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G4E1Probability.cc
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26 // $Id$
27 //
28 //---------------------------------------------------------------------
29 //
30 // Geant4 class G4E1Probability
31 //
32 // by V. Lara (May 2003)
33 //
34 // Modifications:
35 // 18.05.2010 V.Ivanchenko trying to speedup the most slow method
36 // by usage of G4Pow, integer A and introduction of const members
37 // 17.11.2010 V.Ivanchenko perform general cleanup and simplification
38 // of integration method; low-limit of integration is defined
39 // by gamma energy or is zero (was always zero before)
40 //
41 
42 #include "G4E1Probability.hh"
43 #include "Randomize.hh"
44 #include "G4Pow.hh"
45 #include "G4SystemOfUnits.hh"
46 
47 // Constructors and operators
48 //
49 
51 {
52  G4double x = CLHEP::pi*CLHEP::hbarc;
53  normC = 1.0 / (x*x);
54  theLevelDensityParameter = 0.125/MeV;
55  fG4pow = G4Pow::GetInstance();
56 }
57 
59 {}
60 
61 // Calculate the emission probability
62 //
63 
65  G4double gammaE)
66 {
67 
68  // Calculate the probability density here
69 
70  // From nuclear fragment properties and the excitation energy, calculate
71  // the probability density for photon evaporation from U to U - gammaE
72  // (U = nucleus excitation energy, gammaE = total evaporated photon
73  // energy). Fragment = nuclear fragment BEFORE de-excitation
74 
75  G4double theProb = 0.0;
76 
77  G4int Afrag = frag.GetA_asInt();
78  G4double Uexcite = frag.GetExcitationEnergy();
79  G4double U = std::max(0.0,Uexcite-gammaE);
80 
81  if(gammaE < 0.0) { return theProb; }
82 
83  // Need a level density parameter.
84  // For now, just use the constant approximation (not reliable near magic
85  // nuclei).
86 
87  G4double aLevelDensityParam = Afrag*theLevelDensityParameter;
88 
89  // G4double levelDensBef = std::exp(2*std::sqrt(aLevelDensityParam*Uexcite));
90  // G4double levelDensAft = std::exp(2*std::sqrt(aLevelDensityParam*(Uexcite-gammaE)));
91  // VI reduce number of calls to exp
92  G4double levelDens =
93  std::exp(2*(std::sqrt(aLevelDensityParam*U)-std::sqrt(aLevelDensityParam*Uexcite)));
94  // Now form the probability density
95 
96  // Define constants for the photoabsorption cross-section (the reverse
97  // process of our de-excitation)
98 
99  G4double sigma0 = 2.5 * Afrag * millibarn; // millibarns
100 
101  G4double Egdp = (40.3 / fG4pow->powZ(Afrag,0.2) )*MeV;
102  G4double GammaR = 0.30 * Egdp;
103 
104  // CD
105  //cout<<" PROB TESTS "<<G4endl;
106  //cout<<" hbarc = "<<hbarc<<G4endl;
107  //cout<<" pi = "<<pi<<G4endl;
108  //cout<<" Uexcite, gammaE = "<<Uexcite<<" "<<gammaE<<G4endl;
109  //cout<<" Uexcite, gammaE = "<<Uexcite*MeV<<" "<<gammaE*MeV<<G4endl;
110  //cout<<" lev density param = "<<aLevelDensityParam<<G4endl;
111  //cout<<" level densities = "<<levelDensBef<<" "<<levelDensAft<<G4endl;
112  //cout<<" sigma0 = "<<sigma0<<G4endl;
113  //cout<<" Egdp, GammaR = "<<Egdp<<" "<<GammaR<<G4endl;
114  //cout<<" normC = "<<normC<<G4endl;
115 
116  // VI implementation 18.05.2010
117  G4double gammaE2 = gammaE*gammaE;
118  G4double gammaR2 = gammaE2*GammaR*GammaR;
119  G4double egdp2 = gammaE2 - Egdp*Egdp;
120  G4double sigmaAbs = sigma0*gammaR2/(egdp2*egdp2 + gammaR2);
121  theProb = normC * sigmaAbs * gammaE2 * levelDens;
122 
123  // old implementation
124  // G4double numerator = sigma0 * gammaE*gammaE * GammaR*GammaR;
125  // G4double denominator = (gammaE*gammaE - Egdp*Egdp)*
126  // (gammaE*gammaE - Egdp*Egdp) + GammaR*GammaR*gammaE*gammaE;
127 
128  //G4double sigmaAbs = numerator/denominator;
129  //theProb = normC * sigmaAbs * gammaE2 * levelDensAft/levelDensBef;
130 
131  // CD
132  //cout<<" sigmaAbs = "<<sigmaAbs<<G4endl;
133  //cout<<" Probability = "<<theProb<<G4endl;
134 
135  return theProb;
136 
137 }
138 
140  G4double gammaE)
141 {
142  // From nuclear fragment properties and the excitation energy, calculate
143  // the probability for photon evaporation down to last ground level.
144  // fragment = nuclear fragment BEFORE de-excitation
145 
146  G4double upperLim = gammaE;
147  G4double lowerLim = 0.0;
148 
149  //G4cout << "G4E1Probability::EmissionProbability: Emin= " << lowerLim
150  // << " Emax= " << upperLim << G4endl;
151  if( upperLim - lowerLim <= CLHEP::keV ) { return 0.0; }
152 
153  // Need to integrate EmissionProbDensity from lowerLim to upperLim
154  // and multiply by factor 3 (?!)
155 
156  G4double integ = 3.0 * EmissionIntegration(frag,lowerLim,upperLim);
157 
158  return integ;
159 
160 }
161 
162 G4double G4E1Probability::EmissionIntegration(const G4Fragment& frag,
163  G4double lowLim, G4double upLim)
164 
165 {
166  // Simple integration
167  // VI replace by direct integration over 100 point
168 
169  const G4int numIters = 100;
170  G4double Step = (upLim-lowLim)/G4double(numIters);
171 
172  G4double res = 0.0;
173  G4double x = lowLim - 0.5*Step;
174 
175  for(G4int i = 0; i < numIters; ++i) {
176  x += Step;
177  res += EmissionProbDensity(frag, x);
178  }
179 
180  if(res > 0.0) { res /= G4double(numIters); }
181  else { res = 0.0; }
182 
183  return res;
184 
185 }
186 
187