Thermoluminescence of silica beads for dosimetry up to 250 kGy

The studies herein report on a comprehensive study into the thermoluminescent properties of silica beads, including a variety of beads by; colour, finish and manufacturer as well as irradiation from different sources. The majority of studies have been conducted for 10 different bead colours from the manufacturer Toho Japan, with Pink and Frosted beads showing the most reliable properties when considering thermoluminescent dosemetry characteristics and the highest degree of adherence to applying fits to numerous data sets. The material composition of all bead types has been attempted using EDS and WDS techniques, as well as attaining images of the bead surfaces using SEM. It was also determined through EDS, acid cleaning and annealing that Pink beads are dyed to obtain their colour leaving them clear and colourless after preparation for irradiation. Spectrophotometer studies confirmed that Pink and Frosted beads had the largest transmission % across the detection range of the Risø TL/OSL reader, used for the readout of the TL response, for all colours. The suggested range of luminescence was found to be 250 nm to 300 nm, based on the relative TL responses for different bead colours. The TL studies conducted firstly determined glow-curve parameters such as; the activation energy, E, the order of kinetics, b, and the frequency factor s. Secondly, dosemetric qualities were evaluated such as; homogeneity, reproducibility, dose response and fading. Additional studies such as residual TL responses for the possibility of TL dosimetry were investigated and initial studies into the TL response for neutron irradiation. An interesting observation was the change in colour of beads with increasing dose, this was studied and an attempted characterisation made, limited by the current experimental technique and set-up. However, the oundations laid by this study show potential for an aiding tool for TL dosemetry or a novel dosemetry technique