---

photo.cxx

Go to the documentation of this file.

// -*- C++ -*-  $Id: photo.cxx,v 1.1 2000/09/01 20:20:21 burnett Exp $
//
// This file is part of Gismo 2

#include "EGS.h"
#include "PEGSData.h"
#include "Random.h"

void EGS::photo(const PEGSData& mat)
{
    // adapted from egs4 subroutine photo
    // ----------------------------------
    //                                k-edge version -- 27 jul 1988/2300
    //******************************************************************
    //******* special version for treating k-edge fluorescence *********
    //******************************************************************
    // programmers:  w. r. nelson and t. m. jenkins (slac)
    //               a.f. bielajew (nrc) photoelectric angular distn
    //               d.w.o. rogers (nrc) document
    //******************************************************************
    // this is a special k-edge version of an egs4 subroutine that is
    // patterned after a method developed in 1978 by a. clark (lbl)
    // with the help of w. r. nelson (slac).  it requires subroutine
    // edgset (or equivalent for setting up the branching ratios and
    // fluorescent photon energies).
    //
    // this version adds selection of photo-electron angle
    //   see 'photoelectron angle selection in the egs4 code system'
    //   a.f. bielajew and d.w.o. rogers, nrc report pirs-0052,oct 86
    //
    //   this requires a redefinition of $comin-photo which is done
    //   in nrcc4mac(p).mor and definition of the macro
    //   $select-photoelectron-direction  (nrcc4mac(p).mor)
    //   to select the a.d. in any region, one must set the variable
    //   iphter(ir(np))=1 passed in comin/user;
    //
    //  this version uses a simple model of k-shell fluorescence.
    //  to sample fluorescent x-rays from the k-shell in a given region
    //  the flag iedgfl(ir(np)) (in comin/edge) must be set non-zero
    //  for each region; the value of iedgfl is the value of z used for
    //  that region - the model must treat the region as a single
    //  element for the selection of the fluorescent x-ray.
    //
    //  the routine edgset(region1,region2) must be called for each
    //  sequence of regions region1 to region2 for which the fluorescent
    //  x-rays are to be sampled and iedgfl is set.
    //
    //  the relevant arrays are all zeroed at the end of egs4blok so
    //  that if the user initializes nothing, the code is the same as
    //  the egs4 default system - i.e. no fluorescent x-rays and no
    //  photo-electron a.d.
    //
    //  the output from this routine is complex.
    //  e < be  => edep = e, iblobe=1
    //  e > be     no k-shell                           with k-shell
    //             enew = 0.0                     enew = 0, or kalpha
    //             edep = binda                   edep = ebinda - enew
    //             e(np) = edep                   e(np) = edep
    //
    //      then iarg = 4 call is made i.e. energy discarded in middle
    //
    // then
    // e<be    e(np) = 0 with iq=0,   no e- is set up  iblobe = 1 still
    // e>be    iq(np) = -1, e(np) = einitial - ebinda+rm
    //         and if flags on for fluorescence and sampled, then
    //         np => np + 1 and a gamma is set up
    //
    //
    //******************************************************************
    //    $energy precision peig;
    // $comin-photo; //the next line is the default replacement for this
    //;comin/debug,edge,epcont,media,photin,stack,uphiot,useful/;
    //but for the photo-electron angle selection, see definition in nrcc4mac(p)

    float eig = this->e,
          enew, edep,
          br = 0;;

    double peig=eig,
           prm = rm;
    int iblobe;

    if (eig <= mat.ebinda())
    {  edep=peig; iblobe=1; //below k-edge
    }
    else
    {   // 'k-edge p.e. is possible'
        if ( mat.edge.iedgfl )
        {  // 'fluorescent option on'
           br=Random::flat();; //sample to decide k-edge photon versus either
           //               auger electron or l-edge p.e. interaction

           enew =  (br > mat.edge.bkr1)
                   ? 0.0                //k-edge photon not selected
                   :  (br <= mat.edge.bkr2)
                      ? mat.edge.ekalph          //alpha
                      : mat.edge.ekbeta;         //beta


        }
        else enew=0.0; //fluorescent option off

        edep = mat.ebinda()-enew;
        this->e= edep;
        iblobe=0;  //flag indicating 'not' below binding energy

    }

    // $auscall($photxaus);

    if (iblobe) this->e=0; //below k-edge flag is on
    else
    { // 'set up particle(s)

      this->iq =-1; //photoelectron (always set up)
      this->e  =peig-mat.ebinda()+prm;
      // $select-photoelectron-direction;//defined in nrcc4mac(p).mor

      if ( mat.edge.iedgfl)
      { //set up fluorescent photon
        if ( br > mat.edge.bkr1) return; //however, k-edge not chosen above
        EGS& gam = *new EGS(this);
        // np=np+1;
        gam.e =enew;
        gam.iq=0;

        //photon comes off isotropically
        float rniso= Random::flat();
        float costhe = 2.0*rniso-1.0;
        float phi = Random::flat(2.*M_PI);
        gam.u=0.0; gam.v=0.0; gam.w=1.0; //makes things easier in rotate
        gam.rotate(costhe, phi);
      //end of fluorescent photon set up
      }
    //end of 'set up particle(s)' loop
    }


} //end of subroutine photo

---