A comparative and critical study of X-ray CT and neutron CT as non-destructive material evaluation techniques

X-ray computerized tomography (CT) has traditionally been used as a medical diagnostic tool. This non-destructive technique has developed as an important research tool for a wide variety of scientific subjects. For material research 'medical' CT, microCT and, very recently, nano- or submicroCT have been used as non-destructive material evaluation techniques for engineering and geological purposes. The fact that X-ray CT visualizes the internal structure of natural building stones and yields information on porosity values and pore-size distributions is a major advantage for the study of their conservation. The penetration of fluids like water, consolidants or water repellents inside porous materials is important when dealing with conservation and restoration research. Recently, high-speed neutron tomography has been introduced as a visualization technique for fluids inside porous materials. High-speed neutron tomography can be used as a complementary technique to X-ray tomography as elements like hydrogen, which have a weak attenuation for X-rays, are easy to detect using neutrons. In this paper the basic principles of computerized tomography and more specifically X-ray and neutron tomography are discussed. In addition, application possibilities, advantages and limitations of medical CT, X-ray microCT and high-speed thermal neutron CT are outlined.