Autoradiography of the paintings
The neutron beam from the horizontal channel can also be used to examine the paintings with the neutron autoradiography technique. This technique Was used in the MARIA reactor to study paintings by masters of Venetian painting of the 14th – 18th centuries from the collections of the National Museum in Warsaw, presented as part of the exhibition „Serenissima – the light of Venice” in 2000.
The autoradiography technique consists in irradiating the paintings with thermal neutrons and inducing the radiation capture reaction in some isotopes that are part of the paint layers, e. g. 31P (n, γ) 32P. After the process of neutron irradiation is completed, the resulting radioactive isotopes decay (usually beta decay), e. g. 32P→32S. If the image is covered with β– X-ray film at this time, the emitted particles cause the film to blacken. The pattern created on the plate reflects the distribution of the isotope – emitter of beta particles in the painting layer. This applies not only to the surface of the painting, but also to the deeper structures of the paint layer. The image of the blackening of the plate is characteristic of the pigment used and allows for the analysis of deeper paint layers. Fig. NCBJ-4.6 shows schematically the technique of painting autoradiography.
Picture 1. Autoradiography of paintings – principle of operation
A spectacular example of the use of this technique is the autoradiography of the painting „Portrait of a Venetian Admiral” by Jacopo Tintoretto. Figure 2 shows the original and one of the autoradiographs, indicating the existence of another portrait below the actual image.
Picture 2. „Portrait of the Venetian admiral” and his autoradiogram
