  In the present Ph.D. Thesis we report an experimental investigation on the
effects of gamma- and beta-ray irradiation and of subsequent thermal treatment
on many types of a-SiO2 materials, differing in the production methods, OH- and
Al-content, and oxygen deficiencies. Our main objective is to gain further
insight on the microscopic structures of the E'_gamma, E'_delta, E'_alpha and
triplet paramagnetic centers, which are among the most important and studied
class of radiation induced intrinsic point defects in a-SiO2. To pursue this
objective, we use prevalently the EPR spectroscopy. In particular, our work is
focused on the properties of the unpaired electrons wave functions involved in
the defects, and this aspect is mainly investigated through the study of the
EPR signals originating from the interaction of the unpaired electrons with
29Si magnetic nuclei (with nuclear spin I=1/2 and natural abundance 4.7 %). In
addition, in some cases of interest, OA measurements are also performed with
the aim to further characterize the electronic properties of the defects.
Furthermore, due to its relevance for electronics application, the charge state
of the defects is investigated by looking at the processes responsible for the
generation of the defects of interest. Once these information were gained, the
possible sites that can serve as precursors for defects formation are deduced,
with the definitive purpose to obtain in the future more radiation resistant
a-SiO2 materials in which the deleterious effects connected with the point
defects are significantly reduced.
