8 classG4Event;9

10 class PrimaryGeneratorAction : publicG4VUserPrimaryGeneratorAction11 {12 public:13 PrimaryGeneratorAction();14 virtual ~PrimaryGeneratorAction();15

16 virtual void GeneratePrimaries(G4Event*);17

18 const G4GeneralParticleSource* GetParticleGun() const {returnfParticleGun;}19

20 //Set methods

21 voidSetRandomFlag(G4bool );22

23 private:24 G4GeneralParticleSource* fParticleGun; //G4 particle gun

25 };26

27 //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......

28

29 #endif

1 #include "PrimaryGeneratorAction.hh"

2

3 #include "G4LogicalVolumeStore.hh"

4 #include "G4LogicalVolume.hh"

5 #include "G4Box.hh"

6 #include "G4Event.hh"

7 #include "G4ParticleGun.hh"

8 #include "G4GeneralParticleSource.hh"

9 #include "G4ParticleTable.hh"

10 #include "G4ParticleDefinition.hh"

11 #include "G4SystemOfUnits.hh"

12 #include "G4RandomDirection.hh"

13 #include "G4IonTable.hh"

14 #include "G4Geantino.hh"

15

16 #include "Randomize.hh"

17

18 //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......

19

20 PrimaryGeneratorAction::PrimaryGeneratorAction()21 : G4VUserPrimaryGeneratorAction()22 {23 fParticleGun = newG4GeneralParticleSource();24 }25

26 //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......

27

28 PrimaryGeneratorAction::~PrimaryGeneratorAction()29 {30 deletefParticleGun;31 }32

33 //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......

34

35 void PrimaryGeneratorAction::GeneratePrimaries(G4Event*anEvent)36 {37 fParticleGun->GeneratePrimaryVertex(anEvent);38 }39

40 //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......

使用 G4GeneralParticleSource 的 PrimaryGeneratorAction 很简单。

1 /run/initialize2 /tracking/verbose 0

3

4

5 /gps/particle ion6 /gps/ion 27 60 0 0

7 /gps/pos/centre 0 0 0mm8

9 /run/beamOn 10000

有关 gps的 macro 文件

得到 60Co 的相关能谱，这个能谱比较好理解。

得到 241Am 能谱，这个就不好理解，241Am alpha 能量约为 5.486 MeV，但得到的能谱却很奇怪。

我认为这是我对使用 gps 产生 alpha 源不熟悉导致的，在 G4 的论坛中有类似的问题，回答中提供的图也有类似的问题，我不理解。https://geant4-forum.web.cern.ch/top/monthly