On the thermoluminescence characteristics of NaF and KCl

Abstract

Thermoluminescence (TL) properties of NaF and KCl are investigated in order to assess their suitability as radiation dosemeters for retrospective dosimetry. TL measurements were made on samples irradiated to different doses (1–20 Gy) and heated at a rate ranging from 0.4 to 4 °C/s in a TL/OSL reader. The TL glow curves of NaF, readout at 1oCs−1, exhibited six apparent peaks around 38.7 ± 1.4, 63.5 ± 0.5, 105.5 ± 0.4, 237.5 ± 0.8, 299.0 ± 1.0 and 347.5 ± 0.7 °C with a shoulder around 168.0 ± 2.3 °C. Those of KCl have three clearly identifiable peaks around 44.0 ± 0.3, 95.3 ± 0.8 and 160.5 ± 0.7 °C. Glow curve deconvolution, however, revealed that the glow curves of NaF and KCl are best fitted with nine and five glow peaks respectively. In NaF, all the peaks exhibited linearity of dose-response in the entire dose range considered in this study. Only the peaks around 95.3 ± 0.8 and 160.5 ± 0.7 °C exhibited linear dose-response in the entire dose range for KCl. In NaF, there was thermal quenching of the TL responses of the peaks around 63.5 ± 0.5, 105.5 ± 0.4 and 237.5 ± 0.8 °C, and thermal enhancement of responses for peaks around 299.0 ± 1.0 and 347.5 ± 0.7 °C. With respect to KCl, the TL responses of all the peaks exhibited thermal enhancement as heating rate was increased. The activation energies associated with the thermal enhancement and quenching of the peaks’ TL responses are presented. The repeated use of an aliquot of NaF five times for dose measurements resulted in an acceptable variation in sensitivity, on the other hand the sensitivity of KCl decreased with increasing number of repeat use. The activation energy of the electron traps associated with the glow peaks in both crystals calculated in this study are comparable to previously published values. Both crystals can be used for retrospective dosimetry however change in sensitivity with repeat use of an aliquot will have to be accounted for in the case of KCl.