Synthesis and dosimetric characterization of lithium tetraborate (Li2B4O7:Cu,Ag) thermoluminescent dosimeter with improved reproducibility and reusability

A nano-sized, tissue equivalent, polycrystalline Li2B4O7:Cu, Ag phosphor was synthesized for dosimetric applications. Repeated annealing, irradiation and readouts may alter the color and affect the sensitivity of the phosphor. One of the aims of the present work was to dope Li2B4O7 with an appropriate amount of Ag and Cu atoms in order to diminish such effects and consequently improve reproducibility and reusability of the dosimeter. For this purpose, Li2B4O7 was primarily doped with Ag ions, and the Cu atoms were introduced with minimal concetration. A sample co-doped with 0.35 wt% Ag and 0.015 wt% Cu exhibited optimum TL response. To facilitate handling of the material, the powdered sample was also reproduced in pellet form. Linear integrated TL response was observed from 1 mGy to 20 Gy. No change in material's sensitivity and color was observed after repeated annealing, irradiation and readout episodes. Response of the material was found to be reproducible with a COV between 1.7-2.3%. Thermal quenching effects with increasing heating rate were seen for the current material. Less than 5% fading was observed during a two month study. The obtained glow curve was very simple having a main dosimetric peak at about 200 ± 10 °C with two small shoulder peaks. Kinetic analysis of the glow curve was performed by an experimental method (Tm-Tstop) and by curve fitting approximation. Kinetic parameters (b, s and E) were found within the prescribed limits. The promising dosimetric characteristics and the optimal glow curve favours this new material for use as a field dosimeter.