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// Copyright (c) 2006 The Regents of the University of California.
// All rights reserved.
// UCRL-CODE-224807
//
//
// $Id: G4SmpWatt.cc,v 1.4 2007/06/01 18:30:38 dennis Exp $
//

#define nZAfis 39    /* 38 fissionable isotopes in ENDL + U-232 from ENDF7 */
#define WATTEMIN 1.0e-6
#define WATTEMAX 20.0

#include <cmath>
#include "G4fissionEvent.hh"

G4double G4fissionEvent::G4SmpWatt(G4double ePart, G4int iso) {

/*
  Description
    Sample Watt Spectrum as in TART (Kalos algorithm)
*/

/*
  Input
    ePart     - energy of incoming particle
    iso       - isotope
  Output
              - energy of incoming particle
*/

   static G4int nZA [nZAfis]= {
                      90231, 90232, 90233,
                      91233,
                      92232, 92233, 92234, 92235, 92236, 92237, 92238, 92239, 92240,
                      93235, 93236, 93237, 93238,
                      94237, 94238, 94239, 94240, 94241, 94242, 94243,
                      95241, 95242, 95243,
                      96242, 96243, 96244, 96245, 96246, 96247, 96248,
                      97249,
                      98249, 98250, 98251, 98252
                      };

   static G4double Watta [nZAfis][3] = {
                      {6.00949285e-05, -8.36695381e-03,  9.50939496e-01},
                      {6.54348443e-05, -8.86574327e-03,  9.55404490e-01},
                      {7.08173682e-05, -9.22676286e-03,  9.50088329e-01},
                      {6.35839062e-05, -8.63645973e-03,  9.24583535e-01},
                      {8.21929628e-05,  4.01922936e-03,  1.152121164e00},
                      {6.21335718e-05, -8.45651858e-03,  9.14717276e-01},
                      {6.81386135e-05, -8.99142394e-03,  9.21954824e-01},
                      {7.32627297e-05, -9.36908697e-03,  9.20107976e-01},
                      {8.06505279e-05, -9.95416671e-03,  9.27890410e-01},
                      {8.33208285e-05, -1.01073057e-02,  9.17691654e-01},
                      {8.96944680e-05, -1.06491070e-02,  9.25496030e-01},
                      {9.44608097e-05, -1.08940419e-02,  9.17795511e-01},
                      {1.01395704e-04, -1.15098159e-02,  9.29395462e-01},
                      {6.81110009e-05, -8.91619352e-03,  9.00047566e-01},
                      {7.21126359e-05, -9.20179363e-03,  8.95722889e-01},
                      {7.82371142e-05, -9.67050621e-03,  8.99574933e-01},
                      {8.27256297e-05, -9.99353009e-03,  8.97461897e-01},
                      {7.29458059e-05, -9.22415170e-03,  8.80996165e-01},
                      {8.02383914e-05, -9.78291439e-03,  8.88964070e-01},
                      {8.50641730e-05, -1.01099145e-02,  8.87304833e-01},
                      {9.10537157e-05, -1.05303084e-02,  8.89438514e-01},
                      {9.43014320e-05, -1.07133543e-02,  8.82632055e-01},
                      {1.02655616e-04, -1.13154691e-02,  8.91617174e-01},
                      {1.06118094e-04, -1.14971777e-02,  8.85181637e-01},
                      {9.08474473e-05, -1.04296303e-02,  8.71942958e-01},
                      {9.35633054e-05, -1.05612167e-02,  8.63930371e-01},
                      {1.01940441e-04, -1.11573929e-02,  8.73153437e-01},
                      {9.19501202e-05, -1.04229157e-02,  8.58681822e-01},
                      {9.42991674e-05, -1.05098872e-02,  8.49103546e-01},
                      {1.02747171e-04, -1.11371417e-02,  8.60434431e-01},
                      {1.05024967e-04, -1.12138980e-02,  8.51101942e-01},
                      {1.14130011e-04, -1.18692049e-02,  8.62838259e-01},
                      {1.15163673e-04, -1.18553822e-02,  8.51306646e-01},
                      {1.27169055e-04, -1.27033210e-02,  8.68623539e-01},
                      {1.24195213e-04, -1.24047085e-02,  8.48974077e-01},
                      {1.12616150e-04, -1.15135023e-02,  8.19708800e-01},
                      {1.23637465e-04, -1.22869889e-02,  8.35392018e-01},
                      {1.22724317e-04, -1.21677963e-02,  8.22569523e-01},
                      {1.33891595e-04, -1.29267762e-02,  8.37122909e-01} };

   G4double a;  /* Watt Parameters */
   G4double b=1.0;

   G4double rand1,rand2;
   G4double x,y,z;
   G4double eSmp;
   G4int i;


/*
   Find Watt parameters for isotope
*/
   G4int isoindex=-1;
   for (i=0; isoindex == -1 && i<nZAfis; i++) {
      if (iso == nZA[i]) isoindex = i;
   }
   if (isoindex == -1) {
      std::string errMsg = "No Watt spectrum available for iso " + iso;
      G4fissionerr(6, "SmpWatt", errMsg);
   }
   
   a= Watta[isoindex][2] + ePart*(Watta[isoindex][1] + ePart*Watta[isoindex][0]);

   x= 1. + (b/(8.*a));
   y= (x + std::sqrt(x*x-1.))/a;
   z= a*y - 1.;

   do {

      rand1= -std::log(fisslibrng());
      rand2= -std::log(fisslibrng());
      eSmp= y*rand1;

   } while ((rand2-z*(rand1+1.))*(rand2-z*(rand1+1.)) > b*y*rand1 ||
             eSmp < WATTEMIN || eSmp > WATTEMAX);
 
   
   return eSmp;
}