RANDALL-WILKINS MODEL AND ITS VALIDITY

Numerical calculations of glow curves are carried out for two energy s chemes: (1) one trap and one recombination centre, without retrapping, as in the Randall-Wilkins (RW) model; (2) one type of each: active (A T), thermally disconnected deep traps (DT) and recombination centres. The assumption of a much higher concentration of DT than AT is made, w ith retrapping in both traps. Glow curve behaviour of the first scheme is contrary to the basic characteristics of the RW model, even withou t retrapping. Conversely, glow curves of the second scheme fit the RW model regardless of retrapping. Failure of the RW model in case (1) is due to the finite lifetime of carriers in the de-localised band (tau) , ignored in the RW model. The RW type of glow curve in case (2) is du e to the predominance of recombination and recapture in DT compared to retrapping in AT. Large stocks of DT cause a reduction in tau, leadin g to a quasi-equilibrium-like condition.