Advanced Materials for Radiation Dosimetry

Abstract

<p>The motivation for this work was to find materials that have the following characteristics: good optical transparency, rapid read-out, automation of read-out, good fading characteristic, promise high sensitivity to ionising radiation, and tissue equivalence for use in medical applications. For example, there are medical applications in brachytherapy and high-energy photon therapy for the treatment of cancer. These applications benefit small dosimeters for monitoring radiation during radiotherapy or for dose verification and validation. This thesis studies fluoroperovskite materials that were manufactured as bulk materials or nanoparticles. The techniques of photoluminescence (PL), radioluminescence (RL), thermoluminescence (TL) and optically stimulated luminescence (OSL) were employed in order to get a deeper understanding of the defect distribution in these materials. A detailed model of the trap distribution was developed from the results of these measurements. It was observed that compared to the bulk materials, the nanoparticles show a lower PL lifetime and less dependence on the dose of the RL intensity, which is due to the different defect distribution. The nanoparticles also demonstrate more low temperature peaks in the TL glow curves. PL and RL measurements of Eu3+ doped samples show that the crystal environment of the Eu3+ in the bulk material is more distorted than for the nanoparticles. For the bulk materials, the thermal coefficient of the RL is <0.4 %/K, which is a desirable property of real -time dosimeters. The thermal coefficient of the RL in the nanoparticles has a high uncertainty ( 7 %/K) compared to the bulk materials ( 0.4 %/K). For the fluoride nanoparticles, it was observed that the PL lifetimes for the LaF3 decreases with increasing rare earth concentrations. This can be attributed to energy transfer from luminescence ions in the core to luminescence ions near the surface followed by non-radiative decay. In comparison, the decrease of the PL lifetimes of RbMgF3 and NaMgF3 is predominantly due to non-radiative recombination centres inside the crystal.</p>