Interaction of Ionising Radiations with Nanoparticles

Abstract

The interaction of ionizing radiations such as alpha, beta, gamma, and X-rays with matter-at bulk has been studied intensively for many decades. However, the interaction of ionizing radiations with matter-at-nanoscale is studied sparsely due to the lack of experimental techniques. Thus, there exists a gap in knowledge. The present thesis contributes to the development of an experimental technique for determining the outcomes of the interaction of given ionizing radiation with given nanoparticles. The technique involves obtaining pulse height spectra of ionizing radiation with a liquid scintillator before and after loading the nanoparticles under identical conditions and observing the variations in spectra to infer the outcomes of the interactions. The study investigates the outcomes of interactions of gamma-rays, X-rays, beta- and alpha radiations with about twenty-five types of nanoparticles. It ascertains the effects of the nature and energy of radiations, species, size, and concentration of nanoparticles on the outcome of interactions. It demonstrates that the interaction of ionizing radiations with nanomaterials differs from those with their bulk counterparts. The interaction of low-energy photons (X-rays from 55Fe or a 40 kVp gun or gamma-rays from 241Am or 133Ba) with nanoparticles of Gd2O3, HfO2, and ZrO2 leads to the emission of numerous electrons from the nanoparticles. However, the nanoparticles of Au, Fe2O3, Pd, W, and WO3 interact with low-energy photons but inhibit the exit of electrons from them. Thus, the interaction of low-energy photons varies with the species of nanoparticles. Further, photons of a given energy range interact with the nanoparticles intensely. These are the two new results from this study. High-energy gamma radiations seldom interact with nanoparticles. The interactions of beta- and alpha-radiations result in the emission of electrons from all species of nanoparticles. Practical applications like –nanoparticle radiosensitization for cancer treatment; the development of efficient-fast-large-affordable gamma-detectors; and the development of Pb free, efficient, light-weight gamma-ray shields—rely on the interaction of ionizing radiations with nanoparticles. They either seek or benefit from empirical knowledge of the outcome of interactions. As the lack of mechanistic understanding of nanoparticle radiosensitization has delayed its field implementation, researchers seek the outcomes of ‘physical interaction of ionizing radiations with nanomaterials’. Since the process-related challenges have hindered the upscaling of detectors or shields and have kept their studies in exploratory mode, certainty gained on the outcome of interactions offers much-needed directions. Nanoparticles of Gd2O3, HfO2, and LaF3 suit as dopants in plastic scintillators for developing efficient-fast-large-affordable gamma detectors. Those of WO3, Sn, and Fe2O3 suit as dopants for developing Pb-free, efficient gamma-ray shields. The results reason why the enhancement of photon detection efficiency of plastic scintillators is repeatedly reported with doping of only selected species of nanoparticles. They reason how nanoparticle-loaded polymers offer impressive shielding efficiencies for diagnostic photons.