Transport equations in moving material Part I: Neutrons and photons

Abstract

Transport equations are usually formulated against a static material background in transport applications for neutral (neutrons, photons, mesons) and charged (electrons, protons, ions) particles. When the background is moving, the equations need be modified and corrected. We discuss these modifications and corrections, in both relativistic and nonrelativistic regimes, and contrast equations across applications. Neutron, photon, electron, neutrino, and meson transport are treated in a two part series. This review collects, collates, and expands published and unpublished developments and equations for moving material transport in different particle arenas. Hopefully, such provides a useful reference and source for readers across disciplines, linking basic underlying dynamics and representations. Part I centers on neutrons and photons, and Part II deals with electrons and neutrinos, almost an historical split. While transport equations for these particles share much in common, there are fundamental differences between particles that interact pointwise versus continuously, particles of zero rest mass versus nonzero rest mass, particles with relativistic energy versus nonrelativistic energy, and particles with short range versus long range. Our focuses are the fundamental equations and underlying dynamics of transport in moving backgrounds.The impacts in applications, important and legion, are detailed in the literature as cited. Accordingly, and invoking topic closure, applications are not recounted. Also, numerical techniques, developed with the emergence of supercomputing, are not treated herein. Both applications and numerical techniques are probably subjects of a separate communication Some modern transport codes dealing with moving material issues, however, are cited for reader reference. Many codes have been in existence for 25+ years, undergoing continuous updating, modification, improvement, and physical extension. For Part I, the main points of discussion and development are seen in the following Table of Contents, divided into neutron and photon moving material transport. An attempt at coverage of moving material transport with brevity is sought, and hopefully references provide details minimized, or not recounted, herein.