He+ Irradiation of Quartz for the Identification of Ceramic Forgeries Aged by Radiation

Thermoluminescence (TL) is a powerful tool for authenticating ceramic artifacts, with an accuracy of ±20-30% that is generally sufficient for differentiation between genuine objects and fakes. However, one of the biggest problems about the great diffusion of TL as dating tool is that counterfeiters have learned in time various tricks to mislead the authentication. Whereas the assembling of old and new parts or the carving from ancient but worthless artefacts can be quite easily discovered by means of other techniques, the “aging” of an object induced by artificial irradiation with X or γ rays cannot be detected with certainty so far. The chosen approach for overcoming this issue is the observation of the effect of α particles irradiation on the quartz grains contained in the clay matrix. This kind of irradiation is only present in naturally irradiated samples, and almost impossible to reproduce. An α particle is a Helium nucleus (He 2+ ) with a significant mass, higher than for β or γ particles and hence capable of inducing lattice damage. Since the penetration range of an α particle is smaller than those of β or γ ones, only the surface shell of quartz crystals is involved with the interaction and could show the characteristic traces. In geology, the effect of α particles on quartz is well known as the consequence of constant irradiation, for millions of years, of the portion of crystal surrounding radioactive inclusions, in particular Uranium and Thorium. The visible effect results in the formation of a luminescent halo, easily detectable with cathodoluminescence (CL) imaging.