This article discusses in some detail principles and methods used in the application of neutron activation analysis, including autoradiography, to the fields of art and archaeology as well as other disciplines. Pottery excavated in the agora of Athens, manufactured between 1000 BC and the 4th century AD showed that the compositions of Classic and later ceramics differed significantly from earlier Athenian pottery, and that the later pottery could be assigned securely to Athenian manufacture. Autoradiography of a painting of Van Dyck in the collection of the Metropolitan Museum of New York, showed that an angel had been added to the original design, and that an upside-down self-portrait of the artist had been overpainted. Autoradiography also was used to detect overpainting of part of the signature on another painting (by the daughter of Blakelock) the resulting difference in attribution having made the painting potentially more valuable. Autoradiography, thus, is effectively used to detect alterations in paintings, which at times are made with fraudulent intent. -- AATA