Alpha particle thermoluminescence in LiF:Mg,Ti in the framework of conduction band/valence band dynamics

Kinetic models of thermoluminescence (TL) glow curves and dose response are based on the assumption that electrons and holes released from trapping centers during heating are thermally elevated to the conduction band (CB) and valence band (VB) where they are completely delocalized. The implication is that during heating the released charge carriers can recombine with the entire population of charges of the opposite sign. In the experiments described herein the CB/VB delocalization of the charge carriers preceding recombination is investigated by alpha particle irradiation of 0.1 mm and 0.9 mm samples of LiF:Mg,Ti (TLD-100). Following irradiation some trapped electrons escape from the alpha particle tracks during readout. Since the Bragg peak occurs at a depth of ∼10⁴ Å, the alpha particle track serves as a source of low energy electrons limited to this depth of penetration. The sum of the two glow curves following irradiation on opposite sides of the sample is compared with the single glow curve obtained following irradiation on both sides. In the latter geometry, the electrons escaping the tracks, if delocalized, will be able to recombine with the charge carrier distribution on the opposite side of the sample, thereby altering the intensity and shape of the TL glow curve. The results do not reveal evidence for such behaviour and are in conflict with kinetic models involving CB/VB delocalization preceding recombination.