Instrumentation and technique developments at the
thermoluminescence dating laboratory of the University of Turin
L. Guidorzi (a,b), A. Lo Giudice (a,b), F. Fantino (b,c), A. Re (a,b), D. Angelici (b,c) & Chimica (d)
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(a) Physics Department, University of Turin, Via Pietro Giuria 1, 10125 Torino (Italy) (b) INFN – Sezione di Torino
(c) TecnArt S.r.l. – Via Modena, 58, 10153 Torino (Italy)
(d) Chemistry Department, University of Turin, Via Pietro Giuria 5, 10125 Torino (Italy)
laura.guidorzi@unito.it
In the last decade, a thermoluminescence (TL) laboratory for dating and authentication of ceramic archaeological artefacts has been developed at the Physics Department of the University of Turin, in collaboration with INFN (National Institute of Nuclear Physics) and currently operating within the INFN-CH-Net network.
The TL technique allows to obtain the age of a clay object by measuring the radiation dose absorbed since its last firing in some of its compositional minerals (e.g. quartz and feldspars), that is due to natural occurring radioactivity and proportional to the luminous signal emitted by the material when heated at a few hundred degrees Celsius in laboratory [Aitken, 1985]. This means that not only the absorbed dose (paleodose) is to be known, but also the dose rate at which the artefact has been subjected in time (annual dose), that depends from the conservation conditions and varies with the geographical area; the age can be consequently calculated by the simple ratio between the two quantities. A lot of measurements are therefore required for a complete dating: first of all, the evaluation of the paleodose by TL signal acquisitions, obtained via
increasing artificial irradiation of samples using a 90Sr beta source and a 241Am alpha source. In the last few
months, our laboratory installed a new beta irradiation system, designed also for the recently established TL
laboratory in Pyay (Myanmar) within an international cooperation, equipped with a 90Sr/90Y source with
nominal activity of 1,48 GBq that allows faster and completely automated irradiation of four samples in series. This has been a great improvement for the augmented statistics of measurements and their repeatability. The data needed for the calculation of the annual dose are then collected by the measure of the alpha activity (caused by decay chain events of Uranium and Thorium atoms contained in the clay matrix), the quantification of the environmental dose rate using LiF dosimeters collocated in situ and/or by gamma
spectroscopy on a burial ground sample and finally the ICP-OES measure of 40K isotope concentration in the
material (in collaboration with the Chemical Dept. of the University of Turin). In addition, further corrections for water absorption, supralinearity and anomalous fading are performed.
Thermoluminescence is an invasive technique, that needs the sampling of a minimal amount of ceramic powder (up to 1-2 grams) for the preparation of samples by the fine grain technique [Aitken, 1985]. Clay material from archaeological objects is often contaminated by organic matter and carbonates (the latter enhanced by long time-spans spent in highly-humid burial grounds). This requires a chemical pre-treatment
of the powder before the fine grain; in our laboratory the procedure described in [
Vieillevigne et al., 2007
]was initially adopted, then, learning by experience, we became able to balance the use of each chemical step (reagent and time of use) depending mainly on the available quantity of material and the knowledge of the
clay composition and provenance. The new standard procedure, employing mainly HCl and CH3COOH, will
be presented, along with some applications in recent case studies of dating and authentication.
References
Aitken M. J., Thermoluminescence Dating, Academic Press, London, 1985
Vieillevigne, E., Guibert, P., Bechtel, F. Luminescence chronology of the medieval citadel of Termez, Uzbekistan: TL dating of bricks masonries, J. Archeol. Sci., 34 (2007) 1402-1416.
Guidorzi et al X Congresso Nazionale AIAr
