Intensity Growth with Dose

Abstract

This chapter deals essentially with the nonlinear growth of thermoluminescence (TL) intensity with radiation dose. After a brief review of earlier theories and earlier works on this subject, the discussion takes up the so-called heating stage competition model to explain the nonlinear behavior of TL growth with dose. As against the arbitrary competitors assumed by earlier workers, in the proposed model the competitors are thermally disconnected deep traps (TDDT) which when empty act as competitors and when filled cause increase in the number of recombination centers (RC). When the active traps (AT) and TDDTs get filled up during irradiation, the reduction in competition and the increase in filled active trap population takes place simultaneously. As a result, the TL intensity growth becomes superlinear. The treatment of the model takes into account the irradiation and heating stages together. Using this model, expressions are derived for the TL intensity growth curve, supralinearity factor (SF), and predose sensitization factor (PDSF). Also derived is a new expression called the sensitization factor (S_nF). The factor S _n F which has been introduced by this author is used to give a unified explanation for the mechanisms that give rise to the SF and the PDSF. The computed profiles of SF, PDSF, and S _n F are compared with the experimentally obtained profiles of these factors for the case of LiF:Mg, Ti TLD phosphor. Apart from providing a theoretical basis underlying the phenomena of supralinearity and predose sensitization, the model dispels the doubt of some workers that the mechanism involved in these two phenomena may be altogether different from each other.