Asymptotic and Transient Analysis of Pulsed Moderators

The time dependence of neutron transport is investigated using various approximations in moderating media. Transients and asymptotic solutions are clearly distinguished. It is shown that there is no real asymptotic eigenvalue for large bucklings. Transients are classified and shown to arise from a mismatch of the initial flux with the asymptotic distribution in energy or in angle or from a finite source. These features are demonstrated by means of analytic solutions of pulsed problems using low order approximations. The demonstrations are also extended to arbitrary P-L approximations (but not time-dependent diffusion theory) for an arbitrary number of energy groups.