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// $Id$
//

#ifndef G4ParticleGun_h
#define G4ParticleGun_h 1


#include "globals.hh"
#include "G4VPrimaryGenerator.hh"
#include "G4ThreeVector.hh"
#include "G4ParticleDefinition.hh"
#include "G4PrimaryVertex.hh"
#include "G4ParticleMomentum.hh"

class G4Event;
class G4ParticleGunMessenger;

// class description:
//
//  This is a concrete class of G4VPrimaryGenerator. It shoots a particle of given type
// into a given direction with either a given kinetic energy or momentum.
//  The position and time of the primary particle must be set by the corresponding
// set methods of G4VPrimaryGenerator base class, otherwise zero will be set.
//
//  The FAQ to this class is for randomizing position/direction/kinetic energy of primary
// particle. But, G4ParticleGun does NOT have any way of randomization. Instead, the user's
// concrete implementation of G4VUserPrimaryGeneratorAction which transmits G4Event object
// to this particle gun can randomize these quantities and set to this particle gun before
// invoking GeneratePrimaryVertex() method.
//  Note that, even if the particle gun shoots more than one particles at one invokation of
// GeneratePrimaryVertex() method, all particles have the same physical quantities. If the
// user wants to shoot two particles with different momentum, position, etc., invoke
// GeneratePrimaryVertex() method twice and set quantities on demand to the particle gun.
//

class G4ParticleGun:public G4VPrimaryGenerator
{
  public: // with description
     G4ParticleGun();
     G4ParticleGun(G4int numberofparticles);
     G4ParticleGun(G4ParticleDefinition * particleDef, 
                   G4int numberofparticles = 1);
     // costructors. "numberofparticles" is number of particles to be shoot at one invokation
     // of GeneratePrimaryVertex() method. All paricles are shot with the same physical
     // quantities.

  public:
     virtual ~G4ParticleGun();

  private:
     G4ParticleGun(const G4ParticleGun&);
     const G4ParticleGun & operator=(const G4ParticleGun&);
     G4int operator==(const G4ParticleGun&) const;
     G4int operator!=(const G4ParticleGun&) const;

  public: // with description
     virtual void GeneratePrimaryVertex(G4Event* evt);
     // Creates a primary vertex at the given point and put primary particles to it.
     // Followings are set methods for the particle properties.
     //   SetParticleDefinition should be called first.  
     //   By using SetParticleMomentum(), both particle_momentum_direction and
     //   particle_energy(Kinetic Energy) are set.
     //   
     void SetParticleDefinition
       (G4ParticleDefinition * aParticleDefinition);
     void SetParticleEnergy(G4double aKineticEnergy);
     void SetParticleMomentum(G4double aMomentum);
     void SetParticleMomentum(G4ParticleMomentum aMomentum);
     void SetParticleMomentumDirection
                 (G4ParticleMomentum aMomentumDirection)
     { particle_momentum_direction =  aMomentumDirection.unit(); }
     void SetParticleCharge(G4double aCharge)
     { particle_charge = aCharge; }
     void SetParticlePolarization(G4ThreeVector aVal)
     { particle_polarization = aVal; }
     void SetNumberOfParticles(G4int i)
     { NumberOfParticlesToBeGenerated = i; }

  public:
     G4ParticleDefinition* GetParticleDefinition() const
     { return particle_definition; }
     G4ParticleMomentum GetParticleMomentumDirection() const
     { return particle_momentum_direction; }
     G4double GetParticleEnergy() const
     { return particle_energy; }
     G4double GetParticleMomentum() const
     { return particle_momentum; }
     G4double GetParticleCharge() const
     { return particle_charge; }
     G4ThreeVector GetParticlePolarization() const
     { return particle_polarization; }
     G4int GetNumberOfParticles() const
     { return NumberOfParticlesToBeGenerated; }

  protected:  
     virtual void SetInitialValues();

     G4int                 NumberOfParticlesToBeGenerated;
     G4ParticleDefinition* particle_definition;
     G4ParticleMomentum    particle_momentum_direction;
     G4double	           particle_energy;
     G4double              particle_momentum;
     G4double	           particle_charge;
     G4ThreeVector         particle_polarization;

  private:
     G4ParticleGunMessenger* theMessenger;
};

#endif