181 lines
6.4 KiB
C++
181 lines
6.4 KiB
C++
// Geant4 simulation for MuSR
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// AUTHOR: Toni SHIROKA, Paul Scherrer Institut, PSI
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// DATE : 2008-05
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//
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//
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// ********************************************************************
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// * License and Disclaimer *
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// * *
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// * The Geant4 software is copyright of the Copyright Holders of *
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// * the Geant4 Collaboration. It is provided under the terms and *
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// * conditions of the Geant4 Software License, included in the file *
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// * LICENSE and available at http://cern.ch/geant4/license . These *
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// * include a list of copyright holders. *
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// * *
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// * Neither the authors of this software system, nor their employing *
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// * institutes,nor the agencies providing financial support for this *
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// * work make any representation or warranty, express or implied, *
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// * regarding this software system or assume any liability for its *
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// * use. Please see the license in the file LICENSE and URL above *
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// * for the full disclaimer and the limitation of liability. *
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// * *
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// * This code implementation is the result of the scientific and *
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// * technical work of the GEANT4 collaboration. *
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// * By using, copying, modifying or distributing the software (or *
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// * any work based on the software) you agree to acknowledge its *
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// * use in resulting scientific publications, and indicate your *
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// * acceptance of all terms of the Geant4 Software license. *
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// ********************************************************************
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//
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// ------------------------------------------------------------
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// GEANT 4 class header file
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//
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// History:
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// 17 August 2004 P. Gumplinger, T. MacPhail
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// ------------------------------------------------------------
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//
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#include "G4DecayWithSpin.hh"
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#include "G4Step.hh"
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#include "G4Track.hh"
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#include "G4DecayTable.hh"
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#include "G4MuonDecayChannelWithSpin.hh"
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#include "G4Vector3D.hh"
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#include "G4TransportationManager.hh"
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#include "G4PropagatorInField.hh"
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#include "G4FieldManager.hh"
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#include "G4Field.hh"
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#include "G4Transform3D.hh"
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G4DecayWithSpin::G4DecayWithSpin(const G4String& processName):G4Decay(processName){}
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G4DecayWithSpin::~G4DecayWithSpin(){}
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G4VParticleChange* G4DecayWithSpin::DecayIt(const G4Track& aTrack, const G4Step& aStep)
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{
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// get particle
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const G4DynamicParticle* aParticle = aTrack.GetDynamicParticle();
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G4ParticleDefinition* aParticleDef = aParticle->GetDefinition();
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// get parent_polarization
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G4ThreeVector parent_polarization = aParticle->GetPolarization();
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if(parent_polarization == G4ThreeVector(0,0,0))
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{
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// Generate random polarization direction
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G4double cost = 1. - 2.*G4UniformRand();
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G4double sint = std::sqrt((1.-cost)*(1.+cost));
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G4double phi = twopi*G4UniformRand();
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G4double sinp = std::sin(phi);
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G4double cosp = std::cos(phi);
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G4double px = sint*cosp;
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G4double py = sint*sinp;
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G4double pz = cost;
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parent_polarization.setX(px);
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parent_polarization.setY(py);
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parent_polarization.setZ(pz);
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}else{
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G4FieldManager* fieldMgr = aStep.GetTrack()->GetVolume()->
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GetLogicalVolume()->GetFieldManager();
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if (!fieldMgr) {
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G4TransportationManager *transportMgr =
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G4TransportationManager::GetTransportationManager();
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G4PropagatorInField* fFieldPropagator =
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transportMgr->GetPropagatorInField();
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if (fFieldPropagator) fieldMgr =
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fFieldPropagator->GetCurrentFieldManager();
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}
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const G4Field* field = NULL;
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if(fieldMgr)field = fieldMgr->GetDetectorField();
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// if (field && !(fieldMgr->DoesFieldChangeEnergy())) {
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if (field) {
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// G4cout << "++++ LOCAL VERSION OF G4 DECAY WITH SPIN !!!! ++++"<< G4endl;
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G4double point[4];
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point[0] = (aStep.GetPostStepPoint()->GetPosition())[0];
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point[1] = (aStep.GetPostStepPoint()->GetPosition())[1];
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point[2] = (aStep.GetPostStepPoint()->GetPosition())[2];
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point[3] = aTrack.GetGlobalTime();
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G4double fieldValue[3];
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field -> GetFieldValue(point,fieldValue);
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G4ThreeVector B(fieldValue[0],fieldValue[1],fieldValue[2]);
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if ((B.mag2())>0) { // Call the spin precession only for non-zero mag. field
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parent_polarization = Spin_Precession(aStep,B,fRemainderLifeTime);
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}
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}
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}
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// decay table
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G4DecayTable *decaytable = aParticleDef->GetDecayTable();
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if (decaytable) {
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G4MuonDecayChannelWithSpin *decaychannel;
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decaychannel = (G4MuonDecayChannelWithSpin*)decaytable->SelectADecayChannel();
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if (decaychannel) decaychannel->SetPolarization(parent_polarization);
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}
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G4ParticleChangeForDecay* pParticleChangeForDecay;
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pParticleChangeForDecay = (G4ParticleChangeForDecay*)G4Decay::DecayIt(aTrack,aStep);
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pParticleChangeForDecay->ProposePolarization(parent_polarization);
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return pParticleChangeForDecay;
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}
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G4ThreeVector G4DecayWithSpin::Spin_Precession( const G4Step& aStep,
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G4ThreeVector B, G4double deltatime )
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{
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G4double Bnorm = std::sqrt(sqr(B[0]) + sqr(B[1]) +sqr(B[2]) );
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G4double q = aStep.GetTrack()->GetDefinition()->GetPDGCharge();
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G4double a = 1.165922e-3;
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G4double s_omega = 8.5062e+7*rad/(s*kilogauss);
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G4double omega = -(q*s_omega)*(1.+a) * Bnorm;
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G4double rotationangle = deltatime * omega;
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G4Transform3D SpinRotation = G4Rotate3D(rotationangle,B.unit());
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G4Vector3D Spin = aStep.GetTrack() -> GetPolarization();
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G4Vector3D newSpin = SpinRotation * Spin;
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#ifdef G4VERBOSE
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if (GetVerboseLevel()>2) {
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G4double normspin = std::sqrt(Spin*Spin);
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G4double normnewspin = std::sqrt(newSpin*newSpin);
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//G4double cosalpha = Spin*newSpin/normspin/normnewspin;
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//G4double alpha = std::acos(cosalpha);
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G4cout << "AT REST::: PARAMETERS " << G4endl;
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G4cout << "Initial spin : " << Spin << G4endl;
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G4cout << "Delta time : " << deltatime << G4endl;
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G4cout << "Rotation angle: " << rotationangle/rad << G4endl;
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G4cout << "New spin : " << newSpin << G4endl;
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G4cout << "Checked norms : " << normspin <<" " << normnewspin << G4endl;
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}
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#endif
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return newSpin;
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}
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