Speaker
Chad Dean Pelwan
(University of the Witwatersrand (ZA))
Description
In an attempt to understand the effects of ionizing radiation on various scintillation plastics, a number of studies are currently under way with a hope that favourable properties of scintillator plastics, such as high light output and fast decay time, can be optimized. In this investigation, MBTS irradiated plastics that were situated on the TileCal of the ATLAS detector at CERN were sent to the University of Witwatersrand where they were prepared for electron paramagnetic resonance (EPR) and nuclear magnetic resonance (NMR) analysis. EPR spectroscopy allows for the study of unpaired electrons and protons within these scintillators and offers a deeper insight into the organic or inorganic free radicals present. Furthermore, a computational approach will be taken using density functional theory (DFT) to isolate the optically active molecule and reproduce the EPR and NMR results seen. These techniques will used to validate the assumption that dangling bonds in the plastics were as a result of ionizing radiation damage caused in the testing phase. Three plastics, EJ200, EJ208, and EJ260 were used in this investigation as well as one Dubna scintillator plastic. These samples were irradiated at the iThemba Labs in Gauteng. The Dubna samples that were irradiated on the TileCal detector were compared to the un-irradiated samples as well as irradiated and un-irradiated Eljen samples. EPR experimental results show that damage to the plastics reduced the amount of paramagnetic centres seen and that new peaks form from new paramagnetic species formed due to irradiation and, over time, certain bonds would re-form within the plastics and further investigation is required to understand this effect.
