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2 | // ******************************************************************** |
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18 | // * This code implementation is the result of the scientific and * |
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24 | // ******************************************************************** |
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25 | // |
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26 | // $Id: G4E1Probability.cc,v 1.11 2010/11/23 18:05:07 vnivanch Exp $ |
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27 | // GEANT4 tag $Name: geant4-09-04-ref-00 $ |
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28 | // |
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29 | //--------------------------------------------------------------------- |
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30 | // |
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31 | // Geant4 class G4E1Probability |
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32 | // |
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33 | // by V. Lara (May 2003) |
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34 | // |
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35 | // Modifications: |
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36 | // 18.05.2010 V.Ivanchenko trying to speedup the most slow method |
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37 | // by usage of G4Pow, integer A and introduction of const members |
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38 | // 17.11.2010 V.Ivanchenko perform general cleanup and simplification |
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39 | // of integration method; low-limit of integration is defined |
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40 | // by gamma energy or is zero (was always zero before) |
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41 | // |
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42 | |
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43 | #include "G4E1Probability.hh" |
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44 | #include "Randomize.hh" |
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45 | #include "G4Pow.hh" |
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46 | |
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47 | // Constructors and operators |
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48 | // |
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49 | |
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50 | G4E1Probability::G4E1Probability():G4VEmissionProbability() |
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51 | { |
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52 | G4double x = CLHEP::pi*CLHEP::hbarc; |
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53 | normC = 1.0 / (x*x); |
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54 | theLevelDensityParameter = 0.125/MeV; |
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55 | fG4pow = G4Pow::GetInstance(); |
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56 | } |
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57 | |
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58 | G4E1Probability::~G4E1Probability() |
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59 | {} |
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60 | |
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61 | // Calculate the emission probability |
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62 | // |
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63 | |
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64 | G4double G4E1Probability::EmissionProbDensity(const G4Fragment& frag, |
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65 | G4double gammaE) |
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66 | { |
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67 | |
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68 | // Calculate the probability density here |
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69 | |
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70 | // From nuclear fragment properties and the excitation energy, calculate |
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71 | // the probability density for photon evaporation from U to U - gammaE |
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72 | // (U = nucleus excitation energy, gammaE = total evaporated photon |
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73 | // energy). Fragment = nuclear fragment BEFORE de-excitation |
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74 | |
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75 | G4double theProb = 0.0; |
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76 | |
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77 | G4int Afrag = frag.GetA_asInt(); |
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78 | G4double Uexcite = frag.GetExcitationEnergy(); |
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79 | G4double U = std::max(0.0,Uexcite-gammaE); |
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80 | |
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81 | if(gammaE < 0.0) { return theProb; } |
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82 | |
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83 | // Need a level density parameter. |
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84 | // For now, just use the constant approximation (not reliable near magic |
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85 | // nuclei). |
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86 | |
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87 | G4double aLevelDensityParam = Afrag*theLevelDensityParameter; |
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88 | |
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89 | // G4double levelDensBef = std::exp(2*std::sqrt(aLevelDensityParam*Uexcite)); |
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90 | // G4double levelDensAft = std::exp(2*std::sqrt(aLevelDensityParam*(Uexcite-gammaE))); |
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91 | // VI reduce number of calls to exp |
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92 | G4double levelDens = |
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93 | std::exp(2*(std::sqrt(aLevelDensityParam*U)-std::sqrt(aLevelDensityParam*Uexcite))); |
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94 | // Now form the probability density |
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95 | |
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96 | // Define constants for the photoabsorption cross-section (the reverse |
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97 | // process of our de-excitation) |
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98 | |
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99 | G4double sigma0 = 2.5 * Afrag * millibarn; // millibarns |
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100 | |
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101 | G4double Egdp = (40.3 / fG4pow->powZ(Afrag,0.2) )*MeV; |
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102 | G4double GammaR = 0.30 * Egdp; |
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103 | |
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104 | // CD |
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105 | //cout<<" PROB TESTS "<<G4endl; |
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106 | //cout<<" hbarc = "<<hbarc<<G4endl; |
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107 | //cout<<" pi = "<<pi<<G4endl; |
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108 | //cout<<" Uexcite, gammaE = "<<Uexcite<<" "<<gammaE<<G4endl; |
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109 | //cout<<" Uexcite, gammaE = "<<Uexcite*MeV<<" "<<gammaE*MeV<<G4endl; |
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110 | //cout<<" lev density param = "<<aLevelDensityParam<<G4endl; |
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111 | //cout<<" level densities = "<<levelDensBef<<" "<<levelDensAft<<G4endl; |
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112 | //cout<<" sigma0 = "<<sigma0<<G4endl; |
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113 | //cout<<" Egdp, GammaR = "<<Egdp<<" "<<GammaR<<G4endl; |
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114 | //cout<<" normC = "<<normC<<G4endl; |
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115 | |
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116 | // VI implementation 18.05.2010 |
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117 | G4double gammaE2 = gammaE*gammaE; |
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118 | G4double gammaR2 = gammaE2*GammaR*GammaR; |
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119 | G4double egdp2 = gammaE2 - Egdp*Egdp; |
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120 | G4double sigmaAbs = sigma0*gammaR2/(egdp2*egdp2 + gammaR2); |
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121 | theProb = normC * sigmaAbs * gammaE2 * levelDens; |
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122 | |
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123 | // old implementation |
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124 | // G4double numerator = sigma0 * gammaE*gammaE * GammaR*GammaR; |
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125 | // G4double denominator = (gammaE*gammaE - Egdp*Egdp)* |
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126 | // (gammaE*gammaE - Egdp*Egdp) + GammaR*GammaR*gammaE*gammaE; |
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127 | |
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128 | //G4double sigmaAbs = numerator/denominator; |
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129 | //theProb = normC * sigmaAbs * gammaE2 * levelDensAft/levelDensBef; |
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130 | |
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131 | // CD |
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132 | //cout<<" sigmaAbs = "<<sigmaAbs<<G4endl; |
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133 | //cout<<" Probability = "<<theProb<<G4endl; |
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134 | |
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135 | return theProb; |
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136 | |
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137 | } |
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138 | |
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139 | G4double G4E1Probability::EmissionProbability(const G4Fragment& frag, |
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140 | G4double gammaE) |
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141 | { |
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142 | // From nuclear fragment properties and the excitation energy, calculate |
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143 | // the probability for photon evaporation down to last ground level. |
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144 | // fragment = nuclear fragment BEFORE de-excitation |
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145 | |
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146 | G4double upperLim = gammaE; |
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147 | G4double lowerLim = 0.0; |
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148 | |
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149 | //G4cout << "G4E1Probability::EmissionProbability: Emin= " << lowerLim |
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150 | // << " Emax= " << upperLim << G4endl; |
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151 | if( upperLim - lowerLim <= CLHEP::keV ) { return 0.0; } |
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152 | |
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153 | // Need to integrate EmissionProbDensity from lowerLim to upperLim |
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154 | // and multiply by factor 3 (?!) |
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155 | |
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156 | G4double integ = 3.0 * EmissionIntegration(frag,lowerLim,upperLim); |
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157 | |
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158 | return integ; |
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159 | |
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160 | } |
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161 | |
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162 | G4double G4E1Probability::EmissionIntegration(const G4Fragment& frag, |
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163 | G4double lowLim, G4double upLim) |
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164 | |
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165 | { |
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166 | // Simple integration |
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167 | // VI replace by direct integration over 100 point |
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168 | |
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169 | const G4int numIters = 100; |
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170 | G4double Step = (upLim-lowLim)/G4double(numIters); |
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171 | |
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172 | G4double res = 0.0; |
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173 | G4double x = lowLim - 0.5*Step; |
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174 | |
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175 | for(G4int i = 0; i < numIters; ++i) { |
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176 | x += Step; |
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177 | res += EmissionProbDensity(frag, x); |
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178 | } |
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179 | |
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180 | if(res > 0.0) { res /= G4double(numIters); } |
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181 | else { res = 0.0; } |
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182 | |
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183 | return res; |
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184 | |
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185 | } |
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186 | |
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187 | |
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