X-ray 3D Computed Tomography of large objects: investigation of an ancient globe created by Vincenzo Coronelli

X-ray cone-beam Computed Tomography is a powerful tool for the non-destructive investigation of the inner structure of works of art. With regards to Cultural Heritage conservation, different kind of objects have to be inspected in order to acquire significant information such as the manufacturing technique or the presence of defects and damages. The knowledge of these features is very useful for determining adequate maintenance and restoration procedures. The use of medical CT scanners gives good results only when the investigated objects have size and density similar to those of the human body, however this requirement is not always fulfilled in Cultural Heritage diagnostics. For this reason a system for Digital Radiography and Computed Tomography of large objects, especially works of art, has been recently developed by researchers of the Physics Department of the University of Bologna. The design of the system is very different from any commercial available CT machine. The system consists of a 200 kVp X-ray source, a detector and a motorized mechanical structure for moving the detector and the object in order to collect the required number of radiographic projections. The detector is made up of a 450x450 mm2 structured CsI(Tl) scintillating screen, optically coupled to a CCD camera (Apogee Alta U32), by means of a lens and a 45o degree mirror. In this paper we will present the results of the tomographic investigation recently performed on a celestial globe, measuring 113 cm in diameter, created by the famous cosmographer, cartographer and encyclopedist Vincenzo Coronelli.