XRF (X-ray Fluorescence) is a well known analytical technique particularly suited for the non-destructive characterization of artefacts in the Cultural Heritage field. In particular, it has been used in the analysis of ancient coins and, in general, of metallic alloys. This is a superficial technique, then the analysis is limited to the near surface layers (some tens of microns). It is well known that surface effects like corrosion, migration or plating can be responsible of strong in homogeneities in the metallic samples. These processes affect the possibility of a correct knowledge of the composition of the alloy constituting the internal part of the body of the artefact. In the present work we report on the XRF analyses carried out by using a 241Am and 109Cd radioactive sources, on ten Greek bronze coins. The results displayed a strong variation, from about 4% to about 16%, of the tin content. Drill samples have been extracted from the interior of the coins showing a rather constant tin content of about 5%. To overcame this difficulty a new version of the known Proton Activation Analysis method is proposed. It is based on the observation that the typical excitation function for isotope production displays a "bell shaped" behaviour with a maximum at about the incident Coulomb energy (in general 10-12 MeV for incoming protons on medium mass number targets). By suitably choosing the incident proton energy on the coin and by considering the effect of the particles slowing down due to the energy loss it is possible to limit the radioactive isotopes production only to the interior of the coin so avoiding any surface effect. Preliminary data on "dummi" coins are presented.
SURFACE EFFECTS EVIDENCE IN THE NON-DESTRUCTIVE XRF ANALYSIS AND THE NEW DEEP PROTON ACTIVATION ANALYISIS (DPAA) METHOD
FP ROMANO;
2004
Abstract
XRF (X-ray Fluorescence) is a well known analytical technique particularly suited for the non-destructive characterization of artefacts in the Cultural Heritage field. In particular, it has been used in the analysis of ancient coins and, in general, of metallic alloys. This is a superficial technique, then the analysis is limited to the near surface layers (some tens of microns). It is well known that surface effects like corrosion, migration or plating can be responsible of strong in homogeneities in the metallic samples. These processes affect the possibility of a correct knowledge of the composition of the alloy constituting the internal part of the body of the artefact. In the present work we report on the XRF analyses carried out by using a 241Am and 109Cd radioactive sources, on ten Greek bronze coins. The results displayed a strong variation, from about 4% to about 16%, of the tin content. Drill samples have been extracted from the interior of the coins showing a rather constant tin content of about 5%. To overcame this difficulty a new version of the known Proton Activation Analysis method is proposed. It is based on the observation that the typical excitation function for isotope production displays a "bell shaped" behaviour with a maximum at about the incident Coulomb energy (in general 10-12 MeV for incoming protons on medium mass number targets). By suitably choosing the incident proton energy on the coin and by considering the effect of the particles slowing down due to the energy loss it is possible to limit the radioactive isotopes production only to the interior of the coin so avoiding any surface effect. Preliminary data on "dummi" coins are presented.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
