Email:anna.galli@unimib.it
Keywords : absolute dating, luminescence techniques
The applications in the archaeological field of thermoluminescence (TL) dating technique are well known and their reliability has been amply demonstrated since the early 1970s. These techniques are specific to the ceramic material or, in general, to any material containing quartz or feldspar that has undergone prolonged heating at temperatures of the order of a few hundred degrees. There are several materials and objects of archaeological, historical or artistic interest that can be dated: first of all ceramics, terracotta, bricks and porcelain but also furnaces, hearths, burnt flints, smelting earth and metallurgical slag. For them it is usually possible to obtain dating with an accuracy of 5-10% in the indicative age range between 50 and 20,000 years. This technique belongs to the class of so-called destructive methods, since they require the removal of a non-negligible, albeit limited, amount of material. This aspect, if it does not generally represent a problem in the case of archaeological excavations characterized by abundant discovery of "expendable" material, becomes very delicate when the dating of objects of historical or artistic interest is required, given the need to preserve their integrity.
Over the past 30 years, a dating technique has been developed that can be applied to geological sediments: Optically Stimulated Luminescence (OSL). It lends itself to dating materials that have been subjected to illumination by sunlight in some instant of their life. Therefore, with this technique it is possible to determine the geological epoch of formation of a sediment rather than the burial age of an artefact. The use of OSL for dating presents many more critical aspects than TL but it is essential to extend (also in terms of time) to materials of historical and artistic interest that have not undergone firing the fields of application of techniques based on accumulation of electrons in insulating and semiconductor materials.
The complexity of the procedures and the good knowledge of radiation physics, necessary to obtain the high accuracy required, have led to a limited international diffusion of laboratories dating with TL and OSL. In Italy, only the Laboratories of the Materials Science Department of the University of Milan Bicocca and the University of Catania are able to apply these techniques to dating.
Some possible innovative applications recently developed in the Materials Science Department are presented, in relation to new luminescence dating techniques and new materials to which they can be applied.