Real-time observation of particle interactions in matter using laser-driven accelerators

Abstract

The research presented in this thesis aims to provide a gateway to a better understanding of how the nanoscopic structure of a material and localised response to radiation contributes to the overall macroscopic picture of particle-matter interactions. This is achieved by exploiting advances in laser technologies that enable transient absorption experiments via pump-probe methodologies across numerous materials, using picosecond scale bursts of x-rays and protons generated via Bremsstrahlung and Target Normal Sheath Acceleration (TNSA) respectively, as the pump source and chirped light with an adjustable wavelength as the probe. The role of localised and delocalised particle interactions within ordered and disordered media is examined in various forms of SiO2. By tracking the transient opacity the recovery time of excited electrons is found to be > 150 times greater in nanostructured aerogel than in bulk fused silica, a magnitude of > 15 more than expected. While the bulk response behaves as expected the introduction of disorder in matter demonstrates the significance of characteristic heterogeneity on the nanoscale in material response. Next, ultra-fast pulsed-ion radiolysis is performed in liquid water to investigate the behaviour of radiation chemistry towards the formation of solvated electrons. A temporal broadening at either side of the Bragg region, 10 times greater than predicted by proton stopping data. This discrepancy can be reconciled by considering the formation of a heterogeneous density distribution of H2O molecules through the formation of nanocavities, post irradiation. A two colour chirped optical probe pulse is generated using non-linear crystal media to simultaneously to track the formation of hydroxyl radicals simultaneously with the formation of solvated electrons. These radiolytic species are observed across 100 ps and 1.2 ns respectively, marking the first ever recording of their evolution in pristine water samples in real time due to proton irradiation.

Date of Award	Dec 2021
Original language	English
Awarding Institution	Queen's University Belfast
Supervisor	Brendan Dromey (Supervisor) & Mark Yeung (Supervisor)