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(α,β) 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 ................................................