PENELOPE 2003 - OECD Nuclear Energy Agency

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200 Chapter 6. Structure and operation of the code system The upper plot in fig. 6.4 shows the distribution of energy E d deposited into the NaI crystal volume (per primary photon). The lower figure displays the distribution (per primary photon) of the energy E b of “backscattered” photons, i.e. photons that emerge from the system pointing “downwards”, with W = cos θ < 0. These distributions show three conspicuous structures that arise from backscattering of incident photons in the crystal volume or in the Al backing (B), escape of one of the ∼511 keV x-rays resulting from positron annihilation (A) and escape of ∼30 keV iodine K x-rays (C). The peak A is so small because pair production is a relatively unlikely process for 1.25 MeV photons (the energy is too close to the threshold). 6.3 Selecting the simulation parameters The speed and accuracy of the simulation of electrons and positrons is determined by the values of the simulation parameters E abs , C 1 , C 2 , W cc , W cr and s max , which are selected by the user for each material in the simulated structure 2 . Here we summarize the rules for assigning “safe” values to these parameters. The absorption energies E abs are determined either by the characteristics of the experiment or by the required space resolution. If we want to tally dose or deposited-charge distributions, E abs should be such that the residual range R(E abs ) of electrons/positrons is less than the typical dimensions of the volume bins used to tally these distributions 3 . In other cases, it is advisable to run short simulations (for the considered body alone) with increasing values of E abs (starting from 100 eV) to study the effect of this parameter on the results. The allowed values of the elastic scattering parameters C 1 and C 2 are limited to the interval (0,0.2). For the present version of penelope, these parameters have a very weak influence on the results, weaker than for previous versions of the code. As discussed in section 4.4.1, this is mostly due to the improved modelling of soft energy losses and to the consideration of the energy dependence of the hard mean free paths (see sections 4.2 and 4.3). Our recommended practice is to set C 1 = C 2 = 0.05, which is fairly conservative, as shown by the example given below. Before increasing the value of any of these parameters, it is advisable to perform short test simulations to verify that with the augmented parameter value the results remain essentially unaltered (and that the simulation runs faster; if there is no gain in speed, keep the conservative values). We have already indicated that the cutoff energies W cc and W cr have a very weak influence on the accuracy of the results provided only that they are both smaller than the width of the bins used to tally energy distributions. When energy distributions are of no interest, our recommendation is setting these cutoff energies equal to one hundredth of the typical energy of primary particles. 2 To specify simulation parameters for a single body we can simply assign a specific material to this body, different from that of other bodies of the same composition. 3 penelope prints tables of electron and positron ranges if subroutine PEINIT is invoked with INFO=3 or larger.
6.3. Selecting the simulation parameters 201 3 1 E- 5 1 E d p(E d ) (eV −1 ) 1 E- 6 ➤ ➤ B A 1 E- 7 C 0.0E+0 4 .0E+5 8 .0E+5 1 .2 E+6 E d (eV) 6 E- 7 3 B 1 p(E b ) (eV −1 ) 4 E- 7 2 E- 7 E b ➤ ➤ C A 0E+0 0.0E+0 4 .0E+5 8 .0E+5 1 .2 E+6 E b (eV) Figure 6.4: Partial results from PENCYL for the NaI photon detector described in the text. Top: distribution of energy deposited in the NaI crystal (MAT=1). Bottom: energy distribution of backscattered photons.
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Data Bank ISBN 92-64-02145-0 PENELO
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FOREWORD The OECD/NEA Data Bank was
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TABLE OF CONTENTS Foreword ........
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4.3 Combined scattering and energy
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PREFACE Radiation transport in matt
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The present version of PENELOPE is
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Chapter 1 Monte Carlo simulation. B
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1.1. Elements of probability theory
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1.1. Elements of probability theory
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1.2. Random sampling methods 7 Tabl
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1.2. Random sampling methods 9 Nume
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1.2. Random sampling methods 11 whe
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1.2. Random sampling methods 13 can
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1.2. Random sampling methods 15 mus
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1.2. Random sampling methods 17 the
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1.3. Monte Carlo integration 19 Con
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1.4. Simulation of radiation transp
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¡ ¢ 1.4. Simulation of radiation
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1.5. Statistical averages and uncer
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1.6. Variance reduction 31 also imp
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1.6. Variance reduction 33 weight a
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Chapter 2 Photon interactions In th
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2.1. Coherent (Rayleigh) scattering
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2.1. Coherent (Rayleigh) scattering
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2.2. Photoelectric effect 41 ➤E E
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F 2.2. Photoelectric effect 43 1E+7
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2.3. Incoherent (Compton) scatterin
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C u 2.3. Incoherent (Compton) scatt
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2.4. Electron-positron pair product
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2.5. Attenuation coefficients 63 di
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2.6. Atomic relaxation 65 2.6 Atomi
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2.6. Atomic relaxation 67 two vacan
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Chapter 3 Electron and positron int
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3.1. Elastic collisions 71 nucleus
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3.1. Elastic collisions 73 1 E - 1
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ρ ρ ρ λ λ λ ρ ρ ρ λ λ λ
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3.1. Elastic collisions 77 becomes
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B ' B ' 3.1. Elastic collisions 79
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3.2. Inelastic collisions 81 where
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3.2. Inelastic collisions 83 global
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3.2. Inelastic collisions 85 plays
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3.2. Inelastic collisions 87 optica
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3.2. Inelastic collisions 89 The DC
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3.2. Inelastic collisions 91 In the
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3.2. Inelastic collisions 93 where
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c b c b 3.2. Inelastic collisions 9
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A l A u 3.2. Inelastic collisions 9
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3.2. Inelastic collisions 99 After
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3.2. Inelastic collisions 101 Table
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3.2. Inelastic collisions 103 In re
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3.2. Inelastic collisions 105 1Ε+4
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3.3. Bremsstrahlung emission 107 an
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3.3. Bremsstrahlung emission 109 1
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3.3. Bremsstrahlung emission 111 1
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3.3. Bremsstrahlung emission 113 wh
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3.3. Bremsstrahlung emission 115 Al
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3.3. Bremsstrahlung emission 117 Th
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3.4. Positron annihilation 119 (198
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3.4. Positron annihilation 121 It i
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Chapter 4 Electron/positron transpo
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4.1. Elastic scattering 125 Lewis (
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4.1. Elastic scattering 127 ⎡ ⎛
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4.1. Elastic scattering 129 simulat
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4.1. Elastic scattering 131 The sim
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4.2. Soft energy losses 133 soft in
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4.2. Soft energy losses 135 deviati
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4.2. Soft energy losses 137 scatter
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4.3. Combined scattering and energy
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4.4. Generation of random tracks 14
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Page 165 and 166: Chapter 5 Constructive quadric geom
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Page 169 and 170: 5.2. Quadric surfaces 157 Given a f
Page 171 and 172: 5.2. Quadric surfaces 159 Table 5.1
Page 173 and 174: 5.3. Constructive quadric geometry
Page 175 and 176: 5.4. Geometry definition file 163 1
Page 177 and 178: 5.4. Geometry definition file 165
Page 179 and 180: 5.5. The subroutine package pengeom
Page 181 and 182: 5.5. The subroutine package pengeom
Page 183 and 184: 5.6. Debugging and viewing the geom
Page 185 and 186: 5.7. A short tutorial 173 MODULE (
Page 187 and 188: 5.7. A short tutorial 175 Writing a
Page 189 and 190: Chapter 6 Structure and operation o
Page 191 and 192: 6.1. penelope 179 and/or numbers in
Page 193 and 194: 6.1. penelope 181 1986). The format
Page 195 and 196: 6.1. penelope 183 The connection of
Page 197 and 198: 6.1. penelope 185 that has to be lo
Page 199 and 200: G y y y y y 6.1. penelope 187 CALL
Page 201 and 202: 6.1. penelope 189 It is the respons
Page 203 and 204: 6.2. Examples of MAIN programs 191
Page 211: 6.2. Examples of MAIN programs 199
Page 215 and 216: ! 6.3. Selecting the simulation par
Page 217 and 218: 6.5. Installation 205 radiation is
Page 219 and 220: 6.5. Installation 207 To get the ex
Page 221 and 222: Appendix A Collision kinematics To
Page 223 and 224: A.1. Two-body reactions 211 Clearly
Page 225 and 226: A.2. Inelastic collisions of charge
Page 227 and 228: m A.2. Inelastic collisions of char
Page 229 and 230: Appendix B Numerical tools B.1 Cubi
Page 231 and 232: B.1. Cubic spline interpolation 219
Page 233 and 234: B.2. Numerical quadrature 221 B.2 N
Page 235 and 236: Appendix C Electron/positron transp
Page 237 and 238: C.1. Tracking particles in vacuum.
Page 239 and 240: C.1. Tracking particles in vacuum.
Page 241 and 242: C.2. Exact tracking in homogeneous
Page 243 and 244: C.2. Exact tracking in homogeneous
Page 245 and 246: Bibliography Abramowitz M. and I.A.
Page 247 and 248: Bibliography 235 Briesmeister J.F.
Page 249 and 250: Bibliography 237 James F. (1990),
Page 251 and 252: Bibliography 239 Reimer L. and E.R.
Page 253: Bibliography 241 Yates A.C. (1968),
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