The calculation of neutron flux and exposure in the Hanford reactors

Discussion of the behavior of the neutron in a graphite moderated reactor quite naturally falls into three categories, each of which may be defined more or less by energy limits, but more meaningfully by describing the conduct of the neutrons in each category. Thus, a thermal neutron is properly designated as a neutron which is in thermal equilibrium with the atoms of the graphite moderator; a resonance energy neutron by the fact that it is in a state of being slowed down or moderated; and a fast neutron, for the most part, by virtue of having been born in fission and still in a state of early flight. Approximate energy limits for thermal, resonance, and fast neutrons will be considered later. The section of this document concerning thermal neutrons is primarily intended for technical persons with but little previous experience with neutron flux problems. The sections on resonance and fast fluxes are designed to serve as a guide for those with some familiarity with the neutron. All calculations and data in this document pertain to the 8 3/8-inch lattice piles.