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25 //
26 // G4NeutronBetaDecayChannel class implementation
27 //
28 // Author: H.Kurashige, 18 September 2001
29 // --------------------------------------------------------------------
30
31 #include "G4NeutronBetaDecayChannel.hh"
32
33 #include "G4DecayProducts.hh"
34 #include "G4LorentzRotation.hh"
35 #include "G4LorentzVector.hh"
36 #include "G4ParticleDefinition.hh"
37 #include "G4PhysicalConstants.hh"
38 #include "G4RotationMatrix.hh"
39 #include "G4SystemOfUnits.hh"
40 #include "G4VDecayChannel.hh"
41 #include "Randomize.hh"
42
43 G4NeutronBetaDecayChannel::G4NeutronBetaDecayChannel(const G4String& theParentName, G4double theBR)
44 : G4VDecayChannel("Neutron Decay")
45 {
46 // set names for daughter particles
47 if (theParentName == "neutron") {
48 SetBR(theBR);
49 SetParent("neutron");
50 SetNumberOfDaughters(3);
51 SetDaughter(0, "e-");
52 SetDaughter(1, "anti_nu_e");
53 SetDaughter(2, "proton");
54 }
55 else if (theParentName == "anti_neutron") {
56 SetBR(theBR);
57 SetParent("anti_neutron");
58 SetNumberOfDaughters(3);
59 SetDaughter(0, "e+");
60 SetDaughter(1, "nu_e");
61 SetDaughter(2, "anti_proton");
62 }
63 else {
64 #ifdef G4VERBOSE
65 if (GetVerboseLevel() > 0) {
66 G4cout << "G4NeutronBetaDecayChannel:: constructor :";
67 G4cout << " parent particle is not neutron but ";
68 G4cout << theParentName << G4endl;
69 }
70 #endif
71 }
72 }
73
74 G4NeutronBetaDecayChannel::G4NeutronBetaDecayChannel(const G4NeutronBetaDecayChannel& right)
75 : G4VDecayChannel(right)
76 {}
77
78 G4NeutronBetaDecayChannel&
79 G4NeutronBetaDecayChannel::operator=(const G4NeutronBetaDecayChannel& right)
80 {
81 if (this != &right) {
82 kinematics_name = right.kinematics_name;
83 verboseLevel = right.verboseLevel;
84 rbranch = right.rbranch;
85
86 // copy parent name
87 delete parent_name;
88 parent_name = new G4String(*right.parent_name);
89
90 // clear daughters_name array
91 ClearDaughtersName();
92
93 // recreate array
94 numberOfDaughters = right.numberOfDaughters;
95 if (numberOfDaughters > 0) {
96 daughters_name = new G4String*[numberOfDaughters];
97 // copy daughters name
98 for (G4int index = 0; index < numberOfDaughters; ++index) {
99 daughters_name[index] = new G4String(*right.daughters_name[index]);
100 }
101 }
102 }
103 return *this;
104 }
105
106 G4DecayProducts* G4NeutronBetaDecayChannel::DecayIt(G4double)
107 {
108 // This class describes free neutron beta decay kinematics.
109 // This version neglects neutron/electron polarization
110 // without Coulomb effect
111
112 #ifdef G4VERBOSE
113 if (GetVerboseLevel() > 1) G4cout << "G4NeutronBetaDecayChannel::DecayIt ";
114 #endif
115
116 CheckAndFillParent();
117 CheckAndFillDaughters();
118
119 // parent mass
120 G4double parentmass = G4MT_parent->GetPDGMass();
121
122 // daughters'mass
123 G4double daughtermass[3];
124 G4double sumofdaughtermass = 0.0;
125 for (G4int index = 0; index < 3; ++index) {
126 daughtermass[index] = G4MT_daughters[index]->GetPDGMass();
127 sumofdaughtermass += daughtermass[index];
128 }
129 G4double xmax = parentmass - sumofdaughtermass;
130
131 // create parent G4DynamicParticle at rest
132 G4ThreeVector dummy;
133 auto parentparticle = new G4DynamicParticle(G4MT_parent, dummy, 0.0);
134
135 // create G4Decayproducts
136 auto products = new G4DecayProducts(*parentparticle);
137 delete parentparticle;
138
139 // calculate daughter momentum
140 G4double daughtermomentum[3];
141
142 // calcurate electron energy
143 G4double x; // Ee
144 G4double p; // Pe
145 G4double dm = daughtermass[0]; // Me
146 G4double w; // cosine of e-nu angle
147 G4double r;
148 G4double r0;
149 const std::size_t MAX_LOOP = 10000;
150 for (std::size_t loop_counter = 0; loop_counter < MAX_LOOP; ++loop_counter) {
151 x = xmax * G4UniformRand();
152 p = std::sqrt(x * (x + 2.0 * dm));
153 w = 1.0 - 2.0 * G4UniformRand();
154 r = p * (x + dm) * (xmax - x) * (xmax - x) * (1.0 + aENuCorr * p / (x + dm) * w);
155 r0 = G4UniformRand() * (xmax + dm) * (xmax + dm) * xmax * xmax * (1.0 + aENuCorr);
156 if (r > r0) break;
157 }
158
159 // create daughter G4DynamicParticle
160 // rotation materix to lab frame
161 //
162 G4double costheta = 2. * G4UniformRand() - 1.0;
163 G4double theta = std::acos(costheta) * rad;
164 G4double phi = twopi * G4UniformRand() * rad;
165 G4RotationMatrix rm;
166 rm.rotateY(theta);
167 rm.rotateZ(phi);
168
169 // daughter 0 (electron) in Z direction
170 daughtermomentum[0] = p;
171 G4ThreeVector direction0(0.0, 0.0, 1.0);
172 direction0 = rm * direction0;
173 auto daughterparticle0 =
174 new G4DynamicParticle(G4MT_daughters[0], direction0 * daughtermomentum[0]);
175 products->PushProducts(daughterparticle0);
176
177 // daughter 1 (nutrino) in XZ plane
178 G4double eNu; // Enu
179 eNu = (parentmass - daughtermass[2]) * (parentmass + daughtermass[2]) + (dm * dm)
180 - 2. * parentmass * (x + dm);
181 eNu /= 2. * (parentmass + p * w - (x + dm));
182 G4double cosn = w;
183 G4double phin = twopi * G4UniformRand() * rad;
184 G4double sinn = std::sqrt((1.0 - cosn) * (1.0 + cosn));
185
186 G4ThreeVector direction1(sinn * std::cos(phin), sinn * std::sin(phin), cosn);
187 direction1 = rm * direction1;
188 auto daughterparticle1 = new G4DynamicParticle(G4MT_daughters[1], direction1 * eNu);
189 products->PushProducts(daughterparticle1);
190
191 // daughter 2 (proton) at REST
192 G4double eP; // Eproton
193 eP = parentmass - eNu - (x + dm) - daughtermass[2];
194 G4double pPx = -eNu * sinn;
195 G4double pPz = -p - eNu * cosn;
196 G4double pP = std::sqrt(eP * (eP + 2. * daughtermass[2]));
197 G4ThreeVector direction2(pPx / pP * std::cos(phin), pPx / pP * std::sin(phin), pPz / pP);
198 direction2 = rm * direction2;
199 auto daughterparticle2 = new G4DynamicParticle(G4MT_daughters[2], direction2 * pP);
200 products->PushProducts(daughterparticle2);
201
202 // output message
203 #ifdef G4VERBOSE
204 if (GetVerboseLevel() > 1) {
205 G4cout << "G4NeutronBetaDecayChannel::DecayIt ";
206 G4cout << " create decay products in rest frame " << G4endl;
207 products->DumpInfo();
208 }
209 #endif
210 return products;
211 }
212