Lecture Notes on: Neutron- and gamma -Gauges, Their Principle, Theory, Use and Calibration

摘要

The lecture notes are divided into five parts. In part I neutron sources based on ( alpha ,n) and ( gamma ,n) reaction as well as on spontaneous fission and the use of accelerators are discussed. The source spectra are considered and the slowing-down of fast source neutrons is calculated. Finally, the basic concepts of neutron transport such as nuclear cross sections, mean free path, reaction rate and neutron flux are discussed. In part II a formula for the neutron current density is derived and from this the two-group and three-group diffusion equations for fast and thermal neutrons are established. For a fast neutron point source in an infinite medium, the flux-distribution around the source is calculated by use of two- and three-group theory and by Fermi-age theory. Neutron detectors are also discussed. In part III (n,n)-gauges, containing a fast neutron source and a thermal or near-thermal neutron detector, are considered together with their practical applications, in particular measurements of water content. The calibration of such gauges is described and the factors influencing the measurements such as dry bulk density and chemical composition are discussed. In part IV the interactions of gamma -quanta with matter are discussed and formulas for reaction cross sections, absorption coefficients, build-up factors and gamma -flux are presented. Simplified models for ( gamma - gamma )-gauges, containing a gamma -source and a gamma -detector, are derived both for a backscatter and a transmission gauge. Different types of gamma -detectors are discussed. In part V (n- gamma )-gauges based on both capture- gamma analysis and activation- gamma analysis are considered. In both cases the experimental set-up is discussed, simplified models derived and practical applications described. Finally, a comparison between the two methods is made. (Atomindex citation 14:779667)