OpBoundaryProcessSimple.hh

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/**
 * @file   larsim/LArG4/OpBoundaryProcessSimple.hh
 * @author Ben Jones (bjpjones@mit.edu)
 * @date   March 2010
 * @see    larsim/LArG4/OpBoundaryProcessSimple.cxx
 */

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////////////////////////////////////////////////////////////////////////
// Optical Photon Boundary Process Class Definition
////////////////////////////////////////////////////////////////////////

#ifndef OpBoundaryProcessSimple_h
#define OpBoundaryProcessSimple_h 1

#include "Geant4/G4ForceCondition.hh"
#include "Geant4/G4OpticalPhoton.hh"
#include "Geant4/G4ProcessType.hh"
#include "Geant4/G4String.hh"
#include "Geant4/G4Types.hh"
#include "Geant4/G4VDiscreteProcess.hh"
#include "Geant4/Randomize.hh"

class G4ParticleDefinition;
class G4Step;
class G4Track;
class G4VParticleChange;

/////////////////////
// Class Definition
/////////////////////

namespace larg4 {

  // Possible statuses of a particle after each step.
  enum OpBoundaryProcessSimpleStatus {
    Undefined,
    NotAtBoundary,
    SimpleAbsorbedNoRefl,
    SimpleAbsorbed,
    SimpleDiffuse,
    SimpleSpecular,
    StepTooSmall,
    NoRINDEX
  };

  /**
   * @brief Discrete process for reflection and diffusion at optical interfaces.
   * @see `G4VDiscreteProcess`
   *
   * This class invokes a simplified model of optical reflections at
   * boundaries between different materials.  The relevant reflectivities
   * are ultimately read from `detinfo::LArProperties` via
   * `larg4::MaterialPropertiesLoader`.
   *
   * The required parameters are total reflectance
   * (`detinfo::LArProperties::SurfaceReflectances()`)
   * and ratio of diffuse to specular reflectance
   * (`detinfo::LArProperties::SurfaceReflectanceDiffuseFractions()`). Each
   * photon crossing a boundary with a defined reflectance is randomly either
   * reflected or absorbed and killed according to the supplied probability.
   *
   * Every reflected photon with a defined diffuse reflection fraction
   * is then randomly either diffusely or specularly reflected according
   * to the supplied probability.  All materials with no defined
   * reflectance are assumed to be black and absorb all incident photons.
   *
   * This physics process is loaded in `larg4::OpticalPhysics` physics
   * constructor.
   *
   * This class is based on the `G4OpBoundaryProcess` class in Geant4 and was
   * adapted for LArSoft by Ben Jones, MIT, March 2010.
   */

  class OpBoundaryProcessSimple : public G4VDiscreteProcess {
  public:
    OpBoundaryProcessSimple(const G4String& processName = "OpBoundary",
                            G4ProcessType type = fOptical);

    // Returns true -> 'is applicable' only for an optical photon.
    G4bool IsApplicable(const G4ParticleDefinition& aParticleType);

    // Returns infinity; i. e. the process does not limit the step,
    // but sets the 'Forced' condition for the DoIt to be invoked at
    // every step. However, only at a boundary will any action be
    // taken.
    G4double GetMeanFreePath(const G4Track&, G4double, G4ForceCondition* condition);

    // This is the method implementing boundary processes.
    G4VParticleChange* PostStepDoIt(const G4Track& aTrack, const G4Step& aStep);

    // Returns the current status.
    OpBoundaryProcessSimpleStatus GetStatus() const;

  private:
    // Generate a random bool to decide which process to execute
    G4bool G4BooleanRand(const G4double prob) const;

    OpBoundaryProcessSimpleStatus fTheStatus;
    G4double fCarTolerance;

    int fVerbosity;
  };

  inline G4bool
  OpBoundaryProcessSimple::G4BooleanRand(const G4double prob) const
  {
    /* Returns a random boolean variable with the specified probability */
    return (G4UniformRand() < prob);
  }

  inline G4bool
  OpBoundaryProcessSimple::IsApplicable(const G4ParticleDefinition& aParticleType)
  {
    return (&aParticleType == G4OpticalPhoton::OpticalPhoton());
  }

  inline OpBoundaryProcessSimpleStatus
  OpBoundaryProcessSimple::GetStatus() const
  {
    return fTheStatus;
  }

}

#endif /* OpBoundaryProcessSimple_h */