ABSTRACT

Monte Carlo N-Particle (MCNP) is a Monte Carlo code package allowing coupled neutron, photon, and electron transport calculations. Also, the possibility of performing heavy charged particle transport calculations was recently introduced with the twin MCNPX code package. An arbitrary three-dimensional problem can be formulated through the use of surfaces

CONTENTS

Brief History and Code Availability ................................................................. 154 Code Structure ..................................................................................................... 155

Running MCNP .............................................................................................. 155 Geometry Speci‰cation ................................................................................. 157 Data Cards ....................................................................................................... 157

Physics, Tallies, and Detectors........................................................................... 158 Photons ............................................................................................................ 159 Electrons .......................................................................................................... 160 Tallies ................................................................................................................ 161

Variance Reduction ............................................................................................. 164 Cell Importance .............................................................................................. 165 Energy Splitting .............................................................................................. 165 Time Splitting .................................................................................................. 165 Photon Weight ................................................................................................ 165 Exponential Transform .................................................................................. 165 Vector Input ..................................................................................................... 165 Forced Collision .............................................................................................. 165 Weight Windows (Energy, Time, or Cell-Based) ........................................ 165 Weight Window Generation ......................................................................... 166 Superimposed Importance Mesh for Mesh-Based Weight Windows ..... 166 Detector Contribution .................................................................................... 166 DXTRAN Contribution ................................................................................. 166 Bremsstrahlung Biasing ................................................................................. 167

Problem Visualization ........................................................................................ 167 References ............................................................................................................. 170

de‰ning building blocks (“cells”) that are assigned density, material, and relevant cross-section tables. The source can be speci‰ed as point, surface, or volumes using generic or as a phase/space ‰le.