Alfio Torrisi*, Lorenzo Giuffrida**,***, Francesco Caridi****, Tiziana Serafino*****, Eligio Daniele Castrizio******, Guglielmo Mondio*****, Lorenzo Torrisi**
* Dipartimento di Fisica, University of Catania, Italy (
** Dipartimento di Fisica, University of Messina, Italy
*** INFN-LNS of Catania, Italy
**** Facoltà di Scienze M.F.N., University of Messina, Italy
***** Dipartimento di Fisica della Materia e Ing. dei Mat., University of Messina
****** Dipartimento Scienze dell’Antichità, University of Messina, Italy
Abstract
A Nd:Yag pulsed laser (3 ns pulse duration, 532 nm wavelength, 15-150 mJ pulse energy, 1-10 Hz repetition rate) is employed to irradiate ancient bronze coins placed in vacuum (10-6 mbar). During Laser Ablation a Mass Quadrupole Spectrometry (MQS) permits to detect the ablated masses from the sample surfaces with less than 1 amu mass resolution, in a range of 1-300 amu,
with a sensitivity of the order of 1 ppm. Coins from IV – X century A.D. coming from different Mediterranean sites (Egypt, Greece and Italy) are ablated, in a controllable manner to remove about 1 mm per laser shot from 0.5 mm2 spot size. During laser ablation the removed atomic and molecular species are analyzed with MQS relatively to the elemental composition, chemical compounds and isotopic species. The elements of interest are those of the surface and bulk composition, preliminary checked out through XRF analysis. The chemical compounds concerns the main species of the patina and of the first bulk layers. Pb isotope ratios measurements on the lead contents in the coin patinas have been compared with literature. The used technique, the obtained measurements and the result correlations are presented and discussed.
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