PIXE, XRF and GRT for the global investigation of ancient gold artefacts

Abstract

The study of ancient gold jewellery artefacts often requires surface and bulk characterisation using non-destructive methods. Curators of musea or owners of private collections do not allow any sampling (even at microscopic level) for the investigation of the bulk of massive gold objects, which often contain less noble metals. Neutron Activation Analysis of the whole sample is generally prohibited even if no danger may be feared from delayed radioactivity. Weight and density measurements are easy and convenient to assert the presence of a cavity or a core of lower density. A combination of PIXE (at various incident proton energies in a non-vacuum geometry) for the elemental distribution in the first 10 μm below the surface, XRF (induced by γ-rays of 59 keV and of higher energy from a source of 241Am) to investigate the material up to several hundreds of microns, and GRT (Gamma Ray Transmission) of 662 keV photons (137Cs) may give a more complete answer on the surface and bulk compositions of the artefacts. Examples are given for Hellenistic and Mesoamerican jewellery items.