Investigation of the impact of ionising radiation on the physico-chemical properties of microparticles in view of non-invasive dosimetry

The research in this PhD covers two dosimeters systems. First, an existing commercial radiochromic radiation dosimeter, and second, a novel non-invasive in-vivo dosimeter system based on ultrasound contrast agents. The first part of the research focuses on GafChromic EBT3 films which become increasingly dark when exposed to ionising radiation. The darkening originates from the formation of light-absorbing diacetylene polymers in the film material which initially consists of a dense layer of transparent monomer crystals. A suite of experimental, spectroscopic techniques are employed to shed light on the influence of ionising radiation on the molecular properties of the film. Based on these findings, the absorption spectrum of EBT3 films was modelled in the framework of the Franck-Condon theory. Further building on this description, a model was proposed for the dose dependence of the vis-absorption spectrum based on a modified version of the “gamma-distributed single hit model” which takes into account the microscopic structure of the active layer of the films. The second research topic dealt with in the present thesis comprises the design of a radiation sensitive ultrasound contrast agent in view of the development of a non-invasive in-vivo dosimeter system. The proposed ultrasound contrast agent is a micrometer-sized gas bubble encapsulated by a polymerizable lipid shell onto which gold nanoparticles are coupled. This approach relies on the radiation-induced polymerization reaction of diacetylene molecules, similar to the mechanism that is responsible for the radiation sensitivity of EBT3 films. However, instead of using the optical properties as a measure of the radiation dose, here, the change in the mechanical properties that is associated to the polymerization reaction is exploited. The mechanical properties of the microbubble shell strongly determine the stability and the acoustic response of the microbubbles. Hence, the polymerization reaction provides the means by which the effect of ionising radiation on the acoustic response of ultrasound contrast agents can be quantified.

Jaar van publicatie:2017

Toegankelijkheid:Closed