[819] | 1 | // |
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| 2 | // ******************************************************************** |
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| 3 | // * License and Disclaimer * |
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| 4 | // * * |
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| 5 | // * The Geant4 software is copyright of the Copyright Holders of * |
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| 6 | // * the Geant4 Collaboration. It is provided under the terms and * |
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| 7 | // * conditions of the Geant4 Software License, included in the file * |
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| 8 | // * LICENSE and available at http://cern.ch/geant4/license . These * |
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| 9 | // * include a list of copyright holders. * |
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| 10 | // * * |
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| 11 | // * Neither the authors of this software system, nor their employing * |
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| 12 | // * institutes,nor the agencies providing financial support for this * |
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| 13 | // * work make any representation or warranty, express or implied, * |
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| 14 | // * regarding this software system or assume any liability for its * |
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| 15 | // * use. Please see the license in the file LICENSE and URL above * |
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| 16 | // * for the full disclaimer and the limitation of liability. * |
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| 17 | // * * |
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| 18 | // * This code implementation is the result of the scientific and * |
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| 19 | // * technical work of the GEANT4 collaboration. * |
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| 20 | // * By using, copying, modifying or distributing the software (or * |
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| 21 | // * any work based on the software) you agree to acknowledge its * |
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| 22 | // * use in resulting scientific publications, and indicate your * |
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| 23 | // * acceptance of all terms of the Geant4 Software license. * |
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| 24 | // ******************************************************************** |
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| 25 | // |
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| 26 | // $Id: G4LowEnergyPolarizedRayleigh.cc,v 1.7 2006/06/29 19:40:27 gunter Exp $ |
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| 27 | // GEANT4 tag $Name: $ |
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| 28 | // |
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| 29 | // -------------------------------------------------------------- |
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| 30 | // |
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| 31 | // File name: G4LowEnergyPolarizedRayleigh.cc |
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| 32 | // |
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| 33 | // Author: Capra Riccardo |
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| 34 | // |
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| 35 | // Creation date: May 2005 |
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| 36 | // |
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| 37 | // History: |
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| 38 | // ----------- |
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| 39 | // 02 May 2005 R. Capra 1st implementation |
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| 40 | // 20 May 2005 MGP Changed name of a local variable hiding |
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| 41 | // a data member of the base class |
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| 42 | // |
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| 43 | //---------------------------------------------------------------- |
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| 44 | |
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| 45 | |
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| 46 | #include "G4LowEnergyPolarizedRayleigh.hh" |
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| 47 | |
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| 48 | #include "G4LogLogInterpolation.hh" |
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| 49 | #include "G4VCrossSectionHandler.hh" |
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| 50 | #include "G4VEMDataSet.hh" |
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| 51 | #include "globals.hh" //G4Exception |
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| 52 | |
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| 53 | |
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| 54 | G4LowEnergyPolarizedRayleigh::G4LowEnergyPolarizedRayleigh(const G4String& processName) |
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| 55 | : |
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| 56 | G4VLowEnergyDiscretePhotonProcess(processName, "rayl/re-cs-", "rayl/re-ff-", new G4LogLogInterpolation, 250*eV, 100*GeV), |
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| 57 | intrinsicLowEnergyLimit(10*eV), |
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| 58 | intrinsicHighEnergyLimit(100*GeV) |
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| 59 | { |
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| 60 | if (GetLowEnergyLimit() < intrinsicLowEnergyLimit || |
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| 61 | GetHighEnergyLimit() > intrinsicHighEnergyLimit) |
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| 62 | G4Exception("G4LowEnergyPolarizedRayleigh::G4LowEnergyPolarizedRayleigh - Energy limit outside intrinsic process validity range"); |
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| 63 | |
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| 64 | |
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| 65 | } |
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| 66 | |
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| 67 | |
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| 68 | G4VParticleChange* G4LowEnergyPolarizedRayleigh::PostStepDoIt(const G4Track& aTrack, const G4Step& aStep) |
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| 69 | { |
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| 70 | // aParticleChange comes from G4VProcess |
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| 71 | aParticleChange.Initialize(aTrack); |
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| 72 | |
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| 73 | const G4DynamicParticle* incomingPhoton = aTrack.GetDynamicParticle(); |
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| 74 | G4double incomingPhotonEnergy = incomingPhoton->GetKineticEnergy(); |
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| 75 | |
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| 76 | if (incomingPhotonEnergy <= GetLowEnergyLimit()) |
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| 77 | { |
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| 78 | aParticleChange.ProposeTrackStatus(fStopAndKill); |
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| 79 | aParticleChange.ProposeEnergy(0.); |
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| 80 | aParticleChange.ProposeLocalEnergyDeposit(incomingPhotonEnergy); |
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| 81 | |
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| 82 | return G4VLowEnergyDiscretePhotonProcess::PostStepDoIt(aTrack, aStep); |
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| 83 | } |
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| 84 | |
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| 85 | const G4VCrossSectionHandler* crossSectionHandle = GetCrossSectionHandler(); |
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| 86 | const G4MaterialCutsCouple* couple = aTrack.GetMaterialCutsCouple(); |
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| 87 | G4int zAtom = crossSectionHandle->SelectRandomAtom(couple, incomingPhotonEnergy); |
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| 88 | |
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| 89 | G4double outcomingPhotonCosTheta = GenerateCosTheta(incomingPhotonEnergy, zAtom); |
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| 90 | G4double outcomingPhotonPhi = GeneratePhi(outcomingPhotonCosTheta); |
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| 91 | G4double beta=GeneratePolarizationAngle(); |
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| 92 | |
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| 93 | // incomingPhoton reference frame: |
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| 94 | // z = versor parallel to the incomingPhotonDirection |
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| 95 | // x = versor parallel to the incomingPhotonPolarization |
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| 96 | // y = defined as z^x |
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| 97 | |
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| 98 | // outgoingPhoton reference frame: |
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| 99 | // z' = versor parallel to the outgoingPhotonDirection |
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| 100 | // x' = defined as x-x*z'z' normalized |
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| 101 | // y' = defined as z'^x' |
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| 102 | |
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| 103 | G4ThreeVector z(incomingPhoton->GetMomentumDirection().unit()); |
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| 104 | G4ThreeVector x(GetPhotonPolarization(*incomingPhoton)); |
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| 105 | G4ThreeVector y(z.cross(x)); |
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| 106 | |
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| 107 | // z' = std::cos(phi)*std::sin(theta) x + std::sin(phi)*std::sin(theta) y + std::cos(theta) z |
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| 108 | G4double xDir; |
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| 109 | G4double yDir; |
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| 110 | G4double zDir; |
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| 111 | zDir=outcomingPhotonCosTheta; |
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| 112 | xDir=std::sqrt(1-outcomingPhotonCosTheta*outcomingPhotonCosTheta); |
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| 113 | yDir=xDir; |
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| 114 | xDir*=std::cos(outcomingPhotonPhi); |
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| 115 | yDir*=std::sin(outcomingPhotonPhi); |
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| 116 | |
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| 117 | G4ThreeVector zPrime((xDir*x + yDir*y + zDir*z).unit()); |
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| 118 | G4ThreeVector xPrime(x.perpPart(zPrime).unit()); |
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| 119 | G4ThreeVector yPrime(zPrime.cross(xPrime)); |
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| 120 | |
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| 121 | // outgoingPhotonPolarization is directed as x' std::cos(beta) + y' std::sin(beta) |
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| 122 | G4ThreeVector outcomingPhotonPolarization(xPrime*std::cos(beta) + yPrime*std::sin(beta)); |
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| 123 | |
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| 124 | aParticleChange.ProposeEnergy(incomingPhotonEnergy); |
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| 125 | aParticleChange.ProposeMomentumDirection(zPrime); |
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| 126 | aParticleChange.ProposePolarization(outcomingPhotonPolarization); |
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| 127 | aParticleChange.SetNumberOfSecondaries(0); |
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| 128 | |
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| 129 | // returns aParticleChange though pParticleChange and G4VProcess::PostStepDoIt |
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| 130 | return G4VLowEnergyDiscretePhotonProcess::PostStepDoIt(aTrack, aStep); |
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| 131 | } |
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| 132 | |
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| 133 | |
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| 134 | |
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| 135 | |
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| 136 | G4double G4LowEnergyPolarizedRayleigh::GenerateCosTheta(G4double incomingPhotonEnergy, G4int zAtom) const |
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| 137 | { |
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| 138 | // d sigma k0 |
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| 139 | // --------- = r0^2 * pi * F^2(x, Z) * ( 2 - sin^2 theta) * std::sin (theta), x = ---- std::sin(theta/2) |
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| 140 | // d theta hc |
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| 141 | |
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| 142 | // d sigma k0 1 - y |
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| 143 | // --------- = r0^2 * pi * F^2(x, Z) * ( 1 + y^2), x = ---- std::sqrt ( ------- ), y = std::cos(theta) |
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| 144 | // d y hc 2 |
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| 145 | |
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| 146 | // Z |
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| 147 | // F(x, Z) ~ -------- |
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| 148 | // a + bx |
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| 149 | // |
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| 150 | // The time to exit from the outer loop grows as ~ k0 |
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| 151 | // On pcgeant2 the time is ~ 1 s for k0 ~ 1 MeV on the oxygen element. A 100 GeV |
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| 152 | // event will take ~ 10 hours. |
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| 153 | // |
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| 154 | // On the avarage the inner loop does 1.5 iterations before exiting |
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| 155 | |
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| 156 | const G4double xFactor = (incomingPhotonEnergy*cm)/(h_Planck*c_light); |
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| 157 | const G4VEMDataSet * formFactorData = GetScatterFunctionData(); |
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| 158 | |
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| 159 | G4double cosTheta; |
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| 160 | G4double fCosTheta; |
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| 161 | G4double x; |
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| 162 | G4double fValue; |
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| 163 | |
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| 164 | do |
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| 165 | { |
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| 166 | do |
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| 167 | { |
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| 168 | cosTheta = 2.*G4UniformRand()-1.; |
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| 169 | fCosTheta = (1.+cosTheta*cosTheta)/2.; |
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| 170 | } |
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| 171 | while (fCosTheta < G4UniformRand()); |
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| 172 | |
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| 173 | x = xFactor*std::sqrt((1.-cosTheta)/2.); |
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| 174 | |
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| 175 | if (x > 1.e+005) |
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| 176 | fValue = formFactorData->FindValue(x, zAtom-1); |
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| 177 | else |
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| 178 | fValue = formFactorData->FindValue(0., zAtom-1); |
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| 179 | |
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| 180 | fValue/=zAtom; |
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| 181 | fValue*=fValue; |
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| 182 | } |
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| 183 | while(fValue < G4UniformRand()); |
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| 184 | |
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| 185 | return cosTheta; |
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| 186 | } |
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| 187 | |
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| 188 | |
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| 189 | |
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| 190 | G4double G4LowEnergyPolarizedRayleigh::GeneratePhi(G4double cosTheta) const |
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| 191 | { |
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| 192 | // d sigma |
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| 193 | // --------- = alpha * ( 1 - sin^2 (theta) * cos^2 (phi) ) |
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| 194 | // d phi |
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| 195 | |
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| 196 | // On the average the loop takes no more than 2 iterations before exiting |
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| 197 | |
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| 198 | G4double phi; |
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| 199 | G4double cosPhi; |
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| 200 | G4double phiProbability; |
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| 201 | G4double sin2Theta; |
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| 202 | |
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| 203 | sin2Theta=1.-cosTheta*cosTheta; |
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| 204 | |
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| 205 | do |
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| 206 | { |
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| 207 | phi = twopi * G4UniformRand(); |
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| 208 | cosPhi = std::cos(phi); |
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| 209 | phiProbability= 1. - sin2Theta*cosPhi*cosPhi; |
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| 210 | } |
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| 211 | while (phiProbability < G4UniformRand()); |
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| 212 | |
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| 213 | return phi; |
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| 214 | } |
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| 215 | |
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| 216 | |
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| 217 | |
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| 218 | |
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| 219 | |
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| 220 | G4double G4LowEnergyPolarizedRayleigh::GeneratePolarizationAngle(void) const |
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| 221 | { |
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| 222 | // Rayleigh polarization is always on the x' direction |
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| 223 | |
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| 224 | return 0; |
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| 225 | } |
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