Estimation of accidental radiation exposure by EPR measurements of induced point defects in smartphone screens

In case of a large-scale radiological accident with external exposure, there is no current method to sort out the exposed individuals and decide the immediate medical care. This thesis aims to participate in the development of a method of retrospective dosimetry with large throughput as a part of IRSN's strength line n°8 dedicated to developing methodologies and decision support tools of an operational nature. The proposed method is the use of smartphone touchscreen or protective glass for dose determination by using Electron paramagnetic Resonance spectroscopy (EPR). The advantage of the smartphones is its availability to everyone providing a fortuitous & quasi-universal dosimeter. Our goal is to build a robust analysis protocol to extract the main features of the EPR signals induced by irradiation among all unwanted signal components. The variability in composition of the tempered glass found in different smartphones is one of the main difficulties. Composition's changes induce different EPR radio-induced signatures and affect the sensitivity to dose. We need to study the variability of the EPR signal components in the various glass types. Thus, signals prior irradiation, induced by UV and ionizing radiation are studied in detail (thermal stability, UV effect on stability, dose sensitivity) to understand the mechanism and nature of radio-induced defects' formation. Glass chemical analysis will be preformed to facilitate these point defects' identification. Afterwards, we will produce our own glass with similar but controlled composition. Varying the concentration of elements possibly involved in the mechanism of formation in those lab-made glasses will help us to understand the different radio-chemical mechanisms. Once the nature of point defects is identified, it will be possible to simulate the different associated EPR components building up the spectra regardless of smartphone glass type providing a robust automated analysis approach. One of the leading companies for touchscreen production is Corning ® featuring Gorilla ® Glass (GG) generations (8 in total) where I am currently investigating its latest generations 5 & 7. They are known to be alkali-alumino-silicate glasses, but their compositions are not published. In GG5, two radio-induced components have been identified. After analysis of GG7 spectra, Fe3+ and Mn2+ ions have been identified. These ions, acting as quencher, could explain its lower sensitivity to dose. UVB Irradiation induces EPR components -contrarily to previous generations- that can be differentiated from the gamma-induced ones. It is worth noting that UVB irradiation generates less intense contribution in GG7 than in other type of GG