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25 //
26 //
27 // Author: A. Forti
28 // Maria Grazia Pia (Maria.Grazia.Pia@cern.ch)
29 //
30 // History:
31 // --------
32 // Added Livermore data table construction methods A. Forti
33 // Modified BuildMeanFreePath to read new data tables A. Forti
34 // Modified PostStepDoIt to insert sampling with EPDL97 data A. Forti
35 // Added SelectRandomAtom A. Forti
36 // Added map of the elements A. Forti
37 // 24.04.2001 V.Ivanchenko - Remove RogueWave
38 // 06.08.2001 MGP - Revised according to a design iteration
39 // 22.01.2003 V.Ivanchenko - Cut per region
40 // 10.03.2003 V.Ivanchenko - Remove CutPerMaterial warning
41 // 24.04.2003 V.Ivanchenko - Cut per region mfpt
42 //
43 // -------------------------------------------------------------------
44
45 #include "G4LowEnergyCompton.hh"
46 #include "Randomize.hh"
47 #include "G4PhysicalConstants.hh"
48 #include "G4SystemOfUnits.hh"
49 #include "G4ParticleDefinition.hh"
50 #include "G4Track.hh"
51 #include "G4Step.hh"
52 #include "G4ForceCondition.hh"
53 #include "G4Gamma.hh"
54 #include "G4Electron.hh"
55 #include "G4DynamicParticle.hh"
56 #include "G4VParticleChange.hh"
57 #include "G4ThreeVector.hh"
58 #include "G4EnergyLossTables.hh"
59 #include "G4RDVCrossSectionHandler.hh"
60 #include "G4RDCrossSectionHandler.hh"
61 #include "G4RDVEMDataSet.hh"
62 #include "G4RDCompositeEMDataSet.hh"
63 #include "G4RDVDataSetAlgorithm.hh"
64 #include "G4RDLogLogInterpolation.hh"
65 #include "G4RDVRangeTest.hh"
66 #include "G4RDRangeTest.hh"
67 #include "G4RDRangeNoTest.hh"
68 #include "G4MaterialCutsCouple.hh"
69
70
71 G4LowEnergyCompton::G4LowEnergyCompton(const G4String& processName)
72 : G4VDiscreteProcess(processName),
73 lowEnergyLimit(250*eV),
74 highEnergyLimit(100*GeV),
75 intrinsicLowEnergyLimit(10*eV),
76 intrinsicHighEnergyLimit(100*GeV)
77 {
78 if (lowEnergyLimit < intrinsicLowEnergyLimit ||
79 highEnergyLimit > intrinsicHighEnergyLimit)
80 {
81 G4Exception("G4LowEnergyCompton::G4LowEnergyCompton()",
82 "OutOfRange", FatalException,
83 "Energy outside intrinsic process validity range!");
84 }
85
86 crossSectionHandler = new G4RDCrossSectionHandler;
87
88 G4RDVDataSetAlgorithm* scatterInterpolation = new G4RDLogLogInterpolation;
89 G4String scatterFile = "comp/ce-sf-";
90 scatterFunctionData = new G4RDCompositeEMDataSet(scatterInterpolation, 1., 1.);
91 scatterFunctionData->LoadData(scatterFile);
92
93 meanFreePathTable = 0;
94
95 rangeTest = new G4RDRangeNoTest;
96
97 // For Doppler broadening
98 shellData.SetOccupancyData();
99
100 if (verboseLevel > 0)
101 {
102 G4cout << GetProcessName() << " is created " << G4endl
103 << "Energy range: "
104 << lowEnergyLimit / keV << " keV - "
105 << highEnergyLimit / GeV << " GeV"
106 << G4endl;
107 }
108 }
109
110 G4LowEnergyCompton::~G4LowEnergyCompton()
111 {
112 delete meanFreePathTable;
113 delete crossSectionHandler;
114 delete scatterFunctionData;
115 delete rangeTest;
116 }
117
118 void G4LowEnergyCompton::BuildPhysicsTable(const G4ParticleDefinition& )
119 {
120
121 crossSectionHandler->Clear();
122 G4String crossSectionFile = "comp/ce-cs-";
123 crossSectionHandler->LoadData(crossSectionFile);
124
125 delete meanFreePathTable;
126 meanFreePathTable = crossSectionHandler->BuildMeanFreePathForMaterials();
127
128 // For Doppler broadening
129 G4String file = "/doppler/shell-doppler";
130 shellData.LoadData(file);
131 }
132
133 G4VParticleChange* G4LowEnergyCompton::PostStepDoIt(const G4Track& aTrack,
134 const G4Step& aStep)
135 {
136 // The scattered gamma energy is sampled according to Klein - Nishina formula.
137 // then accepted or rejected depending on the Scattering Function multiplied
138 // by factor from Klein - Nishina formula.
139 // Expression of the angular distribution as Klein Nishina
140 // angular and energy distribution and Scattering fuctions is taken from
141 // D. E. Cullen "A simple model of photon transport" Nucl. Instr. Meth.
142 // Phys. Res. B 101 (1995). Method of sampling with form factors is different
143 // data are interpolated while in the article they are fitted.
144 // Reference to the article is from J. Stepanek New Photon, Positron
145 // and Electron Interaction Data for GEANT in Energy Range from 1 eV to 10
146 // TeV (draft).
147 // The random number techniques of Butcher & Messel are used
148 // (Nucl Phys 20(1960),15).
149
150 aParticleChange.Initialize(aTrack);
151
152 // Dynamic particle quantities
153 const G4DynamicParticle* incidentPhoton = aTrack.GetDynamicParticle();
154 G4double photonEnergy0 = incidentPhoton->GetKineticEnergy();
155
156 if (photonEnergy0 <= lowEnergyLimit)
157 {
158 aParticleChange.ProposeTrackStatus(fStopAndKill);
159 aParticleChange.ProposeEnergy(0.);
160 aParticleChange.ProposeLocalEnergyDeposit(photonEnergy0);
161 return G4VDiscreteProcess::PostStepDoIt(aTrack,aStep);
162 }
163
164 G4double e0m = photonEnergy0 / electron_mass_c2 ;
165 G4ParticleMomentum photonDirection0 = incidentPhoton->GetMomentumDirection();
166 G4double epsilon0 = 1. / (1. + 2. * e0m);
167 G4double epsilon0Sq = epsilon0 * epsilon0;
168 G4double alpha1 = -std::log(epsilon0);
169 G4double alpha2 = 0.5 * (1. - epsilon0Sq);
170 G4double wlPhoton = h_Planck*c_light/photonEnergy0;
171
172 // Select randomly one element in the current material
173 const G4MaterialCutsCouple* couple = aTrack.GetMaterialCutsCouple();
174 G4int Z = crossSectionHandler->SelectRandomAtom(couple,photonEnergy0);
175
176 // Sample the energy of the scattered photon
177 G4double epsilon;
178 G4double epsilonSq;
179 G4double oneCosT;
180 G4double sinT2;
181 G4double gReject;
182 do
183 {
184 if ( alpha1/(alpha1+alpha2) > G4UniformRand())
185 {
186 epsilon = std::exp(-alpha1 * G4UniformRand()); // std::pow(epsilon0,G4UniformRand())
187 epsilonSq = epsilon * epsilon;
188 }
189 else
190 {
191 epsilonSq = epsilon0Sq + (1. - epsilon0Sq) * G4UniformRand();
192 epsilon = std::sqrt(epsilonSq);
193 }
194
195 oneCosT = (1. - epsilon) / ( epsilon * e0m);
196 sinT2 = oneCosT * (2. - oneCosT);
197 G4double x = std::sqrt(oneCosT/2.) / (wlPhoton/cm);
198 G4double scatteringFunction = scatterFunctionData->FindValue(x,Z-1);
199 gReject = (1. - epsilon * sinT2 / (1. + epsilonSq)) * scatteringFunction;
200
201 } while(gReject < G4UniformRand()*Z);
202
203 G4double cosTheta = 1. - oneCosT;
204 G4double sinTheta = std::sqrt (sinT2);
205 G4double phi = twopi * G4UniformRand() ;
206 G4double dirX = sinTheta * std::cos(phi);
207 G4double dirY = sinTheta * std::sin(phi);
208 G4double dirZ = cosTheta ;
209
210 // Doppler broadening - Method based on:
211 // Y. Namito, S. Ban and H. Hirayama,
212 // "Implementation of the Doppler Broadening of a Compton-Scattered Photon Into the EGS4 Code"
213 // NIM A 349, pp. 489-494, 1994
214
215 // Maximum number of sampling iterations
216 G4int maxDopplerIterations = 1000;
217 G4double bindingE = 0.;
218 G4double photonEoriginal = epsilon * photonEnergy0;
219 G4double photonE = -1.;
220 G4int iteration = 0;
221 G4double eMax = photonEnergy0;
222 do
223 {
224 iteration++;
225 // Select shell based on shell occupancy
226 G4int shell = shellData.SelectRandomShell(Z);
227 bindingE = shellData.BindingEnergy(Z,shell);
228
229 eMax = photonEnergy0 - bindingE;
230
231 // Randomly sample bound electron momentum (memento: the data set is in Atomic Units)
232 G4double pSample = profileData.RandomSelectMomentum(Z,shell);
233 // Rescale from atomic units
234 G4double pDoppler = pSample * fine_structure_const;
235 G4double pDoppler2 = pDoppler * pDoppler;
236 G4double var2 = 1. + oneCosT * e0m;
237 G4double var3 = var2*var2 - pDoppler2;
238 G4double var4 = var2 - pDoppler2 * cosTheta;
239 G4double var = var4*var4 - var3 + pDoppler2 * var3;
240 if (var > 0.)
241 {
242 G4double varSqrt = std::sqrt(var);
243 G4double scale = photonEnergy0 / var3;
244 // Random select either root
245 if (G4UniformRand() < 0.5) photonE = (var4 - varSqrt) * scale;
246 else photonE = (var4 + varSqrt) * scale;
247 }
248 else
249 {
250 photonE = -1.;
251 }
252 } while ( iteration <= maxDopplerIterations &&
253 (photonE < 0. || photonE > eMax || photonE < eMax*G4UniformRand()) );
254
255 // End of recalculation of photon energy with Doppler broadening
256 // Revert to original if maximum number of iterations threshold has been reached
257 if (iteration >= maxDopplerIterations)
258 {
259 photonE = photonEoriginal;
260 bindingE = 0.;
261 }
262
263 // Update G4VParticleChange for the scattered photon
264
265 G4ThreeVector photonDirection1(dirX,dirY,dirZ);
266 photonDirection1.rotateUz(photonDirection0);
267 aParticleChange.ProposeMomentumDirection(photonDirection1);
268
269 G4double photonEnergy1 = photonE;
270 //G4cout << "--> PHOTONENERGY1 = " << photonE/keV << G4endl;
271
272 if (photonEnergy1 > 0.)
273 {
274 aParticleChange.ProposeEnergy(photonEnergy1) ;
275 }
276 else
277 {
278 aParticleChange.ProposeEnergy(0.) ;
279 aParticleChange.ProposeTrackStatus(fStopAndKill);
280 }
281
282 // Kinematics of the scattered electron
283 G4double eKineticEnergy = photonEnergy0 - photonEnergy1 - bindingE;
284 G4double eTotalEnergy = eKineticEnergy + electron_mass_c2;
285
286 G4double electronE = photonEnergy0 * (1. - epsilon) + electron_mass_c2;
287 G4double electronP2 = electronE*electronE - electron_mass_c2*electron_mass_c2;
288 G4double sinThetaE = -1.;
289 G4double cosThetaE = 0.;
290 if (electronP2 > 0.)
291 {
292 cosThetaE = (eTotalEnergy + photonEnergy1 )* (1. - epsilon) / std::sqrt(electronP2);
293 sinThetaE = -1. * std::sqrt(1. - cosThetaE * cosThetaE);
294 }
295
296 G4double eDirX = sinThetaE * std::cos(phi);
297 G4double eDirY = sinThetaE * std::sin(phi);
298 G4double eDirZ = cosThetaE;
299
300 // Generate the electron only if with large enough range w.r.t. cuts and safety
301
302 G4double safety = aStep.GetPostStepPoint()->GetSafety();
303
304 if (rangeTest->Escape(G4Electron::Electron(),couple,eKineticEnergy,safety))
305 {
306 G4ThreeVector eDirection(eDirX,eDirY,eDirZ);
307 eDirection.rotateUz(photonDirection0);
308
309 G4DynamicParticle* electron = new G4DynamicParticle (G4Electron::Electron(),eDirection,eKineticEnergy) ;
310 aParticleChange.SetNumberOfSecondaries(1);
311 aParticleChange.AddSecondary(electron);
312 // Binding energy deposited locally
313 aParticleChange.ProposeLocalEnergyDeposit(bindingE);
314 }
315 else
316 {
317 aParticleChange.SetNumberOfSecondaries(0);
318 aParticleChange.ProposeLocalEnergyDeposit(eKineticEnergy + bindingE);
319 }
320
321 return G4VDiscreteProcess::PostStepDoIt( aTrack, aStep);
322 }
323
324 G4bool G4LowEnergyCompton::IsApplicable(const G4ParticleDefinition& particle)
325 {
326 return ( &particle == G4Gamma::Gamma() );
327 }
328
329 G4double G4LowEnergyCompton::GetMeanFreePath(const G4Track& track,
330 G4double, // previousStepSize
331 G4ForceCondition*)
332 {
333 const G4DynamicParticle* photon = track.GetDynamicParticle();
334 G4double energy = photon->GetKineticEnergy();
335 const G4MaterialCutsCouple* couple = track.GetMaterialCutsCouple();
336 size_t materialIndex = couple->GetIndex();
337
338 G4double meanFreePath;
339 if (energy > highEnergyLimit) meanFreePath = meanFreePathTable->FindValue(highEnergyLimit,materialIndex);
340 else if (energy < lowEnergyLimit) meanFreePath = DBL_MAX;
341 else meanFreePath = meanFreePathTable->FindValue(energy,materialIndex);
342 return meanFreePath;
343 }
344