Development and characterization of a neutron imaging system for cultural heritage

The use of non-destructive methods is highly relevant for cultural heritage objects, due to their uniqueness. Investigations by means of X-ray imaging is often sufficient to gain an overview of their constituent materials, manufacturing techniques and conservation state, but there are cases where this method reaches its limits. Hence, neutron imaging can provide new insights into the studied object, due to neutrons different interactions with matter. In Italy, INFN-CHNet (Cultural Heritage Network of the Italian National Institute for Nuclear Physics) NICHE (Neutron Imaging for Cultural HEritage) experiment aims to implement the first thermal neutron imaging facility in Pavia, at TRIGA reactor. The present work, as a part of NICHE project, provides the characterization of the detector of the neutron imaging system and tomographic analyses of different samples. In particular, the thesis describes the experimental tests carried out to select the scintillator for the CCD-based detector. The spatial resolution of the system was evaluated both with a visual method, through the acquisition of a radiography of a gadolinium bar pattern, and by calculating the Modulation Transfer function. Further tests were performed to verify the linearity of response of the imaging system and the trend of the Signal-to-Noise Ratio as a function of the acquisition time of the CCD camera. Finally, three tomographies were executed with several samples, allowing their 3D external and internal visualization. A calibration curve was obtained for converting gray levels of the reconstructed images of samples with known composition, into the neutron total macroscopic cross section for the corresponding materials. The experimental tests described in this work have provided satisfactory results, but they have also highlighted some critical points of the neutron imaging system. Therefore, the first prototype of the CCD-based detector has been recently upgraded in order to improve its performance.