MedicalBeam.cc

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#include "MedicalBeam.hh"
#include "Randomize.hh"
#include "G4Event.hh"
#include "G4ParticleTable.hh"
#include "G4PrimaryVertex.hh"

using namespace CLHEP;

#include <cmath>

// --------------------------------------------------------------------------
MedicalBeam::MedicalBeam()
  : particle(0), kineticE(1.*MeV), sourcePosition(G4ThreeVector()),
    SSD(1.*m), fieldShape(MedicalBeam::SQUARE), fieldR(10.*cm)
{

  G4ParticleTable* particleTable = G4ParticleTable::GetParticleTable();
  particle = particleTable-> FindParticle("proton");

  kineticE = 200.*MeV;
  sourcePosition = G4ThreeVector(0.,0.,-125.*cm);
  SSD = 100.*cm;
  fieldXY[0] = fieldXY[1] = 5.*cm;
}

// --------------------------------------------------------------------------
MedicalBeam::~MedicalBeam()
{
}

// --------------------------------------------------------------------------
G4ThreeVector MedicalBeam::GenerateBeamDirection() const
{
  // uniform distribution in a limitted solid angle
  G4double dr;
  if ( fieldShape == MedicalBeam::SQUARE ) {
    dr = std::sqrt(sqr(fieldXY[0]/2.) + sqr(fieldXY[1]/2.));
  } else {
    dr = fieldR;
  }

  G4double sin0 = dr/SSD;
  G4double cos0 = std::sqrt(1.-sqr(sin0));

  G4double dcos = 0.;
  G4double dsin, dphi, z;

  G4double x = DBL_MAX;
  G4double y = DBL_MAX;

  G4double xmax, ymax;
  if ( fieldShape == MedicalBeam::SQUARE ) {
    xmax = fieldXY[0]/2./SSD;
    ymax = fieldXY[1]/2./SSD;
  } else {
    xmax = ymax = DBL_MAX-1.;
  }

  while(! (std::abs(x) < xmax && std::abs(y) < ymax) ) {
    dcos = RandFlat::shoot(cos0, 1.);
    dsin = std::sqrt(1.-sqr(dcos));
    dphi = RandFlat::shoot(0., twopi);

    x = std::cos(dphi)*dsin*dcos;
    y = std::sin(dphi)*dsin*dcos;
  }
  z = dcos;

  return G4ThreeVector(x,y,z);
}

// --------------------------------------------------------------------------
void MedicalBeam::GeneratePrimaries(G4Event* anEvent)
{
  if ( particle == 0 ) return;

  // create a new vertex
  G4PrimaryVertex* vertex = new G4PrimaryVertex(sourcePosition, 0.*ns);

  // momentum
  G4double mass = particle-> GetPDGMass();
  G4double p = std::sqrt(sqr(mass+kineticE)-sqr(mass));
  G4ThreeVector pmon = p*GenerateBeamDirection();
  G4PrimaryParticle* primary = 
    new G4PrimaryParticle(particle, pmon.x(), pmon.y(), pmon.z());

  // set primary to vertex
  vertex-> SetPrimary(primary);

  // set vertex to event
  anEvent-> AddPrimaryVertex(vertex);
}