Interaction of ionising radiations with nanoparticles

includes bibliographical references and index

PhD; 2023; Instrumentation and Applied Physics

The interaction of ionizing radiations such as alpha, beta, gamma, and X-rays with matter-atbulk 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 alpharadiations 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 Pbfree, 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.