Geant4  10.01
G4SmpTerrell.cc
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51 // Copyright (c) 2006 The Regents of the University of California.
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53 // UCRL-CODE-224807
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56 // $Id: G4SmpTerrell.cc 67966 2013-03-13 09:38:38Z gcosmo $
57 //
58 
59 #include <cmath>
60 #include "G4fissionEvent.hh"
61 
62 #define TWOPI 6.283185307
63 #define SQRT2 1.414213562
64 #define BSHIFT -0.43287
65 #define WIDTH 1.079
66 
68 /*
69  Description
70  Sample Fission Number from Terrell's modified Gaussian distribution
71 
72  method uses Red Cullen's algoritm UCRL-TR-222526
73 */
74 
75 /*
76  Input
77  nubar - average number of neutrons per fission
78  Output
79  G4SmpTerrell - sampled multiplicity
80 
81 */
82 
84  G4double temp1, temp2, expo, cshift;
85  G4double rw, theta, sampleg;
86 
87 
88  if (nubar < WIDTH) {
89  std::ostringstream o;
90  o << nubar;
91  std::string errMsg = "fission nubar out of range, nubar=" + o.str();
92  G4fissionerr(6, "SmpTerrell", errMsg);
93  }
94 
95  width = SQRT2 * WIDTH;
96  temp1 = nubar + 0.5;
97  temp2 = temp1/width;
98  temp2 *= temp2;
99  expo = std::exp(-temp2);
100  cshift = temp1 + BSHIFT * WIDTH * expo/(1. - expo);
101 
102  do {
103  rw = std::sqrt(-std::log(fisslibrng()));
104  theta = TWOPI * fisslibrng();
105  sampleg = width * rw * std::cos(theta) + cshift;
106  } while (sampleg < 0.0);
107 
108  return std::floor(sampleg);
109 }
#define SQRT2
Definition: G4SmpTerrell.cc:63
static G4double fisslibrng(void)
Definition: G4rngc.cc:65
#define width
G4double G4SmpTerrell(G4double nubar)
Definition: G4SmpTerrell.cc:67
#define BSHIFT
Definition: G4SmpTerrell.cc:64
void G4fissionerr(G4int iSever, std::string chSubNam, std::string chMsg)
Definition: G4fissionerr.cc:65
#define WIDTH
Definition: G4SmpTerrell.cc:65
double G4double
Definition: G4Types.hh:76
#define TWOPI
Definition: G4SmpTerrell.cc:62