Dottorato in ENERGIA E AMBIENTE

Titolo della tesi: Enhancing Radiological Characterization Through Static 2D and Free-Moving 3D Gamma-Ray Imaging

Radiological characterization of radioactive materials, waste, and areas often relies on gamma-ray spectrometry for rapid, low-cost, yet reliable quantification of gamma-ray-emitting radionuclides. However, the applicability of gamma-ray spectrometry can be limited by the static nature of commonly used systems (such as High Purity Germanium crystals), and performance can be affected by the lack of knowledge regarding the matrix and distribution of radioactivity. These limitations can be mitigated by using a gamma-ray spectrometry system equipped with gamma-ray imaging capabilities. In recent years, this has become possible thanks to advancements in crystal manufacturing, electronics, and imaging and calculation algorithms. State-of-the-art systems, such as the 3D position-sensitive CdZnTe, now provide radioactivity distribution data as 2D heat maps superimposed on optical images of the space. However, the adoption of this technique has not yet become widespread among end-users in the nuclear field, partly due to the lack of trusted reference experiences. Therefore, the primary goal of this thesis was to conduct a series of experiments that could serve as reference cases for the application of gamma-ray imaging. The three tasks investigated were: radiological surveys (including the evaluation of gamma irradiation channels and the assessment of Special Nuclear Materials), direct quantification of gamma-ray emitters through spectrometric capabilities, and qualitative 3D reconstruction of radioactivity in a generic item. Special attention was given to integrating the results of these radiological surveys into the 3D model of a generic installation, following the Building Information Modeling (BIM) methodology. The experiments confirmed the reliability of imaging techniques for all these tasks, leading to improvements in accuracy and significantly enhancing the level of information available to users. However, they also revealed certain limitations of current gamma-ray imaging technology, particularly the native 2D output and the subjective positioning of the gamma-ray imager, even though this flexibility is typically an advantage in practical in-situ applications. To overcome these limitations and enhance gamma-ray imaging performance, a new device concept was designed and realized: a space-aware, free-moving detection system that pairs gamma-ray imaging (and potentially other sensors) with a Simultaneous Localization and Mapping (SLAM) tool. This system tracks the detector’s position and orientation in real-time, reconstructing the environment as a point cloud, which allows for the generation of a 3D model of radioactivity. Several tests were conducted using this system, validating its performance with known sources and mock-ups of real waste.