Presents the first book treatment of Monte Carlo N-Particle simulations for special nuclear materials measurements

Provides step-by-step examples based on real-world problems

Imparts the authors' insights based on decades of experience in Monte Carlo code design and use

This book is open access, which means that you have free and unlimited access

Table of contents:

Contents .......................................................................................................................................... 4

Introduction ..................................................................................................................................... 8

1.1 Geometry ............................................................................................................................... 8

1.1.1 Simplest possible input file............................................................................................. 8

1.1.3 Simple Input File .......................................................................................................... 12

1.1.4 Running and plotting MCNP geometries ..................................................................... 14

1.1.5 Surfaces and Complicated Cells: Intersections and Unions ......................................... 17

1.1.6 Duplicate Cells, Compliments and Translations: LIKE BUT and TRCL .................... 22

1.1.7 Filled Cells: Universes.................................................................................................. 26

1.1.8 Lattice Geometries ........................................................................................................ 32

1.1.9 Fully Specified Lattice Geometries .............................................................................. 40

1.2 Materials and Cross Sections .............................................................................................. 45

1.2.1 Specifying Materials ..................................................................................................... 45

1.2.2 Neutron cross sections .................................................................................................. 46

1.2.3 Low-energy neutron problems ¿ thermal free gas treatment ........................................ 49

1.2.4 Low-energy neutron problem data ¿ S(¿,ß) thermal treatment .................................... 50

1.2.5 Photon cross sections .................................................................................................... 53

1.2.6 Electron stopping powers for coupled photon and electron problems ......................... 57

1.2.7 Data and models for Ions and Charged Particles .......................................................... 61

1.2.8 Additional data diagnostics and recommendations ...................................................... 62

1.3 Sources ................................................................................................................................ 63

1.3.1 SDEF Fixed Sources ..................................................................................................... 63

1.3.2 SDEF Source Distributions .......................................................................................... 66

1.3.3 SDEF Dependent Distributions: DS ............................................................................. 69

1.3.4 Criticality Sources ........................................................................................................ 71

1.3.5 Surface Source Read and Write (SSR, SSW) ......................................................... 77

1.3.6 Checking sources .................................................................................................... 87

1.4 Output and Tallies ............................................................................................................... 87

1.4.1 Output Files .................................................................................................................. 87

1.4.2 MCNP Estimators and Tally Types .............................................................................. 93

DRAFT

1.4.3 Basic Tally Format ....................................................................................................... 95

1.4.4 Special Tally Treatments ............................................................................................ 111

1.4.5 Pulse-Height Tallies ................................................................................................... 128

1.4.6 Point Detectors and Next-Event Estimators ............................................................... 134

1.5 Plotting .............................................................................................................................. 143

1.5.1 Geometry Plotting and Command Files ..................................................................... 143

1.5.2 Cross Section plotting ................................................................................................. 145

1.5.3 Tally Plotting .............................................................................................................. 150

1.5.4 Mesh, Radiography, and Ring Tallies ........................................................................ 167

1.6 Statistics and Convergence ................................................................................................ 186

Section 2: Examples for nuclear safeguards applications ........................................................... 198

2.1 Example 1: Fuel Assembly in Water Tank ....................................................................... 198

2.1.1 Description.................................................................................................................. 198

2.1.2 Geometry description ................................................................................................. 203

2.1.3 Other data: sources, materials, tallies, and more ........................................................ 204

2.1.4 MCNP Output ............................................................................................................. 206

2.2 Example 2: Coincidence Counter with F4 and F8 Tallies for Coincidence and Multiplicity Counting Rates ........................................................................................................................ 207

2.2.1 Description.................................................................................................................. 207

2.2.2 Materials ..................................................................................................................... 212

2.2.3 Source ......................................................................................................................... 212

2.2.4 Tallies ......................................................................................................................... 213

2.2.5 Warning Messages ...................................................................................................... 214

2.2.6 Results ........................................................................................................................ 216

2.2.6A: From the Point Model ............................................................................................. 216

2.2.6B: Rates Calculated without Point Model assumptions............................................... 221

2.3 Gamma pulse height (to be completed) ................................................................................ 227

2.4 Active Neutron Example: Cf Shuffler ............................................................................... 231

2.4.1 Description and input file ........................................................................................... 231

2.4.2 Results ........................................................................................................................ 234

Section 3: Examples of Advanced Concepts .............................................................................. 240

Section 3.1 Variance Reduction .............................................................................................. 240

3.1.1 Introduction ................................................................................................................ 240

DRAFT

6

3.1.2 Multigroup Weight Windows and Time Splitting: Lead Slowing Down Spectrometer ............................................................................................................................................. 242

3.1.2.1 Input File Notes ....................................................................................................... 253

3.1.2.2 Variance Reduction Step 1: simplify problem and add weight window generator . 256

3.1.2.3 Iteration 2 ................................................................................................................. 261

3.1.2.4 Additional iterations ................................................................................................ 263

3.1.2.5 Cylindrical Mesh Weight Window Summary ......................................................... 267

3.1.3 Cell-based weight windows for the Lead Slowing Down Spectrometer .................... 271

3.1.4 Time splitting .............................................................................................................. 277

3.1.5 Variance Reduction for the Cf Shuffler ......................................................................... 280

3.1.5.1 Cf Shuffler modified input...