Contribution to the analysis of the decay of charged samples

Following the pioneering works of Wintle and Perlman, the discussion is focussed on the drift of the excess carriers across the sample thickness under the field they radiate. General features are displayed by the early and asymptotic decay functions and by the motion of the charge edge and charge centroid, irrespective of the initial distribution and field dependence of the effective carrier mobility. The partial differential equation for the field is solved and the decay function derived for particular charge distributions. Field dependent effective carrier mobility and charge retention on the open face are also reconsidered. Provided that the initial charge distribution does not extend to the rear side of the sample, the theory predicts that the decay rate should be constant and proportional to the square of the charge level, up to the transit time. This is not confirmed by the data on polyethylene, but the initial decay rate for a sample charged by corona at various levels suggests that charge retention takes place. The extrapolated retention coefficient for high charge level yields reasonable values of the effective carrier mobility