Quasi-Exponential Decay of Neutron Fields

Abstract

This chapter discusses the phenomenon of quasi-exponential behavior. The neutron field often behaves in an exponential manner. In a pulsed neutron experiment, the behavior may be exponential in time. In a diffusion length experiment or its generalization, the wave experiment, the field may be exponential in space. The decay constants that characterize these exponentials are natural data for the description of the system. The decay constants are eigenvalues. They depend upon the nature of the material in which the neutron field is established and upon the shape of the assembly. Sometimes, the effects can be separated, though never completely. More precisely, the observed decay constants are discrete eigenvalues. The operators associated with these eigenvalues have a continuous and a discrete spectrum. The number of eigenvalues in the point spectrum is often quite small; in some systems, the point spectrum is empty.

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