G4SmpNugDist.cc

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// UCRL-CODE-224807
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#include <cmath>
#include "G4fissionEvent.hh"
#include "G4Exp.hh"
#include "G4Log.hh"
#include "G4Pow.hh"

#define nfissg 40
#define alphanegbin 26

G4int G4fissionEvent::G4SmpNugDist(G4int isotope, G4double nubar) {

/*
  Description
    Sample Number of Photons from neutron induced fission in 
    all isotopes using Tim Valentine's model (negative binomial
    distribution, using nubar as a model parameter)
*/

/*
  Input
    iso          - isotope
  Output
    G4SmpNugDist - sampled multiplicity
*/
 
  static G4double logcoeff[nfissg+1] = {
     0.00000000000000e+00,
     3.25809653802149e+00,
     5.86078622346587e+00,
     8.09437844497297e+00,
     1.00753799138395e+01,
     1.18671393830676e+01,
     1.35093671183247e+01,
     1.50291928720691e+01,
     1.64462588918558e+01,
     1.77753948391357e+01,
     1.90281578076311e+01,
     2.02137814732888e+01,
     2.13397927361450e+01,
     2.24124295384099e+01,
     2.34369338549243e+01,
     2.44177631079360e+01,
     2.53587464524005e+01,
     2.62632027266277e+01,
     2.71340310844251e+01,
     2.79737817391769e+01,
     2.87847119553932e+01,
     2.95688309141589e+01,
     3.03279360625106e+01,
     3.10636428574894e+01,
     3.17774093252521e+01,
     3.24705565058120e+01,
     3.31442856005149e+01,
     3.37996924530920e+01,
     3.44377798564689e+01,
     3.50594680730467e+01,
     3.56656038766170e+01,
     3.62569683628670e+01,
     3.68342837279018e+01,
     3.73982191769817e+01,
     3.79493960962713e+01,
     3.84883925970040e+01,
     3.90157475227212e+01,
     3.95319639951220e+01,
     4.00375125617872e+01,
     4.05328339990172e+01,
     4.10183418147990e+01
  };
  G4int i, A, Z;
  G4double cpi[nfissg+1];
  G4double p, q, nubarg;
  G4double r;

/* 
  No data is available for induced fission gamma number
  distributions. Sample the negative binomial cumulative 
  probability distribution.
*/
  A = (G4int) (isotope-1000*((G4int)(isotope/1000)));
  Z = (G4int) ((isotope-A)/1000);
  G4Pow* Pow = G4Pow::GetInstance();
  nubarg = ((2.51-1.13e-5*Pow->powA(G4double(Z),2.)*std::sqrt(G4double(A)))*nubar+4.0)
           /(-1.33+119.6*Pow->A13(G4double(Z))/G4double(A));
  p = 1.*alphanegbin/(alphanegbin+nubarg);
  q = 1.-p;
  cpi[0] = G4Exp(logcoeff[0]+26.*G4Log(p));
  for (i=1; i<=nfissg; i++) cpi[i] = cpi[i-1] + G4Exp(logcoeff[i]+26.*G4Log(p)+i*G4Log(q));
  for (i=0; i<=nfissg; i++) cpi[i] = cpi[i]/cpi[nfissg-1];

  r=fisslibrng();

  for(i=0; i<=nfissg; i++) if (r <= cpi[i]) return i;

  //
  // Fall through
  //

  G4cout << " SmpNugDist: random number " << r << " out of range " << G4endl;
  return -1;

}