Evaluation of hydrogen content in metallic samples by neutron computed tomography

Neutron radiography is currently a well-known technique, which is employed for non-destructive testing in a number of industrial and environmental applications. Originally developed for reactor fuel examinations, it is now effective in detecting small amounts of corrosion and infiltrations of hydrogen or light materials within thick metallic structures due to the particular behaviour of total neutron cross sections. Nevertheless, improvements related to the development of tomographic systems, which allow far better imaging performances, have been achieved only in the last few years, as a consequence, primarily, of the production of large, charge coupled device (CCD) arrays. Nowadays, neutron computed tomography is the technique most suited for the study of the distribution of hydrogen within metallic matrices. In this field, a series of experimental tests were carried out employing a set of nickel samples containing a H₂0-D₂0 solution in known percentages. It was possible, therefore, to obtain a calibration curve for the total neutron cross section vs. gray level in the reconstructed image