/* University College London Dept of Physics Course in OO 3C59 
| all rights reserved 2000
|
| Utility: The Photomultiplier class
|
|   This class represents a photomultiplier used in the compton scattering
|   experiment. 
|   It contains the concept of a finite front window and detectes
|   whether Particles thrown at it would enter and be detected.
|
|   For such detected particles it simulates the PMT energy resolution of
|   80 kev and adds the detected energy to a running average fo all particles which
|   have entered it so far.
|
| Author: P.Clarke 
*/

import java.util.* ;


// Define the class

public class PhotoMultiplier 
{

    // Attributes fo detector
    private double m_centralAngle ;  // Position of centre in degrees
    private double m_lolim ;         // lower angular acceptance
    private double m_hilim ;         // higher angular acceptance
    private double m_resolution ;    // Energy resolution of this detector in keV

    // Needed to accumulate average energy.
    private int   m_numberDetectedParticles ;
    private double m_totalEnergy ;

    // Needed to generate gaussian random numbers
    Random m_generator ;

    //To assimilate Photon attributes in the case of a detected particle
    private void assimilate( Photon p )
	{
		//First increment the number of detected particles
		m_numberDetectedParticles++ ;

		//Now smear the energy using the Gaussian class
		double detectedEnergy ;
		detectedEnergy = p.energy() + ( m_generator.nextGaussian() * m_resolution );

		//Now add this smeared energy to the total
		m_totalEnergy += detectedEnergy ;

	}


    //---------------
    //Constructor taking:
    //  center = angle setting of centre of detector
    //  dist   = distance of entrance window of PMT from centre of experiment
    //  window = widthe of entrance window
    //  res    = energy resolution of detector
    public PhotoMultiplier( double centre, double dist, double window, double res ) 

	{
		//Set the central position of the PMT
		m_centralAngle = centre ;
  
		//Set the acceptance angles 
		double halfAngle = ( Math.atan( window/2.0/dist ) ) * 180.0 / Math.PI ; 
		m_lolim = m_centralAngle - halfAngle;
		m_hilim = m_centralAngle + halfAngle ;

		//Set the resolution
		m_resolution = res ;

		// statistic counters
		m_totalEnergy = 0.;
		m_numberDetectedParticles = 0;

		// create random object
		m_generator = new Random() ;

	}



    //-----------------------
    // Method to fire a Photon into the detector
    public void tryit( Photon p ) 
	{
	  //Does the supplied particle fall within this range

      if( (p.angle() > m_lolim) && (p.angle() < m_hilim) )
      {
        //Great - it is accepted. To keep the code simple I delegate the operations
        //to do with adding this particle to the totals to a private method
        this.assimilate( p ) ;
      }

    } 

 
    //-------------------
    // Method to return number of particles detected so far
    public int numberAccepted( ) 
	{
	   return m_numberDetectedParticles ;
	}


    //-----------------------------
    // Method to return average energy of detected particles
    public double  averageEnergy( ) 
	{	   
		double average ;

		if( m_numberDetectedParticles > 0 )
		{
			average = m_totalEnergy / (double) m_numberDetectedParticles ;
		}
		else
		{
			average = 0. ;
		}

		return average ;
	}
  

    //---------------------
    // Method to return central angle 
    double angle( ) 
	{
	  return m_centralAngle ;
	} 

}